diyAudio Forums Archive > Top > Source > Analogue Passive Preamp - Click HERE for Original Thread Rarkov Hi, I've ordered a dual 100k and 50k log potentiometer and a 2 pole 6way rotary switch. I want to make a passive preamp using these components. I was thinking, 5 pairs of inputs (1 is off) into the switch and the ouput from the switch goes to one side of the pot. I'd put the other side to ground and use the centre tap as my signal ouput. So, here are the questions: Will this work with only two components? Should I use the 50k or 100k pot for volume? If I wanted to add balance (same but with input signals to pot reversed) should I use the 50k or 100k Will the volume at 50k/100k resistance be (virtually) nill? Thanks for any help!!! Gaz Bobken Hi, From what you say, I don't wish to discourage you nor appear to be negative, but I would suggest that you do some research into these things before you start, as it doesn't seem that you understand how pots are conected up for attenuators. I mean no disrespect in saying this, but for example, *any* value of pot if used in the correct intended manner, will effectively kill all of the signal. The reason being that with the output at 0 (fully anti-clockwise) the wiper of the pot, which is connected to the succeeding stage, will be shorted out to ground and there will no signal there to be passed on to this next stage. It doesn't matter if the pot is 10 Ohms, or 1Meg Ohms. :nod: As a general rule , most SS gear will use a lower value pot with 10K being perhaps the most common, but valve gear seems to use much higher values like 100K, I believe, although I am not a valve man! What you need to be aware of is the effect of the pot's impedances associated with the capacitances of the cables etc. (which feed into, and more importantly out of the passive attenuator) as where the pot's impedances are higher, the capacitance of the cable will act like an HF attenuator. In short, the higher the impedance, the lower the cable capacitance must be to avoid any curtailing of the HF response. There are other factors like the output impedance of the preceeding gear and the input impedance of the succeeding equipment to take into account as well.:goodbad: There must be a lot of info and guidance on this on the 'net, and I would encourage you look at this to grasp the important issues, as otherwise you will probably be dissatisfied with the results, which would be a shame. :) Don't be deterred by anything I have said, as properly executed passives can and do sound very good, but you do need to pay attention to the points I mentioned. Regards, Sch3mat1c What's a passive preamp? (Be aware I already know the colloquial answer.) TIm Rarkov Hi, Bobken: thanks for all your advice... Maybe I should shed a bit more light on why I'm doing this. I've built a pair of Randy Slone OptiMOS monoblocks (with a slightly raised rail voltage). I do not have a preamp, so I modified a cheap second hand integrated amp to bypass the amps and run as a preamp. It sounds just awful! I am planning to get a Marantz 4300 or 5300 (can't remember which) HC amp. This outputs preouts but for music, I want a really simple preamp. In my "junk box" I have an Alps 100K dual log pot and a 2 pole 6way switch. These are fixed (preferrably). I suppose what I am asking is: Can I make a good/great sounding passive preamp from these components? I have a virtually unlimited supply of resistors and caps if I need any in the circuit too. Thanks, Gaz Bobken quote: Originally posted by Sch3mat1c What's a passive preamp? (Be aware I already know the colloquial answer.) TIm Don't understand the question, Tim, if you already know the answer. :cool: Regards, Christer Don't forget to check the tech. specs. of the CDp and other sources you'll be using. For instance, my Sony CDP should have a load of at least 50kOhm according to the specs. I don't know how important this is, though. Maybe it just means that it won't give the specified output voltage if going below 50kOhm. Anyway, you should keep this in mind and be aware of it. Also remember that a passive pre will have an input impedance that varies when you turn the pot. Well, there might be some clever ways to avoid this, perhaps, but not with any of the straightforwards solutions. halojoy Yes, I think that it just the components I would buy. If you should use 50k or 100k depends on the situation. I am in favor of low inputimpedance. From where comes the signal. The source. And to where goes the signal - input impedance of real Amplifier. Best is to have the Volume Control near to the Input of a power amp. Incorporation of balance can be done in a number of ways. ----------------------------- Rarkov, draw us a suggestion. Then post a preliminary schematic here. Then we can say more precise. It is always better to start out with something and then alter, than to think on the best way for a long time, without doing anything. /halo - likes the stuff Rarkov will use ;) Bobken quote: Originally posted by Rarkov Hi, Bobken: thanks for all your advice... Maybe I should shed a bit more light on why I'm doing this. I've built a pair of Randy Slone OptiMOS monoblocks (with a slightly raised rail voltage). I do not have a preamp, so I modified a cheap second hand integrated amp to bypass the amps and run as a preamp. It sounds just awful! I am planning to get a Marantz 4300 or 5300 (can't remember which) HC amp. This outputs preouts but for music, I want a really simple preamp. In my "junk box" I have an Alps 100K dual log pot and a 2 pole 6way switch. These are fixed (preferrably). I suppose what I am asking is: Can I make a good/great sounding passive preamp from these components? I have a virtually unlimited supply of resistors and caps if I need any in the circuit too. Thanks, Gaz As far as the first part of your query goes, you will need to know the various impedances of your existing gear (output of 'send' & input of 'receive') and associated capacitances/ foot and the lengths of cable used etc., to get this right, as I said earlier. In this connection, it is best to look up some more comprehensive info on the net, as it is too involved for me to explain. Simply put, if you don't 'match' (i.e. get the ratios correct) the input to output impedances very well of any interconnecting equipment, the signal will not 'transfer' properly from the 'sending' gear to the 'receiving' gear. Unfortunately, with a passive arrangement, the impedances of the pot are not even constant, as they vary with rotation of the pot, which complicates the issue and it has to be a well-chosen compromise, still bearing in mind the overall capacitances of your cables. It is possible (and it is frequently done) to modify the 'value' of a pot by using what is known as a 'law-faking' resistor, and in your case the result could be something satisfactory, as in such cases is it usual to end up with a 'final' pot value of about one tenth of the original pot value. So you could end up with a pot of about 10K which would probably be OK with most SS gear. However, it is also usual to use a *linear* pot in these cases, because the addition of this resistor affects the 'taper' of the pot in action, and you say yours is a *log* pot. In case you don't know the difference, with a linear pot, half the resistance occurs at half rotation, two thirds at two thirds rotation etc. etc., but with a log pot this not so, and the 'taper' can be many different shapes. Almost anything is possible, but I think if you try with a log pot, you will end up with 'all of the action' so to speak, squeezed up at one end of the pot's rotation, so it will not be very useful to you. As I said before, you would do well to research the matter before you start, as, otherwise there are too many variables to get wrong, and I am sure with a bit of effort you can find many references to both Passives and law-faking resistors, which should give you what you need to know. Regards,:) halojoy quote: Originally posted by Rarkov Maybe I should shed a bit more light on why I'm doing this. I've built a pair of Randy Slone OptiMOS monoblocks). I suppose what I am asking is: Can I make a good/great sounding passive preamp from these components? Thanks, Gaz You can make a good Volume control and switch box with that. In fact it will be better for the sound, hifi, than to have active preamplifiers. So, if only the impedances match in a fairly good way and you check up on capcitors, the variations of the volume will not make any real harm to the signal. The outputcap from CD etc. form a RC filter together with the volumepot. /halo - waits for the first version drawing :idea: traderbam "Can I make a good/great sounding passive preamp from these components?" In my opinion: YES :) As you say you want to keep it simple. For good volume range use a LOG pot. Most sources have an output Z < 100-ohms and will happily drive loads in the low K-ohms. A Krell CD will probably drive a power drill directly. There are a couple of things to bear in mind: 1) When you use a pot the source resistance seen by your amp will vary from zero (when volume is off) to Nohms (on full volume) where N is the CD output R in parallel with the pot R. So typically, the maximum R seen by the amp is the pot R divided by 2. The only problem here is that this R is in series with the amp input capacitance and can cause a low pass filtering effect. You need to do a calculation to ensure this has negligible effect within the audio band. I imagine pots of 50k or less will be ok; I'd go for 10k myself but use what you've got. 2) Make sure you block any dc from the switch and the pot. If there is any dc (even small) flowing through the pot you can get a nasty sound when turning it and any dc on the switch may cause loud clicks when selecting inputs. Use dc blocking caps and 1M-ohm bleed resistors liberally. Have a go. It is definitely worth putting your concept into action. Shoog I built a passive preamp and got very favourable results with just a 7way switch and a 100k pot. I was using it with a valve amp which was fairly forgiving. I used "Shark Cable" which is availble from Maplin-I highly recommend this for all internal wiring, and its really cheap. I did find that the log pot that I used tended to have very poor adjustment with the useful range been bunched at one end. I ended up adding faily high resistances infront of the pot. The reason I could get away with been so lax with the technical issues was because i had a Musical Fidelity X10D line conditioner between the pre and power amp, which acted as a buffer stage. If you have little joy with getting things working properly a simple op-amp buffer stage might been a cheap and easy solution. If you wanted to splash out, a stepped attenuator presents a stable load to the sources whatever the volume setting and eliminates at least one of the problems- those who are serious about their passive preamps always use them. Whats all this **** about "Whats a Passive Preamp ?", pedantry is at the root of most of the worlds evils. if it works (and it does) then use it. Shoog Sch3mat1c quote: Originally posted by Bobken Don't understand the question, Tim, if you already know the answer. :cool: The answer I was looking for is "oxymoron". Why would you want an inline pot anyway? Don't any of your amps/preamps/signal source/etc. have a built-in volume control? Tim Bobken quote: Originally posted by Sch3mat1c The answer I was looking for is "oxymoron". Why would you want an inline pot anyway? Don't any of your amps/preamps/signal source/etc. have a built-in volume control? Tim Impressive command of the English language, Tim, but not much value in a Forum like this which is about DIY Audio. :bigeyes: I am 'too long in the tooth' to fall for that one, anyway! :nod: The originator of the thread has explained why he needed this arrangement, which is always referred to as a "passive preamp" even if to pedantics this may appear to be a contradiction in terms. A question I have for you is, are you interested in DIY audio, or what?:goodbad: Regards, Rarkov Hiya, Sorry to confuse anyone...Here is my: 1) Passive Pre-processor 2) Passive Pre-Volume, Balance box 3) Passive Pre (meaning 'before') Power Amplifier (AKA Preamp) ;) No offence...Hadn't even thought of it as a condradiction until you mentioned it. Anyway...Here is a design. I have the parts - just have to build it. I'm not going to add the balance just yet...Oh, and I forgot the DC blocking caps (You'll have to imagine them! ;) ) Red lines denote a 'ganged' component...My CD player does have a volume control, but these are usually to get all of your source components at the same level. Using it as a full scale volume introduces a very loud hiss at low volumes. It sounds awful. I always have the CD player on "full volume" for it to sound at it's best. I wish I had a Krell player...but I'm afraid it's just an old kenwood! :( On the other hand my Tuner, Modded Xbox, TV Preout, Free2View box all come without a means of volume control. And Finally, as for my Amps, since they are monoblock Power Amplifiers, I didn't want to put volume controls on them...I think they are too difficult to keep at the same levels to be convienient. Hope you like the Schematics... P.S. Isn't Oxymoron a type of anti-spot wash? ;) Sch3mat1c Ah, ok. (I have a problem with the words "passive preamp". :rolleyes: ) The design looks fine to me, but if you have marginal signal levels now (like, listening levels just fall within control levels), this will attenuate the signal a lot, meaning you won't even get to listening level before your controls hit the wall. But I take it you still have the headroom on your monoblocks' controls? I'm not sure of the balance...don't one of the sides have to be antilog for that to work? Tim Audiofanatic Hi Gaz, I recomend you not to use the balance part. Keep the Audio Synthesis in mind! IMHO, It souds better without balance !:rolleyes: ;) :) :nod: P.S. correct me if i'm wrong! Christer quote: Originally posted by Sch3mat1c (I have a problem with the words "passive preamp". :rolleyes: ) It is illogical in the sense that it is an amplifier that doesn't amplify, but it is logical in the sense that it is used in the same way and in the same place in the signal chain as a preamplifier. Either way, the term has been around for over ten years, I think. They started to appear when many people had switched over entirely to CD and didn't need a phono amp anymore. Rarkov Hi, Thanks for all the helpful replies! As I said, the balance is totally optional, so I'll leave it out. When my sources are fed directly into the amps, I can't listen to them. In fact, I have my setup in a typically "american setup" (don't flame me - I read it in a magazine!). That is where you have your source and amps etc. between your speakers. I couldn't get close enough to turn it all off without seriously hurting my ears - Thank god for remotes! ;) My monoblocks have absolutly no controls on them whatsoever (apart from a power switch.) Here is a link to some pics of them... PICS (They're from about half way down the page) Thanks, Gaz Bobken Hi Rarkov, I am sorry to see that you appear to be disregarding some of the advice which has been given to you in this thread, and fear that you may end up with an arrangement which is as unsatisfactory in use, as you say your first effort was.:goodbad: If what I, and several others, have said is ignored you will almost certainly end up with something which is definitely *not* Hi-Fi, but if that is OK with you, as I also said before, almost *anything* will do. One cannot simply overcome the 'physical laws' associated with impedances and capacitances, and with your present proposal, you will inevitable end up with a severely curtailed HF response. As Traderbam suggests, you need to keep the pot's value low, and even the 10K which he (and I) have suggested is not ideal here, although it is probably about the best compromise, especially for SS gear. The output impedance of the 'passive' will depend entirely on the output impedance of the various bits of preceeding gear you use as your source, together with the value of the pot chosen, and you do need to take these into account. If, for example, the output impedance of the passive ends up at perhaps 50K at full rotation (quite possible with say a 100K pot) and the capacitance of the following cable is 300pF (again, quite likely), the 3dB time constant (i.e. where the power is *halved*!!) will occur at just over 10KHz. This is well within the human hearing range, especially for someone quite young, like yourself, whose 'upper limit' will be very much higher than an old guy like me! As the reduction in power *commences* at a decade *lower* than the 3dB point, the signal will start to be reduced from just over 1KHz!:nod: Is that what you want in use? Under these circumstances, you will find that the volume control will act more like a tone control, unfortunately! As I said earlier, I don't wish to deter you in any way, but with a little effort in research, you can overcome (most of) the problems, but the result will inevitably always be a compromise, based on all of the parameters of your existing equipment and the chosen cables etc., and only you can make the right choice here. However, you do also need to understand the other requirements over impedance 'matching' which I, and some others have referred to, as otherwise, you may end up with very little signal being transferred between the source and the amp, even though the signal might not be reduced severely at HF. Incidentally, I would certainly dispense with the proposed balance control, as someone else has said, as this will also tend to have a deleterious affect on the sound. Regards, DRC Rarkov, Apart from the balance circuit your schematic will work. If you knew the recomended minimum load impedance of all your source components, and it was below 10k (I would bet they are), I would choose a 10k log pot rather than the 100k shown. As Bobken pointed out the effective output impedance will interact with the cable capasitance (and amp input capasitance) to form a lowpass filter - the 10k pot would improve the situation and with short / low capasitance cable the effect would be negligable. If you must stick with 100k vol pot you should think about going the active-passive-pre-amplifier route :clown: with a unity gain buffer. Even with half-reasonable source components you won't need balance - I don't and find it a blessing as there is one less thing to fiddle with. BTW I don't think you will need a blocking capasitor, just put 1M to ground on each input and on the output. This will pull any source component coupling capasitors to ground. If you get a thump when you switch you will know I was wrong :bawling: . :idea: Maybe you could add the coupling caps only to those inputs that need them, with a 1M to ground. Dave till This is very interesting. Some days ago i played around and tryed to connect my CDP direct with Zen V4 instead of using my BOZ. Disadvantage is no volume control, so it is a little loud, but the impression was it sounds better without the preamp. I took a look in the manual for the DAC in the CDP: http://www.daisy-laser.nl/homeoptics/tda1305t.pdf and it says minimum R load is 3k. What value for Volume pot shoul i use between TDA1305 and ZEN v4, cables are about 0,5m from CDP to Volume control and 0,5m to ZEN V4. I donīt need source switches, i want to connect only the CDP, nothing else. Do i need any of the additional coupling Cīs ? for what purpose, and why the 1M reswistors?? Thanks, Till DRC Til, I would go for 5k log pot if you can find a good quality one but otherwise use a 10k log. With only 0.5M of cable (after the pot) you should get good results. Computing turnover frequency. ----------------------------------- The maximum output impedance will be about half the value of the pot, call this RV/2. If the load capasitance is C (pF per metre of cable after the pot * length of cable + amplifier input capasitance) then :- Xc=1 / (2*Pi*F*C) Let Xc=RV/2 exchange Xc and F cancel out the 2's -> F (-3db point) = 1 / (Pi*Rv*C) Bobken's ears :devily: tell us this should be at least 200kHz for undetectable attenuation Dave Audiofanatic Gaz I would say, give it a try and find out for yourself if it's worth the effort! That's the way I'v learn to deal with electronics. If it's to expensive, try it out with cheaper and/ or used parts. If it sounds great, use better parts, if not, at least you know that the guy's who told you not to do that where right. Remember " The proof of the (Electronic)pudding is in the (audio-hearing)eating! All the best and don't giveup! We are here to help you! Audiofanatic!:nod: :idea: Bobken Bobken's ears :devily: tell us this should be at least 200kHz for undetectable attenuation Dave [/B][/QUOTE] Hi, I only wish that was true!:bawling: Regrettably due to advancing years my threshold for pure tones runs out not much higher than 10kHz, but Rarkov's should be nearer 16kHz, I would have thought. However, interestingly, I can still hear the effect of curtailing the frequencies at say 40kHz, which seems to rob the sound of 'air', for want of a better expression, and some recording venue ambience, which detracts from the overall enjoyment of listening. This particular phenomenon is well recognised in audio circles, and very likely relates to some kind of 'beat' effects, due to some harmonics which have been removed. I have built many passive pot arrangements and some switched type attenuators, the nicest-sounding of which I still use from time-to-time. This was constructed with the very best available components I am aware of (a silver contact Shallco switch and all Vishay bulk foil resistors), but good-sounding though it may be, it is still, unfortunately, subject to the normal laws of physics. The maximium output resistance is only 13.5kHz, but at near full volume, I (originally) noticed this quite obvious loss of 'air' around instruments and performers, which I mentioned. With my (then) 300pF capacitance interconnects, I calculated the 3dB point which was about 39kHz, and I was puzzled by what I heard. I also checked it out on my 'scope which indicated about 40k, so there was no other un-accounted-for effects, but it was clearly audible to me, in its effect on the sound. Also, looking at the 'scope trace for a while it became apparent that the signal level *commenced* rolling off much lower than this, and it didn't take me long to figure out why. As I said, from calculation it actually commenced at a decade lower, i.e. at about 4khz, which is well within my (restricted) threshold! I only overcame this problem in the end by making up some very low capacitance (30pF) DIY 'output' cables, and I can not now hear any loss of ambience with this passive attenuator. With Rarkov's proposed arrangement very likely showing a *half power* output at merely 10.6 kHZ (and roll-off commencing at 1kHz), it seemed very wise to me to get Rarkov to look into the matters I had suggested, since he said he had already been dissatisfied following the first attempt he had made. There must be very many references to passives available, as I constantly come across them by accident, and as Rarkov has his own electronics web site, now seems to be good time for him to fully appreciate the basic engineering matters to be taken into account here. As I said several times before, I don't wish to deter Rarkov in any way, and of course more or less *anything* will *do*, but if he wishes to make a good job this (the second!) time, he cannot ignore the relevent requirements and limitations. :) Regards, fdegrove Hi, For those wanting to look into the topic of attenuators and passive preamps there are at least a dozen threads about it in various sections; Solid State,Everythings Else...etc. Just doing a search on "Attenuator" will yield a few pages already. Rarkov's hearing could well be into the 20kHz range but as Bob states correctly IME,you can still easily discern HF roll offs well over 50KHz. Cheers,;) Rarkov Hiya, Thanks for all your help. Bobken - I'm not ignoring yours, or anyones advice - but I am guilty of glossing over things I don't really understand! ;) I really shouldn't be doing an electroncis degree - but there you go! :goodbad: I think that Audiofanatic gives good advice, and I will try a few things. But here is a shocker for you...When I was young I burst my eardrums twice (my brother shouted in my ear as a baby and the other time I can't remember what happened)...I forgot about these, but when I was diving recently, at about 20m under, it burst again. Apart from being exceedingly painful - my hearing isn't fantastic! I would expect (although I have not yet conducted tests) that my hearing rolls off quite early. :bawling: If anyone knows the effect of burst ear drums on hearing - I'd be interested in hearing it. I am going to take your advice and get some cheap 10k 50k and my expensive 100k pots and have ago. I will also try the unity gain buffer. Where would I put that in? Just after the volume or before or both?! Thanks for all your help! Gaz dhaen All, When I was younger I could hear the difference between sine, square and sawtooth waveforms of around 15KHz. Even so, my hearing could not (for sure) detect a sinewave above 19 or 20KHz. This told me that there is more to it than meets the (eye?). Rarkov, My hearing is considerably "down" on what it was, but even so, I have become more fussy about what I can hear. Cheers, fdegrove Hi, quote: I will also try the unity gain buffer. Where would I put that in? Just after the volume or before or both?! Having a buffer behind the vol.control should do the trick. Cheers,;) planet10 I surprised no-one has pointed you to this long thread on the subject. dave Rarkov You star! That's exactly what I'm looking for...Now I can use my Alps 100k dual gang pot! I have the 1% metal film resisotors so that's cool...and the rest of it is on its way! Thanks... I'll keep you posted about opinions...If I don't like the sound, I'll try a different approach. The preamp (modified integrated amp) starts "flapping" the speakers around at anywhere near decent volumes, yet when I use the CD player directly, it sounds great...Therefore I know it's the preamp... As I said - I'll let you know...I'm very excited about this! ;) Gaz choky quote: Originally posted by Sch3mat1c The answer I was looking for is "oxymoron". Why would you want an inline pot anyway? Don't any of your amps/preamps/signal source/etc. have a built-in volume control? Tim :redhot: :redhot: :redhot: :redhot: :redhot: :redhot: :redhot: Bobken Hi Rarkov, What a surprise you now come up with, and I am very sorry to hear of these problems with your ears. :bawling: However, if you are studying for an EE Degree as you now admit, the calculations necessary here are very basic, and it is starting to seem that you are just not bothered to do something for yourself but you expect others to do it for you. :eek: That's it from me then, and I wish you luck for the future as you'll surely need it, if that is your approach to problems, especially when you eventually need to earn yourself a living. :nod: Regards, Rarkov whoa...where did that come from?! :dead: My degree is Communication & Electronic Eng (BEng Hons) but my sandwich year placement is as a systems engineer writing software for PLCs and SCADA. I much rather be using my electronics skills and keeping in touch with topics closer to my degree but life's a *****, eh? Anyway, as you may have gathered, my knowledge of basic electronics is rather sketchy until I get back into regular workouts of the brain...Also, there is the topic of not reinventing the wheel. When I performed a search on this subject - I didn't go back as far as I should have to find the linked article. It does discuss problems of cable interfacing, yet it uses the components I have to hand. I wouldn't blame anyone for wanting to try great reviews and simplicity over resolving a solved problem. Please don't think that I take peoples' input for granted...I really do appreciate any help I get. Thanks again...I'll keep you posted... Gaz Bobken Hi, "whoa...where did that come from?!" came from your post #26 where you clearly said "electronics degree". I don't wish to fall out with you though, but why couldn't you have simply taken the advice in my very first post, reiterated several times, and finally reinforced by Frank? You only needed to search on "passive" as I said. :goodbad: Regards,:) fdegrove Hi Bob, The link Dave posted is well worth going through. It has number of different approaches to the concept of a passive preamp and discusses a number of topics that will surely be of interest to you too. I wish more members would read it through so that we can point to it instead of keeping rehashing our wisdom to the youngsters. (no offense to any of you).:rolleyes: Later,;) Rarkov No - I admit it - at 20, I do not have much practicle knowledge...but I am learning. This is a forum and whilst I certainly do not want to fall out with anyone (our prime minister is doing a good enough job for everyone!), lots of people offer conflicting (or indeed correlating) advice. It is difficult to choose between them. It just so happens that an oppertunity presented itself that solves my problem exactly. I hope we can put any differences behind us - and get on with what matters...and I believe that is the music. Thanks, Gaz Bobken Hi Frank, Yes, your advice here is good and now that I am aware of this particular thread, I would in future point any enquirer to it. It would have saved me some time in attempting to help with the enquiry. However, as I only joined the Forum myself in December, I was not aware of it before, and I did suggest at least three times that Rarkov should do a simple search for himself, as did you, but for reasons best known to himself, he didn't do this. When he finally said he was taking an Electronics Degree (or words to that effect), I was amazed! :goodbad: Regards, Edit : Having just seen Rarkov's last post (since I typed the above) I agree with him wholeheartedly, in that it is the music that really matters.:) transducer You all might be interested in this passive preamp thread. It was inspired by Harry Haller's post. http://www.diyaudio.com/forums/atta...s=&postid=82996 It worked very well, once I added the input shunt resistor. Without it I had hum problems. RonS Bobken quote: Originally posted by fdegrove Hi Bob, The link Dave posted is well worth going through. It has number of different approaches to the concept of a passive preamp and discusses a number of topics that will surely be of interest to you too. I wish more members would read it through so that we can point to it instead of keeping rehashing our wisdom to the youngsters. (no offense to any of you).:rolleyes: Later,;) Hi Frank, Just read through the entire thread, and it has taken me well over an hour!:cool: Nothing new in it for me, but it was worth spending the time to compare my experiences with those of the others. Hopefully Rarkov now understands why I gave him the advice I did, and I see that all of my caveats and the associated considerations I advised him about, are covered 'in spades', even though it took 10 pages of posts! I particularly enjoyed Promitheus' referenced article from AV Extreme Mag, as I had not read this before, and I wish I had been on the Forum then, as I could have added somewhat to the information. The very best method from the sonic viewpoint is to use an 'L' pad attenuator like I referred to earlier in this thread. This way there is merely one resistor in the signal path at any one time, and only one in shunt to ground. I bought all the parts from Audio Synthesis in about '95, and they use all Vishays (you like these BFs, I know) and massive military style coin-silver contact Shallco switches, with 31 steps. For two mono attenuators it cost me over Ģ500 for the parts alone, way back then! :bawling: There really is nothing to touch these, as Martin Colloms has said many times, even recently, and they still outperform my passive Audio Synthesis 'Passion Ultimate' (like your pal's) which is nearly as good, but because of its being a remote-operated job (very much more convenient!), the quality of switching in the 'Passion Ultimate' is marginally less good. MC is quite right in awarding it a couple of points less than the dual mono manual 'Passion'. My previous best, having tried all of the usual Panasonic, Noble, Alps, and Sfernice arrangements with law-faking resistors (like HH favours) was a Penny & Giles pot with Vishay 'law-fakers', but that pot cost over Ģ90 about 15 years ago. This was very slightly better, if anything, than an 'L' pad made of all Holcos, which I also tried at one time. The only attenuator which might be marginally better would be if the Vishays (or similar bulk-foils) had been surface-mount jobs, thus avoiding the (very short) leads, and I do believe that Jonathan Carr uses this arrangement in his Connoisseurs. Once heard, never forgotten comes to mind! :cool: Regards, jcarr Bob: The resistors that I use are both surface-mount and nude - that is, they have neither leads nor protective package. There is only a ceramic substrate, the resistive element, two tiny solder pads, and a thin coat of lacquer to stop short-circuits and environmental elements from touching the resistive element. Compared to the so-called "nude" Texas Components TX2352, the overall construction is far flimsier, and the amount of physical protection provided for the resistive element is far less. The result is a resistor that sounds good, yes, but also one that is much easier to break than any other resistor that I have ever tried. I always have an excess of each value made, as I know from experience that some will inevitably break during the production process. regards, jonathan carr Peter Daniel I've been hearing comments that transformer based attenuators are the way to go. Never tried them though. Peter Daniel What about the resistor based attenuators used in balanced lines, where there is a single series resistor in both positive and negative side and then one resistor between both sides? fdegrove Hi, Bob, Sorry if you feel you wasted your time...both of us are aware of Ben D's work and it is beyond doubt extraordinary. I'm,myself however no big fan of passive preamps, preferring the active stages. Naturally the same priciples for VC can be applied...It's easier for me to have a more universally usable device. Attention to detail always pays and that's where the Audio Synthesis stand out. Jonathan, No comment really...I expect the nudes to sound better and from the 'feedback" I get they do. They're more fragile...so be it. In a semi-conductor environment I'd expect the SMDs to even sound better...me I think tubes and hardwiring,you know that,don't you. Peter, quote: I've been hearing comments that transformer based attenuators are the way to go. Never tried them though. I hear enthusiastic comments from Benny Glass at Aquablue,Brett,John and others...mostly this is tube oriented stuff though and not easy to implement at all. I have no idea whether anything usable for semi-conductor based gear is available...unless of course the emperor is changing clothes...and turns tubes???;) One situation I consider is in a phono preamp using LCR RIAA correction where I think xformer coupled stages may be the more "elegant" way to go. That's still in the pipelines though,so don't hold your breath. quote: What about the resistor based attenuators used in balanced lines, where there is a single series resistor in both positive and negative side and then one resistor between both sides? That's what I use now,only one R in the signal path and a fixed R as input R, balanced or not it is to my ears the better arangement bar perhaps the xformer. Mind you,in my system the attenuator is looking at the gridleak R of the buffer,so you can't call that passive. You'll need to figure out what works best for you here,IMO. I adhere to the minimalist filosophy,not everyone agrees though. Cheers,;) planet10 quote: Originally posted by Bobken do a simple search... didn't do this This could be partially blamed on the current search system which can be somewhat cumbersome. If i didn't know it was there i would not have been able to find the link i did... and it still wasn't a simple search. dave Bobken quote: Originally posted by planet10 This could be partially blamed on the current search system which can be somewhat cumbersome. If i didn't know it was there i would not have been able to find the link i did... and it still wasn't a simple search. dave Notwithstanding this, there is wealth of relevant information on the Internet, for anyone who makes the effort to seek it out, as I had advised, many times!:goodbad: Regards, :) Bobken Hi Jonathan, Thanks for yours comment, which shows my assumption about your choice for attenuators to be correct. My own view is that, when you get to the level of refinement we are dealing with here, the switches become the limiting factor, and I have not so far seen any better way of doing this than the 'old-fashioned' rotary 'self cleaning' style which we use. As I mentioned to Frank, my 'old' A/S Shallco switch based attenuator still outperforms the newer A/S Passion Ultimate, which (apart from the switching) uses much the same 'ingredients'. However, the convenience of having remote operation with the latter is not to be ignored, but for all of my serious listening tests on components etc. (except where front-end phono gear is concerned, of course), I always revert to the 'old' manual 'L' pad attenuator, as it is simply more revealing. Regrettably, I have not yet been very impressed, sonically, with any solid-state switching which I have tried. I know nothing about transformer-based attenuators save that I prefer to avoid transformers wherever possible (as they can be problematic in construction for good-sounding ones, and they are expensive etc.), but common-sense tells me that there must still be some associated switching, so we are back to the very same limitations here. If my understanding about this is anything like right, I wouldn't favour swapping out a Vishay with a coil of wire of the quality found in most transformers! I'd rather keep the resistor.:cool: Hi Frank, Where did "wasted Time" come from? :bawling: What I said was "but it was *worth spending the time* to compare my experiences with those of the others":nod: I am certainly not omniscient in *any* audio-related matters, and there is nearly always something to be learnt from what others have to say for themselves. Also, unlike some people, I am always prepared to give up the necessary time to carefully read about what others have to say, even if I don't happen to agree with it. However, in this case, (unusually) I didn't learn anything new about attenuators, as it happened, but I felt that I could have perhaps added some value to what had been said, as passives have been an interest of mine for 15+ years, and I do have a little experience with them.:goodbad: As you know, I admire and get on well with David Heaton of A/S, simply because I empathize with his approach towards audio matters, and like me, he is passionate about details, and will go to the ends of the earth to get things right! Also, whilst he's very much into choosing components by ear, he will not put up with any b*l*s*i* or 'snake oil', and it is interesting (now I think of it) that he is another staunch supporter of BGs! Regards, Brett quote: Originally posted by Peter Daniel What about the resistor based attenuators used in balanced lines, where there is a single series resistor in both positive and negative side and then one resistor between both sides? I used this arrangement (U attenuator) before I went to the S&B transformers. At wide open throttle, there is little to choose between the two (Tx still best), but as you attenuate, the Tx gets better and better. I set my system up so that I'm listening at around the -20 to -25dB range for most material, at most times, or around 80dB SPL. The difference between the two is even greater when you have long cables to drive. It would be interesting to hear the S&Bs driven by some sand, like the BalZen. Later I want to add a tape monitor output to my pre, using a BZ or one of the Aleph P designs, so I'll try it then. There simply isn't any more room in my pre for more tubes and transformers, and besides, I have all the parts in my parts box. fmak The only attenuator which might be marginally better would be if the Vishays (or similar bulk-foils) had been surface-mount jobs, thus avoiding the (very short) leads, and I do believe that Jonathan Carr uses this arrangement in his Connoisseurs. Regards, [/B][/QUOTE]-------------------------- Not necessarily, I have not heard Jonathan Carr's but the Danish Audio DACT? ones don't sound good to me (rather dim and muted) compared with the Audio Synthesis ones (tends slightly to be dry and brighter than neutral). The Carver Lightstar Direct balanced passive is excellent. Do a serach in Stereophile archive. Mark A. Gulbrandsen "I've been hearing comments that transformer based attenuators are the way to go. Never tried them though." ___________________________________________________ Transformers are just ok in my book, even if they are really high quality. There will ALWAYS be more phase shift in a transformer and be sure not to saturate the core , especially at low frequencies. With added features like phase shift, ringing, and possible core saturation in ones system that ought to add some special effects.... Personally I'd stay away from using them and use a simple resistor attenuator...you'll find it does less to an audio signal then even the best of the best audio transformers. Companies like Jensen are pushing their use, and to me its probably more due to the fact that so many devices have been made transformerless(for good reasons too!). These companies have to explore new inroads to keep their sales up. I believe Jeff Rowland uses some Jensen transformers, but then they also use I.C.'s in the output stages of at least one of the high priced amplifiers they sell. Leaves me wondering......... Mark Bobken Quote.*** Not necessarily, I have not heard Jonathan Carr's but the Danish Audio DACT? ones don't sound good to me (rather dim and muted) compared with the Audio Synthesis ones (tends slightly to be dry and brighter than neutral). The Carver Lightstar Direct balanced passive is excellent. Do a serach in Stereophile archive. [/B][/QUOTE]*** Hi, I agree entirely with your findings on the DACT attenuators but they (or at least the one I listened to, did!) have much poorer quality metal film resistors in them and a much less good Elma type of switch, so this should be no surprise. Bulk foils and coin silver switches 'sound' much better, in my experience, and Jonathan's Connoisseur will be in a different league from a DACT, as a result of this. I, also, have not heard Jonathan's Connoisseur, but according to the recent comments in Hi-Fi+, he must have got most of it right!:cool: I don't agree at all, with your suggestions over the Audio Synthesis (manual passive, as opposed to the latest remote-based Passion Ultimate) as I find this extremely neutral. If quoting reviewers' opinions as a 'reference' holds any merit, it seems that Martin Colloms agrees with me.:goodbad: By neutral, *I* mean compared with a 'straight wire' which can be done as a comparison. Have you done this 'direct' comparison in forming your opinions, or, if not, what was the yardstick you used in reaching this conclusion? I regret to say that I am not overly impressed with some of what I have seen recommended in 'Stereophile', but I have not read the comments to which you refer about the Carver Lightstar Direct. Many of the opinions seen therein appear to be purely subjective and based on comparisons (if any) with other similar equipment, which in my view has little real merit as the yardstick is merely one of 'familiarity', as opposed to being truly 'neutral'. I will, however, reiterate that the Shallco/Vishay attenuator is IMHO extremely neutral, and it is hard to imagine how this could be much improved upon, as I had said. Regards, :) fmak By neutral, *I* mean compared with a 'straight wire' which can be done as a comparison. Have you done this 'direct' comparison in forming your opinions, or, if not, what was the yardstick you used in reaching this conclusion? ------------------------------------------- Straight wires sound different and so how does one do a comparison? I have not tried the new Passions but I understand it is more 'neutral'. ======================= I regret to say that I am not overly impressed with a some of what I have seen recommended in 'Stereophile', but I have not read the comments to which you refer about the Carver Lightstar Direct. Regards, :) [/B][/QUOTE]------------------------------------------ Many Sterophile reviews are fine. I have the Carver and it is truly excellent, one of the few with balanced remote operation. I am not impressed by the reviews in HI Fi+. Seems to be a 'selling' mag with reviewers of unknown pedegree. I find some of their exhaltations to be rubbish, from personal experience. Bobken Hi Fmak, I don't mind at all if we don't see eye to eye on some of these matters, since our experiences have been rather different, but, as before, I will answer the points you have raised. :) For the comparison test I suggested, merely set up different value 'fixed' attenuators elsewhere (immediately before or after the passive) so that in order to balance out (accurately) the overall sound levels, the DUT is in one circuit, but not at all in the other. (i.e. fully rotated, so no *variable attenuator* resistors are in the signal path on one side) However, it is adviseable here to ensure that everything else possible is in a similar 'state' and that both identical (mono) signals pass through exactly the same cables and components etc. I also tried this with three different types of resistors for the 'fixed' attenuation arrangement (Vishays, Caddocks, and Holcos) in case the results might be skewed by any 'synergy' or untoward 'clashes' between the resistive elements in the attenuators and the resistors used for the 'fixed' arrangements. Fortunately, I have never heard of any claims that resistors of the same type vary noticeably in accordance with their values in their sonic attributes, and, indeed in my own long-term experiments, I find that they all have a family semblance based more on the type of construction and materials used, whatever their individual values may be. Having done these trials, I also set up another test which used *only* the fixed resistive attenuator in one side, and with the passive in the other, but (as I had made the passive anyway and I had other similar phonos and jacks to hand) I used these connectors in exactly the same way to replicate those used in the Vishay/Shallco attenuator, in an effort to avoid any other unnecessary variables. With some care, full details of which I won't reiterate as I have shown this elsewhere in several places on the Forum, but which include siting speakers together in the middle of a large room, and because no two speakers even with hand matched components (like mine) ever sound *exactly* alike, and neither do two channels of (also matched component) amps or preamps, you do need to 'ring the changes' from time to time, by swapping these components around. It is then merely a matter of patiently switching from one channel to the other, however many times as is found necessary, in order to identify any *differences* which must be due to the DUT, when compared with 'nothing'. (i.e about as close as one can practically get to a straight wire.) This kind of arrangement is a little less easy with attenuators such as here, but similar methods are used (by me, at least) frequently in any such 'comparison trials', as I have said before. Having done this, I could detect no *significant* differences repeatably and consistantly, between having the Shallco/Vishay attenuator, in circuit or not, over many many hours of careful listening. Of course, there will be *some* albeit minor differences, as this is inevitable with using *any* different component, but even in my own very revealing system, they were not significant enough to be able to identify and describe properly. I am therefore satisfied that as much as is humanly possible, these were very effective 'straight wire' comparisons, in the same manner as all others which are undertaken in similar circumstances, and it is not possibly IMO to do any better. If any others have developed an easier or more effective method of carrying out such tests, I will be grateful to learn of them. Certainly, the above tests will outdo any such ordinary subjective 'sit back and listen' tests (which I have also been conducting for about 30 yrs, and which definitely have their place in audio development), which are more about whether one *prefers* the sound or whatever, rather than if it is more *accurate*. As I indicated by my earlier comments, I don't take much notice of *any* reviews, preferring to find out for myself in such cases, and I am sure that many Stereophile Reviews are "fine", as you suggest. I just wished to know, and I still don't as you have omitted to say so, whether your opinions (or maybe Stereophile's, as you mentioned this mag and appear to hold them in esteem) were based on *comparisons* with other gear (frequently so with Stereophile), or whether, like me, you (or they) have attempted to conduct any more *valid* tests in deciding that the A/S attenuators exhibit the problems to which you referred? Regrettably, your comments on the two A/S devices should be completely reversed, since as mentioned by me earlier (and, again, for what it is worth, by Martin Colloms) the 'old' A/S Passion is sonically a couple of points *ahead* of the later remote Passion Ultimate (both of which I use, as also advised), which reinforces my view that either you are not very familiar with these devices, personally, or that you have never done an A/B comparison between them. The remarks relating to Jonathan's Connoisseur, were in relation to the comments made by Roy Gregory in Hi-Fi +, and Roy is very well known and has been on the audio scene for many years. Interestingly, for anyone who is not familiar (perhaps like yourself?) with the review concerned, the article was all about Boulder equipment, but Roy simply raved about the Connoisseur in that review!:nod: It is the first time in some 45 years that I have ever seen such a situation, where so much praise was awarded (and so much space allotted) to another make of equipment within a review of an alternative manufacturer, incidentally, whose (Boulder's) products were also thought quite highly of. As I said originally, merely from my own knowledge and experience of the components used by Jonathan in his attenuator, it *will* be in an entirely different league, sonically, from a DACT , with which you had drawn some comparisons. Maybe, Jonathan might care to add something here, since as I said, I have never heard his preamp, although I am aware that it is considered to be at the very 'top of the heap' within knowledgeable audio circles. :cool: Regards, Peter Daniel Hi Bob, Your Shallco/Vishay attenuator is of a Series type or Ladder L-Pad? Bobken quote: Originally posted by Peter Daniel Hi Bob, Your Shallco/Vishay attenuator is of a Series type or Ladder L-Pad? Most defenitely 'L' type, Peter. I had already tried about half a dozen of both styles using different resistors (like Holcos) and the Swiss Elma switches, and, always, the 'L' types were markedly superior, except when running at (almost) full volume, which I rarely do!:bigeyes: Otherwise, I guess it is the fact that the signal goes thro far too many separate resistors and soldered joints, which, as we all should know, will not help with the very best sonics.:nod: The main problem with these jobs is getting hold of (small quantities of) the necessary frequently obscure values of resistors of this quality level, in order to get the steps correctly matched. Mine are in 0.5 dB steps down to -42 dB, and then in 3 steps down to '0', although apart from '0', I don't ever use these last few steps. They are very 'usable' gradations, and the channel balance due to the use of 0.1% tolerance bulk foils, is as near as one can get to perfect! I was very fortunate, when I made this attenuator in '95, in being friendly with David Heaton of Audio Synthesis (a smashing chap, and very talented!) as he used these components in attenuators which he built for sale, and he very kindly sold me the relevant bits. I can never thank him enough, as my system resolution then took an almighty jump, even though it was quite good before.:cool: Regards, Peter Daniel I also think that L Pad is more prefferable choice, yet when looking at Connoisseur production photos (below), it seems like their attenuator is of a series type using 39 resistors (although, I might be wrong here). Because of both surface mount and naked type, they probably less intrusive sonically, even when so many are in series. I would be interested in Jonathan's comments on choices made here. My approach to preamp is that when you don't need it, don't use it. This narrows my selection to only one source component, but this is what I mostly listen to, so why make sacrifices by complicating signal path with switches and additional wiring and jacks? I'm using CD source and separate DAC with a volume built in at the output. It consists of a fixed series resistor (50 ohm Vishay) and variable switch with 24 resistors selection to ground. Some may think that it's not enough, but for my needs it's more than enough. I'm mostly using selection between 15 and 20th position. The switch is based on Elma and I like it because of a small size. Initially I had some pops but after spraying contacts, they are fine. Resistors are variable between 0.5 - 500 ohm and the output resistance is usually 100 ohm. Bobken Hi Peter, Don't be too hasty in thinking that Jonathan's attenuator is a 'series' job, merely from the picture. I hope Jonathan will share some more of his valuable comments with us, but, in the meantime, I don't know if you are aware of it but a 'true' 'L' pad (impedance matched) should switch a different shunt resistor *and* a different series resistor into the circuit at each stage. This is needed to preserve the same input and output resistances seen by the cables and the surrounding components (i.e. source and amp) to suit their output and input impedances. Most, (including mine!) don't because of the doubling of the already high cost, and the poor availability of good-sounding resistors in the required values. In normal positions of rotation, the use of only one 'fixed' series resistor is a reasonable compromise, but, as I kept on telling Rarkov, such things are still a compromise, nevertheless, and the input and output impedances of the passive will vary according to rotation etc., which can have bad effects on the surrounding gear. Somehow, I cannot see Jonathan going for any such compromise, and it is my guess that he uses the full 'L' pad arrangement, but this is only a guess and we will have to wait and see if he kindly replies to us. :) Regards, Edit: Incidentally, that picture you show looks to me like a Shallco, alright, and they are superb switches from the sonic aspect! Peter Daniel It may be true that having a fixed series resistor and changing only shunt resistor's value is a compromise, but to me the impedance change between let's say 60 ohm and 250 ohm (this is what I'm mostly using) is much less compromise then having a switch in a signal path and a longer path as well. Please correct me if I'm wrong.;) Bobken quote: Originally posted by Peter Daniel It may be true that having a fixed series resistor and changing only shunt resistor's value is a compromise, but to me the impedance change between let's say 60 ohm and 250 ohm (this is what I'm mostly using) is much less compromise then having a switch in a signal path and a longer path as well. Please correct me if I'm wrong.;) As I said, I am quite content with the same kind of arrangement as you, and if it wasn't for the impedance matching with surrounding gear, there would be no issue here, so it will (to some extent) depend on the parameters of what you use. Again, this was why it was impossible to give Rarkov any definitive advice over this. You do really need to know the various impedances involved, to ensure proper and adequate signal transfer. I only mentioned my thoughts on Jonathan's setup (and I could still be wrong, here!) bearing in mind that it is possible at extra cost and complication, to avoid this particular compromise, and I don't see Jonathan doing much in the way of unnecessary compromising, if I am any judge!:cool: I hope he will tell us. Regards, Peter Daniel quote: Originally posted by Bobken I don't see Jonathan doing much in the way of unnecessary compromising:cool: I noticed that too.;) Bob, Are you using your attenuator at the input or output? It's been sugested by Nelson Pass that actually the better placement is at the output, providing you don't present too much signal at the input. And what value of resistance are you using in your setup? I'm asking, because knowing your experience in that matter I might built something similar, maybe even using Shallco switch. With having so many choices in resistance selection it's quite hard to spend $400 or more for premium parts, only to learn later that the choice was inappropriate.;) Bobken Hi Peter, Thinking again about what you said, I guess it will depend also on the quality of the switch, and as I believe you had already probably posted before my edit, you may not have seen my comment on the Shallco (?) switch picture you posted. These (or something similar with coin silver contacts, perhaps) are really a step ahead of *all* others I have tried (including Elmas, which are not bad) and they are just about as transparent and reliable in use as it is possible to go. I guess they were developed for military use originally, where maybe lives are at stake if they don't work well (!), but by chance, as they are so well made and put together with sonically good materials, they also 'sound' superb. In such a case, I am (only) guessing that a double-switching arrangement with a proper two resistor 'L' pad, would sound as good as the types we use, and there is the added advantage of completely avoiding the otherwise varying impedance issue, which is more elegant, and (I am also guessing) would be more 'aesthetically' appealing to Jonathan. Regards,:) Bobken quote: Originally posted by Peter Daniel I noticed that too.;) Bob, Are you using your attenuator at the input or output? It's been sugested by Nelson Pass that actually the better placement is at the output, providing you don't present too much signal at the input. And what value of resistance are you using in your setup? I'm asking, because knowing your experience in that matter I might built something similar, maybe even using Shallco switch. With having so many choices in resistance selection it's quite hard to spend $400 or more for premium parts, only to learn later that the choice was inappropriate.;) Peter, I have just seen this and it 'crossed' with my last comments. I have just been called for dinner, which, on Sunday here, is a big Do! nod: I will post again in a couple of hours. Regards, :) Steve Eddy quote: Originally posted by Mark A. Gulbrandsen Transformers are just ok in my book, even if they are really high quality. There will ALWAYS be more phase shift in a transformer and be sure not to saturate the core , especially at low frequencies. With added features like phase shift, ringing, and possible core saturation in ones system that ought to add some special effects.... Well, phase shift is rather meaningless as typical phase plots are the result of both frequency dependent and frequency independent delays. What matters is whether or not all the frequencies are arriving at the same time. And that question is answered in a plot of group delay, or as Jensen refers to it, deviation from linear phase (DLP). Taking a look at the DLP plot of the Jensen JT-11P-1 shows a difference of just 0.6 degrees at 20 Hz. Sure, a resistor won't have such an effect because there is no high pass filter function involved. But this needs to be considered in the proper context. We don't just listen to preamplifiers and amplifiers. Y'ever see a group delay plot of a loudspeaker? :) Core saturation is a concern but is dealt with by using an appropriate core size for the task at hand. You wouldn't want to slap an input transformer on the output of a power amplifier. Ringing isn't a problem for properly designed and properly loaded transformers. However this is one concern I have about transformer-based attenuators. Each position gives you what amounts to a different transformer, yet every position will be loaded exactly the same as every other position. quote: Personally I'd stay away from using them and use a simple resistor attenuator...you'll find it does less to an audio signal then even the best of the best audio transformers. Companies like Jensen are pushing their use, and to me its probably more due to the fact that so many devices have been made transformerless(for good reasons too!). These companies have to explore new inroads to keep their sales up. Last time I talked to the folks at Jensen, they had no interest whatsoever in doing any sort of transformer-based attenuator. Jensen only pushes transformers for what they've always been superior at; ground isolation and noise rejection. And as far as I'm aware, Sowter and S&B only produced their transformer attenuators at the behest of Thorsten Loesch, who is the preeminent transformer attenuator proponent. quote: I believe Jeff Rowland uses some Jensen transformers, but then they also use I.C.'s in the output stages of at least one of the high priced amplifiers they sell. Leaves me wondering......... Which leaves me wondering just what it is that you're wondering. :) se Bobken Hi Peter, I don't fully understand what you mean by the input or output here, but I assume it may be related to the BOSOZ (or one of these preamps) which has some attenuation at both input and outputs. If that is the case it doesn't apply with me as my (active!) preamp is a much modded Spectral, which strictly-speaking has the attenuator in the middle of it! It is perhaps a rather unusual arrangement in the Spectral, but there are two very similar stages (in each channel) with the first being an RIAA stage of almost identical topology to the second stage (except for the passive feedback RIAA) which is merely to amplify the signal. Between the two stages, there are several switches which permit the connection of other inputs, and this then feeds directly on to the attenuator, which 'fronts' the second stage dual FET input. This attenuator (third version!) is now a dual mono Shallco/Vishay job with a mechanical 'tandem' arrangement I made using plastic gears, with a 'swing arm' central sprocket which can be lifted out of engagement to permit shifting balance etc., if ever needed. I only use this balance provision normally for testing purposes, as all of my sources are well balanced anyway, and all of my equipment has lids which are never screwed down, so I can carry out mods easily. :nod: In fact the Spectral has a rather attractive (in my opinion) smoked Perspex see-through lid which I made because the gold-plated circuit board looks so pretty! You may empathise with this, but the sound is also a little nicer with this lid than with the original aluminum one! :nod: In addition, I have a separate dual mono A/S type of passive attenuator in a small alumium enclosure which can be plugged into the system in place of the (active) preamp, even for vinyl, as I have a separate (from the Spectral) HQ RIAA and pre-preamp stage, also in an aluminium box. Finally, to complete the lineup (apart from about 5 other DIY passives using differing pots and resistors!) I have the choice of using an A/S Passion Ultimate, which is the latest version from A/S with a remote control, which I use when I am (infrequently) feeling lazy!:goodbad: This is the passive I mentioned which was slightly less good sonically than the 'old' manual Shallco/Vishay passive, because it is optically switched using "a single Vishay foil resistor leading to a light controlled shunt resistor driven by an accurately programmed and balanced light source." instead of a Shallco switch. Although I say "slightly less good", it was described by Martin Colloms in HFN (Aug 2001) for what this is worth, as "top of the class"... "its great clarity and low level resolution, plus stereo images, fine depth and a very natural character, both in mid and treble, are all on its side. The Ultimate was *free from artifice* and very easy to live with."..and... "This is one of the worlds best remotely controlled passive line units". These comments, apart from my own findings, are what makes me rather tend to doubt that Fmak has had any worthwhile experience of these units. The slightly better sounding 'stand alone' manual version I have has a series resistor of 7k5 and the shunts vary from 3R8 to 47k, generally to give 1.5 dB steps (not 0.5 which I notice I incorrectly typed earlier). My Spectral ones, do have some differences in resistor values necessary to obtain the correct impedances, but, otherwise they are the same in construction and components. As you may see from this , I have had a little experience of passives at the high-end (and many lesser passives over some 15 years!) and if you want any further info, like some of the intermediate step resistor values, let me know, and I will look at them. I would urge you to try a Shallco switch if you are after the very best, Peter, but I warn you now, they are very bulky and take up quite a lot of space. Its now 1.30 AM, and time for bed! :angel: Regards, :) fdegrove Hi, quote: (not 0.5 which I notice I incorrectly typed earlier) Ah,those flamin' typos...happens to me all the time. I was wondering already how all these 0.5 dB steps would fit the Shalco. Personally I use 2dB steps with a 24 pos. Elma switch and since I use the 10 to 12 o'clock positions most of the time,I only fit Vishay S102s there. The shunt R is a Holco which is not varied anyway,the other positions are fit with the same non-magnetic Holcos. BTW,where can one buy these Shalco switches in the EC? Cheers,;) P.S.First you eat for hours,now you go to bed?:devily: Bobken quote: Originally posted by fdegrove Hi, Ah,those flamin' typos...happens to me all the time. I was wondering already how all these 0.5 dB steps would fit the Shalco. Personally I use 2dB steps with a 24 pos. Elma switch and since I use the 10 to 12 o'clock positions most of the time,I only fit Vishay S102s there. The shunt R is a Holco which is not varied anyway,the other positions are fit with the same non-magnetic Holcos. BTW,where can one buy these Shalco switches in the EC? Cheers,;) P.S.First you eat for hours,now you go to bed?:devily: Hi Frank, I don't know, here we are on the brink of war, and I am just enjoying myself all the while!;) Sorry about the typo, but you must agree it is rather unusual for me. :goodbad: Actually, whilst I can hear 0.5 dB changes readily, the difference is so small that it would hardly be a sensible way of making a switched passive, in my view.:nod: The Shallcos, are simply the best IMHO, but they are a problem to get hold of in small quantities. Last year, I spent ages researching this, and came up with sweet nothing, regrettably, so I too would be interested in hearing of any others' positive experiences with supplies of these. David Heaton has none of them left, as he only uses the newer optical arrangements now, and when I enquired from Shallco direct, and some USA suppliers, the minimum quantities in all cases was 10 off. Michael Percy does have some, but their configuration didn't suit my requirements, unfortunately. In the end, I had a UK company make me up a special, which was not any cheaper than a Shallco, and it appears to be of almost identical rugged construction. Very similar large body, and silver contacts, and very well put together, but although it seems to be very good sonically, I have not done a true A/B comparison with a Shallco, as I don't have a 'counterpart' to compare it with. This switch was for input (source) switching, and only (at my choice) had six positions, whereas all of my Shallcos have 31 posns. I guess, if there was sufficient interest, that this would be an ideal candidate for a WIKI (or whatever it is called!) purchase, possibly direct from Shallco, themselves. Your 'hybrid' idea with different makes of resistors is a very good way of keeping costs down, and one of my (very many!) 'intermediate' attenuators was made this way. I started out with all Holcos, and wishing to see (hear!) what difference Vishays would make in practice (but as a 'dipping the toes into the water' for the first time exercise), I merely substituted some Vishays for the middle few resistors. In fact, as I had already said that I might have added somewhat to the earlier thread had I been around then, I will mention the following, which (from memory, and I am not going to spend another 90 mins checking back!) I don't think was covered. In my experience, I found that (generally) with 'fixed' resistors, the series resistor accounted for say two-thirds of the sonic benefit, and the shunt about one third. So if costs need to be kept down, use a higher quality R for the series, rather than for the shunt. The same was apparent with law-faking resistors used with pots, and here a similar ratio was observed, with it seeming to be more advantageous to spend proportionately more on the fixed resistor than the pot. A quite average (Alps Black Beauty) bypassed with a Vishay will sound better than say a (normally better sounding when used alone) Panasonic 'For Audio' pot used with a Holco law-faker. :nod: As a complete 'off-topic' aside, I have regularly read that the name 'Holco' stems from: wHOLe COpper: which is another complete audio myth. It comes from the fact that the company making them was called Holdsworthy Co (in Devon, UK) before it was taken over by (or merged with) Meggitt, and about twenty years ago I used to get my Holcos direct from them! Incidentally, I am still awaiting fmak to come back on this thread to tell us all about his experiences (after criticising the Shallco/Vishay types), and I hope he will let us know which method of switching, and what the resistive elements are, in his 'favoured' Carver job.:goodbad: Regards, fdegrove Hi Bob, You know I was only teasing you,don't you? It appears that once again our experiences concur nicely. BTW,FYI Holsworthy is actually a place in Devon where I assume the factory is located. Didn't you just love the way they did/do the packaging? Lovely old fashioned little carton boxes,the resistors laying on a piece of soft paper? And even when they only stated a 1% tolerance they were always spot on from what I measured. Too bad they have abandoned the copper endcaps and leadouts.:bawling: quote: In the end, I had a UK company make me up a special, which was not any cheaper than a Shallco, I think I know this company,I once browsed through their website and they got me confused there,not clear what to order at all. I suppose having them custom made or, as you suggest ordering them in quantities from Shalco may be the best way to go. Could it be that Fmak is *carving* up the beef? :devily: Cheers,;) fmak [Incidentally, I am still awaiting fmak to come back on this thread to tell us all about his experiences (after criticising the Shallco/Vishay types), and I hope he will let us know which method of switching, and what the resistive elements are, in his 'favoured' Carver job.:goodbad: Regards, [/B][/QUOTE]---------------------------------------------- I have never criticised the Shallco/Vishay type; you have read that into my post. I said that the AS passives I have are not totally neutral. Part of the reason is the existence of the rec switch and part due to the kind of wiring used. On the former, check with AS if you like. I am happy to make short contributions of views but do not intend to be involved in long debate. PAM [QUOTE If you must stick with 100k vol pot you should think about going the active-passive-pre-amplifier route :clown: with a unity gain buffer] Look at :Aunt Corey's Homemade Buffered Passive Preamplifier http://www.stereophile.com/showarchives.cgi?54 It a very intereresting story about a buffered preamp. I will take a BUF 634 instead of an BUF 03 or a BUF 04. I made a buffer after my CD-player with the BUF 634. Compared with the X10D from from Musical Fed. it is mutch better and very cheap. You find also a story on fast soft recorery diodes and the importance of dual mono powersupply. Peter. Bobken quote: Originally posted by fmak [Incidentally, I am still awaiting fmak to come back on this thread to tell us all about his experiences (after criticising the Shallco/Vishay types), and I hope he will let us know which method of switching, and what the resistive elements are, in his 'favoured' Carver job.:goodbad: Regards, ---------------------------------------------- I have never criticised the Shallco/Vishay type; you have read that into my post. I said that the AS passives I have are not totally neutral. Part of the reason is the existence of the rec switch and part due to the kind of wiring used. On the former, check with AS if you like. I am happy to make short contributions of views but do not intend to be involved in long debate. [/B][/QUOTE] Hi, If you wish to be pedantic about it, yes, you are absolutely correct that you did not "criticise the Shallco/Vishay type", and this being the case, I owe you a most sincere apology. :ashamed: However, if your clearly-stated criticisms are brought about as you *now* say by the "rec switch and kind of wiring used" why did you bring this up in direct response to (and actually quoting!) my earlier comments which were all about the use of a Shallco/Vishay arrangement? (Irrespective of wherever I sourced the necessary parts) Now being similarly pedantic myself, you also did *not* say that "the AS passives *you have* are not totally neutral." What you did say was a sweeping generalisation relating to AS passives (without any qualification, like perhaps you constructed it, yourself, so this could be why) which included "dry and brighter than neutral". This (unqualified) statement was to my knowledge an incorrect and misleading comment applied to A/S passives generally, in the same manner as your subsequent comment "understand that the new Passion is more neutral", when the converse is actually true! Again, I don't mind differing in opinion with anyone over such matters, but it is all too easy for someone to toss in some crumbs of unsubstantiated 'wisdom' in a thread, in an apparrently authoritative manner, but this will doubtless have some (possibly incorrect) influence on the future thoughts of other readers. I note with regret that (unlike me) you decline to offer any further explanations about these *conclusions*, nor do you even comment on how the suggested 'comparisons' were made, in a similar way that I did when I explained my methodology at great length. i.e. Was the suggested "dry and brighter" result heard in comparison with what you are familiar with, or was it in comparison with some *known* reference, as I had tried to do? It now seems most unlikely that you will let the rest of us know anything worthwhile about what the resistive elements and switching arrangements are in your 'favoured' Carver passive, so I guess like me, many other readers will be wondering quite what was the point of your posting in this thread at all! Playing devil's advocate must be a very rewarding experience! :nod: Regards, Steve Eddy quote: Originally posted by PAM Look at :Aunt Corey's Homemade Buffered Passive Preamplifier http://www.stereophile.com/showarchives.cgi?54 It a very intereresting story about a buffered preamp. I will take a BUF 634 instead of an BUF 03 or a BUF 04. It's interesting alright. Here's the original that Corey based his on: <center> <img src="http://www.q-audio.com/images/al1.jpg"> </center> Just call me Elvis. :) se Bobken quote: Originally posted by fdegrove Hi Bob, You know I was only teasing you,don't you? It appears that once again our experiences concur nicely. BTW,FYI Holsworthy is actually a place in Devon where I assume the factory is located. Didn't you just love the way they did/do the packaging? Lovely old fashioned little carton boxes,the resistors laying on a piece of soft paper? And even when they only stated a 1% tolerance they were always spot on from what I measured. Too bad they have abandoned the copper endcaps and leadouts.:bawling: I think I know this company,I once browsed through their website and they got me confused there,not clear what to order at all. I suppose having them custom made or, as you suggest ordering them in quantities from Shalco may be the best way to go. Could it be that Fmak is *carving* up the beef? :devily: Cheers,;) Hi Frank, Yes! :nod: Yes! :nod: And yes! In fact I knew as I have been through the village many times as my brother retired to Devon quite near there some years ago, but I also knew from their address when I needed to send Holsworthy some money!:bawling: It is said that "there is no future in nostalgia", Frank, but I still keep many of these Holcos in the original little brown envelopes, which looked rather like the very first wage packets I got 40+ years ago!:bigeyes: Right again about the tolerances, but they were also available in tighter tols than the nominally 1% (I had some 0.1%) which probably measured at 0.01%, or similar! Oh, those were the days when they were a couple of pennies each!:goodbad: I don't know from any experience about the change in endcaps, apart from reading somewhere about it, as I haven't bought any for maybe ten years. I used to get them in tens or hundreds from the factory, and I still have most useful values left. Now that my system is Vishay throughout (save for a few Caddocks for higher PD) I don't use Holcos any more except if I am trying out some new circuit, which I will develop to finalisation, and then swap out with Vishays. Actually, in all the years I used them, I never had any failures, nor excessive noise etc., but I am always careful not to bend *any* leads close to the body of components as this is simply asking for trouble, anyway. The work-hardening stresses (effectively the opposite of annealing!) resulting from all tight bends in leads will also badly affect the sonics, because of the breakdown of the crystalline structure, exactly as it does with wires like we have discussed before. I don't presently recall (but will look it up on request) the name of the switch company I referred to who were in Wales I believe, and I don't think they had a website (last year) from memory. They needed (then) to fax me most of their tech info. However it could be the same place, as this firm's info was rather alarming to look through with many hundreds of possible variations, all coded with numbers or letters, and which you had to get right when ordering anything! I cheated, and had several chats with a tech guy there as I wanted to know more about the consuction (i.e. what was the contact pressure, were the contacts welded or riveted, the quality of silver used, how long and what was the 'path' made of between the contacts themselves and the tags etc.) so he simply did the job for me.:cool: These kind of details are all too easy to overlook, but will be just as responsible for the ultimate 'sound' as some of the more obvious parameters like contact resistance, and mean-time before failure etc. Whenever I look at non-audiophile bits for the first time, I think about these matters, since for say military use, what is important to us, simply may not matter at all in combat!:goodbad: Regards, mlloyd1 Steve: What product is pictured there? Is that somebody's homebrew? mlloyd1 quote: Originally posted by Steve Eddy It's interesting alright. Here's the original that Corey based his on: .... se transducer quote: Originally posted by mlloyd1 Steve: What product is pictured there? Is that somebody's homebrew? mlloyd1 ;) Well, I'm not Steve, but that was HIS commercial version of the Buf03 buffered preamp, which came out before Corey's article. Hey Steve, I never received my shipment of knobs from that preamp. You were going to send me about a million of them :rolleyes: Cheers, RonS </