| Gabster |
Hi folks,
I made a few audio projects so far (amps, etc.) and I believe I'm ready for the next step.
I'm wondering what would be the ultimate amplifier to build (>100W, solid state). I'm seeking for the "highest-fi". Best THD, best S/N, best everything. I know there're always compromises but I still want to know.
At this point I'm considering elektor's crescendo, but I would like to have as many opinions as possible before making a move.
Thanks.
:)
P.s.: Don't forget about schematics ? |
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| Lisandro_P |
| A friend of mine built a stereo amp with two Elliot's AB (project 3a)... wonderful, wondeful sound. That amp can be pushed up to 100w; if that's enough, that's where i'd put my money :) |
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| Oz_Audio |
Have a look at the AKSA @ www.printedelectronic.com
I have built the 55 watt and it is stunning.
Don't be fooled by specs.
Sonic ability is better. |
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| traderbam |
You want the very best? Excellent!
What you go for sort of depends on your experience and your access to test equipment. If you can get hold of a spectrum analyzer, network analyser, scope and function generator, each with bandwidth of >10MHz, then a high-speed feedback design is a good approach. If not, then a low or no feedback design may be more fruitful because it is easier to get them stable and to get a clean sound out of them.
You won't find schematics for the top brands like Krell and Mark Levinson on the web although Nelson Pass is generously open with his designs. The Naim amp schematics can be found at: http://www.neilmcbride.co.uk/ |
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| Gabster |
Hi,
I don't have an spectrum analyzer at home, but I've a 100MHz scope and an 11MHz function generator.
The AKSA is a kit and is not necessarly what I'm looking for. However, they're selling heatsinks, hardware that I'm having a hard time to find (any other suggestions for heatsinks?)
The Naim power amp design looks interesting but I haven't been able to find speficications. Power, THD, etc.? However it is well documented and I would like to hear other comments on it.
Keep feeding me with suggestions, this is the only I'll be able to make the best choice for my needs.
Thanks. |
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| traderbam |
Hi Gabster,
You'll be able to get quite a way with a scope and FG. I would recommend not building a Naim since it is a high feedback design and needs considerable "tuning" to sound great and you don't have the equipment.
Actually, I just had alook at Neils's site and the schematic he has there isn't quite right. C9 should be 22uF not 220pF! D5 shouldn't be there. C6 is 39pF. Q1/Q2 should be BC549. Q9/Q10 should be MJE243/253. Q11/Q12 are Naim proprietary but are essentially extremely fast transistors (not chosen for linearity). The base networks of Q9/Q10 need to be tailored to the output stage.
You won't find the AKSA schematic on the web site but you can deduce it from the PCB layout graphic. It has simple bipolar PP topology with local feedback around each output transistor. A sort of complementary version of the Naim circuit but with lower feedback and a bootstrap thing on the gain stage (I still don't approve Hugh!). This circuit would be a good place to start and can be fine-tuned.
Most circuits can be made to produce >100W by beefing up their component specs. You need >42V supplies for bipolar outputs and >50V for FET. |
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| audionut |
I would build one of the Aleph Series amps found at the Pass Web site. (Passlabs.com) They are easy to build, sound great, and most importantly, you will find a lot of construction support. For example, you can go to Mark Finnis's web site for complete details including PCB's on building an Aleph 4. This is a 100 watt amp.
http://members.ozemail.com.au/~dkfi...slabs/index.htm |
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| dice45 |
| quote: | Originally posted by Gabster
... The AKSA is a kit and is not necessarly what I'm looking for. |
There is a 100W version of the AKSA kit available; i ordered mine yesterday. Cannot yet tell from own experience how it sounds, but my order was triggered by three buddies' raving about this amp's sound. |
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| Jocko Homo |
traderbam:
I have network analyzers, spectrum analyzers, and probably stuff you haven't seen. You are right it is easier to build no-feedback designs, but you are never going to convince me "then a high-speed feedback design is a good approach." We could go on for years about this, but let's not!
If that is what you prefer, then fine. Just remember how much harder they are to build, and that doesn't automatically mean better, too.
Jocko |
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| tiroth |
| I'd like to cast another vote for the Elliot P3A. It is capable of 0.0025% THD or better, and 100dB S/N without component matching/boutique parts/etc. Also it sounds rather nice. ^_^ Very inexpensive PCBs are available. |
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| mlloyd1 |
traderbaum says:
..... A sort of complementary version of the Naim circuit but with lower feedback and a bootstrap thing on the gain stage (I still don't approve Hugh!).....
I hear what you're saying :) What I've read on this kind of design in the past is that you can delete the bootstrap circuitry if you simply supply the driver circuit with a higher rail voltage than the output stage.
I suppose the question is - what magic has Hugh built in to the AKSA that doing this would upset?
mlloyd1 |
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| Koy |
| I am afraid I can not encourage you to build Alephœ power amps. I did it.Yes it sounds quite good but it is not anything outstanding.I class it to the 1000EU device category. |
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| lohk |
Traderbam:
Please let us not make things more difficult here.
Neil McBride's schematics may be not "the orginal thing" (one has to read the text also...), but in the 250/135 clone (following the numbering)
1. C9 definitly IS a 220pF styroflex (22uF is WAY off)
2. D5 definitly MUST be there !!! (back to the start... :-) ). Please read basic writings, JLH for example.
3. C6 is 39pF indeed. But I think there will not be much of a difference.
4. Q1/Q2 are NOT BC549s (at least not in the orginal). The changed them several times, I think, I use BC239Cs and BC182s.
5. Q9/Q10 should be MJE243/253. You are RIGHT here !
6. The base networks of Q9/Q10 really needs to be tailored to the output stage. But the details shown are not so far off.
7. The AKSA schematic has not very much to do with the Naim schematic, at least they are both SS amplifiers...
Gabster:
OK, the Naim circuits need some tuning, but I my experience no DIY amp sounds perfect from start. My "Naim-clones" sound very good :-) after all.
You are somebody with experience in making more complex devices, so you can try them. Some equipment you will need anyway ALWAYS, like a scope, a sinus generator, multimeter, etc. You know that already.
But beware: ALL amps have a destinctive "sound", more or less, you may like it or not. That is one of the many reasons we all are constantly talking here... (Did you hear a Naim-Audio amp at your home or some other place yet ?)
The AKSA could be a tempting thing, many people are raving about it, and the actual cost of the kit does not exceed the cost of the parts and the "cost" of the time selecting them (NO construction of a good amp without selection of parts, sorry).
ESP's project 3a is a very good amp indeed, but somebody took mine away from me already... It is so cheap and simple, you can use for a secondary room if you do not like it.
There is no solution, except to try out and listen. Forget the specs, when you consider the sound quality you want to reach.
But if you are not satisfied with your existing amps, did you consider a better CD / record player and better speakers too ? Sound quality is about synergy too (bad CD-player + good amp = worse sound, you know).
Klaus
ps: I heard the elektor crescendo twice, I have actually forgotten how it sounded, but I remember having blown them away with a much cheaper lo-poered little "british" amp. Not my kind of thing. |
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| lohk |
Koy,
a well-done ALEPH sounds terrific, a bit like magic actually, - yes, if is connected to a good source and speakers, if not you may well be disappointed.
Klaus |
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| traderbam |
Iohk,
Thanks for correcting me in such a forthright manner (I think). When I wrote D5 I meant D8 - the LED. Q1/Q2 BC239 yes ok. The last time I took a NAP110 apart C9 was a 22uF tantalum. The design must have changed. Odd.
You have the confidence of an expert. At the risk of making things more difficult here ;) , may I ask you a couple of clarifying questions?
1) What do the base networks of Q9/Q10 do?
2) What output transistors have you used and what diode for D5 and why?
IMO the NAP and AKSA are very similar in topology - much moreso than say the Leach or Adelph. We are both, of course, entitled to have different opinions.
BAM |
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| Pete Fleming |
Gabster, since you stated you're seeking the "highest-fi" then by all means find the amplifier with the best specs possible. Look for a design with very high feedback, as generally they will provide the best specs. Think Japanese amplifiers in the 70s and 80s. I would suggest you look at the Halcro amplifier at http://www.halcro.com/ and do a US patent search for the schematics. It's not too difficult to come up with the missing values if you know anything about amplifier design (and just goes to prove that despite all the hype it's obviously not difficult to be issued with a patent these day ... but I never said that!).
HOWEVER! If you are building an amplifier to listen to, forget the specs as they are simply meaningless and sometimes contra-indicative as to which amplifier sounds better. As convenient as specs are, they are generally a poor representation of how the amplifier will reproduce music. To prove my point, look at the number of designs out there. If there was an ideal design based on the best specs there would be only one typology used in high end amps.
Unfortunately once you start circulating at this level, the “best” amplifier is a subjective decision based on your own personal taste. The difficulty is that in DIY there’s often little opportunity to listen to a design before you build it. That’s the price you pay. However it’s not impossible in some cases, for example the Pass designs.
Good luck with your search, and happy listening.
Cheers,
Pete |
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| lohk |
| quote: | | C9 was a 22uF tantalum |
There are normally two (mostly tantalum) caps near the front end: The input cap, usually 10uF, and the DC blocking cap, usually 47uF, in the feedback loop to input ground.
The 220p cap goes from the base of the npn driver to ground, you cannot use a 22uF cap there, I think. The amp will work also if you leave this cap out. So you probably mean the cap cross the bias transistor ?
| quote: | | What do the base networks of Q9/Q10 do? |
They are a kind of frequency/time compensation of the output stages, that is also why they are different on both halves. It is a part of Naims secrets to this designs. The compensation circuit seem to refer to the special TO3 output transistor Naim is using in their bigger amps. In my smaller clone I left it out (like in the NAP90 or in the Nait) without any problem.
| quote: | | What output transistors have you used and what diode for D5 and why ? |
I have used different transistors, always sad about not having the original. I used f.e. for the bigger mono versions the PT77, made by ST for the Cyrus amps, or the Sanken 2SC2921. For the smaller ones I tried the PT7 or the BD911 with success, both made by ST.
I am trying a "El-cheapo" version with the BD241C now, because I have lots of them. I do not yet know if they will work. But it is more a switching transistor anyway...
But my "quest" for the right transistor is far from beeing finished.
The diode is used to linearize the semi-complimentary output pair. I always use a 1N4148. I will try to find the text by JLH for you.
BTW, the LED in Neil McBride's naim schematics is seen as an alternative to the two diodes.
I do not like to discuss the differences between the topology of the AKSA and the Naim amps here, because it is not the topic of this thread. But we could start another one...
Looking at the schematic shows several differences, it seems only similar "from the outside".
Both have indeed in common that they are more or less optimized "oldfashioned" circuits (sorry, Hugh), based on proven techniques.
best wishes
Klaus |
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| Gabster |
Alright folks,
This is getting very interesting. You're giving me really good suggestions and I'm realizing that I'll have to build them all!
At this moment I think I will pass on the Naim design...maybe too tricky. The same way, I don't think I'll get into cloning a Halcro amplifier.
The specs of the Elliot P3A are very interesting and it's sure that I'll build one in a near future.
All the Pass Aleph amps are very interesting (simple designs but seem to require huge heatsinks). Is there web sites out there that present all the variations as well as schematics(Aleph4,5,60,etc.). This is probably the amp I'll be considering, but once again I will have to make a choice. Any comments on these amps would be appreciated.
Finally could someone else comment on the crescendo, it's a complicated design, does it worth it?
Thanks a lot |
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| dice45 |
| quote: | Originally posted by Jocko Homo
I have network analyzers, spectrum analyzers, and probably stuff you haven't seen. You are right it is easier to build no-feedback designs, but you are never going to convince me "then a high-speed feedback design is a good approach." We could go on for years about this, but let's not!
If that is what you prefer, then fine. Just remember how much harder they are to build, and that doesn't automatically mean better, too. |
Jocko,
shouting over from the tube world :) .... still have to get adjusted how you say things (all , does the guy wear his teacher's badge outside ? :) ) but i have to agree with you to100%. From listening exprerience. I thoroughly know Allen Wright's differential preamp going far into the MHz BW realm, no loop feedback but hefty FB with most stages. And must admit it is the best super-hifi preamp i ever heard, no sonic flaws. But for listening to music, for getting lost in a Beethoven piano sonata e.g., i prefer ironman Thomas Mayer's design (vinylsavor) who doesn't give a §$%& on bandwidth and i have given up to count the "slow" iron pieces in his tube preamp's signal path. Zero feedback, bandwidth just enough to ensure proper phase for audio frequencies. This simply is it.
I have particiapted on repeated listening to a SS amp having feedback and BW reduced on and on up to 100 and some kHz until the sucker was enjoyable. We had the same experience with a nice lil' PP power amp having 340 kHz BW before and finally sounding best with BW of 120 to140 kHz and everything taken out which could cause the amp to get a high frequency orgasm. Funnily, both amps, SS and tube amp ended up with about the same BW for best sonics.
I doubt the BW hype is it. And a loop FB always is a regulating loop. For getting alive, the error amp needs an error signal. Then, not earlier it can correct the error. Hence the error amp always is late. Too late? Depends. Depends on the design, depends also whether the listener is sensitve to those corrected errors. I admit it is possible to get the error small and bearable. |
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| traderbam |
Klaus,
Thanks for the info. I have built several amps of the op-amp (or Naim) style with pseudo-complementary output stages. This type of output stage is cunning because it enables close matching of the power transistors and use of high speed transistors (since both are npn). Of course, our valve friends automatically benefit from close device matching since they have no choice but to use all N type devices. I would like to see what JLH has to say about D5. I can tell you that if you are using a 1N4148 it is unlikely to be optimum - try a wide variety of diodes and listen to the differences, you may be quite surprised.
Bernhard/Jocko
I agree that THD and other "standard" measures don't correlate well with perceived sound quality. I have also experienced the terrible music killing effects of feedback in some circuits. In fact I used to believe feedback was the work of the Devil and simply bad for sound in any form. However, I am now a lot wiser and I understand a lot more about why sound degrades. I can confidently say that it isn't feedback itself that is the problem. It is rather a widespread ignorance of how feedback performance is affected by non-linearities and thus a lack of due care in the open-loop circuit design. Having an error signal isn't a problem: no-feedback designs also have an error signal and it is usually much greater. |
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| pmkap |
BAM,
I'm not sure I follow-
This type of output stage is cunning because it enables close matching of the power transistors and use of high speed transistors (since both are npn).
In a valve pp amp each side is being used exactly the same way. I do not believe this is true in this update of Shaw's improved quasi-complementry. Aren't the tranfer characteristics of both halves quite different, which is not the case in a hollow state amp? I'm not implying this isn't an excellent sounding topology as I've heard some great amps using it, Edge....
Paul |
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| traderbam |
Hi Paul,
To my reckoning the two halves are very nearly electrically equivalent if the right components are used. The choice of the diode is crucial and the driver transistors need to be well matched (which is achievable with drivers). Other than that they are practically identical. To be absolutely identical a resistor and diode are needed in the collector of the npn driver, but this will have negligible affect.
BAM |
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| AudioFreak |
For listening purposes specs are almost totally useless.... Aleph's are great amps and once a few of us have had a chance to build the XA we'll will be more qualified to judge it on it's merits. If your looking to build soon i'd go for the Aleph, you can check out the gallery pages @ www.passdiy.com and the "Aleph 2 and others as a project" thread in this forum........ the Aleph requires huge heatsinks because it operates in Single Ended Class A mode which means that a great deal of the power that goes into it becomes heat not sound.
Also just let me remind you that the system is only as good as the weakest link so if the rest of the system is not up to the task, then you may not be pleased with the result. Finally, you may initially find that the Aleph's or other hifi amps dont sound like what you perceive to be flat.... they usually sound a little dark in the midrange and this perception is generally due to the poor quality amps most us were used to listening to before we got involved in diy audio. |
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| mefinnis |
I may as well give my 2cents worth as well .... :)
Gabster, you have undoubtedly realised there is no "highest-fi", or not yet anyway. You need to define what you are looking for a little more carefully. Can you accept SE class A, with the large hardware and enormous heat? Or, do you require an amp which is class AB, ie. less power inefficient? Do you really need 100W, or have you just plucked this figure out of the air because it sounds impressive?
If you are using reasonably efficient speakers (>=85dB/W, say) then you are actually unlikely to need this sort of power and your choices will be much wider.
Class A/B the Leach amps are a good choice. I used them for many years and they are honest performers (the one I built in 1978 is still working in my garage). Some of the other suggestions would likewise be suitable.
Class A, I obviously have a bias to Passlabs but there are others out there (JLH for example http://www.gmweb.btinternet.co.uk/jlh1996.htm ). The A40 (http://www.passdiy.com/pdf/a40.pdf) is push-pull class A so not quite as inefficient as the Alephs and is an excellent amplifier. Once you traverse the 100W mark here (Aleph4, 1.2) you are talking really serious hardware and heat. Most of us only listen in the <10W range anyway, so the remainder is just room warming!
If you do really need some serious power, see the 1kW beast on Anthony's site:
http://www.aussieamplifiers.com/poweramp.htm
Rod Elliot makes some good amplifiers:
http://sound.westhost.com/project03.htm
There are also a number of very good articles on his site. (he also has an interesting section on the "Death of Zen" ..... but that's stoning material around here :) )
If you can handle the heat, I would recommend the Alephs above the Leach amps (and virtually all "quasi-class-A" amps I have heard), simply they sound better.
Unless you really do need the additional power I would recommend the Aleph5 (65W - OR, the Volksamp equivalent) .... the hardware is just a little more bearable. Remember the Aleph4 (100W) only gains a couple of dB over this anyway, so if you are saying 65W is not enough you really ought to be going to 200W+ !!
cheers & good luck, mark :cool: |
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| Gabster |
mefinnis,
I must admit, I'm not the most experienced listener/builder around here and I must rely on people like you to make good choices for my listening experiences. On the other hand, that's why I'm more likely to look at specs before building an amp.
At this point I'm almost set on the Aleph. I would like to build the Aleph 4 with its 100 watts, but if you say that the 5 sounds better I will let my greed away.
Finally, is this common for a class A amplifiers to have 1% distortion (talking about the Aleph). So far, all the amps I've seen perform better? (I'm aware that good sounding amps don't mean low distortion).
thanks
;) |
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| mefinnis |
Nelson states THD specs at maximal output - ie, this is "worst figure" from this amp. Many manufacturers do not do this, they will give you the figure at 1W, which is dramatically better. The THD specs for Nelson's amps in the typical listening range are vastly less than the maximum.
Yes, there are amplifiers with better THD specs, no question but there is more to it than that. What order harmonic the distortion is, xover effects etc are all "different" to the ear and are not strictly comparable by "average percentage".
You really should try to listen to the different amplifier topologies if possible. If you want a class A amp with less THD then Rod Elliot's would be a good bet.
In selecting power you really do need to appreciate that a 100W amplifier does not produce 2xdB of a 50W amplifier. The scale is logarithmic and as I stated eralier you only gain a few dB going from 60W to 100W. The Aleph5 in general listening will (I expect - haven't finished my A5 yet) be "near indistinguishable" from the A4 and it will cost you less to build, be smaller, use less power and generate less heat.
The call is yours. I only built the A4.v.A5 because I found some toroids at this supply voltage cheap and at that stage I was under the false illusion both amps used the same compliment of FETs.
Starting from scratch, now, I would build the A5, or, if I really needed the extra power I would build A1.2 monoblocks (with a reduced FET compliment by choice). The later however will cost lots more money and be 3x the size overall.
Rememeber, there are really only 2 things which matter, 1) the music at the end, and 2) that you have fun in the process :)
cheers, mark |
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| Gabster |
Thanks for your advice. Very appreciated.
Do you know other websites that
http://members.ozemail.com.au/~dkfi...slabs/index.htm
that talks about the construction of these amps. On this site, the link to the circuit schematics is not working.
I've also search the pass labs forum without luck (the link that was refering to pass' website is down too).
regards |
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| mefinnis |
Since that's my website ...... which link where exactly?
I had to redo many of them when Nelson upgraded his website and split-off Passdiy.com. Obviously I have missed something :(
See the download page:
http://members.ozemail.com.au/~dkfi...h4_download.htm
I have checked these just now and all appears in order.
regards, mark |
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| Gabster |
| Thanks, works fine now. |
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| paulb |
| quote: | Originally posted by mefinnis
Rememeber, there are really only 2 things which matter, 1) the music at the end, and 2) that you have fun in the process :) |
I love this site. |
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| annex666 |
I agree totaly - as long as it pleases you, either to make it or listen to it, then it's got to be worthwhile.
:D |
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| planet10 |
Just a couple points i'd like to make:
1/ Simple distortion measurements are pretty much meaningless. for example: A single THD number tells you almost nothing (although a number that is very low will scare me off), but a picture of the harmonic distortion's spectrum can tell you alot.
Lots of feedback to get a really low number, tends to just move the distortion elsewhere (ie presence of more objectionable higher harmonics -- time distortion).
2/ from listening, not building. Amps with 1 (SE) or 2 (PP) devices usually sound better than amps with more devices. Corallary to this is that the best sounding amps usually have lower power.
dave |
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| planet10 |
| quote: | Originally posted by lohk
Both have indeed in common that they are more or less optimized "oldfashioned" circuits (sorry, Hugh), based on proven techniques.
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I'm pretty sure Hugh has said as much himself. The circuit is not radical, just that care has been taken with the execution.
dave |
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| kevin gilmore |
Go to www.uspto.gov and search for patent # 5,892,398
This is the halcro patent. Study the schematic carefully.
The tricks used to get the distortion down very very low
are pretty clever.
Yet a few of the reviews of this amplifier say its sound
does not corellate with the extremely low distortion. |
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| jgwinner |
Wow, quite an old thread that got resurrected.
I know I'll get flammed for this, :D but I sort of like the Opti-MOS amp. I've read both of Randy Sloan's books and like his design philosophy.
However, I have Self's book on order, and he makes some different conclusions regaring BJT's and MOSFET's.
Net result is I'm still 'arm chairing' but will be building something soon!
Randy Sloan makes the point that THD should be measured both at 1Khz AND at 20Khz. I rarely see the latter. Without both measurements it's essentially a meaningless statistic. Also, IMHO slew rate is important - it's one distinguishing characteristic in feed back designs.
"The topology is a mirror-image, L-MOSFET type, incorporating a dual-cascode input stage (for ultra low-noise operation - SNR better than -100 dB) and a unique type of "nested feedback" system incorporated into the VA stage, providing exceptional linearity and stability. It is capable of providing continuous 200-watt RMS outputs into 8-ohm speaker loads. Distortion performance is excellent (THD less than 0.005% @ 1 KHz @ 0 dBm), with high-frequency distortion reduced to only about 0.014% (20 KHz @ 0 dBm) due to the implementation of a double two-pole compensation network. Input impedance is 10 Kohm. Input stage zener overload protection and an improved multislope output overload and short-circuit protection network provide virtual "bullet-proof" reliability. "
Seal Electronics - Opti-MOS
I think this is the one I'll build.
I haven't read Self's books yet but he has some PCB's and info on his web site:
Douglas Self's Amplifier Institute |
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| mozfet |
I'm interested to hear how the Opti Mos actually sounds, no mention of this on the Seal Site!!! Have you built one yet?
Mozfet |
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| mlloyd1 |
Kevin:
Thanks for the Halcro pointer :D . Good reading for my trip to Madison today. I'm very curious about the clever tricks becuase the specs on these amps seem to good to be true.
mlloyd1| quote: | Originally posted by kevin gilmore
Go to ... the halcro patent. ... |
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| Christer |
Does anybody know if the OptimMOS is an older or newer design
than those in Sloanes book? I understand it appeared in a
magazine in 1999, but the book was also published that year.
The puzzling thing is that the OptiMOS goes against some of
his own "design rules" in the book, so I wonder if he
changed his mind before or after writing the book and how
this amp compares to the "optimal" one in the book?
jgwinner,
what do you mean by 'a unique type of "nested feedback" system incorporated into the VA stage'? I can't find any such
feedback, unless you are referring to the two-pole compensation
network.
I haven't read Selfs book, so I am interested in how his and
Sloanes conclusions differ regarding BJT vs. MOSFET. Would it
be too much to ask for a brief summary of this? |
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| jgwinner |
Mozfet:
I haven't built one yet. I'll let you know as soon as I do! |
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| Christer |
jgwinner,
I take back the question on VA-stage feedback. I had another
look at the diagram an found I had missed it. I thougt he was
ony using ordinary cascoding as in many of his other designs.
This is even more strange, however, since he argues very strongly
against nested feedback loops in his book. :scratch: :scratch: |
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| Nelson Pass |
Reading Randy Sloane's book I am left with the impression
that while published in 1999, it was written in the late 80's.
This from his references to topologies and available devices.
This is not intended as a criticism of the book, but rather
a potential explanation why his 1999 design might incorporate
some slightly different ideas. |
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| Christer |
Maybe, but why it should take ten years to publish the book...?
Anyway, I don't think the OptimMOS is really a more modern
topolgy. All the principles he uses are mentioned in his book
as possible solutions, some of them even used in particular
cases. However, he seems to have changed his mind about
which is the best solution for certain things, now using the
ones he dismissed as inferior or pointless in the book. For
instances he spent many pages praising current mirrors but
said that there was not much point in cascoding a BJT
diff pair. Now uses a cascode, but no current mirror. He did
not like nested feedback, but now uses it. He seemed to prefer
CFB output stages to emitter followers, while now using the
latter, although this was somewhat arbitrary also in the book,
varying from design to design. As for old components, well
he use som new devices for the diff pairs, otherwise it is
exactly the same ones as he uses in the book.
Of course, anyone is free to change his/her mind whenever
it seems appropriate, and I am sure Sloane has some reason
for it. Perhaps, he tried to make a somewhat cheaper version
of the "optimal" amp in the book, and concluded that doing
things the other way would be better in this particular case.
Still, having recently read his book I can't help being curious
about this change of mind.
BTW Nelson, would you label the OptiMOS as more modern than
the designs in the book or was it just that you considered those
in the book old-fashioned? |
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| Nelson Pass |
It's not a question of old-fashioned, just an observation
of the probable date it was written. We should expect
designers to change their opinions.
Both Sloane's and Self's designs are conventional. I
personally think that the Opti-mos is more mature
simply because it has a simpler gain path, in spite of
the cascoding and output limiting circuits.
When I started out, I put everything but the kitchen sink
into my circuits, but over the course of 30 years I have come
to have a better appreciation of what you can get done
simply, either from the objective or subjective viewpoint,
and I would be interested to see if other designers mature
in a similar way.
I find both dogmatic in their views, particularly with regards
to the subjective side of audio. To be sure, there are plenty
of excesses in the subjective side, but that's not a good reason
to dismiss subjectivism entirely. |
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| Christer |
I agree that Sloane represents the conventional, or even
conservative, school. I haven't bothered so much about
audio electronics for over 20 years, except for listening to
music, of course, but in the past year I have started to get
interested in the area again. I bought Sloanes book by impulse
and found it interesting. On the one hand the designs
seemed familiar from what high-end used to look in the 70s,
but I got the impression that there is a much more rigid
understanding nowadays of how the conventional topologies
work and what are important design criteria (within the
conventional paradigm, that is). My idea was to build one of
Sloanes amps, or something similar, but first read up and
polish off the rust from my old knowledge in the area.
I have been very sceptic towards most other design schools,
but following disussions here and in other places I have
realized that there are at least a few of you minimalists, if I may call you so, who seem to have a more well-founded and
nuanced (maybe thats swenglish?) view of what you are
doing, being not only extreme subjectivists but also relating it
to sound engineering principles. I must say I am becoming
increasingly curios to study your designs closer than I have done
so far. It may end up that I build both a conventional amp and
one of yours. We'll see. One reason that I am reconsidering
my view on minimalistic and even valve (tube) designs is that
I am fan of historical recordings and it surprises me more and
more how good the sound can be in the best of the
old recordings. Sometimes I wonder if much has happened
since 1930. Amplifiers were probably very straightforward
and simple then, often without feedback. Yet it can still sounds
so good, with more realistic acoustics than most modern
recordings. There must have been something they were doing
right back then.
Having followed this forum for some time I must say that my
respect for you Nelson has been constantly growing, just
because of the sound views you just put into words yourself
in the previous post. You represent one design school, but you
are not dogmatic and seem quite happy to discuss and
appreciate other types of designs in an relatively unbiased way.
Having that combination of experience and open mind that you
show is a quite rare human quality, in my experience. |
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| haldor |
| quote: | Originally posted by Nelson Pass
I find both dogmatic in their views, particularly with regards
to the subjective side of audio. To be sure, there are plenty
of excesses in the subjective side, but that's not a good reason
to dismiss subjectivism entirely. |
It's hard to read Self on subjectivists view (takes up most of the first chapter of both his books) without hearing a note of fanatism in his comments.
I imagine when I get old and cranky I'll probably sound about the same.
Phil |
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| peranders |
| quote: | Originally posted by Christer
a more well-founded and
nuanced (maybe thats swenglish?) view of what you are
|
I was forced to look in a dictionary, never heard of nuance before. Christer means "nyanserad" and my book has also "shade of meaning". What do you say really, well-balanced point of view?
Mr Pass is a man with deep insight.:angel: Maybe I will get tired of my overloaded designs and join the minimalistic club :)
My contribution to this thread is RT75 based on Matti Ottala's ideas in the 70's about low feedback and low open-loop gain.
The swedish magazine Radio & Television (later Elektronikvärlden) had articles about this new thinking which was really new at that time. If you check my homepage you can catch a glimpse of it.
http://home5.swipnet.se/~w-50719/hifi/rt75/index.html
Many people built this amp (>1000) inlcuding myself (when I was 16). This amp (you can see the pictures) works still! The basic design needed some development which was published later. |
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| Christer |
Per-Anders,
I remember the RT75. There was quite a lot of talking about it
here in Sweden when it was new, and I remember a friend of
mine building one. Since you still have one up and running,
do you have any opinion on how it performs compared to
modern amps of the conventional school? Just curious to know.
And yes, although I usually try to avoid making up english
words without checking, I thought making an adjective out
of "nuance", as we do in swedish, would be straightforward
enough to be understood. Still don't know if the word exists in
english, though. I checked this morning, and it's not in my
Oxford and I don't have my Webster at hand. |
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| peranders |
You have to get "Prisma" dictionary from 2000!
The RT75 had an outout stage with gain (3), rather odd and also not easy to handle. I omitted that in my QRO amp.
RT75 is soundwise OK but it lacks off some basic "stability". It's easy to break it with short power interruptions. Turn off and turn on fast, don't do that! = Fried output transistors!
The QRO amp was designed to have a well-controlled startup procedure. Smooth and easy. I have the same thing in my monster designs, headphone and phono amps (which adds up complexity a bit).
The RT75 also had no over current protection, fuses don't do the job in a BJT stage. Easy tho break the transistors with a short circuit. My QRO had MOSFET's much more reliable in that respect. MOSFET's can take a short circuit with only fuses and zener at the gates. I hate foldback current limitation! Bad with "difficult" speakers at high volume of course. |
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| carlmart |
Peranders
Why didn't you put more inforamtion on the QRO on your site?
Diagram, pcb, etc.
Carlos |
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