| uncle_leon |
Hi,
This is my first post on this forum, so hi to everyone out there ;) I used to be quite deep into overclocking processors, but recently I became hooked into making a Gainclone amp. I didn't have much experience (none, to be honest, at least not with audio stuff), so I decided to make it easy for myself, and ordered Peter Daniel's basic LM3875 kit. The amp isn't finished yet, but I already started thinking about possible ways of making it better. If anyone can make some suggestions as to what has the biggest impact on amp's sonics, I'll be very grateful.
First, let me tell you where I am now:
- Nuvotem Talema trafo, 225VA, 2x18V (20.8V real), encapsulated.
- MUR680 diodes, ordinary resistors, Panasonic FC caps. No Zobel, snubber etc., just simple basic Peter's NI design.
- mains cable and plug from gutted computer PSU
- for internal power wiring - 2x0.75mm stranded copper cable in nice, thick&flexible insulation.
- for internal signal wiring - cable i made myself, cutting 3 leads off computer hard disk ATA ribbon, braiding them together and wrapping in insulating tape.
- a rather pathethic 10K pot, that I took off some old PC speakers
- heatsinks taken off broken PCs, they seem more than adequate for LM3875s.
- ordinary, nickel plated RCA sockets
- plastic 3A terminal block connectors as speaker binding posts.
As you can see, the config is a rather cheapskate/scavenger one. So, I started to think what could make an audible difference without terminally harming my wallet. I came up with a list of all possible points to upgrade:
- resistors (4 per amp board, 8 in total)
Upgrade to Caddock/Riken would cost 31-35$, and should bring significant improvement in noise level and overall clarity. I consider this a good option.
- small caps (4.7 or 10uF/50V, 2 on rectifier board)
Upgrade to Black Gate N would cost 7$. Probably not much to be gained here, but it's not expesive so I'd give it a try.
- big caps (1000 or 1500uF/50V, 2 on each amp board, 4 in total)
Upgrade to Black Gate STD would cost almost 70$ - ouch!... Quite possibly an audible improvement, but since Panasonic FC are really good, and the cost of upgrade is so high, I'd rather invest my money elsewhere, for now. (I don't event take into consideration an option of Black Gate 'N' series, they simply CAN'T be that good to be worth that kind of money)
- transformer
I've heard opinions that higher rail voltages tend to give better sound, but I was afraid I could run into problems if I changed speakers to some low impedance ones. I also read that 300VA isn't too much for a GC. So I might give some 2x25V 300VA trafo a try. But I'm going to do it later, as it would cost me around 90$... Yes, much later.
- power wire
Well, I can't honestly think what could I upgrade it to? It seems thick enough, and is easy to work with.
- signal wire
Since so little of it is needed, I was seriously considering upgrading to pure silver, teflon insulated wire (not that I honestly believe it would bring astonishing improvement, but it would be a nice thing to impress friends with ;). The thing is, I don't know which one to choose... Jupiter from PartsconneXion (silver solid core/cotton wrapped) looks nice and is inexpensive, but I don't know if it is thick enough - 28awg.
- signal sockets, speaker binding posts, mains cable&plugs
I'm not much of a 'cable believer', so if I upgrade connectors or mains wiring, it will be purely because of esthetic reasons. Or am I wrong?
Thanks in advance for any comments and suggestions. |
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| Nuuk |
IMHO, and after trying most things, a simple GC is still the best GC!
Don't bother with BGs in a GC. Panasonic FCs and MUR 860's work well in a GC (although not necessarily elsewhere)
Solid core wiring for signal is fine (you don't need silver etc for those short lengths). Just keep it short and tidy.
Dual mono PSU is best with 37 volt rails (if you have 6-8 ohm speakers).
I prefer the PSU in a separate enclosure. I also prefer a non metallic enclosure for the amp.
Resistors - won't cost much so try what you fancy.
Zobel - won't cost much so try with and without.
:attn: One of the biggest improvments I got with GCing was to build a four channel amp and bi-amp the speakers. :att'n:
Finally, remember that a lot depends on what goes before the GC! ie you may need an active pre or buffer stage. |
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| uncle_leon |
Thanks for the response, Nuuk.
I forgot to mention 'preamp section' - I'm going to upgrade it to a simple Noble potentiometer - and probably leave it this way, until I'm stinkin' rich and can afford one of those fancy hi-end preamps ;)
As to biamping - I was actually thinking about that, inspired by this crossover project. But for now, I think it's a bit too advanced for me :P Simple biamping is an interesting option though, especially that you say it brings significant improvement.
With signal wires - correct me if I'm wrong, but logically reasoning, a perfect signal cable should:
- have no capacitance (very important)
- have low resistance (quite important too)
- shield out any interference coming from higher voltaged wires/RF.
The first is achieved by insulating the core, with teflon being probably the best material to use.
The second is achieved by use of the best conductive material (i.e. silver); its thickness doesn't matter much as currents flowing in it are very low.
And the last can be done with braiding wires and/or shielding them.
With internal power wires, things change by 180 deg.:
- capacitance doesn't really matter much
- low resistance is prefferred, but not crucial
- fairly high current capability is important
- shielding is irrelevant as voltages are quite high
So, basically any copper cable of diameter, say, 0.75mm or more will do just fine.
This is how I thing wires work. Only thing I have no clue about is how does compare braided wire vs solid core one.
I know that braided are generally more flexible, they don't snap, and are easier to solder. But what is the trade-off? Is there any? I guess, there should be, and my bet was that they have higher capacitance than comparable solidcore. Can someone experienced shed some light on this, please? |
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| Hartono |
Hi,
without active pre-amp the high frequency could be rolled off.
"shielding is irrelevant as voltages are quite high"
actually, the high voltage signal can cause interference with the small signal on the pcb and adjacent wire, but shielding is not very effective at low frequency.
"I know that braided are generally more flexible, they don't snap, and are easier to solder. But what is the trade-off? Is there any? I guess, there should be, and my bet was that they have higher capacitance than comparable solidcore. Can someone experienced shed some light on this, please?"
This one is tougher to answer and subject to some controversy, so I'll try to explain minimally ;) .
Capacitance is practically the same with solid core, it's governed by cable geometry and insulation material. cable that's not paired (figure 8, twisted pair) have lower capacitance but higher inductance.
Extreme example is : ribbon wire (Goertz) have higher capacitance and very low inductance.
the problem with cheap cable is, in some condition (humidity) the insulation material can attack the surface of the conductor, causing oxidation and corrosion. PVC / PVDC is known to be very bad in this regard. with stranded cable, the corrosion will be terrible, much worse than solid core. Solution : don't use PVC/PVDC ;)
http://ecmweb.com/ops_maintenance/e...focating_swine/
Hartono |
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| pinkmouse |
| Some new music, and a bottle of something nice to drink whilst you listen. :) |
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| uncle_leon |
Thanks for a good point, Hartono. I actually forgot about inductance completely (it was one of the things about electricity, that I had trouble understanding, to be honest).
I've just read a bit about it on Wikipedia, and it seems to me, that, basically, inductance derives from resistance (i.e. higher resistance -> higher inductance), length and diameter of the conductor. But why then, coaxial wires have so high inductance (which makes them useless for audio signals, from what I heard)? I initially thought they would make very nice signal wires - shielded and all...
Ahh... I wish I had paid more attention to physics back then, at school :P
As to "actually, the high voltage signal can cause interference with the small signal on the pcb and adjacent wire", you are of course absolutely right. I felt it, sort of intuitively, and kept power wires separated from signal ones, while designing casing for my GC. |
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| Hartono |
Hi,
tin plated cable might be ok with PVC/PVDC since tin is acid resistant. but the pvc/pvdc still can release gases and might affect other metal inside the equipment. Tin plating is the cheap solution.
inductance is the inverse of capacitance , coaxial cable has high capacitance, and relatively low inductance, not the other way around. some coax inner conductor is made from copper clad steel , steel is not good for audio (magnetic) and add distortion.
Inductance in cable is usually more benign in audio frequency, unless a "single" conductor/cable is coiled (inductor,coil, the name is self explanatory). if one of the conductor carry + signal and the other - signal(or ground) the inductance is lowered (example: speaker cable).
I notice you used nickel plated connector , some nickel plating contain iron (magnetic).
Cheers,
Hartono |
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| Arx |
| quote: | Originally posted by uncle_leon
I've just read a bit about it on Wikipedia, and it seems to me, that, basically, inductance derives from resistance ( |
Nope, they're not tied together.
If you think of capacitance as being a resistance(impedance is a better word) to a change in voltage, you could think of inductance as a resistance(impedance) to change of current.
So, as a rule of thumb, capacitance is going to be more of a problem for low level (voltage based) signals, since a certain amount of the signal energy is going towards discharging and recharging the capacitance. Inductance doesn't really matter, since the current flow is so small.
For high level (current based) signals like speaker outputs, inductance will be more of a problem, since a lot of energy is taken trying to reverse the high current flow back and forth. Reasonable amounts of capacitance are easily swamped by the high current output.
There are, of course, exceptions. This is a very simplified description.
-Nick |
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| uncle_leon |
| So, what you mean is that braiding the signal wire - like I did - in Litz fashion is no use for signal wire? And that it would be actually better idea to use single, widely spaced wires, in order to get the least capacitance possible? |
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| uncle_leon |
Sorry for double posting, but why 'edit' feature on this forum is limited to 30mins after posting?...
Anyway, I was thinking about what Hartono said, regarding possible hi-freqency roll-off with passive preamp. And I think I found the perfect solution - a stepped attenuator. I found one, based on Vishay 1% resistors, for as little as 50AUD (yes, it is in Australian dollars and no, I have no clue as to how much would it cost to post it from there). I think this kind of solution will be quite hard to beat, even for good quality active preamps. |
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| Arx |
Yes, I believe you are right regarding the capacitance on internal cables. In my chipamps, I've instead minimized the length to be insignificant. (input connector is right beside the amp chip), so I can't say how much difference it makes. I think not much.
As far as high frequency rolloff is concerned, it's not going to make a difference whether you use a pot or a stepped attenuator.
If you have a problem with high frequency rolloff, the only ways to fix it is to either increase the input impedance of the amp (making it more sensitive to noise) or reduce the loading on the input by buffering with an active preamp, which doesn't necessarily need to be complicated.
Whether this will be a problem or not depends on your source.
Try it and see.
That said, if you want very good channel balance, the stepped attenuator might be nice.
-Nick |
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| Leolabs |
| Do add some regulators consider an upgrade too??? |
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| Peter Daniel |
| quote: | Originally posted by Nuuk
IMHO, and after trying most things, a simple GC is still the best GC!
Don't bother with BGs in a GC. Panasonic FCs and MUR 860's work well in a GC (although not necessarily elsewhere)
Solid core wiring for signal is fine (you don't need silver etc for those short lengths). Just keep it short and tidy.
Dual mono PSU is best with 37 volt rails (if you have 6-8 ohm speakers).
I prefer the PSU in a separate enclosure. I also prefer a non metallic enclosure for the amp.
Resistors - won't cost much so try what you fancy.
Zobel - won't cost much so try with and without.
:attn: One of the biggest improvments I got with GCing was to build a four channel amp and bi-amp the speakers. :att'n:
Finally, remember that a lot depends on what goes before the GC! ie you may need an active pre or buffer stage. |
That's right on, a simple GC is still the best GC and I was promoting it for last three years without basically changing anything in my initial circuit.
Regulated supplies, batteries, switching supplies, snubbers, Zobels, big caps, all came and are gone now (at least for me), and simple GC still rules.;-)
Panasonic FC caps are indeed the best value for the money and it's hard to improve on them.
The biggest change, in my system, came with using small BG N caps directly at the chip and larger BG STD at the rectifiers. That changed the sound in a right direction and for me there was no way back. Although some of my friends still prefer large BG STD at the amp.
The 10uF caps that come with a kit are not neccessary to be used, depending on a setup, the amp may actually sound better without them, so try both ways. I noticed that placing only one cap in negative supply may be better than using both of them (but that was mainly with BG N caps)
I would not go with standard resistors any longer though, as more"exotic" types offer more flavour and definition, but you need a right system to notice that. However, you may save by skipping input series resistor (220R in my kit) as that resistor is not really needed for the amp to function properly. Riken can be replaced by Kiwame, although there is slight difference in their signatures: Kiwame is more sweet and lacks the "bite" which I find quite desirable with Rikens (Rikens are out of production now, and if they are gone I will start using Kiwames). Input shunt 22k is equally important as 22k feedback resistor and Caddock MK132 is still best for me here.
Transformer is probably responsible for some 20% of good sound and if you use really cheap stuff the bass and PRAT may suffer. I find Plitrons quite good and only custom made toroids with amorphous cores were better, but I can't source them any longer.
PS wire makes probably 8% of the sound, for me Cardas is best suitable here, however much cheaper DH Labs hook up wire wasn't bad either and the difference was like comparing Rikens and Kiwames (too sweet for my taste).
Input signal wire is more critical than output wire, but I would not go with anything special here. Solid core silver from DH Labs is good, as well as gold plate copper I use most frequently now for signal. Just try to keep all connections short and you may be able to go away with most everything. For output, I use either Kimber or DH Labs (19ga). Altough one person I know about found GC addictive only after replacing signal wire with solid core silver. Cardas silver wire offered by Percy is pretty cheap and quite good.
Now, it may sound surprising to some, but chassis is actually pretty important and depending how you build it the sound may vary quite substantially. I can't offer any receipe here and I usually approach it with an open mind attitude, where everything can matter. My best creation so far was described here: http://www.diyaudio.com/forums/show...6609&highlight=
Please note, that if you have balanced source, the bridged GC will be better than regular one, especially when it comes to dynamics and bottom end extention. But you need the speakers that are at least 6ohm.
The bi-amping is also a big advantage, and the GC will sound only as good as the rest of your system, if it sounds bad, the fault is usually somwhere else ;-)
Attached is schemnatic of my Patek amp. |
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| BWRX |
Most effective upgrades:
- Stiff power supply (consider regulated supplies if using lower rail voltages and/or higher impedance speakers)
- Low impedance drive for the inputs
- Balanced or differential operation
- Adequate heat sink
- Replace gainclone with class d amp*
* ;) |
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| Peter Daniel |
| quote: | Originally posted by BWRX
- Replace gainclone with class d amp*
* ;) |
Forget Class D amp. If you really want to upgrade from GC, use properly built Zv9 with tweeter crossover cap connected directly to the amp's output (bypassing the usual high value electrolytic). |
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| BWRX |
| quote: | Originally posted by Peter Daniel
Forget Class D amp. |
I would but I really like how some of them sound in my system :) The higher efficiency is a nice benefit too. |
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| ttan98 |
Peter,
Your input is timely, thanks... |
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| Arx |
| Yes, chassis is important. My amplifier sounded 6.454% better after I brushed the aluminum. ;) |
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| Jonathan Bright |
| Hi uncle leon re: your question in Post #10 about the editing function. I think it is to stop people adjusting previous posts when they get into contenious debates. This current thread is very civilised but some are fairly intense debates and go on for months or years with a lot of "quoting" from the various participants. If the edit function had no time limit then the less scrupulous antagonists may be tempted to go back and "re write history" and "ammend the records" etc with all sorts of helpful/funny/scandalous results. Or simply they may just like to be able to change a previous faux pas so as to not look like a complete goose! I may be wrong but I think this is the reason. Seems reasonable to me. |
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| pinkmouse |
:cop:
Correct in just about every aspect Jonathan. :) |
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| Poindexter |
Well, guys,
Panomaniac is coming over to my house this weekend, and bringing his quiver of D amps (all Tripath chip, if I am not mistaken), and we are going to audition with the latest version of the Machine.
I have clients on the Machine who have owned and heard the Heavy Hitters in boutique audio, and are ecstatic with their five watt solution. I'm not pitching, I'm just pointing out that we have a pretty good baseline to A-B these D amps with, although not a 'clone. The D amps will be much more powerful, of course, but my own breadboard can have my eardrums kissing and making up in the middle of my skull with the 94dB Fostii, so I don't think that will be a factor.
Now, there's a slight problem here in that I have never properly heard a gain*, but there we go.
Stay tuned, film at eleven.
Aloha,
Poinz |
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| uncle_leon |
Thank you all for your thoughts, I began to think the thread was dead already :P
Anyway, I'm having some difficulties getting my amp together. I think I actually managed to destroy good half of it... All because I was rushing to get it up and running... I know, I should have known better, especially with my experience on computers field - but i have an impression that these new PCs tend to be much more forgiving than an amplifier :P
What I've done is: I wired and soldered everything just fine (voltages on rectifier's outputs were fine and everything), EXCEPT that I swapped V+ with V- on one of the amp boards. The result was burned copper path on rectifier PCB as soon as I turned the power on (this was the only visible result). I was hoping that everything might still be ok when I replace the board and put the wires as they should be.
Unfortunately, the story pretty much repeated - the same copper path as in the first rectifier went on fire.
I disconnected the rectifier board from amp boards, patched it up with two pieces of thin wire (VERY thin wire, just in case). And it seems that those diodes are tough sons of the (ekhm, ekhm) - the bridge puts out pretty much the same voltage as previously.
My bet is that the initial reverse voltage damaged the chip (and the first rectifier board by the way), and then, the newly-created internall short-circuit in that chip caused fire on the other rectifier board.
So, I was thinking why not try connecting at least a single channell (the one which was wired properly from the beginning). Does it make any sense to do it, or is it best to replace both chips and not risk another fireworks show? |
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| BrianDonegan |
| quote: | | Panasonic FC caps are indeed the best value for the money and it's hard to improve on them. |
Panasonic FM are a better deal. Cheaper, much lower ESR. Some say better sound too, but I try to not comment on such things. |
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| Russ White |
| Also the color of the FM is more aesthetically pleasing to the eye than the FC. :) Oh and wood cases are 3.32% better than aluminum. |
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| t. |
| Has anybody actually compared the Panasonic FM's against the FC's in the Gainclones? Just interested to know, funny thing is I don't like the FC's or the MUR860's in any other amps yet they work excellent in the GC's:) |
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| Arx |
| quote: | Originally posted by uncle_leon
So, I was thinking why not try connecting at least a single channell (the one which was wired properly from the beginning). Does it make any sense to do it, or is it best to replace both chips and not risk another fireworks show? |
I'd double check everything and then give it a go with the other board. You've already uglied up your rectifier boards anyways, so if the voltages are ok after the repair, I don't see much point in replacing good parts.
As far as trying to improve it with fancy parts, I wouldn't even bother. Get it working with standard cheap parts and you'll probably be happy with it the way it is. I've never felt the need to change any of the parts in the standard kit I got from Peter, and when I decided it was time for another amp, I did it point to point with the same parts.
Personally, I think all this stuff about resistors and capacitors sounding different is in peoples' heads (within reason of course).
If you want to blow some money on "bling" for your amp, I think it's better spent on a better volume knob and connectors.
I picked up a "PEC" brand pot from digikey at the recommendation of some others on this board, and am really quite happy with it. Not because I think it sounds better, but because it is solid, and tracks evenly between the 2 channels. Unlike the cheap pots, I expect that it will still be working perfectly in 10 years, and not all scratchy and crackly. When I'm listening very quietly, the balance isn't off centre like with a lot of cheap amps.
Also, I hate RCA connectors, so I used XLRs.
I'm not saying you shouldn't give different caps/resistors a try. I doubt I could tell the difference, and I doubt most people who claim to could recognize anything in an ABX test, but there may be exceptions.
What I am suggesting is that it's probably not the first thing to mess with. Chassis, controls, and connectors are all better places to spend your dough. (Especially if it's in short supply)
-Nick |
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| uncle_leon |
| Thanks Arx, I'm only wondering now if there should be anything connected to the amp on power-up? I guess that zero input signal and infinite impedance output are the safest setup? |
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| BrianDonegan |
| Short your input (+In to GND) for startup. This will ensure 0dB input signal. Open outputs are fine. |
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| BWRX |
| quote: | Originally posted by t.
Has anybody actually compared the Panasonic FM's against the FC's in the Gainclones? |
I like the FMs because they're a little cheaper than the FCs and have lower ESR. I doubt you would hear much, if any, difference between the two. |
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| scottw |
Curious if anyone has "taste tested" Rubicon ZL's in a chipamp PS?
Been listening to Panny FC's for years in a GC and planning to build another, but not sure I want to cough up the $'s for Black Gates.
Scott |
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| Arx |
| quote: | Originally posted by uncle_leon
Thanks Arx, I'm only wondering now if there should be anything connected to the amp on power-up? I guess that zero input signal and infinite impedance output are the safest setup? |
As Brian says, Shorted is better than open. Open shouldn't cause any problem either, since it's held to ground by 22k in that circuit if I remember correctly, but if it's shorted you know it's at 0, and shouldn't be picking up any noise across the input resistor, so you can measure your DC offset to be sure it's safe to hook up some speakers. Then hook up a cheap throwaway speaker, and play with that until you're confident you've gotten any potentially speaker frying bugs out.
-Nick |
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| Hartono |
Hi,
Nick mean shorting the input. not the output, be careful.
Hartono |
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| pinkmouse |
| quote: | Originally posted by scottw
Curious if anyone has "taste tested" Rubicon ZL's in a chipamp PS? |
I've been using and recommending them since the first ever GC thread here. :) |
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| Nuuk |
| I also tried Panasonic for Audio caps in one of my OPA541 amps! :att'n: |
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| Poindexter |
The Panasonics that are most highly considered in tube amp building, where voltages are higher and values lower, are the TSHA and TSHB. I've also had very good luck with the ED series.
Aloha,
Poinz |
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| Arx |
| quote: | Originally posted by Hartono
Hi,
Nick mean shorting the input. not the output, be careful.
Hartono |
Yes, That's correct.
Though, shorting the outputs would do wonders for the dc offset.:flame:
PS: for anyone who doesn't know better, that's a joke. Don't short your outputs. :rolleyes: |
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| scottw |
| quote: | Originally posted by pinkmouse
I've been using and recommending them since the first ever GC thread here.
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Were you able to compare the Ruby ZL's to other PS caps like the Pannys or others?
Scott |
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| pinkmouse |
| Yup, I tried the Pannies as well as various Elnas and others, and to me, the ZLs were the best, but the Pannies were good. Still haven't tried BGs though. If I seem a bit vague, it was about six years ago, and I've built a lot of stuff since then! ;) |
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| uncle_leon |
My amp sang for me today! :) Just one channel obviously, but it will give me some idea about its sound.
So, my initial impressions were:
- very expressive, life-like vocal (MJ, Kate Melua)
- well detailed treble
- very tight&controlled bass, extending deep into low frequencies
- sound is a bit on the bright side
- very good instrument separation
But after some more listening, I decided that there is something wrong with tonal balance. Bass seems to lack 'filling'. It does slam nicely, but it is nowhere near richness of my NAD 3225PE.
The other problem is upper-mids - they are screamy and overexposed. Add the fact, that there was way too much trebles, and you have one really shrilly&shouty amp.
And I don't like being shouted at... After hooking speakers back to NAD, the feeling was like if I was sat in an soft padded, comfy armchair. Relaxed, rich, but polite sound, enjoyable even in spite of the lack of that last detail. Gainclone seems to be much more involving, but for now, NAD remains my main amp.
So now I'm wondering WHY? Can anyone please give me a hint as to possible causes of such imbalanced sound?
I also have one less important question, as to optimal temperature for this chip. During normal, moderately loud listening it was getting more than warm, but wasn't burning. But after putting the volume really loud, it got to over 80deg.C. Is it still safe or should I install fan/larger heatsink? |
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| okapi |
80 degrees is definitely on the hot side.
i found, by attaching a thermocouple at the heat sink right next to the chip, that thermal protection started to kick in at around 85 degrees C (at the time i had quite small heat sinks and my speakers are rated at 6ohms).
into an 8 ohm load the lm3875 does not need a very large heat sink but, if the load is less and the listening level is loud, the heat production definitely can get to levels that need a larger heat sink.
nevertheless, it has been my experience that passive cooling was always able to do the job with the lm3875.
lastly, with my first cobbled together gainclone, i found it was getting quite hot until i discovered that a single thread of my speaker wire was shorting. the amp still sounded fine with the short but the heat production was definitely increased.
hope this helps. |
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| Arx |
| quote: | Originally posted by uncle_leon
The other problem is upper-mids - they are screamy and overexposed. Add the fact, that there was way too much trebles, and you have one really shrilly&shouty amp.
So now I'm wondering WHY? Can anyone please give me a hint as to possible causes of such imbalanced sound?
|
A couple of possibilities.
1. Your music just sounds like that, and your other amp is just masking the top end.
2. You're bouncing off the protection circuitry.
3. Oscillation
For #1 there isn't much you could do other than get used to it, or apply some lowpass filtering to take the treble down a tad.
For #2 A better heatsink maybe? I don't know how loud you were listening, but mine has a case made of 3" by 1/8" aluminum angle. And stuck on there with heatsink paste it gets a little warm at my normal listening levels. Certainly not anywhere near what I would call hot.
For #3 You need some way to damp the oscillations. Maybe add in the "zobel" components if they came with your kit. I've never had that problem, so I can't say whether it will help, but it's certainly cheap to try.
When I first built mine, I noticed that good recordings sounded better than on my old amplifier, but bad ones sounded worse. I wouldn't be surprised if that's all it is. Now you can hear how your recordings suck. :D
-Nick |
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| salas |
| quote: | Originally posted by uncle_leon
My amp sang for me today! :) Just one channel obviously, but it will give me some idea about its sound.
So, my initial impressions were:
- very expressive, life-like vocal (MJ, Kate Melua)
- well detailed treble
- very tight&controlled bass, extending deep into low frequencies
- sound is a bit on the bright side
- very good instrument separation
But after some more listening, I decided that there is something wrong with tonal balance. Bass seems to lack 'filling'. It does slam nicely, but it is nowhere near richness of my NAD 3225PE.
The other problem is upper-mids - they are screamy and overexposed. Add the fact, that there was way too much trebles, and you have one really shrilly&shouty amp.
And I don't like being shouted at... After hooking speakers back to NAD, the feeling was like if I was sat in an soft padded, comfy armchair. Relaxed, rich, but polite sound, enjoyable even in spite of the lack of that last detail. Gainclone seems to be much more involving, but for now, NAD remains my main amp.
So now I'm wondering WHY? Can anyone please give me a hint as to possible causes of such imbalanced sound?
I also have one less important question, as to optimal temperature for this chip. During normal, moderately loud listening it was getting more than warm, but wasn't burning. But after putting the volume really loud, it got to over 80deg.C. Is it still safe or should I install fan/larger heatsink? |
That's how it sounded to me too, compared to good valve amps, and that is why I only built a couple of GCs. Good value, transparent, but stressful in the long term IMHO. |
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| Hartono |
go to next step:
Class A amp |
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| lgreen |
85C is very hot, I'd go with a larger heatsink.
On one of my GC's (parallel LM4780, see link in my sig line) I installed a thermoswitch that shorts at 45C and lights a red LED. Even with the fan turned off it can go for hours without reaching 45C, but when you play it loud it immediately gets hot and trips the switch.
Not sure what advice to give you on the sound, are you using a zobel network on the output? You might want to add/tweak it. |
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| Arx |
What are you using for a heatsink anyways?
What's the impedance of your speakers?
Voltage of your rails?
with an 18v transformer, you're probably only around 30-34v at the rails and shouldn't be running all that hot unless either something is wrong, or your speakers are very low impedance, or you've got a very small heatsink.
-Nick |
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| uncle_leon |
The temperature must have had some substantial influence, because when I auditioned the amp at low to moderate volume levels, the sound was much better balanced.
I found another problem though - the amount of bass is rather low. And when I tried "fixing" it with Winamp's equaliser (I simply put 60Hz at +12dB), strange thing happened... The bass did not became more dominant at all, but instead whenever there was a big "oomf" (or I should rather say "whenever there SHOULD be an oomf"), the rest of the sound was fading for a moment. I suspect that there must be some problem with power. Maybe those tiny-thinny wires, that I patched the rectifier bridge with, are a problem. I'll swap them against some thicker cable and see what happens. |
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| Hartono |
| check your supply capacitor |
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| uncle_leon |
...which means? The small ones, 10uF on rectifier board? And what can be possibly wrong with them, how do I check it?
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| uncle_leon |
I replaced those tiny 0.1mm wires on the rectifier board with proper 0.75mm ones, but it made any difference, it was not audible. The amp still seems to be very current-limited.
I also checked out all caps and they look alright to me... My multimeter doesn't measure capacitance, so I can't make sure they are really ok.
Edit:
Oh, and by the way, I'm getting pretty high noise floor from that crappy laptop soundcard. I guess a pot on input would help supress it? The noise comes from the source, of course, the amp itself is perfectly silent.
E2:
In case it matters, the speakers are Mission 70 MKII, they are rated at 75W, 8Ohm. I think they should be really easy load on any amp. Even some utterly poor 5W amplifier I took off some cheap active PC speakers managed to drive them to reasonable volume levels without clipping.
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| Hartono |
| Hi there must be bigger caps than that in your supply (10uF is way too little), I'm not sure about your gainclone PCB, maybe the supply caps is onboard in the main pcb, you should have something like between 1000-10000uF somewhere. |
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| uncle_leon |
| Yes, there are 1500uF caps on amp board. But still, I can't see anything wrong with them... Apart from one small dent in jacket on one of them (I touched it with my soldering iron accidentaly). |
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| Russ White |
| quote: | Originally posted by uncle_leon
Yes, there are 1500uF caps on amp board. But still, I can't see anything wrong with them... Apart from one small dent in jacket on one of them (I touched it with my soldering iron accidentaly). |
What size caps are on the power supply?
Cheers!
Russ |
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| Hartono |
Hi Uncle_leon,
"heatsinks taken off broken PCs, they seem more than adequate for LM3875s"
can you tell more about the heatsink size? did you use thermal compound/grease between the IC and the heatsink ?
Hartono |
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| Panelhead |
I am far from the first to do this, but try reversing the order of the caps. Like 1500 ufd on the rectifiers and 10 ufd on the pins of the chip. Then maybe 220 ufd where you have the 1500 ufd.
Using 10 ufd caps right on the power pins give a lower esl than any 1500 ufd cap. I have installed 22 ufd 50V FM caps in a couple amps lately. Being away from the power supply they do not increase diode noise, like using a low esl cap at the rectifiers.
If your rails are low enough, the Silmic II 10 ufd 35 volt caps are perfect. Plus 7.5 cents each at Digikey. These will work great to about 30 volt (dc) rails.
What I really recommend for bass, mids and highs is 10,000 ufd Panasonics, bypassed with 0.047 ufd film and 0.4 ohm resistor in series. Then a 220 ufd ZL cap, and 10 - 22 ufd low esl soldered to the bottom of the power pins. And a 0.1 ufd film cap (100 volt) going rail to rail.
This combo is quiet and stores a lot of energy. But the real cat is the small cap on the power pins. It makes a huge difference in the dynamics and percieved bass.
George |
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| Russ White |
1500uf simply is not enough capacitance per rail to provide decent smoothing. A quick test on the bench shows massive supply ripple even with just a 10Vpp 1Khz sine into 8ohms, at 20khz it is simply horrid. This is even with very good low ESR caps. This effect will have detrimental effects on PSRR (of course) and produce a lot of distortion and make the amp sound thin, certainly not great.
Such low capacitance on the rails will also result in a lot of mains induced ripple (100 or 120hz) being on your rails (very easy to see). This is also not a good thing at all. Even with very good diodes arranged as a dual bridge you should have at a minimum 10,000uF per rail at 30V to produce a decently smooth power supply. 20K being much better. 4700uf may be passable, but I would not personally go that low.
A pair of 1500uf may be simple, but it will not produce an amp that can deliver the goods. It is easy enough to prove both in simulation and with the most rudimentary of scopes.
There is simply no transformer with low enough impedance that you can get away with 1500uf rails. Especially at higher frequencies where the inductance of the transformer secondaries plays a large role.
Cheers!
Russ |
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| sharpi31 |
The last LM3875 amp I built easily betters my previous efforts. First I built the Peter Daniel basic kit (which sounds brilliant) then modified the psu by adding 15000uF per channel (which sounded dreadful - slow, detached bass and no excitement - just as others have reported).
My second build was a Peter Daniel premium LM3875 kit, but with 100uF black gate N on each amp pcb with 0.1uF BG Nx bypasses on the pins of the chips. I built a cap bank with panasonic FM caps to give me 18000uF per rail (or there abouts..). No snubbers were used - I hoped the paralleled 1000uF caps used in the 18000uF bank would not sound as slow as the single 15000uF caps I'd tried in my first amp. This amp was a big step up on my first effort.
My latest amp has 4.7uF BG N on the rectifier board, with a 39ohm 0.1uF snubber (optimised to reduce noise at 256KHz). I have a single pair of 2200uF 100V sikorel caps upstream of the amp boards, which have 940uF sikorel 125 (2x 470uF) per rail per channel. I have no low value bypasses on the chip pins, but a single 47uF BG standard between V+ and V-. All resisitors are 2W Kiwame except for the feedback, which is a Welwyn RC55. I managed to shorten the feedback loop considerably by mounting this to the rear of the chip, soldered directly to where the pins come out of the chip body. A Kiwame would have been too large for use here. The volume pot is a 1meg PEC with 39ohm Kiwame in fake-law.
There are far too many variables for me to claim why my new amp sounds so much better than my old efforts. I now have raw dynamics and bass weight without loosing the open mid and top of my first basic PD kit. My suspicion is that the sikorels behave like faster smaller caps (totally unqualified statement, i know) so don't seem to slow the sound as much.
I ended up buying loads of the 470uF 35V sikorels on Ebay (100 i think!) and I'd happily mail eight to anyone who wants to give them a try... I'd be interested for someone with more experience than I to try them and report back. |
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| uncle_leon |
| quote: | Originally posted by Hartono
Hi Uncle_leon,
"heatsinks taken off broken PCs, they seem more than adequate for LM3875s"
can you tell more about the heatsink size? did you use thermal compound/grease between the IC and the heatsink ?
Hartono |
Hi Hartono, the heatsink is 6.5cm L x 6cm W x 4cm T, aluminum, with 10x8 fins. At normal listening levels I could not record any temperature above 42C (which simply HAS TO be low enough). I have massive experience with cooling computer processors (including water cooled / below 0C systems), so believe me, I did everything about this part right.
This "bass fade", occuring when over-equalizing low frequencies (as I descibed above), persists even at lower volume / low temperature. So I guess it wasn't the temperature that was the problem after all.
Is it possible that I damaged my caps somehow, while I was soldering them?...
Panelhead, sharpi31 - thanks for your ideas, I will certainly come back to them after my amp starts working properly. For now, it is not the matter of taste or quality, there's simply something wrong with the amp.
Russ White - I know that those 1500uF caps seem way too little, but everyone I asked told me that swapping them against some proper big caps only made their amp sound worse. I'm not an expert so I just rely on other's opinions. |
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| Russ White |
| quote: | Originally posted by uncle_leon
Russ White - I know that those 1500uF caps seem way too little, but everyone I asked told me that swapping them against some proper big caps only made their amp sound worse. I'm not an expert so I just rely on other's opinions. |
Oh I would keep the 1500uf caps, they are good for decoupling, but they should indeed be supplemented at the power supply side.
There is nothing peculiar about the way the LM3875 or any other chipamp "sees" the power supply. It the same as any other amp in that regard. While it does have decent PSRR it is not so great that you can ignore having stiff rails.
This is not to say you should throw any old cap you like in there. The thing should be suitable for the task.
There is nothing to argue here. This is a simple matter of math/engineering and very simple to test. 1500uf is simply not enough, not that it won't work, and not that some folks might say it sounds better (for who knows what reason) but I can tell you flat out it measures terribly, and all things tangible say 1500uf on the rails will never a great amp make. :)
In the end all that matters is that you are happy with what you built. Have fun!
Cheer!
Russ |
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| Hartono |
Hi Leon,
ok since you have tried it without boosting the bass, and it works ok in that condition, list of few things might go wrong:
1. your 1500uF supply caps is broken.
2. some of the rectifier is broken/miss-wired.
3. the bass boost pull down your supply rail (your caps is only 1500uF, bass eats power very quickly).
and.......other possible problems.
what happened with your previous problem you mentioned ? about the pcb track burning, this might give some clue.
Hartono |
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| pwan |
Q: The most effective Gainclone upgrades
A: Speaker! Try any full range and high sensivity like Fostex fe12x, or fe16x. |
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| uncle_leon |
| quote: | Originally posted by Hartono
Hi Leon,
ok since you have tried it without boosting the bass, and it works ok in that condition, list of few things might go wrong:
1. your 1500uF supply caps is broken.
2. some of the rectifier is broken/miss-wired.
3. the bass boost pull down your supply rail (your caps is only 1500uF, bass eats power very quickly).
and.......other possible problems.
what happened with your previous problem you mentioned ? about the pcb track burning, this might give some clue.
Hartono |
You're probably right Hartono, I started thinking too that something have gotten damaged by that first power surge after all... Well, I was going to place another order at Peter's shop anyway :P |
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| Peter Daniel |
| quote: | Originally posted by Russ White
There is nothing to argue here. This is a simple matter of math/engineering and very simple to test. 1500uf is simply not enough, not that it won't work, and not that some folks might say it sounds better (for who knows what reason) but I can tell you flat out it measures terribly, and all things tangible say 1500uf on the rails will never a great amp make. :)
|
Those all are amps built with small caps, good the people who judged them where not engineers ;)
http://audiosector.com/images/pfo2005.jpg
http://www.6moons.com/audioreviews/bo05/srajan.html
Links to reviews are on my website. |
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| Hartono |
Actually there are some reason to use smaller caps, and single supply.
"with plenty of image density" <--------hint. |
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| Russ White |
No probably not, and there is no accounting for that type of review. :) Does not mean much to me when I can test the exact same circuit for myself and know it both sounds( to me ) and measures (to everyone) inferior to a chipamp with a decent supply.
Audiophile reviewers are a colorful bunch indeed, but in all I cannot take them very seriously. :) I think, listen, design, and decide for myself.
Cheers!
Russ |
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| Russ White |
| quote: | Originally posted by Hartono
Actually there are some reason to use smaller caps, and single supply.
"with plenty of image density" <--------hint. |
Low order distortion? Not exactly appealing to me... |
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| Hartono |
"Low order distortion? Not exactly appealing to me..."
you got 1 right, there's another one. |
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| Russ White |
| quote: | Originally posted by Hartono
"Low order distortion? Not exactly appealing to me..."
you got 1 right, there's another one. |
Low manufacturing cost? :) |
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| Hartono |
"Low manufacturing cost?"
I like that one :D
it's simultaneous rail clipping of both channel.
Hartono |
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| Russ White |
| quote: | Originally posted by Hartono
"Low manufacturing cost?"
I like that one :D
it's simultaneous rail clipping of both channel.
Hartono |
Ah right, yikes... imagine a 4-6ohm load with just 1500uf...
Its amazing to see how much of the output signal is apparent on the rails with 1500uf, it is quite a lot.... And that can never be considered a "good" thing. At least if your aim is low distortion.
I bet IMD is also not great. But I cannot measure that here.
Cheers!
Russ |
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| uncle_leon |
Russ, have you actually tested all the things that you say? I mean, do you have GC with sockets and have tested everything out on a real thing by swapping different parts?
The reason I'm asking is that your opinions are... how to put it... in (vast) minority compared to what I have read / heard so far from GC owners. Maybe there's simply something wrong with your amp too? |
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| Russ White |
| quote: | Originally posted by uncle_leon
Russ, have you actually tested all the things that you say? I mean, do you have GC with sockets and have tested everything out on a real thing by swapping different parts?
The reason I'm asking is that your opinions are... how to put it... in (vast) minority compared to what I have read / heard so far from GC owners. Maybe there's simply something wrong with your amp too? |
Yes I have, and it is not difficult. :)
I started out with the same exact sort of amp you are building(but from BrianGT), and yes at the time I thought it was the best thing since sliced bread, but you live and learn. :)
I am sorry what I am saying does no jibe with your expectations, but the facts are facts.
Also, nobody has or will dispute my points, they are accurate.
My thoughts are not in the minority of engineers and astute audio junkies I can assure you (not that I am an engineer). What I am saying is common knowledge. In fact if you look around this forum for power supply threads I think you will find I am quite correct.
You are more likely to find much more accurate views on the subject in the other forums on this site such as the solid state and Pass forums. In fact there is a whole space for power supplies. They are not trivial.
Most of the arguments you are hearing are purely subjective. While I appreciate such views, I like a more analytical approach to design.
There are several good PS write ups on the web you can wibble for.
Keep your mind open by all means, but don't put the blinders on to good engineering just because somebody says you should not care. :)
I have no stake in your amp, and I have nothing to prove. I am just here trying to offer some good advice. At the end of the day I just sincerely hope your happy with your project.
Cheers!
Russ |
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| steenoe |
| quote: | Originally posted by pinkmouse
Some new music, and a bottle of something nice to drink whilst you listen. :) |
This is the most sensible comment I found on this thread:D
Steen:cool: |
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| Russ White |
| quote: | Originally posted by steenoe
This is the most sensible comment I found on this thread:D
Steen:cool: |
I would second that. :) |
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| jeff mai |
| I'd be wary of anyone telling me what an amp sounds like from looking at the schematic. Why not build a few different circuits yourself and compare? |
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| Russ White |
| quote: | Originally posted by jeff mai
I'd be wary of anyone telling me what an amp sounds like from looking at the schematic. Why not build a few different circuits yourself and compare? |
Absolutely, why not! :) Nobody can say what you will like and what you won't.
Cheers!
Russ |
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| alleycat |
| Didn't Nuuk on his website say, essentially, that the most effective gainclone upgrade is an SMPS? |
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| justblair |
| quote: | Originally posted by Hartono
which SMPS ? |
It's the Skynet 8080, or to be more exact four of them. 2 in series 2 in parrallel. This gives you 24v with good power available. NUUK reckons that 2 smps giving 12v is very good, I found that I needed the 24v to get a sound that delighted me. You have to make a small and very esy mod to the smps to produce these arrangements. It's nothing to be scared of and Decibel Dungeon gives clear instructions on how to do it.
I unfortunately have not tried a conventional torroid gainclone so I can't tell you if the SMPS is better or worse. What I can say is that to my ears it sounds very very good. |
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| uncle_leon |
A little update on my Gainclone story:
I bought today a pair of Wharfedale MFM5 - proper sized, bass-vented, 3-way floorstanders.
Obviously, I hooked them instantly to my GC to see what happens. And the result was... fantastic, actually :)
First, they have bass-reflex, so I thought to myself, that most likely they have better efficiency than close-cased Missions. So I thought I might push the amp just a bit harder than the low-to-moderate volume. The sound was alright, so I pushed more... and more... And I ended up with the 125W speaker almost spitting its cones out while pumping incredible sound! The radiator did get hot, but I haven't noticed any impact on sound.
So I went on to check if that singular bass-related sound fainting would occur on these speakers too.
I set up the same ridiculous +12dB boost at 60Hz in Winamp, but forgot to lower the "preamp" bar, so the sound got completely distorted. I lowered "preamp" all the way to -12dB, turned up the volume and... clean, balanced sound in mids and trebles + wildly THUMPING bass.
Apparently, the cause of the problem was simply a weak sound card. Or rather GC's input resistance was too low for it - which comes down to the same.
In my previous tests I was lowering "preamp" bar, but not quite by as much as -12dB. So I reckon the sound was getting messed up simply due to card's output amp being unable to provide enough current.
I feel quite stupid now, because what I thought to be amplifier's fault, turned out to be just inefficient speakers together with poor source :clown:
Anyway - Gainclone IS the best thing since sliced bread ;D I've heard better amps, obviously, but their price was light years away from the 57$ I paid for the kit! |
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| Arx |
Too bad I was out for the weekend. The soundcard was my first thought while catching up on the thread.
Time and time again people blame weak bass on lack of capacitance. I'm not going to suggest that more capacitance can't be a good thing. I built one of the audiosector kits, and it sounded just great with the small cap at the rectifier, and 1500uF per rail at the amps.
My new amp has 68000uF per rail. Supply ripple is around 12mV when playing a 20Hz sine wave at high volume.
I don't think I could really tell the difference between them.
With a good PSRR, I think the main difference you're going to see is earlier clipping, and probably some modulation at the line frequency. Obviously that's bad, but I haven't noticed it at any reasonable power output.
So, I can't really see much reason, other than expense, not to put in some bigger caps. I don't really see how it can be "slow" as others have suggested. Amps just don't work that way.
But they're not going to fix weak bass.
-Nick |
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| Hartono |
Hi Leon,
"Anyway - Gainclone IS the best thing since sliced bread ;D "
glad to hear u fixed your problem :D
happy DIY-ing !
also try not too use equalizer from pc, they usually sounds very bad, use dedicated one instead.
Hartono |
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| uncle_leon |
| Yeah, I know that those software equalizers are rubbish, let alone computer sound cards. It's just the fact that until I get volume pot installed I'm limited to my laptop as the only possible input for the amp - because it is the only source with regulated signal level I have around. |
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| Hartono |
Hi Leon,
more the reason to DIY your own pre-amp !!! it's not expensive, no need to start with expensive component....and it's fun :D
Hartono |
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| Arx |
You probably don't even need a preamp with most sources (assuming you don't want to use your laptop as a source later) Just a pot on the input seems to work well.
Maybe a buffer followed by a pot if you want weak sources to work. Keep it simple. :) |
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| Hartono |
"Maybe a buffer followed by a pot if you want weak sources to work"
which is a pre-amp ~~~~~~ ;) |
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| Russ White |
| quote: | Originally posted by Hartono
"Maybe a buffer followed by a pot if you want weak sources to work"
which is a pre-amp ~~~~~~ ;) |
Usually you want the buffer after the pot, or sometimes before and after (say if you have a very high output impedance source).
The reason is you want the power amplifier to have as low an input impedance as possible.
Cheers!
Russ |
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| Arx |
| quote: | Originally posted by Hartono
"Maybe a buffer followed by a pot if you want weak sources to work"
which is a pre-amp ~~~~~~ ;) |
Well, technically, I think it's not since there's no gain, but really under that logic there's no such thing as a "passive preamp" unless it has a transformer, so I guess you can see it either way.
My point was that it's not a particularly demanding setup, so keep it simple.
| quote: | Originally posted by Russ White
Usually you want the buffer after the pot, or sometimes before and after (say if you have a very high output impedance source).
The reason is you want the power amplifier to have as low an input impedance as possible.
Cheers!
Russ |
Yeah, maybe that's better. OTOH, with the pot on the output any unwanted noise in the preamp/buffer stage will be reduced by the volume control.
I suppose it really should be quiet enough not to matter though.
-Nick |
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| Nordic |
| Haveing the pot between two buffers is ideal, but overkill for this situation... it provides both the source and amp with a more constant impendance... |
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| Russ White |
| quote: | Originally posted by Arx
OTOH, with the pot on the output any unwanted noise in the preamp/buffer stage will be reduced by the volume control. |
Ah yes, indeed. Some preamps actually sound much better this way, a good example BOSOZ, and XBOSOZ often have a pot on the output, which will work just fine so long as the target power amp has sufficiently high input impedance.
The down side to this is that most amps THD increases with voltage output, and with the pot at the output the preamp will always be operating full scale. But it does reduce the hiss of the preamp very very well. :)
Cheers!
Russ |
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| uncle_leon |
I've just thought to myself that since I'm ordering a new chip and two sets of resistors, and I have one spare rectifier board with diodes, I might as well built a second pair of amps and try bi-amping my new speakers.
Only thing is, I'm not entirely sure how to distribute input signal among two amps. Would it be ok to simlply solder input wires of the second amp to the same input sockets as the first's?
Oh, and by the way, it would be very nice to have some kind of source selector... I thought of using a simple double pole switch next to each pair of inputs (so that 'on' position would connect input signal with input wire, while 'off' would connect it to the groud). The downside would be obviously that if someone accidentaly put two switches on, some bad things could happen... Or maybe not? You tell me :P |
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| Hartono |
"Only thing is, I'm not entirely sure how to distribute input signal among two amps. Would it be ok to simlply solder input wires of the second amp to the same input sockets as the first's?"
if you're doing passive biamping, basically you're correct. It's a good idea to use a buffer or pre-amp to avoid loading the source.
"Oh, and by the way, it would be very nice to have some kind of source selector... "
many way to do this, there's special rotary selector switch made for this purpose
Hartono |
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| Arx |
Yeah, You can just hook your source's outputs to both inputs. It will of course increase the loading on those outputs. As always, it depends on your source. Unless something is very poorly designed, nothing will break, but if your source isn't strong enough, twice the load is more likely to distort it.
As far as the switches go, a rotary switch is certainly better, or if you only need 2 sources you could get a dpdt switch to select which one.
If you want to do it with more than that, as you suggest, you'll want to leave the second half open, not grounded. Otherwise you're shorting your source. Most opamps are okay with that, but why push it. ;)
As far as turning two sources on at the same time, that has some (though I would bet negligible) chance of causing damage. The two outputs will fight each other. Depending on their output impedance you'll hear one, the other, or some distorted mix of the two. If they're badly designed, maybe something will break. Extremely unlikely, but theres other ways just as easy without any danger.
A safer scheme for this would be to use the same switches in series each selecting either that source, or the next switch. In that case it would work exactly the same as your way, but if you turn on 2 at the same time, you just get the signal from the first one turned "on", and the rest of the chain is disconnected.
You could either skip the switch for the last device and have it as a default, or tie its pass through to ground and have a good quiet mute when everything is turned off.
-Nick |
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| uncle_leon |
| quote: | | you'll want to leave the second half open, not grounded. Otherwise you're shorting your source. |
| quote: | | tie its pass through to ground and have a good quiet mute |
OMG, one time you tell me that I should not short input and next - just the other way round ;) What does it actually depend on?
I thought about rotary switch, but it would'n fit into my overall chasis design, so I'd rather go with pole switches.
I understand that signal wires from input selector all meet at volume pot? |
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| BrianDonegan |
| You can also tie each input to ground through a 100K resistor, which will help reduce popping when switching between sources. You'll also be presenting a 100K load to your sources at all time, which they will enjoy ;) |
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| uncle_leon |
And it won't have any drawbacks? Sounds like a brilliant idea (even though I don't understand it fully :P).
As to my second GC - do you think I should buy a separate transformer for it? If yes, does it have to be a powerful trafo, or I would get away with a small one? Tweeters won't eat much current anyway, will they?...
At the moment my plan is to use GC on premium resistors with a 80 or 120VA transformer (I haven't decided about the voltage yet) and use it for driving tweeters. I would keep the 'standard' GC on 225VA trafo and drive the mid+bass sections with it. Does such config make any sense?
A bit more on topic: I found this (terribly expensive) shop with some of the most esoteric audio gear parts. And its selection of resistors drew my attention, particularily the most expensive ones, Shinkoh, as I can't find any information about them. Can a mere resistor be really worth that much? (£1 = about 1.95$) |
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| Arx |
Yeah, Shorting inputs to ground is good. Outputs to ground is bad (usually).
I think the switches are a decent solution. I've never really seen it done that way, but have always had bad luck with rotary switches myself. If you wire it the way I suggested it should be safe for your source, and in some ways probably nicer than a rotary. If I ever need an input selector, that's probably how I'll do it.
| quote: | Originally posted by uncle_leon
And it won't have any drawbacks? Sounds like a brilliant idea (even though I don't understand it fully :P). |
Not really. Very slightly higher loading on the source (or buffer), but fairly insignificant. All it will do is lightly pull the input to ground when the input is disconnected, so it won't float around picking up noise. Keep in mind, if you're going to run without a buffer, that there's probably already a resistor to ground on the input, and adding another won't do much.
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As to my second GC - do you think I should buy a separate transformer for it? If yes, does it have to be a powerful trafo, or I would get away with a small one? Tweeters won't eat much current anyway, will they?...
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I actually wouldn't suggest passive biamping personally. I think it's a waste of an amp. Active is another story, but then you need a crossover in your preamp or something.
If you want to try it anyways, I'd suggest you can probably get away with a much smaller transformer, or just use the same one. (I'm in the process of doing a triamped setup, all on one xfmr.)
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At the moment my plan is to use GC on premium resistors with a 80 or 120VA transformer (I haven't decided about the voltage yet) and use it for driving tweeters. I would keep the 'standard' GC on 225VA trafo and drive the mid+bass sections with it. Does such config make any sense?
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It probably makes sense to people who believe in fancy resistors. I don't. Cheap metal films for me.
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Can a mere resistor be really worth that much? (£1 = about 1.95$)
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I don't want to start any arguments, but I think not. If you're that worried about tolerance, you're probably better off buying a hundred cheap ones, and matching them yourself.
I'd actually recommend the miniature Panasonic metal films. They're nice for point to point chipamps, because there's room to solder 2 of the 3 necessary resistors directly to the bottom of the chip, and still have clearance between them and the heatsink.
-Nick |
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| justblair |
| quote: | Originally posted by Arx
I actually wouldn't suggest passive biamping personally. I think it's a waste of an amp. Active is another story, but then you need a crossover in your preamp or something.
If you want to try it anyways, I'd suggest you can probably get away with a much smaller transformer, or just use the same one. (I'm in the process of doing a triamped setup, all on one xfmr.)
-Nick |
I would recommend passive biamping. If you condsider the relatively low cost of adding two more gainclone stages to your existing supply, IMHO the benefits are very much cost effective.
I did exactly this in my current setup, My Mission 753's sounded quite a bit better. The bass was more solid, more controlled and the highs became more fluid and musical. The character of the sound changed substantially for the better.
Of course it was not "twice as good", but I would step outside for a fight with you if you took the extra two stages back off me!
Next stage is to build a further two and convert my 753's to triamps. Then the bass assist will have its own gainclone stages. I'm not sure wether the load might be too much for my smps array, if not I will build a second and run each channel off of four skynets each.
That is not to say that adding a filter(crossover) prior to the amps would not be the best solution, however I dont think I am ready for that project just yet
- I don't understand baffle steps, phase difference etc enough to know how it would effect my sound
- The missions are 2 way with bass assist (possibly) I haven't seen a filter project that gives this
- Active filters tend to use op amps, I dont want to spend time finding the optimum one just yet
- I just spent a few quid replacing the crossover componenets in my missions, I want to get some pleasure from the enhanced sound
- I have just built a 12 chip dddac, its so awsome, I will upgrade to 24 or 36 first
Though Mission 753's with 10 gainclones and an active filter might just be amazing :cloud9: |
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| uncle_leon |
| I think I will just see for myself and then decide. If the secondary amp will improve the sound, then good. If it will not, I'm going to add one more channel, and convert the whole thing to 5-channell surround amp - which can't be bad either ;) |
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