Decent, reasonable GC caps/resistor survey: - diyAudio
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Old 16th July 2003, 02:11 AM   #1
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Default Decent, reasonable GC caps/resistor survey:

First of all, many thanks to all the advice givers out there. I have read and read and read (my wife hates you guys by now, I think) and surely bypassed a lot of dumb mistakes (and possibly minor explosions) that I would have made. Thanks especially to decibel dungeon, Hennesey's pages, and certainly Peter, who has been more than generous with his GC advice.

Like a lot of people, I am building my first gainclone. I am going for the Plitron toroidal trafo and MSR860 diodes, probably 1 trafo with the separate grounds going out to each channel. That looks an elegant solution to the problem of one vs two trafo's, while probably going a long way to avoid the potential grounding issues with the single version.

I am building the PSU on a pine board first, testing the holy bejesus out of it, then crossing my fingers, covering my eyes and hooking it to AC. If she don't explode, my next step is to dip my toe in the GC amp waters. I have LM3875 samples (4) coming from Singapore. So I have "one to give," so to speak, as I can try it out for cheap with the first two chips. BTW, I have built a CMoy headphone amp (not a total noob, but certainly no expert,) and am going to try to wire the GC short as possible P2P. If you are gonna embrace the short-path philosophy, why not go whole hog? If I screw up I can always etch a PCB and start over for what I have in the amp section, $-wise. Which leads me to my question.

Not being a gourmet cap/resistor guy, I need to know which is a good set of decent-but-not-terribly-expensive garden variety caps/resistors. I would hope to get something commonly available at Mouser or Digi-key. The idea is not to make a drastic mistake while not spending too much. Sort of the Toyota Camry of the genre.

Caps are (2) 1000 uf's, the 1 uf from pin 1 to 4 and a 2.2uf input cap.
Resistors are 10k input, 22 output, 220 feedback and something (18? 20) from 7 to ground.

Especially would like to hear from people who did not break the bank on these parts and were still very pleased with the sound. Also, if I am going to splurge, where should it be? (Please, God, not the 1000 uf caps... I would like to get a reasonably priced GC to work before I trusted my experience to those humongously expensive BlackGates.)

Please name names, and be as explicit as possible with the genus and species. For Chrissakes, wading through the caps section at Digikey is worse than getting sent to the grocery story for panyhose for my wife! Too many choices I know nothing about...

Thanks in advance, and when my GC is at long last finished, I promise plenty o'photos. I am by trade a photojournalist and will not be able to be stopped from sharing the baby pix.

Muchas gracias,
GnD
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Old 16th July 2003, 09:31 AM   #2
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Default Re: Decent, reasonable GC caps/resistor survey:

Hi Graham,

I don't know what Digikey are like, but RS and Farnell in the UK sell wide ranges and it can be tough to decide how to choose between them. So, to help narrow down the choices, I look for the following specifications:

Rated temperature - go for 105C over 85C

Manufacturer - choose a recognised brand such as Panasonic, Philips, Rubycon, etc. Most suppliers stock extremely cheap caps from brands I've never heard of - you tend to find these in the cheapest and nastiest of consumer equipement

Lifespan - these are normally quoted at a particular temperature, and the relationship between life and temp is non-linear. As a rule of thumb, reduce the operating temperature by 10C, and you'll double the lifespan of the cap. Other factors are involved, but the running temperature of a bit of kit certainly is important. When comparing between different brands, be sure you're comparing at the same temp.

Impedance and ESR - caused by imperfections inherent in the construction and manufacturing processes. You'll want to select for lowest.

So, look for high temperature, long-life, low impedance/ESR in the specs. You tend to find that these things are related to cost. These properties are desireable in any capacitor, but for a switched-mode power supply they are essential. So, look for caps that are suitable for use in SMPS...

All of the above is just standard good practice, but won't tell you anything about how the cap will sound. There's no spec to cover that, but I would say that from an engineering perspective, the close a cap gets to being "ideal", the more likely you are to get good sound quality from it. So, pick a few different ones based on the above guidlines, and try some listening tests.

You'll notice that I didn't put numbers to most of the specs above - this is because they vary according to value and can size. You'll have to do your own research to get a "feel" for matter. You might like to start with Panasonic FC's - I chose these for my preamp a couple of years ago based on the engineering reasons given above. I was pleased to discover that people have been using them in their GainClones and other projects, and think that they sound good.

So you see, engineering might not have all the answers, but it can get you quite close

Sorry - you asked for simple recommendations. I'm not very good at those - I'd rather give you the tools to make an informed choice... But the Panasonic FC's are a safe bet for the 1000u's because they're good quality and not too expensive. I'm sure you'll recieve some more exotic recommendations from others here, so once your GC's are working you can easily try some comparative listening tests.

For the resistors, Nuuk recommends RN55C's, which you can buy from Farnell (are Digikey connected to Farnell?). He's found them to sound better than normal metal-film resistors. I haven't "auditioned" them yet, but I have used them before for applications that are much more critical than audio , and they are certainly excellent technically. I intend to use them in my final GainClone constructions, as they are not too expensive.

The only thing that I'm not sure about is the input cap. It should be non-polarised, but Farnell don't sell much in the way of decent non-polarised electrolytics.

So, not exactly what you asked for, but I hope it helps,

Cheers,

Mark
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Old 16th July 2003, 12:37 PM   #3
Nuuk is offline Nuuk  United Kingdom
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Hi Graham,

I dread the day I get a feedback form back from Decibel Dungeon from an angry wife/partner/girlfriend!

As Mark said, I am a big fan of the Welwyn RC55 resistors if you can find them on your side of the pond. They sound very good without being painfully expensive.

For the decoupling caps, the Panasonic FC's are very good for the price. Arguably, the next (significant) step up from those are the Black Gates and then you WILL have to ask a friend to order them for you so the SOH doesn't see the bill!

Polypropylene is my choice of lower value caps but many feel that you need at least 4.7uF on the input of the GC. That's why Peter Daniel went for Black Gates. I also use Black Gates but have used 47uF for two reasons. One, because I already had them in my parts box, two because they are the Black Gate NX-Q type, the very top of the range which are said to sound best. (Unfortunately they do not do them in the 4.7uF value)

For input resistor, I like the sound of the carbon film that I am using. I think that it is a good idea to mix-and-match resistors to prevent one type from having too much affect on the sonic signature.

If you have been to my FAQ page you probably know that there is a link to my full GC shopping list.
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Old 16th July 2003, 01:33 PM   #4
tiroth is offline tiroth  United States
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Supply caps: Panasonic FC
Resistors: Dale
Coupling cap: ?
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Old 16th July 2003, 08:06 PM   #5
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Panasonic FC's sounded pretty good but the amp didn't reach the rhapsodic level we read about until I bypassed them with 1 uF Auricaps (metallized polypropylene). Without the bypass it was a bit grainy and harsh. Cheaper film&foil bypass caps would probably work too.

I'd like to know how a non-bypassed Black Gate sounds in comparison to a Panasonic FC bypassed with a good polyprop.
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Old 16th July 2003, 11:38 PM   #6
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Thanks for the responses so far!

About the Auricaps bypassing the 100 uf FC's. I am assuming they just go across in parallel with the 1,000's? Am I right?

Also, are metalized polyprops directional like electrolytics?

TIA,

GnD
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Old 17th July 2003, 12:16 AM   #7
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I have tried the following in my set up (current two channel but eventually a 4-channel setup):

feedback resistors: Radio Shack (5% carbon), and Panasonic ECG (1% metal).
coupling cap: none, aerovox, and BC Components.
by-passing cap: none, Radio Shack, and Panasonic ECG (metalized polypropylene).

I hear no difference.
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Old 17th July 2003, 12:55 AM   #8
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Millwood-

You say no difference. But how do you like your amp's sound on a scale of 1 to 10? Are you running decent components around it?

To me, this is very good info.

People spend a lot of time splitting hairs over the relative benefits of an array of very expensive parts here. Much of this is "last 5% returns" area. IMO, what is equally important is a discussion of the meat of the curve, so to speak.

I am a big proponent of getting 90% of the quality for 40% of the sound, for example, when possible. That is what partially attracted me to DIY. I expect others here feel the same way.

Don't get me wrong. I value very highly the info of those people who are squeezing the last ounce of performance out of their GC's. As a professional photographer, I feel that way about my lenses and cameras. Leicas are a photographer's Black Gates, so to speak!

Anyone have any input on carbon vs metal film in the resistor arena? Some guys are "leg men". I am into smooth midrange. I have a hunch, with nothing behind it whatsoever, that carbon might help in this area. Any experience, anyone?

I said earlier that I am looking for the Camry of Gainclones for my first one out of the block, which, admittedly, might not be the final amp component of the project. But hey, there's a reason a lot of people drive Camry's, huh? And I do, BTW.

I like the idea of Panasonic 1000uf FC's with a good small cap in parallel. Am very interested to hear other's experiences of where to get a lotta-bang-for-a-little-extra-buck, too.

Unfortunately (or fortunately, perhaps) I don't have a bench full of spare parts lying around. So, while I won't build it as cheaply as possible, I won't be forced into a bad component just because it is there, either.
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Old 17th July 2003, 01:44 AM   #9
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The Auricaps have a red lead and a black lead, so I wired them parallel in the same orientation as the Panasonics. They're equally close to the chip on one side (~1 inch) and have a separate ground wire connecting to the star ground.

I wouldn't say the bypass was a matter of last 5%. To me it was the matter of being "good solid state" versus "superlative"; a jump between the $1000 level and the $3000+ level. I'd rate it a 20% improvement in sonics. It only doubled the cost of PSU caps (the Panasonic 1000uF were $6/ea and the 1uF Auricaps were $7/ea).

I appreciate midrange too - my DIY speakers are arrays of fullrange drivers, lacking real bass and highs but very coherent in the midrange. I used metal film resistors. The GC on a friend's truly full range multiway speakers sounded slightly bright and forward relative to his Plinius, but this was before I did the cap bypass, and when I had undersized input caps. Now I might not be able to compare because I left out the input caps entirely - he won't trust the amp to not blow out his tweeters. In any case on my speakers it sounds very clean, accurate, and enjoyable, but definitely not warm and rich like a good SET or even like the Plinius or my MOSFET Belles 150a.
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Old 17th July 2003, 02:24 AM   #10
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Quote:
Originally posted by GrahamnDodder
Millwood-

You say no difference. But how do you like your amp's sound on a scale of 1 to 10? Are you running decent components around it?
it certain sounds good, but nothing spectacular. I have at home a Parasound amp, a Sony AVR and a good old Kenwood stereo. The gainclone does not sound as clear as the others at high volume but at low volume, it is indistinguishable.

The parasound gives the clearest sound under load, followed by the Kenwood and the Sony doesn't have the "punch" of either of them. The gainclone, however, offers as much punch as the Parasound or the Kenwood, but at lower volume.

I would think most people will be happy with Radio Shack based Gainclone and you can always replace the RS parts with better ones if that makes you happy.
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