Electrolytic Recapping - Low ESR?

[NickH]

Hi Folks,

I am recapping a Marshall 6100.

I am just doing the Electrolytic's now, the main reason for the recap is reliability, this is a 'metal' studio amp and been run on 11 with 2 x [4x 12]'s all of it's life (the cabs are in one of the soundproofed 'live' rooms & you really wouldn't wanna be in there when we are recording guitar...) and it has to work like this for full 8 hour days sometimes for weeks at a time.. You get the idea, it doesn't have a happy life...

This amp torcher will probably continue for another 10 years+ as well, so it's time it had some TLC... (and it's getting a bit temperamental & noisy)

Now whenever we are recapping studio gear we always use the very best low ESR caps we can source, but this is the first guitar amp I have recapped, and I am having a hell of a time finding good quality low ESR caps at the higher voltages... (tried Mouser & Digikey) Is there a good reason for this?

Is this because low ESR doesn't matter for that high a voltage? Or just that low ESR doesn't matter for guitar amps?

Sound quality is critical, this is how we make our living, so if spending an extra 2 pounds per cap gets us a 0.1% improvement we will do it in a heartbeat... But there is no point in buying snake oil ether...

Which are the caps that really matter in a guitar amp?

Which are irrelevant as far as sound quality goes? (and can have non low ESR caps for example)

Are there any none Electrolytic's that I should also change at the same time?

Many thanks for your help!



N

[Amp Kat]

IMO if I put a low ESR and a middle of the line and taped each one you could not hear any difference at all because they aren't in the signal chain like a coupling cap or Cathode bypass cap. They are supplying filtration for the power supplies and will only provide so much steady DC from shunting to ground. The lastibility would be the main concern and running the amp at full volume is probably better than running it at low volume or not at all. It ramps up to the same voltage no matter what and will only discharge so much no matter where the volume is. I would try CE Distribution or Tubesandmore.com for direct replacements for the JCM900 series I believe the 50/50uf 500 volt duals are sold there and they are as good as anything you'll find anywhere. There is not a market for high voltage caps because the supply and demand isn't there in large quantities so a Manufacturor isn't going to make these because they would lose tons on them and be stuck with them. The Sprague line is good but those are Axials and you need Radials but at this point you have to almost take what you can get and I agree the choices for high end at high voltages are not very good. You may do a search on Boutique amps and see what those guys are using but then again most of those are point to point Axial versions. Good luck either way.

[6267]

If you really, really want the best you will have to compromise on space somehow...not sure if you have room in the head cab or what, but I'd use motor run caps for that application. Many are rated for high voltage AC, with big inductive spikes & overloads from the motor. They are generally the size of what we call a "tall boy" beer can on this side of the pond, a 24oz one. All the rage in the HIFI circuit, too (not the aluminum beer cans, probably too proly ). They're generally available in a range of values and do not contain an electrolyte, so they don't wear out like electrolytics. Mounting them and running the B+ to them and back is both a question of logistics and safety however. Nonetheless, they'll last forever, and have good properties for filtering. Non-polarized too I think. No backwards-install-fireworks .

[Enzo]

And motor run caps are especially good if you are in a Steppenwolf tribute band.



Get your motor runnin'....






Hey c'mon, I had to...

[Jag]

Ouch!

[6267]

Lookin' for my dentures...

[R.G.]

Hot Dagm!
Somebody besides me stepped in to recommend motor run caps!

Back before electrolytics were good enough to use in electronics, paper-in-oil caps were the standard. Today's polypropylene-in-oil or polypro and metal are better than that. They will work forever and are the obvious choice for an 8-day-a-week metal amp.

Good on ya!

[Amp Kat]

I've done lots of caps jobs on 6100's and JCM''s and good luck installing those motor runs or polyprops in that amp. It is already pretty crammed in there and may be easy for some of these guys but the question is ,will it be feasible for you ? IMO the caps are nice and yes do last forever which is great but not sure for the little difference in noise and a slightly duller tone if it's worth the hassle. Now in a homebrew or a design you can easily use them in I'd say yes in a second but do weigh it out with what you have to work with is all I'm saying.

[Gtr_tech]

And motor run caps are especially good if you are in a Steppenwolf tribute band.



Get your motor runnin'....






Hey c'mon, I had to...

Oh the Hugh Manitee......

[Enzo]

Oh Noooooooo!!!!!

[NickH]

Thanks for the help guy’s!

The Motor Run Caps are a great suggestion, but I don’t think they are practical for this particular application (mainly size/space related)

So.. To summarise:-

• Low ESR caps only of benefit if in the audio signal path.

I am not the greatest schematic reader in the world, and normally have to spend hours with different colour highlighter pens tracing each rail ect before I can see/understand a little about what’s going on with the circuit... I have put more than a few hours into these schematics, but my ‘learner’ ignorance doesn’t help matters, is there a rough guide/rule of thumb as to which Cap’s are in the signal path or which aren’t?

For instance, most caps with a voltage rating over X are unlikely to be in the signal path except x z which will be near the (whatever component)?

Or do I need to persevere with my highlighters for a few more days?

Oh, and while I have your ears, Is there a difference between Low Impedance & low ERS caps? Are they different names for the same thing or different products/grades?

Many thanks



Nick

[Enzo]

I think you shuold learn about it, because why not. But I also look at it like this.

You are shopping for a new car, you ask what kind of tires are on it. At that point I;d stop, rather than then asking where the rubber trees were the tires were made from and what were the names of the guys harvesting the rubber. In other words, don;t get bogged down in the minutia.

The signal path. Not to sound snooty, but that means the path the signal takes through the amp. I won't tell you power supply caps can;t make a difference, they can, but they are not in the signal path. The signal does not come in one end and out the other of them. That is the distinction - does the signal come in one end and out the other. Now sometimes there might be a rolloff cap from the signal path to ground. SOme might argue that cap is also in the pathway. OK, I won;t argue that. I don;t consider it so, but it does affect the signal, so why not?

VOltage? No, in tube amps, some caps face high voltage in the signal path - those connecting to tube plates for example - and other do not, so that is no criteria. The cathode bypass caps are low voltage as a rule, while plate related caps are high voltage. The little brightness cap on a volume control faces low voltage.

The filter caps in the power supply are not in the signal path.

SOmething else to think of in today's parts market. WHen it comes to 25/35/50v caps you have tons of choices. When it comes to 500v caps you don't. I don;t know that ESR is a serious concern for most amp makers in their power supplies anyway. We are lucky anyone even makes 500v e-caps.