The truth about caps

[grooveman1961]

Hello all

I've seen something lately concerning "upgrading" coupling caps and power supply caps. I know Hi Fi guys have strong opinions about such subjects, but I must admit that I am somewhat skeptical. Well, skeptical until I saw a post on another forum by someone I generally think has his head on straight.

He says he payed to have an upgrade done on a GK rb800 bass head, changining out the OP amps, power supply caps, and coupling caps. He said it does sound better than other similar amps he owns, and others amps he's heard.

The op amps, I can see. Lower noise spec, higher slew, etc. But caps?

Now I do understand that there a lot of variables, even in making a heads up comparison, but.....

So, I am trying to keep an open mind....help me out here. If I change out the caps in my own 800's, will I finally have "inky black soundstage" ?

Secondly, are any manufacturers know to have noticably better products?

For example Nichion vs vishay etc, for similar capacitor categories, like power supply alum electros.....

If there's something to this, I'll give it a try.

[defaced]

This is a recent thread that hashes out some of what you're after, particularly toward the end. http://music-electronics-forum.com/t15739/
I know your question has been discussed here before, I just can't seem to put my hand on the thread right now.

And a link from that thread that gives some data and a direct answer to your question.
Cables, Interconnects and Other Stuff - The Truth

And in the end, you'll find this is a hot topic with many opinions. I'd say grab some caps and see for yourself.

[stokes]

I deal only with tube amps.I can tell you that power supply caps definately make a difference in guitar amps.Coupling caps,not so much,but in some cases they do.Such as,if they are such cheap crap or they are leaky.I learned about tube biasing and filter caps from a local TV repair guy when I was 13,I am now over 50,so I've been doing this a long time.When I do a cap job I give the guarantee that if your caps are 10 or more years old,or they are those xicon or similar asian caps,I put in Sprague or F&T brand and if you dont notice an appreciable improvement in tone and response,I will put the old ones back and you pay nothing.In the past 2 years or so I have done about 100 Boogie amps,mostly via another forum,and have yet to have to put any caps back in.Filter caps have a definate life span,which is determined by various factors,but generally after ten years they are done.You will get many who say"my caps are 40 years old and still work" and they are right,they "still work",but they are not as efficient as they can be,and your amp will definately perform better with fresh,good quality caps.As for the xicon brand and such,I can tell you,I've tried them all over the years and there is a difference.I have done about a half dozen newer Fender Blues Devilles and the like in the last year.Replaced the Nichicons they are using these days,with Sprague and F&T's and the owners were amazed at the improvement,and again,nobody wanted their old caps put back in.I do not do solid state amps for the most part,and I would think that since the power supplies in these amps have lower voltages,and the components are more efficient, the caps may have a longer life span,but i cant say 100%.As for coupling caps,Hi-Fi amps are intended for absolute sound repro,so they look for tighter tolerances and "cleaner" circuitry,so the higher quality coupling caps are desired,guitar amps on the other hand are designed to "color" the tone of the guitar,and if the coupling caps will make any difference is purely subjective.I only recommend changing them if the cap is leaking dc.

[cminor9]

I deal only with tube amps.I can tell you that power supply caps definately make a difference in guitar amps.

When I do a cap job I give the guarantee that if your caps are 10 or more years old,or they are those xicon or similar asian caps,I put in Sprague or F&T brand and if you dont notice an appreciable improvement in tone and response,I will put the old ones back and you pay nothing..

Interesting. Can you explain this a bit more? What do these cheap caps in the power supply do? What attribute of the sound is changed with the cap upgrade? I am really, really curious to see what you say about this to see if it lines up with something I have been noticing in several of my builds using various caps (xicon and spragues are among them, and guess which I prefer? The sprague).

[stokes]

Interesting. Can you explain this a bit more? What do these cheap caps in the power supply do? What attribute of the sound is changed with the cap upgrade? I am really, really curious to see what you say about this to see if it lines up with something I have been noticing in several of my builds using various caps (xicon and spragues are among them, and guess which I prefer? The sprague).

They cause the bass to go "flabby" when cranked and an amp wont sound as tight with them when compared to the Sprague or F&T's.Amps with these caps are not as "lively",if you will,kind of flat or duller sounding.I've recently had a brand new Blues Jr and a Blues Deville that each had an oscillation problem caused by one of these caps that otherwise tested okay.I've done about a half dozen newer Fenders for people who have heard my mantra over the past year or so,who otherwise had no complaints about their amps and the improvement left them shaking their heads wondering about what they were led to believe by other techs,close to 100 Boogies over the last 2 years or so as well.There may well be other brands that can compare to the Sprague and F&T's,but I havent found them yet.For the longest time I swore by Spragues only,but I found the F&T's live up to my expectations,so I guess there could be others,but for me right now its just those two.I wont use any others.

[Chuck H]

Filter caps are a double edge sword. Alot of how new filters sound can depend not only on their ESR, but also on how the circuit is effected by the ESR. Consider that a signal of only a few millivolts at the input of an amp will effect the tone. If you have caps with high ESR and the input stage filter shares a ground with the output stage filter it's likely that a few millivolts of signal are riding on the power rail. This can result in NFB and PFB loops that absolutely do effect the tone of the amp, for better or worse. For example, at The Amp Garage where they discuss Trainwreck amps there are several threads about how different filters effect the tone of the amp. Most often the high quality caps make the amp too bright. But they found a way around using cheap caps... Now the cap of choice is a Sozo "replica" cap that is supposedly made the same way caps were decades ago. Since typical aluminum cap impedances were a bit higher decades ago I surmise that these small feedback loops created by higher ESR somehow have a beneficial effect on the Trainwreck Express circuit. This would also partly explain why builders find it so hard to clone that amp without it being too harsh and bright.

Most of the time I think high ESR is a bad thing though. But I try to keep an open mind. A lot would depend on ground scheme, how many stages, lead length and just generally what might be "talking" to what. And after that, how this effects the tone at different stages or the overall amp. It would be almost impossible to calculate for the purposes of design to exploit this phenomenon, so I try to design for a low ESR and carefully layout my grounds to avoid the issue all together. Then I voice from there. This way I can remove some voodoo from the equation.

Chuck

[loudthud]

When I was working on my ultimate bass amp project a few years ago I noticed that you can plainly see a rectified version of the bass guitar signal riding on the B+. The lower the frequency, the bigger it looks. It's hard to see at first because the supply ripple is riding on top of everything. It just looks like a bunch of sawtooth waves bobing up and down until you sync on the bass guitar signal. I installed a PI B+ filter to get rid of most of the ripple. This made it much easier to see the bass guitar signal. Further increases in amount of capacitance were needed to reduce the bass guitar signal on a low E (~40Hz). This increased the clairity of low notes. On a 50W amp with 450V B+ it took about 200uF.

So in guitar amps I would expect modest changes of capacitance with B+ filters in the 50uF range to be audible. As far as I could tell, ESR didn't come into play. It would have to be pretty bad before you could see anything on the B+ but it would tend to effect all frequencies. If ESR was 10 ohms, you might see 2V of guitar signal hidden by 20V of ripple.

I suppose it would be easy enough to do an experiment by installing a rheostat in the ground return of a filter cap to judge how bad ESR has to be to be audible.

How much ESR to these cheap caps have?

[Chuck H]

How much ESR to these cheap caps have?

I dunno. I never use them anymore. Long ago I did compare some cheap Xicon aluminums to the Spragues. The Spragues did sound tighter and there was less "ghosting".

I remember a hands on trial done by Dai some three or more years ago where he added small (one to three ohm) resistors to the filters to test this. He reported that there WAS an audible difference with even small resistances added. Also, The guy's at The Amp Garage have worked hard on the Express design to try and bring down the myth that only Ken Fischer could build one. They are very critical and not generally prone to lore or voodoo. They are also purists for the most part. So their examination of one particular aspect that amps circuit is something I wouldn't just ignore for lack of test sheets and scope data. Though I'm not inclined to go to the trouble myself.

Chuck

[hasserl]

There has been lots of information provided in the past few years comparing Sprague Atom caps to smaller, less expensive caps like Xicon, IC and others. Spragues have been cut open to reveal small caps housed inside of the larger outter can. IME we're dealing mostly with subjective likes/dislikes and preferences based on anecdotal evidence and a lack of emperical evidence or controlled comparisons.

[cminor9]

They cause the bass to go "flabby" when cranked and an amp wont sound as tight with them when compared to the Sprague or F&T's.Amps with these caps are not as "lively",if you will,kind of flat or duller sounding.I've recently had a brand new Blues Jr and a Blues Deville that each had an oscillation problem caused by one of these caps that otherwise tested okay.I've done about a half dozen newer Fenders for people who have heard my mantra over the past year or so,who otherwise had no complaints about their amps and the improvement left them shaking their heads wondering about what they were led to believe by other techs,close to 100 Boogies over the last 2 years or so as well.There may well be other brands that can compare to the Sprague and F&T's,but I havent found them yet.For the longest time I swore by Spragues only,but I found the F&T's live up to my expectations,so I guess there could be others,but for me right now its just those two.I wont use any others.

Interesting. I built a 6G3 using the xicon filter caps, and it has this weird thing that when cranked and I hit a chord, it sounds good for a second and then when the note starts to decay it gets this overtone (I cannot describe it very well I guess) I really don't like. I hate it so much it renders the amp mostly useless for what I built it for: rockin out. It's only on lower notes, the lower I go the worse it is. I don't have a scope, so that's about as much detail as I can give. Maybe that's a ghost note, but it doesn't match the description of ghost notes I have read.

Here's another bit that points me to the filter caps:
1) the 6G3 uses 4 of the xicons (with hammond iron, which I had to zener down so I didn't suspect this was normal sag) and exhibits this problem very noticeably.
2) I *just* built a spitfire clone with salvaged transformers and totally different brands of parts save for the resistors. The filter caps are a F&T can and two of the xicons for the PI and PA, and I just noticed that this amp exhibits the problem ever so slightly when run full out.
3) My 5E3 uses Chicago Transformers and Sprague filter caps, and sounds perfect when run hard.

By process of elimination, that's the filter caps.

These facts plus your post earlier points to the caps as the source of the problem. This might make the difference between my dismantling the 6G3 and building it into something else or keeping it. I figured it was just supposed to sound that way, cause it's not like I can just walk into a music store and play one. But now I think I'll try the caps once I get some cash. I'll certainly report back with results. I appreciate your post, stokes, and had you chosen to mention another brand of filter cap I would have never given it a second thought. This forum rocks.

Thanks, stokes...and others.

[Chuck H]

Spragues have been cut open to reveal small caps housed inside of the larger outter can.

Please point me to that information.

Thanks

Chuck

[defaced]

What's your shipping address? I'll send you one.

[tubeswell]

Interesting. I built a 6G3 using the xicon filter caps, and it has this weird thing that when cranked and I hit a chord, it sounds good for a second and then when the note starts to decay it gets this overtone (I cannot describe it very well I guess) I really don't like.

Hi cminor9

Is there enough room to replace the caps with bigger jobbies? All those 6G3 filter caps could go to 20uF Spragues I reckon (or at least the reservoir cap and the screen supply cap could). Physical size seems to make a difference (from my own experiments) in keeping flab out.

Also, the number of stages you are filtering with each cap is important. The furthest (8uF) cap from the power supply on the schematic is actually filtering 3 stages, which may be part of the 6G3s charm, but if the cap there in particular isn't up to the job, then try going to 20uF in there.

[grooveman1961]

Good and interesting information!

[JoeM]

Please point me to that information.

Thanks

Chuck

Here:


There was also one of a cut open earlier version of the Atom, not at all the same caps as before.