How to improve tube amplifier tone by changing one part

Tube or solid-state, this section goes to eleven!
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bajaman
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Post by bajaman »

Hi folks
Every now and then, one has an "eureka" moment that one feels like sharing, but sometimes the fear of being severely "flamed" forces one to keep it to oneself.
After servicing tube guitar amplifiers for close on 40 years, I have decided to share a very simple component change that I discovered a few years back, because in my humble opinion, it makes a very large tonal difference, but first, some background :wink:
Have you ever wondered why those British tube amplifiers from the 60s sound so good and why they are still sought after today? I am referring to Vox and Marshall amplifiers of course. What makes them sound so good and what do they have in common - besides vacuum tubes ?
The answer is Mullard and Philips branded "mustard" capacitors - so called because of their distinctive colour.
It is my view that this particular style of capacitor played a significant role in the "sound" of these early British amplifiers, although i cannot for certain explain exactly why.
Perhaps their construction has a lot to do with it :wink: . They were constructed I believe, by sandwiching two layers of aluminium foil between two layers of polyester film, and then rolled up in a cylindrical fashion and finally dipped in a mustard coloured epoxy resin to seal them - a tinned copper connection was attached to each layer of foil and these were brought out either end of the rolled up cylinder.
Modern capacitors have simplified this process - they are constructed with vacuum deposited aluminium directly on the polyester film and in my opinion do not sound the same. I am not the only one who believes this to be true :wink:
Unfortunately Mullard and Philips no longer manufacture these "mustard" capacitors and a search for them on ebay will show they still command very high prices - I know why - they sound so good!
Fortunately, the Tube Amp Doctor in Germany has their own version of these mustard capacitors available and i can confirm that they do sound very good - just like the originals.
I must state that I am not affiliated with the this company in any way!
This is a link to their site - check it out: https://www.tubeampdoctor.com/en/tad-mu ... ber=V-MC22
Okay, now what you have been waiting for - the most important capacitor to change in ANY tube guitar amplifier is the output coupling capacitor connected to the plate of the tube performing the very first stage of amplification :!: Do not ask me why - just try replacing it with a "mustard" capacitor it and see for yourself :secret:
I have found on many occasions, that simply replacing this first coupling capacitor has a HUGE impact on the perceived tone of the amplifier -clearer defined high end response and warmer rounded midrange tone. In some cases I have noticed an almost natural reverb and increased sustain of plucked notes by simply changing this ONE capacitor.
I performed this simple capacitor exchange on a Fender Blues Junior a few years ago and could hardly believe the difference in tone compared to the original fitted capacitor.
Please don't flame this post or try to explain that i should check capacitance values etc. - just try it and see, or more precisely hear the difference before making ANY comment.
Stay Safe folks in these coronavirus times - wherever you are :D
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Post by lolbou »

Thanks for the tip Steve, it definitely worth a try! I may follow the advice in my future amp re-build!

Stay safe as well! :hug:
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Post by FiveseveN »

bajaman wrote:Have you ever wondered why those British tube amplifiers from the 60s sound so good
Not at all. I for one have yet to be impressed by anything pre-80s. Is there a consensus about the universal 'goodness' of these amps?
in my humble opinion [...] It is my view [...] i cannot for certain explain [...] Do not ask me why
That's cool and all, but
Image

In them 40 years you couldn't record a test signal before and after making this modification? Just as a sanity check, make sure you're not fooling yourself?

Later edit: since I have an amp on the bench and a sound card, I'm willing to do the work. But these are the only ancient caps in my possession:

Pretty sure "56" is a date, but they look more like paper-in-oil?!
_MG_7511.JPG
Glass envelope, you can see the Al film inside. 1960?
_MG_7517.JPG
Polish, '70s? By the way, Eastern Bloc amps were made with the same technology, how come they're not fetishized?
_MG_7513.JPG
Are any of them suitable for a test?
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Post by plush »

I was hoping, I'd never see such thread here.

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Post by lolbou »

bajaman wrote:the most important capacitor to change in ANY tube guitar amplifier is the output coupling capacitor connected to the plate of the tube performing the very first stage of amplification :!: Do not ask me why - just try replacing it with a "mustard" capacitor it and see for yourself
C'mon guys, it's just a tip, that's all.

Get your hands on a proper mustard, heat the iron and try it out for yourself...

Maybe it's very subjective indeed, maybe you can actually proove it's bullshit or magic. But give it a bloody try?

Edit : in a Deluxe reverb - like amp, would you then change the first coupling cap after the second half of the first 12AX7 (the post EQ one)?
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Post by bajaman »

Edit : in a Deluxe reverb - like amp, would you then change the first coupling cap after the second half of the first 12AX7 (the post EQ one)?
In a 65 Deluxe Reverb, I would suggest changing both C5 and C12.
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Post by lolbou »

I have NOS 18nF/400V (10%) mustards here, not Mullard maybe, but still.... They measure quite good within the tolerance. I'll test it in a Fender Hot Rod. Measure the 22nF installed and have a go at it...
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Post by FiveseveN »

lolbou wrote:give it a bloody try?
I'd love to but I need guidance from the capacitor aficionados. I can't go through all the trouble to be told I didn't use the 'proper' mojo. Would anyone be willing to send me a 'proper mustard' for proper testing?
Or maybe someone who already has some could record a controlled test? Is 2020 the year we finally have proof of the mythical Capacitor Sound? My money is on no.
plush wrote:I was hoping, I'd never see such thread here.
From a guy with a lot of experience and substantial contributions, too. Part of me hopes it's a misscheduled April Fools joke and is still waiting for the punchline.
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Post by bajaman »

From a guy with a lot of experience and substantial contributions, too. Part of me hopes it's a misscheduled April Fools joke and is still waiting for the punchline.
Please read my first post again :wink: then you will understand why I was reticent to post !
All I am asking is that you give my idea a try - nothing more.
You do not need to pay crazy money for NOS Philips mustard caps from ebay - TAD Mustard caps (link in first post) work just as well. Also Mojotone offer their own Mojo Dijon versions if you are in north america - I have not tried these as yet, but i intend to in the near future. Please keep in mind that some things like tone and sound are not easily conveyed by sound bites - one has to experience them to fully understand - a live recording of a music event concert can never replace the "feeling" of actually being there :wink:
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Post by soulsonic »

Good suggestion! Those SoZo caps that got hip 10 years ago are supposed to be like this too? I never got around to trying them, maybe soon... been itching to build an amp again.

I've used some vintage mustard caps that I've salvaged here and there in various things. Never did head-to-head listening tests with them, though.
But I have done that with other caps. I remember listening to a handful of different 22nF caps when building a custom Rat and then selecting the one I liked best. I can certainly hear a difference - though sometimes not enough to care about - and the quantitative reasons for why one sounds the way it does don't really matter to me; like if you say it sounds different because of 20% value tolerance or whatever, so what? Point is, you listen to several different ones and you prefer the sound of that specific one over the others. Doesn't matter why, and doesn't matter if that's a silly thing to do. If you're taking the time to make a special build, may as well have fun with it. I wouldn't dare try something like that with a complicated effect like a delay - you'd go crazy trying all the different possibilities. But with a simple thing like a Rat or a Fuzz Face or booster, go ahead and audition caps, why not?
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Post by bajaman »

yes - i have heard good reports about those sozo capacitors as well. I will order a few and give them a try too.
no need to go crazy replacing all the coupling capacitors though, as in my experience it is that first coupling capacitor after the input tube that makes the most difference to the "sound and feel" of a tube amplifier - replacing all the other capacitors does not seem to make any difference in my experience. I am merely suggesting that folks just give it a try and do not attempt to reason or explain why or if it sounds better or not. Report your findings here in this thread by all means :wink:
all the best
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Post by FiveseveN »

bajaman wrote:Please keep in mind that some things like tone and sound are not easily conveyed by sound bites - one has to experience them to fully understand
What I know is when I take waveform A, flip its phase and add it to waveform B and the result is silence, I should conclude that waveforms A and B are the same. Am I incorrect? What part of the holistic sound experience am I missing by drawing such a conclusion?
My familiarity with the complexities of sound perception and their aesthetics is both professional (as a live mixing engineer), academic (as a Master of Fine Arts) and also stem from a personal interest in how subjective and intersubjective experiences lead to mythologies like 'capacitor sound' and 'tone wood'.

But this has absolutely nothing to do with that, all I'm asking is to record a signal that goes though a 'normal' capacitor and record the same signal, ceteris paribus, going through a 'special' cap, so that they may be compared.
If you think that means "sound bites" of pentatonic doodling recorded by a cell phone that's vaguely in the same room, we're also going to need to have a talk about control variables and experimental design.
just give it a try and do not attempt to reason or explain why or if
You are literally advocating willful ignorance. Sometimes that leads to silly things like paying more for a 'cap upgrade' than what the effect/amp originally cost. Other times the choice to eschew critical analysis leads to people dying.

Of course, if your goal is to "have fun" and "let your ears decide" this is pointless, pedantic if not counterproductive. But if you are to make sweeping statements like "mustard cap make amp good" I'll have to ask you to back that up with some evidence. More so on a platform where one's seniority and popularity can often be mistaken for or considered in lieu of factual legitimacy.
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Post by lolbou »

Now the question : which mustard?

This is a mustard to me (same colour as my mustard from Dijon in the fridge) :

Image

But are these mustards as well?

Image

I thought it was colour related, but is it the same construction inside, with only a different packaging?
FiveseveN wrote: Sometimes that leads to silly things like paying more for a 'cap upgrade' than what the effect/amp originally cost
C'mon, it's just change one cap and hear for yourself. :roll: Although i see your point from a science point of view. It's like for homeopathic medicines. The manufacturers are saying "prove us wrong" but it should be the other way around and they should "prove them right" indeed...

Maybe it's biased from the start. Maybe mustards cap sound better in NZ because they're upside down, who knows? He's not making a claim here, it's just what comes up from 40 years of observation. Can be correlation instead of causality, but again, just give it a try and SHARE your results.

Back in the early 1900s, Robert Milikan thought Einstein's view on light as particles was not correct, because it had been descibed perfectly as a wave. He developped a very accurate experiment that lead to the concusion that... Einstein was right too. Let us be Milikans sharing results, no matter the conclusions! :horsey:
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Post by jubal81 »

I've noticed the same thing as Bajaman, and it's a dramatic difference.

I was a non-believer and used yellow Sozo caps just for the glamour gut shot, but the change in sound was just like how Bajaman described - more focused and '3D.' Now I swear by them. They've always measured within 2% on my capacitance meter. Also handy that they mark the outer foil end with a line.

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Post by uncleboko »

They will no doubt make you play faster too :lol: :lol:

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Post by soulsonic »

I thought it was colour related, but is it the same construction inside, with only a different packaging?
That's what TAD and SoZo are claiming; that the construction of their capacitors is the same technique as a vintage mustard cap.

I have noticed that all electronic circuit exhibit numerous emergent properties that are not easily quantified.
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Post by okgb »

I think any " comparisons " best be done one component at at time and all other conditions equal , all settings the same ,
so a couple of varying performances recorded and played into the electronics in question , and then the result also recorded,
level matching is usually important but if nothing has changed in the equation, the part change should be the only difference in sound.
time & our our eyes [ and bias's ] can fool us.
I recapped one side of a stereo compressor with the Elna electrolytic caps and the two sides compared, the the elna side that I thought would be brighter was not , but
it was more clear and less " murky " some things Do make a difference!

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Post by andy-h-h »

A double blind test using a consistent sounds source, with multiple caps of the same value, is the only way to resolve this in a way that is indisputable. Line up a few caps in a switch, and if you can repeatedly identify the caps, then you have proof. Being a double blind test, neither the person switching or the person listening can know what they are switching or listening to until after the fact. You must repeat this enough times to reduce inaccuracy due to correct guesses from the equation. Anything else is just a matter of perception / opinion.

There's a theory that if you are asked to look for change, you will find change. Your brain is just helping you, by providing an answer that you were looking for.

Back in the day I put some PIO caps in a 335 guitar, and after the effort I put in, I certainly was looking to hear a positive change in tone (which I did by the way). Now knowing what I do now, maybe that was just a slightly different value cap, maybe I heard what I wanted to hear, maybe it was a magic PIO cap....

Apart form my ramblings, don't go too hard on the guy for sharing an opinion, even if you don't agree. Be nice to the other humans. :D

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Post by soulsonic »

andy-h-h wrote:the only way to resolve this in a way that is indisputable.
I'm sure it would still be disputed :lol:

Hey, I just found one in my stash! Time to play. :horsey:
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Post by FiveseveN »

Alright, I did it.
Yes, they even have vastly different values, which shouldn't matter as long as they're > 10n. Or maybe it does and you can show us.


Link to the full uncompressed files:
https://drive.google.com/drive/folders/ ... D_K1ax_FoY
captest.zip Contains (manually) aligned and trimmed samples.
captst_reaper.zip Contains the Reaper session, raw recordings and the dry track.
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