How to improve tube amplifier tone by changing one part

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

Yesterday I had two Fender amplifiers in the workshop - a Hot Rod Deluxe and a Hot Rod Deville. I changed the first 22n capacitor after the input stage in both amps - used a TAD 22n mustard and the results were not subtle - I had the customer watching me for the Deville - first i played my strat into it with the original capacitor and then after snipping it out and fitting the TAD mustard capacitor, I played my strat again - his comment was -= "wow - it sounds clearer" so maybe we both have bad ears perhaps ? ha
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Post by roseblood11 »

Have you recorded that?

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Post by FiveseveN »

bajaman wrote: 18 Jun 2020, 21:23 so maybe we both have bad ears perhaps ? ha
It feels pointless to ask at this point, but do you sincerely not understand that this is about the limits of human brains and not ears? Do you understand that perception is modulated by expectation? Do you understand why test blinding was invented?
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Post by lolbou »

FiveseveN wrote: 19 Jun 2020, 06:25It feels pointless to ask at this point, but do you sincerely not understand that this is about the limits of human brains?
FiveseveN wrote: 19 Jun 2020, 06:25It can be dismissed through theory alone.
Talking about limits of human brain and capacitor theory, i think you actually can't compute exactly what's going on in the bloody cap. Neither do I (it's both brain limitatiuon AND lack of motivation). But i've been through quite a lot of tough electromagnetic equations in my career to know that we neglect a lot of things to make them simplier. You can actually compute what's going on in an ideal capacitor, but there's a lot more involved in a real one, and taking everything into account (provided you can tell) is just impossible.
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Post by phatt »

bajaman wrote: 18 Jun 2020, 21:23 Yesterday I had two Fender amplifiers in the workshop - a Hot Rod Deluxe and a Hot Rod Deville. I changed the first 22n capacitor after the input stage in both amps - used a TAD 22n mustard and the results were not subtle - I had the customer watching me for the Deville - first i played my strat into it with the original capacitor and then after snipping it out and fitting the TAD mustard capacitor, I played my strat again - his comment was -= "wow - it sounds clearer" so maybe we both have bad ears perhaps ? ha
As I said in my first post - do not question just try!
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Hi bajaman,

Not being picky but did you happen to take readings of both the Old and New Caps?
I feel that would be helpful for your observations. (Which by the way I don't doubt what you hear)
There would surely be a reason if one looks in the right place. :hmmm:
I also have occasionally mentioned oddball ideas and copped neg feedback. [smilie=poke.gif]
As my feeble ol brain does not have the learning to explain to those of far greater knowledge how and why,, so I just don't say much about my little urh huh moments.
Cheers mate, :thumbsup
Phil.

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Post by FiveseveN »

lolbou wrote: 19 Jun 2020, 11:40 taking everything into account is just impossible.
This kind of reasoning is consubstantial with the God of the gaps: The more we know about a thing, the less room for magic is left. But surely we can't know eVeRyThInG about capacitors, so the hidden mojo variables can still be hiding somewhere, right?
Well, it's been more than a month and we're still waiting on that proof. Before worrying about how fine a model we need to describe why mustard caps sound special, we have yet to determine whether they do.
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Post by soulsonic »

Whether or why they sound special is completely subjective. Many people probably think they sound like shit. The qualities that make it sound special or like shit are EMERGENT. And I personally feel that when discussing emergent properties, there's not much point in arguing what details explain the motivating processes that creates those properties. I think analyzing my subjective experience of it can be a fun and rewarding pastime, but I don't imagine that I am in any way unlocking the secrets of the universe or that my subjective experience could be completely duplicated in the subjective experience of another. Like Bajaman, I would only say that I like this particular capacitor, and I prefer it, and I would suggest others try it. Maybe a person with a sufficiently similar worldview to mine, might have a similar subjective experience because we share similar values, which in turn affects our perception. But that's as far as I'd go with it. Not interested in convincing anyone with "proof." :lol:

Sorry, if I'm coming off like a philosopher, but I think this is the kind of subject that can't be explained any other way. And I do have a Masters in Fine Art, which makes me an insufferable academic. :lol:
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Post by lolbou »

FiveseveN wrote: 19 Jun 2020, 14:08 This kind of reasoning is consubstantial with the God of the gaps:
No, again you read me too quickly, and you read me wrong. You said you know already from the theory. I've said that your theory is most probably an ideal capacitor one, and that the real capacitor one is much harder to take into account. And it's not gaps, it's just geometry, dielectric behaviour, edge effects (not sure about the english for that)...

I mean, even the output impedance of the previous gain stage is computed using simplified theory, so all in all, you have the basic picture, but you lack the details. And it's precisely what may sound different to well-trained ears.

But for Gaps' sake, don't say a model is like reality : it's not.
FiveseveN wrote: 19 Jun 2020, 14:08 Well, it's been more than a month and we're still waiting on that proof. Before worrying about how fine a model we need to describe why mustard caps sound special, we have yet to determine whether they do.
I agree! I've been busy repairing a Roland VS2480 recorder i've been given, and have a good microphone on hand, so i'm getting closer at taking measurements. Although i wish i had a Jam Man style pedal to send the exact same signal in the amp...
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Post by andy-h-h »

Without actual evidence to support claims, in summary :D

https://youtu.be/xpAvcGcEc0k
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Post by soulsonic »

lolbou wrote: 19 Jun 2020, 20:14But for Gaps' sake, don't say a model is like reality : it's not.
Yes, I believe this is impossible. At least it is impossible with our current system of mathematics. Maybe some day a new mathematics will be invented that can model accurately? But this is almost beyond imagining at this point in time.

The problem is people's erroneous belief that numbers are real things that exist apart from the human mind. They aren't. Numbers are an abstraction we invented to attempt to quantify things. We're able to do lots of amazing things with them, but they are far from objective reality. And objective reality may very well be unknowable. We haven't reached a point we can say definitely one way or the other yet (though, me being the evil post-modernist I am, I tend to lean heavily toward it being forever unknowable). And I think we are still very far away. I won't say impossible ever, but I will say very far away from where we are now.
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Post by george giblet »

I'd be measuring the value of the two caps with a cap meter; 10% difference in capacitance could come across as subtle change in tone. Another thing is leakage. Leakage can change the bias point. I'd only start thinking there was a difference after checking at least that much. Nonetheless I'm happy to see people doing experiments :D

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Post by FiveseveN »

lolbou wrote: 19 Jun 2020, 20:14 I've said that your theory is most probably an ideal capacitor one
It's not. I have access to IEEE Xplore just like everyone else.
you have the basic picture, but you lack the details. And it's precisely what may sound different to well-trained ears.
Yes, that's exactly what I said: no picture/theory/model can ever be technically exhaustively accurate, so corksniffers will always have the excuse that what they believe lies hidden in the details that might have been overlooked. And instead of arguing the facts you get discussions about the properties of physical models and the limits of human perception and overall pedantic armchair philosophy. So let me offer a little reminder, lest you start thinking too deeply about this matter:
You do not require quantum field theory to solve this puzzle. It makes zero difference whether mathematical realism or some form of structuralism is true. All we need for now is someone with a mustard cap and two working brain cells to find the audio recording app on their phone.
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Post by soulsonic »

I have a collection of various caps, including mustard caps. I just sorted through some and have a 6,8nF mustard that measures 6,66nF with my Peak LCR40. I have a yellow box cap (I think made by Kemet?) that measures 6,63nF and another that measures 6,7nF. I think these are close enough to make a comparison that no one would say any perceived difference would be caused by tolerances of the values.
But the yellow box caps are a no-go for use in a tube amp circuit. I wonder what would work well as a test circuit for this? In my experience, I often perceive differences with caps when used as the input cap for a simple booster, because that's where you're getting the most interaction with the guitar's passive pickup. So, I'm thinking a simple one transistor booster. But, if it's being driven by a recording, that changes things completely, you're going to have something totally different happening impedance-wise...

What I'm proposing is a circuit that uses an opamp input buffer to interface with the low-z output of the soundcard. This then goes into the primary of a small transformer being used as an inductor: the "pickup simulator" circuit we are all familiar with. Then is the capacitor under test, which is the input cap for a single transistor boost stage. The output of this is what is recorded. There would be a switch to select between the different capacitors. I am wondering, though if the boost circuit should have a lower input impedance - like you'd see with a Rangemaster or such, or a high input impedance - like you would typically get with a FET circuit. I'm personally thinking lower input impedance booster would be better.

I would do the test with a clean guitar recorded and played back at 192kHz/24bit. The final recording would be the same and saved as an uncompressed .wav
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Post by FiveseveN »

Remember, one of the claims was "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", so plate impedance (and voltage) or you risk "missing the point".
I think there's a lot of confusion about source Z and guitars nowadays that reamping is more popular: have you ever seen a setup when the interface output goes to a "reamp box" and then an overdrive before the amp? :slap: Special award for these guys with the Palmer DI followed by BOSS buffers.
Looking at all the cases where people use pedals, wireless systems or active pickups/preamps/buffers before an amp, I for one decided a phone makes a reasonable signal source for my test.
Another consideration is that if something interesting does happen with them caps, it's reasonable to expect it to be more noticeable at plate bias and singal levels than line level, let alone instrument level.
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Post by soulsonic »

I thought your whole point was that caps don't make any difference in the sound, regardless of circuit?
I've personally heard them make a difference in pedals, it seems fair enough to me to test in a line level circuit. If it MUST be a tube amp, then nevermind, I won't bother. Sold my only amp today!
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Post by andy-h-h »

Just a reminder of size of the claim made re capacitors that is being debated here:

- Huge impact
- Clearer defined high end
- Warmer rounded midrange
- Almost natural reverb
- Increased sustain


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.

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Post by FiveseveN »

soulsonic wrote: 20 Jun 2020, 20:24 I thought your whole point was that caps don't make any difference in the sound, regardless of circuit?
Can you find a post where I said that?
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Post by soulsonic »

Honestly, I think it's strange that you even care.
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Post by bajaman »

Has anyone actually tried my suggestion yet ? I would very much like to hear from you. As I previously stated - I am not interested in proof, recordings measurements etc. If you decide to ACTUALLY TRY my suggestion (with a clean not over distorted signal) then I would be very pleased to hear your thoughts on any percieved subjective sound difference. So far only Soulsonic has any experience of what i am trying to impart on you - like me he likes or prefers the sound of those mustard capacitors. I am not suggesting you spend any more than you would for a cup of coffee, but unless you agree to try my suggestion then i am simply not interested in your demands for recordings or proof etc. As I stated - Tube Amp Doctor do an excellent reproduction of the mustard capacitor and I recently purchased some Dijon capacitors from Mojotone - although i have yet to AUDITION these ones, but will let you know when i do ;-)
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Post by FiveseveN »

bajaman wrote: 21 Jun 2020, 00:43 As I previously stated - I am not interested in proof, recordings measurements etc.
Well then why would anyone be interested in trying it out? Quod gratis asseritur, gratis negatur.
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