Tone transformation in JTM45 amp

5F6-A

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I have a JTM45 style amp in a head format. Until recently it sounded great but all of a sudden it started humming. I took it to my tech and so it happened that one of the filter caps had gone bad. The tech did a service, changed the faulty cap and everything was fine. However, I had a set of NOS real mustard caps in my parts drawer so I thought that that was the perfect occasion for trying them out. Stock, the amp had Sozos (first incarnation) and Auricaps. To be honest the amp sounded great as it was but I wanted to see if the hype about real mustards was real or not so I asked my tech to change the coupling capacitors for the mustards. He tested it and said that the amp was ready to be collected.
To cut a long story short, when I plugged my guitar into the amp with the NOS caps, I was heartbroken... the amp still sounded good but much, much brighter than before and the lows felt loose and flabby. The amp wanted to sound right but somehow couldn't, if that makes any sense..... was that the change I was hopping for? My tech reassured me. He said that although the amp sounded worse now, it would improve after a few days as long as I played through it. He suggested between 50 and 100 hours.... I wanted to believe him but I couldn't help but to feel disappointed and sceptical. The mod had cost me a significant amount of money and the tone was significantly worse.

Anyway, fast forward one week. I lent the amp to my son to try it out. We both played it in turns and after, 50 hours, I couldn't believe the transformation (I was making quick recordings of each stage). After some burning-in, the amp's tone did exactly what my amp tech said. The tone has changed from harsh and spikey to smooth and rich. The low end is more robust, the midrange is more complex and the high end is more refined. The difference is not subtle. It has made the amp a lot smoother and more compressed (in a nice way). Easier to play and more satisfying to listen to. It's difficult to explain but true nonetheless. Wow! So it wasn't mumbo-jumbo after all. ... who would've thought it?! Anyone here with a similar experience?

mustard 3.JPG
 

Brek

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Any one able to explain why? Is it like wood that improves with playing? Some kind of molecular alignment of something or other?
 

AcVox

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The idea of new or NOS electrical components improving with use has always been controversial, understandably so in my opinion.. However..the wealth of, and the numbers of those testifying that the phenomenon is true cannot be casually dismissed.

5F6-A, has just added to the mounting circumstantial evidence for the truth of his testimony.
 

ErictheRed

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You hear these sort of stories (and I'm not implying that anyone is lying or anything), but it's really hard to isolate things in a meaningful sense. In the course of a week various things can change, different rooms will sound different, strings could have been changed, you subtly over time started tweaking and dialing it in differently without thinking about it much (including moving the Tone knob on your guitar a bit), used a different or longer instrument cable which can attenuate some highs, etc. There is also just the purely psychological effect of getting used to a new sound, so that now you start to enjoy what you once did not.

I'm just saying that as an electrical engineer I don't know of any real reason that this would happen. Maybe with heater resistors they will come to more stable temperatures over a period of time, but I don't know of a reason that old capacitors would experience a sudden change in sound after not being in use for a while. My limited understanding of the human mind tells me that this is more of a psychological effect, but I could be wrong.

Without before and after recordings with the same setup, etc, it's really all just anecdotal. Not that I'm accusing anyone of anything wrong here, I'm just saying that I don't have an explanation in the electrical engineering sense, but that there are plenty of plausible alternative explanations.
 

AcVox

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Well 5F6-A mentioned making little recordings, so if we could hear them for ourselves it could be really interesting evidence, one way or the other.
 

el84ster

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Sozo’s website used to have (maybe still does?) a spectrum analysis of capacitors before and after break in. You could see the difference.

I hear it in some caps. I’ve used Philips mustards for years and never noticed it but I do believe it can happen.

ive replaced all caps in several amps with the mustards and never noticed a downgrade in sound quality first. Not saving it didn’t happen in your case, just that I’ve never noticed it.

I do notice it most with sozo caps seems like.
 
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grumphh

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The tone has changed from harsh and spikey to smooth and rich. The low end is more robust, the midrange is more complex and the high end is more refined.
:rofl:
...is it just me, or do you guys all have the same 2003 copy of "High End Marketing Terminology 101" in your drawers?
 

eslover

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Also, 50 hours of playing on the same speaker cab can really break-in a speaker...make it much more pleasant to the ears.
 

ErictheRed

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Here’s sozo’s explanation for the break-in in capacitors.
Thanks for sharing that link. There is no science or engineering there, just words and analogies. "...reacts negatively with the signal flow" has no meaning that I can think of, for instance. "The dielectric absorbs and releases energy as opposed to passing it through the capacitor" just makes me think...what? Do they even know what a dielectric is? It's a material that can support an electric field, i.e. an insulator. Are they suggesting that when a capacitor sits for a long time some of the dielectric becomes conductive, but then when you use it for a while, it goes back to being an insulator? Wouldn't that (conduction in your dielectric) just destroy the capacitor and other parts of the circuit? The answer is yes, yes it would.

I could potentially see heat being at play here (I mentioned heater resistors in my previous post), but I can't imagine that capacitors would need more than 10 or 20 minutes to reach a steady-state value. Certainly not a week.

I would be interested to see some spectral analysis of capacitor break-in. I'm not saying that it doesn't happen, just that I can't think of an explanation for why it would. I'm open to the idea, but the "explanation" they seem to have proposed is just a bunch of meaningless (and worse, contradictory) words. Positing that the skin effect (which they don't explain correctly) could explain this is pretty ridiculous at frequencies anywhere remotely near those that humans could hear.

That link is just a bunch of BS, frankly. I'll probably get a bunch of crap for saying that, but it made absolutely no sense to me, and I teach this stuff for a living (advanced degrees in physics and EE). I've also worked in aerospace for years where electronics are subjected to extremes of temperatures (often with very little air molecules able to cool them, such as in high altitude aircraft), so I have a good amount of experience with this stuff.
 
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markguitar

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something that never seems to be mentioned or thought of with NOS caps of all kind is the orientation of how they are installed. Most newer caps for amps, like SoZo or Synergy mustards caps have a black line to designate orientation. There is an inner and outer foil that the leads attach to. I’ve used many real mustard caps in amp builds and still use some in my MGL amps. In every position throughout the circuit, I can 100% hear a difference when the cap is correctly oriented. In the wrong orientation the cap will sound more harsh, brighter and grainy. Flip the cap 180 and it’s noticeably smoother, more gain and darker in a good way. Take the time to do this in the amp you had the mustards installed in and I guarantee you will hear a difference for the better. Just unsolder each cap one at a time and listen to it in both positions.
 

cmjohnson

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Nobody ever seems to get around to making a pair of "before" and "After" high quality recordings of their amp when they do a component swap, to compare the sound of the "fresh" parts and those same parts after they've "broken in".

I think that SOME of it is just getting used to the sound.

But, yes, components DO change a little as they break into being used. The changes to these components can even be analyzed and measured by sensitive test equipment.
 

grumphh

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Nobody ever seems to get around to making a pair of "before" and "After" high quality recordings of their amp when they do a component swap, to compare the sound of the "fresh" parts and those same parts after they've "broken in".
But you are wrong, recordings have been made :yesway: ...only apparently in so low a quality that it would possibly offend our ears or else they surely would have been posted for us all to hear.

But TRUST the OP. The difference is NOT subtle! :
We both played it in turns and after, 50 hours, I couldn't believe the transformation (I was making quick recordings of each stage).
...
The difference is not subtle.
 

cmjohnson

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It's like UFO photos...lots of them exist but somehow no professional photographer with a 14,000 dollar sports lens and 3,000 dollar 50 megapixel DSLR ever seems to get a photo of one. It's like the aliens know how to avoid GOOD cameras and GOOD photographers or something...

It'd be fun to do a component swap and do recordings before the swap, after the swap, and later down the road after burn-in, all under identical controlled recording conditions.
 

AcVox

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The OP said and I quote "I was making quick recordings of each stage".

A recording documenting the incremental change on the sound of an amplifier as new capacitors go through the theoretical 'break in' phase is a significant finding.

The fact that these changes have been documented is surely an opertunity we could learn from. I just hope the OP isn't in witness protection due to the interest..
 

Brek

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It's like UFO photos...lots of them exist but somehow no professional photographer with a 14,000 dollar sports lens and 3,000 dollar 50 megapixel DSLR ever seems to get a photo of one. It's like the aliens know how to avoid GOOD cameras and GOOD photographers or something...

It'd be fun to do a component swap and do recordings before the swap, after the swap, and later down the road after burn-in, all under identical controlled recording conditions.
Or cameras in general, that’s my experience, every fucking time, I see E.T and no damn camera.
 

cooljuk

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When I wind pickup coils they have absolutely observable changes in electrical properties from when they first come off a winding machine to after some time. It's easy to watch how the properties of the coil change from fresh off a winding machine to an hour or two later and even more a day or so later. It's so predictable I could tell what a coil will measure and do tomorrow based on what it measures and does now, when fresh. No voodoo or hype, there. They change, it's measurable, it's not just a questionable amount. It's significant and consistent.

The coil relaxes, I suppose. Internal tensions settle, I guess. WHY it changes is my speculation. THAT is changes is fact. I'd be glad to document it for all of us here, if it's in any doubt.

....but pickup coils are not capacitors, right? Well, actually, they are. Capacitors are also coils, as well. Temperature and tension have an effect on the physical and electrical properties of coils. It's not hard for me to accept that repeated heating/cooling cycles of a coil made of multiple different materials sandwiched, after sitting idle for years, might allow those materials to adjust and settle in a bit and change the electrical properties a bit as they physically shift internally.

If it's the case that a similar thing is going on with my coils and long-unused capacitors, then the capacitor change should be able to be measured like it can be with my coils, I would think.
 


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