It had to happen eventually... capacitor upgrade question for the Mainline

[Paul Joppa]

It sounds very reasonable. My only caveat is that there will always be some differences between channels. They will usually be very subtle, but then so are the differences between good capacitors. For example, very small differences in level affect preferences even when they are not audible as level differences per se.

A good test might be to see what differences you hear with identical caps. Do you prefer the sound of one channel over that of the other? At the least, try swapping tubes to see if that channel preference changes. When comparing two different caps, you may need to swap caps and repeat the test so they get tested in each channel.

[Thermioniclife]

If I understand you correctly that seems like a reasonable solution. You could build an adaptor that plugs into the output jack, a short cable to the switch and a short cable to an external headphone jack. That way you don't have to make connections inside the amp other than change one cap. Pretty cheap to make, 1 stereo plug, 1 stereo jack, 1 spdt switch and and a box to mount them in.

[Paul Birkeland]

That is certainly an idea worth trying!

[Phippers]

Hi Paul,

> there will always be some differences between channels. They will usually be very subtle,

Yes - this was what I had in mind in step 4 : "Compare L & R with the stock Daytons - satisfy oneself that they sound more or less the same."

Of course there is an assumption being tested there   If they don't sound "more or less" the same, then that is another rabbit hole for exploration!

> very small differences in level ....

Yeah I was thinking about that after I posted. I might measure that. If they were significantly off then perhaps one would need to take steps to trim the levels (maybe at the source).


Hi Lee,

Yes, that's exactly the sort of thing I had in mind.


I did also think that one could sum the two outputs, but with one phase reversed, and directly monitor the difference signal. Of course, as Paul J points out there are other contributing differences in the channels and one would be listening to all of these differences, not just the differences between the caps.

I think that it might be a useful discovery technique though - for example, I would have thought that if there is any extra bottom end change when changing the cap value, then it would be readily discerned in the difference signal.

[Thermioniclife]

As far as summing and phase reversal on one channel is concerned I think you may be disappointed as you will get a null or cancelation of frequencies especially in the lower frequency range. I think your initial thought has merit and would be a good place to start. But having said that, empirical data is always needed to prove or disapprove theoretical solutions. Meaning as James Brown would say " It's your thing, do what you wanna do "

[Phippers]

Hi Lee,

Yes the cancellation is exactly the point.

If the two channels were perfectly identical, then the phase reverse & sum would result in a perfect null - i.e. silence at all frequencies.

Then, if a change in one channel is supposed to (say) extend the bass response, then one would expect to hear just that blob of extra bass in the difference signal.

Not something nice to listen to, but a diagnostic tool. 

Of course in the real world things are far from perfect, but if that (say) extended bass response was significant, I would expect to be able to hear it in the difference signal.

It is a technique that I have used in the past when eq-ing or otherwise treating a mix - for example, applying a de-noise algorithm. It can be all too easy to focus on the one parameter one is adjusting, to go too far and totally miss the havoc that one is wreaking somewhere else in the mix.

The phase reverse trick can be very revealing of what else is going on, unwanted artifacts and suchlike. Once you can isolate the artifacts and learn what they sound like, they are easier to spot in a dodgy mix.

But I digress!  I was just thinking aloud that it might be worth a go here too - was just an idle thought. Easy enough to try.

[Doc B.]

You could just run a response curve of each channel and compare. It's going to be very subtle.

[Phippers]

Hi Doc,

Yep I'll probably do that as well.