Channel mixing question

[DaN0]

Is it possible to mix 2 channels post phase inverter and then share the same output tubes? IE to take the output of 2 phase inverters (a LTP and a cathodyne) and mix it (via 220k resistors) before sending that to the tubes? Would you need a coupling cap between the output of the mixer and the power section? Is there a better way to do this? Is there ANY way to do this?

Many thanks!

[Andy Le Blanc]

Pretty sure you could switch between two (or more) fairly easily.
mixing might not be as practical as it might seem, you'll have to contend with
a total current, or signal, and there will be phase issues with differences
between inverters. A master volume scheme after the inverter could be
used to blend between two, but you'd have to track down a ganged pot. with
four coupled pots, haven't seen one of those in a long time.

[DaN0]

Both preamp channels have the same number of stages and will be in phase. How drastic will the phase difference be from the phase inverter? I was thinking of going PI -> Post PI Master (dual 1M pot) -> mixer -> grid resistors. How bad would the channel leakage be? Also, what do you mean by having to worry about total current?

I guess ultimately I could settle on one PI and just mix before it but it'd be nice to do it post PI as it's a large part of the sound difference between the channels.

Thanks again!

[Alexo]

Both preamp channels have the same number of stages and will be in phase. How drastic will the phase difference be from the phase inverter? I was thinking of going PI -> Post PI Master (dual 1M pot) -> mixer -> grid resistors. How bad would the channel leakage be? Also, what do you mean by having to worry about total current?

I guess ultimately I could settle on one PI and just mix before it but it'd be nice to do it post PI as it's a large part of the sound difference between the channels.

Thanks again!

Ha! I just replied to you on a different website!

If this is what you want to do, I'll tell you that from my experience, the ltp is fairly neutral, while the cathodyne has a lot of character. The LTP has significant gain and the cathodyne has close to unity gain. To me, this all points to setting up your one channel into the LTP, and inserting a cathodyne pi between the second channel and the LTP, so they'd run in series, and your gain structures and impedances and all that would basically stay the same.

In fact, you should be able to run the two outputs from the cathodyne pi into the 2 inputs of the LTP; the LTP grid that's usually grounded can be used as an input. You'd need to mix your two channels pre-ltp, but that shouldn't be a problem.

[Alexo]

...however, your two channels will now be out of phase at the mixing stage, and this might significantly bootstrap the load on either channel; you would want to mix the cathode output from the cathodyne pi with the other channel to maintain the phase relationship.

[DaN0]

So do you expect that the one channel with the LTP would overpower the cathodyne channel? The cathodyne channel will have significantly more preamp gain than the LTP channel. Any thoughts?