5E3 dual tonestack mixing problems continue..

[makepeace]

Hello reverent tube guru's. I have recently rebuilt my 1st 5E3 after loads of tinkering for the past year and a bit.

A persistent demon that I still have not managed to quell is a 'problem', or rather an undesired effect to do with the mixing of signals between the standard 5E3 tone/vol controls when an instrument is plugged into either channel ALONE.

So:

-I plug my Strat into the "Tweed" channel input
-Signal goes into the V1a 12AY7 triode and then into the tweed stack and hopefully straight to the V2a 12AX7 triode etc.

And vice versa when plugged into the "Blackface" channel input, which goes into its own 12AY7 triode etc.

You would hope that the two channels would not interfere with each other, but they do.. So much so that you have fiddle around with 6 controls when trying to dial in a tone when plugged into either channel . Nevermind when you jump the channels .

So as far as I can see I have a couple of propositions (but any extra would be greaaaaat!). Either I put a push pull on the vol control of each channel that disconnects the tone stack completely at the mix point, which WILL work, but won't be ideal for various obvious reasons..

On the unrealistic side, there would be a recovery triode for the blackface channel that would separate the two channels, but I don't have space for that .

I've also drawn up another way of connecting the circuit (using a conventional volume arrangement, with the input signal of each channel connected to the end of a track as opposed to the wiper of their individual vol controls. Will this be a solution? I have drawn up the circuits to compare.. The proposed is on the left.



Cheers and thanks in advance!

Jono

edit: duffed the drawing first time

edit 2: damn, just realized that won't work either.. BF on 10, Tweed on 0... GROUND!

[makepeace]

how about this one?

[loudthud]

For minimal interaction between the two channels you will need mixing resistors like you see on a 5F6A. Something between 220K and 470K from each volume control joined at the grid of the next stage. There will still be some interaction.

[makepeace]

Thanks loudthud,

I had already tried mixing resistors, but to my ears it didn't work at all. Although something in the range of 100k was recommended.. Will try bigger ones. One question, will a series resistor in a signal path cause attenuation or any other ill effects? I understand that it changes the impedance of the circuit. For example, could I use mixers of the order of 1Meg, or would that pose problems?

Cheers

[d95err]

You need some way of separating the channels, otherwise you'll get interaction. Will you actually be using both channels at the same time? If not, just add a switch to select channel.

[makepeace]

It is likely that I will want to jump the channels, or use the interaction of channels (you can get some great tones if you spend some time dialing them in). In the OP I stated that one of the options would be to use a push pull pot for each to turn its respective channel off, but I would prefer another solution..