Channel switching/selection question

[MarkB]

I'm building a single-ended amp with two separate preamp channels. Each has its own input. I don't want to switch during a song, just choose one or the other. Would you use mixing resistors at the power tube grid feed - after the preamps - or a switch at the same place? I just don't want one preamp to affect the tone of the other.

[krash]

I would tend to use a DPDT switch and when you switch to one chanel, ground the other one.

Mixing resistors are going to attenuate the signal and also probably roll off some top end. Maybe this will work for your amp, maybe not.

[UR12]

I'm building a single-ended amp with two separate preamp channels. Each has its own input. I don't want to switch during a song, just choose one or the other. Would you use mixing resistors at the power tube grid feed - after the preamps - or a switch at the same place? I just don't want one preamp to affect the tone of the other.

Mark

You can use 220K resistors to mix the signal before the power amp section. That's what they are there for to keep one channel from affecting the other. Actually though since you are only playing through one channel at a time the grounded input on the input jack of the channel you are not using should be sufficient to mute any affects of the channel not being used. As long as you didn't split the first 12ax7 (if that's what your using) between channel one and two, AND use a common cathode resistor, there should be no interaction between the two preamp channels. If you go with a switch on the grid of the output tube you will hear a nasty pop if it is switched with power on.