Placement of relays

[goldenGeek]

I had this Mesa/Boogie DC-2 in for repairs earlier this year (there is e thread about that somewhere) but I never quite got it fully functional. There is some new issues going on and the owner has decided to let me gut the chassis and build something new in there. I am planning on a pre-amp roughly based on the clean channel of the DC-2 (or subway blues which is almost identical) since the owner kind of really liked that amp. The power amp will be EL34 based and I'm leaning against a cathode biased setup. Anyway - he wants two channels with individual controls (gain, bass, middle, treble, volume and presence), but basically the same pre-amp in both channels so that he can dial in two settings and switch between those. Is it okay to just switch between two tone stacks (including gain) and two master volumes, or is it better to put in separate tubes also for each channel?

I guess relays are the easiest way to go for the switching and I'm curious about where the best placement for those will be regarding noise. Does anyone have some thoughts about that? I probably need two DPDT relays to pull this off the way I want, so I also have the possibility to spread the two relays out or I can keep them close.

[bal704]

When I do this, I put the relay before the PI input. Each channel is it's own thing, with it's own tone stack setup. I feed the output of each pre into the relay, and the output of the relay feeds the PI.

[TUBEDUDE]

Fed by clean and hot channels. Relay output to effects loop.

[romberg]

Is it okay to just switch between two tone stacks (including gain) and two master volumes, or is it better to put in separate tubes also for each channel?

How many gain stages are in the each preamp? It would be a whole lot simpler to have two complete preamps that did not share any components and then use one relay to send one or the other into the P.I.. If for some reason you can't do this then I suppose you could have tubes serve double duty and switch things in and out (The fender super 60 does this. It is kinda messy and involves more than just relays). This makes the switching more complicated and punching in and out tone stacks and coupling caps could lead to big pops that would then have to be dealt with. I'd would not do this kinda dual channel thing without having separate tubes for each channel (unless very large amounts of money were involved .

Mike

[Stevem]

To have the least chance of oscillating with all of the extra wire runs will come from running the plate output leads long and then placing the decoupling cap right at the relay.
This build tactic is to have the shortest lenght of grid leads possible, ( this is a good build practice just in general!) this also means the relay(s) should be right next to the tube / gain stage that they are feeding.

It also does not hurt to take the time to use guitar cavity shielding tape to wrap around these relays and to then ground that local to the tube, as in the tube socket mounting holes.