Twisting Multiple Preamp Signal Wires?

Lancer X

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I am planning for a new build. After rearranged several of the tone pots, some of the signal runs are a bit long (see the yellow and orange wires in the layout below).

Is it effective / acceptable to twist longer signal wire runs to alleviate crosstalk problems? Would this even be necessary? (Note that the purple runs will be shielded - please ignore those.)

Quad Mod signal runs.png


Thanks in advance!
 

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SerpentRuss

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I would bet Fender put the pots on the bassman in schematic order because it made the amp easy to build. I can understand why you might want to switch that. That said, simple is inherently good.;)

The signal that chains through the tone stack is essentially in phase since the tone stack connects two amplification stages. When I think of "cross-talk", I think of cancelation, interference, or bleed-over. Can that be an issue when you're dealing with in-phase segments of a monaural signal? If so, I don't think a significant amount of cross-talk can happen with the short lengths involved. I would definitely avoid twisting signal wires that are out of phase.

Remember, even though some of these signal wires are carrying fairly high peak to peak voltages, the current is low until you get to the OT.
 

drew1d

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I guess I'm a little confused. Typically, wires that are twisted together are out of phase with each other, because that's what reduces the hum. Like aren't filament wires out of phase and that's why they are twisted? But preamp wires, unless it's a phase inverter, wouldn't be out of phase and probably cause more noise if you twisted them. But, I guess you don't know till you try.
 

Lancer X

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I would bet Fender put the pots on the bassman in schematic order because it made the amp easy to build. I can understand why you might want to switch that. That said, simple is inherently good.;)

The signal that chains through the tone stack is essentially in phase since the tone stack connects two amplification stages. When I think of "cross-talk", I think of cancelation, interference, or bleed-over. Can that be an issue when you're dealing with in-phase segments of a monaural signal? If so, I don't think a significant amount of cross-talk can happen with the short lengths involved. I would definitely avoid twisting signal wires that are out of phase.

Remember, even though some of these signal wires are carrying fairly high peak to peak voltages, the current is low until you get to the OT.

Very appreciated - thanks!!

If you don't mind a follow up question, how do you feel about the wires that I've marked in purple (with the intention to use shielded wire for those)? Do you think shielding is necessary for those runs?

One set is the negative feedback return from the output tap, and the other bundle for the "Lead" mod is carrying b+3 plate voltage for V1 as well as the V2 cathode ground. (I couldn't figure how else to switch this mod, since it involved a lot of components in several sections.)

I doubt the NFB runs are a problem, but I am worried about the B+3 supply running all over the place.

Bassman_Micro_EF80_MV_Layout_LRM_Quad Mod.png
 

Lowerleftcoast

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Is it effective / acceptable to twist longer signal wire runs to alleviate crosstalk problems? Would this even be necessary?
It is more effective to have the unshielded signal wires hug the chassis for a partial shield.

I was going to make a comment about the ground scheme but I see Rob provided what you are using. He has decided not to keep the preamp grounds separate from the power side.
 

Lancer X

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I have an aversion to placing high voltage on a switch.
Hmm, I see what you mean. I read about some amp manufacturers using relays to avoid front-to-back panel wire runs, and seems to make even more sense when switching high voltage.

This “lead” voicing is the least important of the four to me, so I could just drop it. But, it will be fun to figure out a way to accomplish this. Appreciate your warning.
 




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