Relay switching volume and/or MV

Discussion in 'Shock Brother's DIY Amps' started by NSB_Chris, Oct 25, 2018.

  1. NSB_Chris

    NSB_Chris Tele-Meister

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    I am planning a build and have considered adding two channels but i don’t think i need two full channels with completely separate preamps sections, tone stacks etc. I was thinking just one preamp circuit but be able to switch between two volume settings. I really like the Hoffman version with the power supply board and separate relay boards. He provides really clear instructions!

    Is there any reason why not to simply relay between two volume pots? Would it be reasonably quiet and not pop when switching?

    Looks like one side of the relay would switch between the inputs of the pots and one side would switch the wiper outputs. It would take two relays to switch both the volume and MV.

    The MV is a simple volume pot before the PI. Any advice or tips from experience would be greatly appreciated!
     
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  2. sds1

    sds1 Tele-Afflicted

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    This doesn't seem any different than relay channel switching in a D-style amp, which isn't really two different channels either but rather inserting 2 add'l gain stages between the preamp and effect loop/PI. In a Dumble ODS the clean/OD relay is connected directly to 2 different pots which should provide assurances as well. The relay switching is completely quiet.
     
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  3. SSL9000J

    SSL9000J Tele-Meister

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    If all you want to do is switch volume settings, I'm thinking a much easier way would be to add a switchable resistor in series with the volume output pot. Like so:
    Vol_Switch01.jpg
    Your volume would be reduced by whatever the percentage of the resistor is with respect to your volume pot. So if it's a 1 meg pot at halfway, about 500K, switching on 100K resistor would back off your volume by 1/5, and so on.
    Is the idea to go from "rhythm" to "lead" mode at the flip of a switch?
    EDIT - Actually, I'm looking at this now and thinking you'd probably need something like a 1meg resistor and/or some sort of capacitor in parallel with the switch to prevent it from popping.
     
  4. Tom Kamphuys

    Tom Kamphuys Tele-Meister

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    I might be wrong as I'm kinda new to this stuff and it's late in the evening, but I don't see how the 100K resistor would reduce the volume. It looks more like a gridstopper, which together with the Miller capacitance will act as a low-pass filter.
     
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  5. rolloman

    rolloman Tele-Holic

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    Last edited: Oct 25, 2018
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  6. SSL9000J

    SSL9000J Tele-Meister

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    Astute observations, thank you! Yes, I stand corrected, you would want to increase the resistance going into the volume pot, not coming out of it. Matter of fact, I think you could increase the volume a bit (if it's not dimed already) by inserting a resistor to ground, on the other side of the volume pot.
     
  7. NSB_Chris

    NSB_Chris Tele-Meister

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    Thanks for the feedback, that helps. I would be using this for rhythm and lead settings rather than a true two channel amp that would have a clean channel and a dirty channel.
     
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  8. SSL9000J

    SSL9000J Tele-Meister

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    Another option would be a switch on the cathode bypass cap(s) on V1. Cap off = "rhythm" / cap on = "lead."
     
  9. DCW74

    DCW74 Tele-Meister

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    Maybe an L-pad attenuator circuit on DPST switch would be easiest way to do a volume cut/boost. You could put it at your output jack, and I doubt you would hear any popping.
     
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