More Cold Clipper madness.

Discussion in 'Amp Tech Center' started by Paul G., Mar 24, 2020 at 11:10 AM.

  1. Paul G.

    Paul G. Friend of Leo's

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    I'm still interested in switchable cold clipper on my AB165 Bassman, but I don't want to change the appearance of the amp, so I have a new plan:

    Replace the 1.5K cathode resistor with a 1.8K, leave it connected to the cathode but put the ground through the SPST Deep switch. Tie a 10K to the cathode direct to ground.

    Now with the switch in the up position, the only path to ground is through the 10K. With the switch in the down position the 1.8K and bypass cap go to ground. The 10K is never disconnected (no pop) and 1.8K + 10K in parallel = 1.525K Ohm -- pretty much stock.

    Whadda ya thinK?

    EDIT: sketch say V3, but I meant V2 which is the third gain stage.


    clipper 2.jpg
     
  2. printer2

    printer2 Poster Extraordinaire

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    Never did like the deep switch, go for it.
     
  3. Paul G.

    Paul G. Friend of Leo's

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    N.G. I need a better switch. Pop, better with a cap across, but I can't get rid of it. Back to normal.
     
  4. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Yea, you can't get rid of the pop with a cathode resistor switch.
     
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  5. LightningPhil

    LightningPhil Tele-Meister

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    Yep, soon as you turn it on, the cap will have to charge up. So you go from a bias of say -3V when the 10k is selected to 0V when the switch is flipped, then back up to -2V after the cap is filled. Then when turned off, it'll go right from -2V to -3V. All voltages give or take - but there to illustrate rough changes.

    This thread is quite similar to your "Any reason this wouldn't work?" thread. Attempted to come up with a suitable circuit simulation solution and realised that since the capacitor is in the signal path, any small disturbance is going to be audible. Thus the switching would need to happen over a period of about 1s and not be a ramp wave change in bias voltage - the start and finish need smoothing too.

    How about learning to love the thump as the modes are changed or only doing it when it's off?

    Perhaps the most sensible solution is to use a pair of relays controlled with a timer (perhaps a microcontroller). Where the signal chain is briefly disconnected while the bias shift is stabilising then reapplied. Not suitable for switching mid riff, but fine for setting up the amp.
     
  6. Paul G.

    Paul G. Friend of Leo's

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    Even with the amp on standby, there was enough of a pop that I decided not to do this.

    After playing the amp both ways, I've actually decided I like the normal cathode bias anyway.
     
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  7. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Turning a downstream master volume full down should kill it.
     
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  8. Lowerleftcoast

    Lowerleftcoast Tele-Holic

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    Hey Paul, there is currently a thread in shock brothers titled Gain boost question.
    It might be a different way to skin the cat.
     
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