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DIYstompboxes.com  |  DIY Stompboxes  |  Building your own stompbox  |  True Bypass - Why not ground the input AND the output? 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: True Bypass - Why not ground the input AND the output?  (Read 3256 times)
Suicufnoc
Posts: 43

Brett N - Missouri


True Bypass - Why not ground the input AND the output?
« on: August 09, 2011, 09:41:07 PM »

I've seen a lot of 3PDT True Bypass wiring methods that ground the Input of the effect when bypassed, but not the output.  Is there any reason not to do this?  (Other than the obvious hassle of adding a second jumper.)
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R.G.
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Re: True Bypass - Why not ground the input AND the output?
« Reply #1 on: August 09, 2011, 09:56:38 PM »

I've seen a lot of 3PDT True Bypass wiring methods that ground the Input of the effect when bypassed, but not the output.  Is there any reason not to do this?  (Other than the obvious hassle of adding a second jumper.)
No particular reason why not. I guess the question I have is what is being achieved. Don't get me wrong - I like using belts and suspenders in parallel backup arrangements.

But if the input is grounded, the output is quiet unless the thing oscillates all by itself and can broadcast  its output across the switch gap that's open from the output to the signal lines. And if the output is grounded, internal oscillation could broadcast through the ether. Maybe a poor wiring job makes the power ground and signal ground share a line and current wobbling on the shared ground could get into the signal line. Grounding the input is probably a better way to keep the circuit quiet.

I've even seen setsups that ground somewhere in the middle of the effect circuit.

Given that hard-contact true bypass will always have some amount of clicking depending on how unlucky you are in where in the signal cycle the contacts close, I prefer one of the several other ways to bypass. And the Millenium C will let you mute as many places in the circuit you like.

Anyway, if it seems good to you, no reason why not.
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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
Suicufnoc
Posts: 43

Brett N - Missouri


Re: True Bypass - Why not ground the input AND the output?
« Reply #2 on: August 09, 2011, 10:04:40 PM »

I've just heard of cases where extreme gain fuzzes or other pedals need the output muted(probably because of self oscillation as you said.)  I'll have to look into this millennium C.  I've Heard of millennium bypass, but not C. 
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darron
Posts: 2303


Melbourne, Australia


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Re: True Bypass - Why not ground the input AND the output?
« Reply #3 on: August 10, 2011, 01:29:46 AM »

that's pretty cool. thoughtful.

i especially like how the input signal only has to pass through one switch to make it to the output bypass.

might have to give this a shot one day (:
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egasimus
Posts: 459

Adam


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Re: True Bypass - Why not ground the input AND the output?
« Reply #4 on: August 10, 2011, 07:00:46 AM »

Here's what RG's talking about: http://www.geofex.com/Article_Folders/Millenium/The%20Next%20Millenium.pdf
However, I can't understand how this is used: how it is even connected to the actual effect circuit, as well as how to "mute as many places in the circuit as you like".
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R.G.
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Re: True Bypass - Why not ground the input AND the output?
« Reply #5 on: August 10, 2011, 08:52:24 AM »

Here's what RG's talking about: http://www.geofex.com/Article_Folders/Millenium/The%20Next%20Millenium.pdf
However, I can't understand how this is used: how it is even connected to the actual effect circuit, as well as how to "mute as many places in the circuit as you like".
It connects to the circuit like the original Millenium: the control line connects to a DPDT switch wired in the special way shown in the original article, here:
http://www.geofex.com/Article_Folders/Millenium/millen.htm

The essence of the Millenium are that it is a very, very sensitive detector of the difference of resistance to ground of air and a real resistor. So it's connected to have the control line connected to the output of the effect when the effect is bypassed, and to be truly open circuit when the effect is running. The true open circuit causes the LED to come on. For this to happen, you need a device which provides a literally nano-ampere current and a switch device that senses that. Diodes are used reverse biased as a current source for the current, and a FET for the sensing device.

The Millenium C takes note of the fact that once you have anything that switches, you can use that switching action to trigger other things. For muting other places in the circuit, you take some device that can mute a signal - a FET, a CMOS switch, even a bipolar device - and trigger it to mute when the Millenium says " the effect is off now."  True, I didn't draw out all the possible ways to do it. Takes a long time.
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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
acromarty
Posts: 62



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Re: True Bypass - Why not ground the input AND the output?
« Reply #6 on: August 11, 2011, 05:54:11 AM »

If the output is d.c. coupled then grounding it is not a good idea, you will short out the output.
In the best case this may only reduce your battery life, worst case it might damage the op-amp or transistors driving the output.
If it is a.c. coupled with a series capacitor then grounding the output should be ok.
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Andy
darron
Posts: 2303


Melbourne, Australia


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Re: True Bypass - Why not ground the input AND the output?
« Reply #7 on: August 11, 2011, 06:50:32 AM »

If the output is d.c. coupled then grounding it is not a good idea, you will short out the output.
In the best case this may only reduce your battery life, worst case it might damage the op-amp or transistors driving the output.
If it is a.c. coupled with a series capacitor then grounding the output should be ok.


if there was DC on the output then it would pop like hell when you toggle the switch anyway, as R.G. recently reminded me.... so there's a safe bet that's not the case.
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Blood, Sweat & Flux. Pedals made with lasers and real wires!
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