Positive ground - how to connect wire shielding

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Hi
I just finished building a Tone Bender MKII. As usually, I used shielded wires from input and output jacks to the 3pdt a from there to the PCB.
My doubt is: do I have to connect the shieldings to the circuit ground (in this case the positive of the battery/power supply), or do I have to connect it to the negative of the power supply, as in a normal negative ground circuit ?
I tried both ways, and I can't really hear any difference. Is there a rule?

[Gurner]

Hi
I just finished building a Tone Bender MKII. As usually, I used shielded wires from input and output jacks to the 3pdt a from there to the PCB.
My doubt is: do I have to connect the shieldings to the circuit ground (in this case the positive of the battery/power supply), or do I have to connect it to the negative of the power supply, as in a normal negative ground circuit ?
I tried both ways, and I can't really hear any difference. Is there a rule?

You don't want to be putting -9V on the signal cable shield....because if you then connect up such an arrangement to a follow on circuit that has a more traditional 'true' grounded shield, then you'll be effectively shorting the -9V on the shield to ground (0V) ....not good!

Connect your signal cable shield(s) to true 0V ground .....which in your situation has the battery + wire connected to it.

[R.G.]

Shields always go to ground, at least until you know a specific reason why they should not.

[Mark Hammer]

I find the easiest way to conceptualize this stuff is to imagine that every battery-operated pedal has a bipolar supply, but in some cases you forgot to include the negative side, and in others its the positive side you forgot.

So, when using a GE/PNP-based circuit, you "remembered" to include the negative side of your bipolar supply, but omitted the positive side.

[bluebunny]

I've always had a bit of a mind-block concerning positive-ground circuits (and haven't yet built one).  But this simple explanation clarifies everything; it suddenly becomes very simple to visualise exactly what's going on.  Thanks Mark!  And then R.G.'s reply becomes obvious too.  What a team!   

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thank you very much guys....me too I've always had serious problems with positive ground circuits, I hoped working on a positive ground build could help...but in fact it didn't 

Anyway, I'll connect the shieldings to ground (positive of the power supply), as you suggest.
I tried the pedal with the shieldings connected and disconnected, and it seems to me that the circuit "generates" enough noise itsels to make it useless to be too picky about shielding the cables.

One more question: I'm trying to bias correctly the thing (for doing this, I put a multiturn trimmer on both Q2 and Q3 collectors) but on fuzzcentral they say that Q3 collector should be at -4,5 V, in other discussions  they say in vintage units it used to go down  to nearly - 9 V.
I tried both, and other less extreme biasings, and in any case it sounds nice. So finally I'll bias it by ear to my taste, but in original units Q3 collector was closer to 4,5 or to 9 V?
The change in tone is huge going to one extreme to the other!

[Arcane Analog]

Biasing the Q3 collector is not the best approach - biasing Q2 is with a trimmer is what you want to do.

If you are going for something like the originals you do not want to have 4.5V on Q3. Vintage units have ~7V-9V on them.

Fuzz Central needs to update their information on the MKII and a few other circuits.

[::::FLARE::::]

I can do both, as I developped a PCB with two trimmers, one on each Q2 and Q3 collectors. So, if I understand well,  you think the best thing to do is to let Q3 collector resistor to 8,2k (project value) and try to get a voltage of above 7V on Q3 collector just biasing Q2?

It seems reasonable because in various schematics I found online, Q2 collector resistor varies from 33K to as high as 100K...

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after some tests, I found that with q3 collector at about 7,3V the tone is beautiful and the noise is very low. Anyway, I think it depends heavily on the transistor gain& leakage, and every circuit has to be biased a differently.