Fuzz face transistor hfe puzzle

[Phend]

They can with separate ("isolated") power supplies.

So if each is battery powered?  Wouldn't the ground on the cable connecting the two see both negative and positive.
Pardon my not "getting" this.

[fowl]

They can with separate ("isolated") power supplies.

So if each is battery powered?  Wouldn't the ground on the cable connecting the two see both negative and positive.
Pardon my not "getting" this.

Both on batteries, one on a battery and one on a wall adapter, both on separate wall adapters, both on individual isolated outputs from a commercial power supply.  Anything but parallel ("daisy chained") will work.  Ground is ground, and just a reference point really, but a paralleled power supply, with both its positive and negative connecting together at this common point "ground" will be shorted.  Hope that makes sense.

[PRR]

...Wouldn't the ground on the cable connecting the two see both negative and positive. ...

Compared to what?

Draw the *circuit* that you think makes trouble.

[Phend]

Add a charge pump ?

[pinkjimiphoton]

Question. Without Modification a positive ground effect can't be connected to a negative ground effect. Sounds true to me.

sure they can. ground is ground. its a neutral point between positive and negative potentials. they can't share the same power supply, necessarily, but you can have npn and pnp circuits both in an audio chain, no problem. so say ya gotta pnp fuzzface and everything else is npn. just use a separate power supply for the pnp, and you're fine.

-9v ground +9v ground is the mid point. may seem weird, but its fine.

[pinkjimiphoton]

No, it's just a stock, negative ground silicon Fuzz Face with modern BC108Cs. The plus lead has an alligator clip, so I clipped it to ground for convenience's sake.

Silicon Fuzz Faces with Q2C voltages over 5V are not uncommon at all.

Wow, to me that's really weird behaviour.   I'm struggling to think what's happening there (sparks flash around my head and seconds later I keel over with a clunk).

hahah, its weird, but its true. often they seem to sound best right around 6 volts on the q2c. more headroom, more bloom. responds better to guitar knob twiddling, more like GE that way. lower voltages equal more fuzz, too low, it gets velcro-ey and gnarly and won't clean up well.

[Rob Strand]

hahah, its weird, but its true. often they seem to sound best right around 6 volts on the q2c. more headroom, more bloom. responds better to guitar knob twiddling, more like GE that way. lower voltages equal more fuzz, too low, it gets velcro-ey and gnarly and won't clean up well.

I actually like the sound when the bias is in the 6V to 7V zone especially on the bridge pickup.   The 4.5V is a little too violinish and woofy. 

I just can't see how BC108C's wired normally can bias to 4.5V (or above) with the stock 8k2 Q2 collector resistor (and 33k Q1 collector resistor).

Normally I see  5k6 for about 4.8V and say 3k3 (2k7 to 3k9) for a higher bias voltage.

[pinkjimiphoton]

can only work if the gain is right for the q's bro.
most of them are way too hot to bias right with stock values. that's why i began messing with e resistors years ago, to get them "in the ballpark". the final iterations of the statesboro bluesman i did for mla used that trick, made 'em sound a lot more like the stock old school ge, once i got them to understand they needed to trust my ears and not their friend's... they had it totally neutered. had to mess with it to get the balls back

proved once again, you can't trust customer preferences.... when ya give them what they ask for, they don't like it. give them what you came up with in the first place that they rejected, and suddenly they love it. go figure! 

[Electric Warrior]

No, it's just a stock, negative ground silicon Fuzz Face with modern BC108Cs. The plus lead has an alligator clip, so I clipped it to ground for convenience's sake.

Silicon Fuzz Faces with Q2C voltages over 5V are not uncommon at all.

Wow, to me that's really weird behaviour.   I'm struggling to think what's happening there (sparks flash around my head and seconds later I keel over with a clunk).

The tolerance (or wear) of the fuzz pot can make a huge difference here. I once auditioned some transistors that biased up just as I expected, only to find out that Q2C was much lower when soldered into the vintage unit I was restoring. The pot I was using measured pretty low. Sounded good, though:

[Phend]

Just to set this straight For everyone who has interest in this daisy chain topic:
Here are two Fuzz Face circuits from Fuzz Centrals Website.
One NPN and one PNP connected together with a standard cable.
Powered with two separate 9 volt batteries.
See picture below I made with Fuzz Centrals circuits off their Website.

Here is where I am getting confused.

This is quoted from General Guitar Gadgets Website:
"We ran across a forum post long ago where R.G. Keen suggested using a charge
pump to convert the power input of a PNP circuit from positive ground to negative
ground. This provides a solution for those of us who like to daisy chain a power
supply to all of our stompboxes. If you've ever tried to daisy chain your modern
pedals (Boss, Ibanez, etc) with a Fuzz Face (or an old 70's Big Muff Pi or any PNP
transistor circuit pedal), you know you can't do it. Now you can! "

Which continues:

"From the DC jack or battery, the charge pump circuit is a negative ground circuit.
From the output of the charge pump circuit, we use the ground and -9v outputs to
power the Fuzz Face. The Fuzz Face circuit sees a positive ground (0v is more
positive than -9v). So here is the solution for the FF5 PNP versions in diagram and
photo. This is a great "wrapper circuit" to install and probably well worth the time in
the long run."

Will this configuration Work Without a plus minus swapping circuit (charge pump) ?

[anotherjim]

For a connection to make a circuit, it has to also find a return path. If it only connects supply ground to cable ground in the signal chain - where is the return path? Neither positive nor negative ground pedals will cause a problem provided any non-grounded part of their respective circuits does not share a DC connection with the opposite. That's where the DC blocking caps come in although they do the same job if they were all negative ground.
How about using Ge Fuzz Face with a Si Cry Baby for example?

[Phend]

Yes, AC DC in the same circuit has been a major hurdle for me. DC from battery for power and then AC (basically) from guitar pickup.
DC doesn't go across the ever present cap before the volume control, hence does not go into the amp, where you certainly don't want it.
So what's up with the GGG charge pump?  Or am I totally confused,  not hard to do in my case, lol.

[anotherjim]

A charge pump supply "inverter" is only allowing a common DC negative ground pedal power daisy chain to also power a positive ground pedal. If you didn't have that, the DC positive wire would meet the ground of the positive ground pedal which is a short circuit to the Ground of the power supply. I think many settle for pedal power for NPN and stick with battery for the PNP.

[Rob Strand]

most of them are way too hot to bias right with stock values. that's why i began messing with e resistors years ago, to get them "in the ballpark". the final iterations of the statesboro bluesman i did for mla used that trick, made 'em sound a lot more like the stock old school ge, once i got them to understand they needed to trust my ears and not their friend's... they had it totally neutered. had to mess with it to get the balls back

Some guys don't like to mess with the values on the standard circuit.   At the end of day all things aren't equal so you need to mess with the circuit to push it into the good zone.

proved once again, you can't trust customer preferences.... when ya give them what they ask for, they don't like it. give them what you came up with in the first place that they rejected, and suddenly they love it. go figure!

I guess people have something in mind and don't want to change from it.   It's not until you hear things side by side you realize maybe that's not the best choice.   A switch is a good idea.   I like boxes with switch for normal and modded.  In the long term the switch will find it's way to the right place 

tolerance (or wear) of the fuzz pot can make a huge difference here. I once auditioned some transistors that biased up just as I expected, only to find out that Q2C was much lower when soldered into the vintage unit I was restoring. The pot I was using measured pretty low. Sounded good, though:

Yes, pot tolerances are a real stinker especially when they are part of setting the bias point.   

Yes, AC DC in the same circuit has been a major hurdle for me. DC from battery for power and then AC (basically) from guitar pickup.
DC doesn't go across the ever present cap before the volume control, hence does not go into the amp, where you certainly don't want it.
So what's up with the GGG charge pump?  Or am I totally confused,  not hard to do in my case, lol.

It's actually very simple.

The whole motivation for GGG's charge pump is from outside the box the PNP pedal maintains a negative ground.   That lets you daisy chain the supply to the pedals.

If you have separate batteries it should be fairly obvious plugging the NPN pedal into the PNP pedal works without any issues.  Both circuits maintain their own ground polarity yet the grounds between the two are connected via the guitar cable.   That's how it's drawn on your schematic.

You only need to think about coupling caps in terms of circuits having different DC on each side of the cap and an AC signal passing through.   If you have NPN buffer circuit feeding into an opamp, like a TS-9 tube screamer, the cap between separates the DC voltage on each side, which just happen to be positive voltages.   If you have a NPN negative ground circuit feeding into a PNP positive ground circuit, you only need to think about the fact the DC is different on each side of the coupling caps.  No different to the TS-9 example.  The PNP circuit will have a negative DC voltage but you don't care what it is, you only care that the DC is different.

So back to the grounding.  As shown your schematic it all works fine just like two independent pedals. So look what happens if you tried to connect the PNP circuit's supply terminals back to the NPN circuit battery.     You get a short across the supply due to the grounds being connected.

If we put in a negative converter, (assume 9V not 5V as shown)



We can see the input supply is a +ve voltage with a -ve ground.   The output is negative voltage with a positive ground.   The ground is common even though the polarity of the ground changes from input to output.

Now if we power the PNP circuit with a -ve converter it can keep its positive ground and get the correct -ve supply rail.     The DC input has negative ground.  So when we daisychain the supply of a the NPN and the PNP circuit we no longer get the two grounds shorting out because the -ve converter flipped the ground polarity for the PNP circuit.

[Phend]

Looking at the circuit I posted,  one battery plus is connected to ground and the other battery negative is connected to ground.  All grounds are connected together.  So a short really hasn't been created yet since the other sides of the two batteries are not connected. Am I looking at this correctly?
Plus the term daisy chain, is it meaning connecting each pedals DC plug to a common power supply OR connecting the pedals inputs outputs together via a guitar cable?

[Rob Strand]

Looking at the circuit I posted,  one battery plus is connected to ground and the other battery negative is connected to ground.  All grounds are connected together.  So a short really hasn't been created yet since the other sides of the two batteries are not connected. Am I looking at this correctly?
Plus the term daisy chain, is it meaning connecting each pedals DC plug to a common power supply OR connecting the pedals inputs outputs together via a guitar cable?

As shown (on your schematic) there's no problem because each pedal has it's own supply/battery.

The problem only shows up when you try to do a DC jack version of each *and* use the same DC supply (ie. daisy chaining the DC using one wall-wart/PSU).

[pinkjimiphoton]

Looking at the circuit I posted,  one battery plus is connected to ground and the other battery negative is connected to ground.  All grounds are connected together.  So a short really hasn't been created yet since the other sides of the two batteries are not connected. Am I looking at this correctly?
Plus the term daisy chain, is it meaning connecting each pedals DC plug to a common power supply OR connecting the pedals inputs outputs together via a guitar cable?

you could think of that as 18v center tapped almost. ground is in the middle of the two voltage potentials... one positive, one negative.
usually you'll have some kinda filtering on each side, one going pos, one neg
the case is gonna still be at neutral.

[PRR]

.

[Phend]

^ make that a double like
Thank you PRR, Rob, Pink and the rest. Clear now.
This has been a topic many times I suppose.
The link below was a hard read
https://www.diystompboxes.com/smfforum/index.php?topic=88263.0