Fuzz Face voltages, please explain?

[half_smith]

how does Q1C have a voltage <1v when it is being fed right off the power rail with only a 33k in between?

Thanks for the help!

[FiveseveN]

You're forgetting what's in between the collector and ground.



If R1 is 33K, R2 is ~2.8K, V_in is your 9V, then what is V_out?

[antonis]

I think OP is confused due to positive GND circuit..

Q1 Collector actually sits 8.3V HIGHER than -9V (what you call "power rail")

That voltage difference divided by 33k calls for a Collector current of about 250μA (conventional current flow fron GND to -9V) and a V_EC of 700mV..

[Vivek]

This article might help to understand transistor bias

https://www.electronics-tutorials.ws/amplifier/transistor-biasing.html

Basically you have -9V at the top rail and 0 on the ground

There is a collector resistor and a voltage drop Vce Collector to emitter in between these rails

There is -8.7V drop across the collector resistor

Hence there is -0.7V across the Collector to Emitter.

Since Emitter is at ground, Collector is at -0.7V


All adds up properly. -8.3V drop and -0.7V drop = -9Volts.

[PRR]

how does Q1C have a voltage <1v when it is being fed right off the power rail with only a 33k in between?

Because Q1 sucks.

[antonis]

Because Q1 sucks.

[half_smith]

another quick one

in this MAX1044 voltage inverter module, is the 9+ from the DC Jack supposed to connect to the "+" on the board that runs to pins 1,8 of the MAX1044? as is there's nothing going to those pins...

Is that 2n3906 loop a buffer?

[antonis]

https://datasheets.maximintegrated.com/en/ds/ICL7660-MAX1044.pdf

@half_smith: Sorry but we can't handle multiple threads simultaneously..
https://www.diystompboxes.com/smfforum/index.php?topic=129334.0

[half_smith]

thanks Antonis, I cross-referenced some other bipolar charge pumps and MAX1044 datasheets, turns out there's a trace from 2n3906 C to the +9V rail (MAX1044 p1,8)
-it was occluded on the above pic by text



I am pretty unclear what that does, buffer I guess?
I had a 1044 pop on me earlier today and so I'm looking at GGG style for more, um, safety.

[antonis]

I am pretty unclear what that does, buffer I guess?

Can't be sure without a schematic but I suspect (mainly by purple jumper between E & C) it's a current series pass transistor..

[half_smith]

Anyway, I'm taking your advice and building out the PNP with positive GND (gonna actually use a battery!)
-I've run out of leads from my board's PSU anyway

[antonis]

I'm taking your advice and building out the PNP with positive GND

It's not MY advice..
It's YOUR choice..!!

[half_smith]

"Don't get me wrong but I'd suggest to start building a Si n-p-n Fuzz Face, then pass to Si p-n-p one, then pass to Ge p-n-p one and THEN pass to Ge p-n-p with bipolar supply.." -Antonis

I agree with your suggestion and choose to follow

[half_smith]

Hey guys, just back with an update.

Took me a few days to make sense of the "positive GND" stuff. I'm dyslexic as is, so trying to think backwards made me nuts.

Anyway, I got it straightened out. Very fuzzy. I put the "Bias" and "Contour" pots on the board so the pedal only has has the two original knobs but I can easily tweak it.

I had my first chance to use it as an outdoor gig and when it got hit by the sun it went out of bias, I kinda enjoyed that knowing what was happening...

*bonus, my transistor tester came in and I was able to get a great combo of Q1 hfe 80, Q2 140, and it's really nice fuzzy stuff.

thanks for the backup!

[antonis]

when it got hit by the sun it went out of bias,

Next project will be a light/temp bias servo..