GE FuzzFace Debug

[Absentidei]

I'm building a germanium fuzz face using some pnp GE transistors I bougth on ebay from china.
When using the component values from the standard fuzz face schematic my biasing is way off.
This causes some gating and sputtering when I lower the volume on the guitar.

Here's the schematic I made:


Here's the layout:


I solder the fuzz pot capacitor directly to the fuzz pot.

My voltages:
Battery: 8.9v
q1:
b 0.07v
e 0
c 0.11v

q2:
b 0.11v
e 0.08v
c 7.63

All those voltages are made with the trimpot set to 10k.
When the trimpot is set to 0 I get 8.56v at q2 collector.

Could I just increase the value of my r3 untill I get closer to 4.5v on the collector on q2, or are there some other resistor values I have to change?

And here's the etching mask I used, if anyone is interested.

Print at 300 DPI.
I release the etching mask as public domain.

[LucifersTrip]

is there a reason you left out the fuzz control on Q2E?



you can adjust the voltage on Q2C with the 10K trimmer or by altering the 33K, which many also do.

you want to hit ~ 4.5V (many like it 5V or higher) close to the stock value (8.2K) or it probably won't sound great

[Solidhex]

Did you make sure to ground lug 1 of the fuzz pot?

[Absentidei]

I just used the schematic I made just to make the layout so I could etch the PCB.
I wired the fuzz pot offboard, and I soldered the bypass capacitor directly onto the pot.

I know I grounded the fuzz pot, becaouse the pot works. (Though, I soldered the capacitor on wrong, so the pot is at max fuzz when it's fully counter clockwise)

So what you're saying is that if I just increase the collector resistor on q2 untill I get closer to 5v it probably won't sound so good as if I replaced the 33k resistor.
Any suggestion as to what value I should try for a start?
Higher or lower?

[LucifersTrip]

So what you're saying is that if I just increase the collector resistor on q2 untill I get closer to 5v it probably won't sound so good as if I replaced the 33k resistor.
Any suggestion as to what value I should try for a start?
Higher or lower?

what I was saying is that you don't want to adjust q2 collector resistor too far from 8.2K. it should be kind of close to 8.2K. I think most try to keep it in the 4 - 15K range.  if you have to adjust it to 30- 40K, the sound prob won't be good. increase to lower voltage.
alternately, you can leave the 8.2K untouched and adjust the 33K instead.

but you also need to sort out q1 voltages. q1c is low, which in turn makes q2b too low and effects the whole sound/voltages...

...on the other forum, someone was cool enough to save all the voltages of good sounding ones that builders reported and then averaged them:

q1e: 0
q1b: 0.1     
q1c: 0.578   

q2e: 0.447
q2b: 0.578   
q2c: 4.51

[Absentidei]

Ok.
Thanks!

What resistors should I change to adjust the voltages of q1?
I'm understand how a simple voltage divider works, but when, as the case is here, there are more resistors that effect each other, I don't quite understand how it works.

[LucifersTrip]

What resistors should I change to adjust the voltages of q1?

the 33K...but you should first look for wiring/soldering errors and also try different q1's

i don't think you should have q1c = 0.11v if you have a "good" q1

[rousejeremy]

Double check your pinouts just in case.

[Absentidei]

I don't know what package the transistors have.
I think it's the same as the TO-1s in the upper left.

Though, if I had the pintouts wrong, wouldn't that mean that I wouldn't get any sound at all?
I'm going to visit my familiy on another part of the country now, so I won't have access the the circuit in question in a couple of weeks.
When I get home I'll try a bunch of different q1s, and try various values for the 33k resistor.

Thanks a bundle for the reply!
I'll report my experiences later.

[petemoore]

I don't know what package the transistors have.
I think it's the same as the TO-1s in the upper left.
  Socketted ?...Choose any transistor...that you are certain have the right polarity and data sheet shows the pinout..even if it sounds coarse, it will allow the debugging process some degree of certitude about transistor pinout, what the rest of the circuit does...on to the next thing...
  Though, if I had the pintouts wrong, wouldn't that mean that I wouldn't get any sound at all?
  There have been times that I've boosted a 'broken' FF and loved the sound, when they fire up you'll know [the two transistor feedback amp is high gain, but there are various bug-in-circuit conditions which allow sound through.
  I'm going to visit my familiy on another part of the country now, so I won't have access the the circuit in question in a couple of weeks.
When I get home I'll try a bunch of different q1s, and try various values for the 33k resistor.
  The GEO article of FF's of course is a best read, that said, I tried 10k - 110k at Q1 collector and noticed Q2 collector resistor value is what tends to make or break the bias arrangement.
  A trace, a 470k instead of 470ohm [did that one a couple times], pinout error..by process of elimination...
  A close-in light to inspect the board with magnifying glass, a DMM 'gone crazy' testing for 'trace overs', connections that shouldn't be, resistor values...polarity, anything else ?
  Clip a lead to ground, cross check that all ground markings are physically present and tested with DMM, then look for ground where it shouldn't be.

Thanks a bundle for the reply!
I'll report my experiences later.

[Absentidei]

Is there any way I can identify the correct pinout on my transistors?

Edit:
It seems my pinout was correct.
I replaced the 33k resistor with a 100k trimpot and with a bit of adjustment I managed to get the following values:


q1:
B: -0.1v
E: 0v
C: -0.58v

q2:
B -0.58v
E: -0.51v
C: -5v

The trimpots are set to 5.5k on q2, and with the 3k resistor in series, that's 8.5k on q2 emitter.
The one that replaces the 33k resistor measures 8.3k.
That seems a bit low. Would any other resistors around there interfere with that measurement?

I'm at my workshop now, and I didn't bother to bring my guitar, so I can't listen to how it sounds untill I get back home.