Help me understand my PNP positive ground Big Muff PI

[3/4 North]

I built his last year and it's left me puzzled, it only works if the transistors are in backwards.

I used this schematic


which shows the emitter (the side with the arrow, right?) the same side as a NPN muff.
I used N4022's from smallbear and checked the pinouts with a transistor tester.

here are the measurements

like-schematic---------backwards
Q1
E 8.64------------------2.01
B 8.01------------------8.07
C 4.62------------------8.65

Q2
E 8.58-------------------8.33 (?)
B 7.92-------------------7.94
C 8.55-------------------8.58

Q3
E 8.64------------------2.64
B 8.01------------------8.07
C 4.79------------------8.65

Q4
E 7.71------------------1.31
B 6.67------------------7.60
C 4.10------------------8.32

So..
Could the PNP ever be biased the way it's shown in the schematic?
Isn't the PNP big Muff just a 4 stage buffer?
What am I missing or reading wrong?

[R.G.]

I think you have either your power supply wiring or your ground for reading voltages mixed up.

All voltages with respect to ground should read negative.

[3/4 North]

I'll check it again tonight, it was confussing but I was as careful as possible.

[mac]

you should read something like this (red to gnd, +9v; black to C, B & E) if hfe=500 and vbe=0.6v, your transistor may have different hfe:

Q1& Q3
vc=-3.8v
vb=-0.62v
ve=-0.22v

Q2
vc=-4.0v
vb=-0.64v
ve=-0.4v

Q4
vc=-3.8v
vb=-1.8v
ve=-1.2v

Q2 in yours seems not ok. The rest seems to be ok. you need to add +9v to compare with your values.

mac

[3/4 North]

You're right, I was hooking the VMM up wrong - putting black to negative and probing with the red.

The problem is around Q2 - I added the 82k resistor from base to ground (the byoc board omitted this) and it looks like I connected it to the +V trace instead of (positive)ground

I never could keep right / left straight in my mind - guess the same is true for positive / negative

I'll fix that and see if it runs with the transistors in the right way

[3/4 North]

It's fixed now, that was the problem.

It actually didn't sound too bad the other way - I just coundn't understand why it would only work with the transistors in backwards.


It sounds much better now, I can even run it with PNP germaniums which I couldn't before - but the 4402's sound smoother.

[mac]

Have you heard a pnp Germanium version? 

mac

[3/4 North]

It was okay, I used nameless tin can germaniums from small bear - the silicon 4402's just sounded smoother. Probably need to bias the germaniums different to get them to run better.

[mac]

Yes you need re biasing.
If you have for example a typical Ge having hfe near 100 leaking 100uA then you can try:
Rc=10k; Re=0.1k; Rfeedback=560k; Rbasetognd=47K
This resistors will set Vc around 4V.
Also the 8.2k between stages, 10k in another schems, can be lowered because of the lower gain Ge. Normally this resistor has more impact in the sound than the bias resistors.
The 8.2k is 10x lower than the 82k from base to gnd, so to keep proportions I'll try 4.7k in this case. I'm not a tech but I guess that this mod will shunt the same amount of signal to gnd.

It's hard to tweak but it worth the try. A nice addition to the Si version if you like Ge fuzz. It is not better just different.

mac