Sola Sound Tone Bender MKII

[Plexi]

Hi forum!

It start to sound only when I push with my fingers over transistor 1.
I'm not 100% sure...but I think its on the Base and ground.
It start to sound slowly...like some cap or something 'charging'.

NPN, used 2N4401 hfe around 100.
Every cap is in correct orientation.

Everything checked 10 times...maybe a simple bug?
I spent a few hours trying to figure out which/where is the problem.
I used the pcb layout from Effects Layout blog.

Sorry, I'm using tapatalk...asap I'm in home, I'll post schematic.

[Plexi]

[newfish]

I had one of these on my breadboard the other week - ideally, the 1st transistor needs to be Ge (AC176 for example) - maybe look at changing the 10k Collector value?

[smallbearelec]

If you measure the voltages at C B and E of Q1, you will probably find that the transistor is completely cut off. The circuit depends on the normal leakage current of a germanium device to bias the first stage into conduction, and silicon doesn't leak. If you don't have an NPN germanium device to try there, connect a 4.7 meg or 2.2 meg resistor from B to C and see if that gets the output going. I'm presuming that everything else is wired correctly.

[Cozybuilder]

The schematic you posted uses PNP transistors, +9V goes to ground. You mentioned using NPN transistors 2N4401, silicon, not Germanium. If thats the case, then your battery needs to be reversed so that 0V goes to ground. The electro caps will also have to be reversed. And as Steve said, you need to bias the transistor base due to essentially no leakage.

[Gus]

Have you seen this?
http://www.diystompboxes.com/smfforum/index.php?topic=114210.msg1059856#msg1059856

[Plexi]

Thanks to everyone..! As always.
It's running now...strangely, but running.
DAMN...! I love this forum 

I had one of these on my breadboard the other week - ideally, the 1st transistor needs to be Ge (AC176 for example) - maybe look at changing the 10k Collector value?

Sure, I thought that some transistor with hfe ~100 will work.
I'll place a trimpot where the 10k res is.

If you measure the voltages at C B and E of Q1, you will probably find that the transistor is completely cut off. The circuit depends on the normal leakage current of a germanium device to bias the first stage into conduction, and silicon doesn't leak. If you don't have an NPN germanium device to try there, connect a 4.7 meg or 2.2 meg resistor from B to C and see if that gets the output going. I'm presuming that everything else is wired correctly.

Thanks! I placed a 4M7 resistor, and didn't work. With 2M2 sounds very very low, so a 1M work.
It's exactly what my finger was doing there...
Sound's very very saturated and boosted mids.

The schematic you posted uses PNP transistors, +9V goes to ground. You mentioned using NPN transistors 2N4401, silicon, not Germanium. If thats the case, then your battery needs to be reversed so that 0V goes to ground. The electro caps will also have to be reversed. And as Steve said, you need to bias the transistor base due to essentially no leakage.

Sure! All the electro caps and transistors was oriented correctly to NPN.

Have you seen this?
http://www.diystompboxes.com/smfforum/index.php?topic=114210.msg1059856#msg1059856

Thanks! Doing it now.

I'll check the 10k resistor to C.

[Plexi]

Ok guys... after some time reading and trying some values to bias.. I think that change this to NPN and silicon will be to create another different beast.
A lot of adds, and modifications...maybe will be easier to start with a new board.

I'll flip the caps, and put 2SB54's in the sockets.

Thanks guys!

UPDATE
Now it doesn't sound...or sound very low and clean.
All transistors are 2SB54, + ground and all caps oriented to.

[Electric Warrior]

Got some voltages? I figure these are probably low leakage with medium to high gain. It shouldn't be all that far off unless you made a mistake somewhere..

[Plexi]

Got some voltages? I figure these are probably low leakage with medium to high gain. It shouldn't be all that far off unless you made a mistake somewhere..

Sure!

Q1
Vc 9.01v

Q2
Vc 8.85v

Q3
Vc 0.69v

Pinout: http://www.semicon-data.com/transistor/tc/2sb/2SB54.html

I forgot to say, that this old japanese guys are measuring ~170 hfe.. could be this the problem?


P.S .: yes .. I used google to search (here and another forums), and there's TONS of info, voltages, mods, etc, etc, etc. of about thousand of transistors...
It seems that's this design have a delicate balance between voltage, hfe, germanium and mojo (¿).

[Electric Warrior]

No, that's not the problem. Q1 seems to bias alright. You messed up somewhere after that. Q2c is way too high - not just misbiased, something is way off here. The collector should measure around 0.15V. That should put Q3c in the right ballpark as well.

[Plexi]

Doubled checked every component..replaced a few ones (just in case).
Nothing happen... should I see some voltage change, but still not sound:
Q1 Vc 8.72
Q2 Vc 0.26
Q3 Vc 7.75

[Electric Warrior]

You fixed it - at least the part that caused the funny voltages. It should be working now. Bet it's something really obvious - like swapping in and outputs.

[Plexi]

I hope you're right... I tried everything there: replace caps, test resistors, omit out volume pot...
I'll keep searching...

[Electric Warrior]

The circuit iteself seems to be working. You probably need to trace the signal going in and out of the circuit to find the problem

[Plexi]

Verified everything again.
Everything correct.

BUT:invert Q1 (C to + ground), and work. Ugly and gated fuzz.

What is going on here?

[Electric Warrior]

  ... interesting. Have you tried swapping transistors in and out? Maybe you picked a set that manages to completely gate the signal out. That would be rather unusual, though...

[Plexi]

I swapped between all the 2SB54 that I have (10).
No idea... checked ALL (traces, cable, pots, voltage, solder, etc) several times... only works very bad with Q1 backward.
And this thing burned out one LM7809.
Why? I don't know....

I surrender...

[Plexi]

Diode and 47uf cap omited.
Volume pot omited.
Electro caps oriented to + ground.

[Electric Warrior]

I can't find any mistake in your layout..