Troubleshooting Trouble - Tonebender Si Piggybacked

[Derringer]

I'm having trouble troubleshooting.

I'm trying to build a piggybacked silicon NPN tranistor version of a MKII Tonebender.
It's all bread-boarded right now.

Here's the schem I'm basing it on:

http://fuzzcentral.ssguitar.com/mkII/mindbenderschematic.gif

I started the whole project by selecting 2N222 NPN radio shack transistors and resistors to get hfe's of @70, 70, and 100 for Q1, Q2, and Q3, spots (respectively). These transistors all read between 240 and 270 hfe individually using my multimeter.
The package that these Q's came in was simply labeled "NPN-Type Switching Transistors" but they are labeled 2N222 A338.

When I piggybacked them, connected the bases, and ran a resistor (between 18K and 22K) between the emitters, I ran jumpers from the E C B to my meter. That's how I arrived at my piggybacked hfes.

I substituted a 10uF fuzz cap because I did not have another 4.7 uF.

Everything else matches up to the schematic.

My battery is putting out 9.4 V

The collector voltages for Q1, Q2, and Q3 are 6.14, 1.7, and 5.14 respectively.

This is only the third fuzz circuit I've attempted. My first was a PNP silicon FF and then an NPN Miss Piggy using the same batch of 2N222 NPN transistors. Those two builds were successful after some minor de-bugging. These were also just bread-boarded.

I tried something new to debug. I don't know if I'm doing it right though. I ran a mono tape cassette signal into the input and poked the output tip around to see where the signal stopped. The output was connected into some amplified speakers so that I could hear the signal.

I get the signal all the way up to the base of Q1 and its piggybacked transistor. When I connect the output lead to the collector of Q1 I just get what I'll describe as a lower volume popping/crackling sound. The popping/crackling may have been in time with the drum track of the cassette but it's hard to tell. I don't know if that means anything or not. But basically, there's signal going in and not coming out.

Please let me have your suggestions.

Thanks,

Bill

[R.G.]

I suggest you measure the rest of the pin voltages. See "What to do when it doesn't work".

That "measure all the pin voltages" is important, because if you only measure the ones you think matter, you're pre-limiting yourself to what you already think is wrong. If that was correct, it would already be fixed, right?

Measure the rest of the transistor pin voltages.

[Derringer]

Thank you RG

here they are:

the notation b references the piggy backed transistor (i.e. Q1 and its piggyback Q1b)

Everything in Volts unless otherwise noted

(Also realized I had also substituted a 5K fuzz pot for the 2K ... can't imagine that's the problem though)

Q1
E 0.2 mV
B 0.2 mV
C 9.4

Q1b
E 0.2mV
B 0.2 mV
C 315mV (this one jumped around a bit, down at @100mV and then climbed)


Q2
E 0.2 mV
B 0.57
C 1.7

Q2b
E 85.9 mV
B 0.57
C 125.5 mV


Q3
E  1.13
B 1.7
C 5.17

Q3b
E 1.17
B 1.7
C 1.18

[Derringer]

GOT IT !!!!

I searched the archives after reading the "What to do when it doesn't work" thread for silicon tonebender

I got one hit http://www.diystompboxes.com/smfforum/index.php?topic=62052.0

Mac posted about the bias for Q1 which I had no idea I needed to do!

just gave a quick test run through my little amp

I'm going to fine tune the bias resistors and run it through a big amp to see what's what

So far, I like it better than my other two builds ... but who the hell doesn't like their most recent build best of all anyway


Thanks RG !

[brett]

Hi
congrats on working through your problem.

Also, thanks for recording the voltages on the piggyback transistors.  I can't say that I've seen them before.
e.g.
Q2b
E 85.9 mV
B 0.57
C 125.5 mV

cheers