Sprout voltages

[Willybomb]

Gudday all, got a small prob. Of all the projects to try, this sprout I'm building in preparation for thurdays workshop is not working...

Project:  Sprout
Problem:  Bypasses fine.  Hit the switch and the LED lights up fine, but no sound.
Substitions:  BC548 and BC549 for Q1 and Q2 respectively.

Doesn't seem to be a solder bridge problem.  The offboard seems to be ok too.  Checked many times.

I've had a bit of a probe around with the DMM, and it seems that the voltages on one of the trannies is fine (?), all around 5v or so, but one is a bit low.  I'm not 100% certain I'm doing it right - one clipped to ground, and touching the solder pads of the tranny legs with the other.

Anyone know what the sprout should measure normally?  I'll stick a pic up later.

[RobA]

I built one on the breadboard and these are the voltages I get with a BC549C for Q1 and a BC550C for Q2 and a power supply voltage of 9.1V.
Q1
E    0
B    0.596
C    1.394

Q2
E    0.791
B    1.397
C    6.70

Changing transistors moves the voltages around a bit, but they are close to these values.

BTW, I had tons of noise (static, hiss, white noise) with the 220pF cap. Lowering it to 100pF helped a ton.
That could be partially due to my having it on the breadboard. But, it might help if you get too much noise.

[Willybomb]

Hmm... I retested after getting your reply.  Q1 looks pretty similar, Q2 is ~3v on all legs.

I'm not worried about noise, I have no output!!

[RobA]

That sounds very weird.  If I'm thinking about this the right way, Q2's base should essentially be at Q1's collector voltage. Q2's emitter should be a diode drop below that. That would then fix the voltage and current at Q2's collector. So, 3V on those would indicate some thing weird is going on. Check the continuity between Q1's collector and Q2's base to start.

I guess photo's would be good at this point too.

[Willybomb]

Will do.  In the meantime, I build another, and ...have the same result.  Hope I have the trannys in the right way.   Here's the pics.



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It's a bit annoying because I've already built one from this batch of boards that worked first go...  Used generic PN100 rannys in that one though.

[RobA]

... Hope I have the trannys in the right way.   
...

That's likely it. Your picture looks like they are in the same way as the layout diagram which looks like it's done to match the 2N3904 pinout. The BC548 and BC549 are exactly backwards to the 2N3904, 2N5088, etc.

[Willybomb]

And..... That was it.  Swapped them around, still didn't work, found a solder bridge, cleared that, and we had a whole lot of buzzy happyness.  Here's to a successful workshop tomorrow!

[RobA]

Great! I hope you have a fun workshop.