Beatle Juice Q3 issues

[ac30irons]

I’ve posted this in general but am not sure how to delete the post so I can put it here.

Oh where do I start !!! I’ve build several of these without hiccup, really easy build - until this one. The pedal was exhibiting a super low volume and then nothing. I ran my probe and all was good until till the output of Q3. I figured that it must of been a dud transistor. I cut the bugger off and tacked on the underside of the board and hey presto - it did what that pedal is supposed to do. Roll forward a few days and it’s exhibiting the very same issue again, all good until Q3 gets involved and messes it all up.

Is it possible something is killing Q3 ? I’m really tempted to run a jumper from the base of Q3 to R14 to bypass the bastard all together but I would sooner work out the gremlin.

Any advise would be really appreciated.

 

[ac30irons]

 

[Nostradoomus]

can you take some pics with better lighting? those 3.3k resistors look like two grey bands instead of orange

take it outta the enclosure and show the back too

 

[ac30irons]

can you take some pics with better lighting? those 3.3k resistors look like two grey bands instead of orange

take it outta the enclosure and show the back too

Thanks. Will whip it out tonight when I get home from work and post some more pics.

 

[ac30irons]

can you take some pics with better lighting? those 3.3k resistors look like two grey bands instead of orange

take it outta the enclosure and show the back too

@Nostradoomus

Are these pics any better. 3.3k are decently 3.3k. I’ve just done the voltages and interestingly the emitter was 8v and the base and collector around 3.6. Q1 and 2 are half these. The base of Q3 shot right up and then settled at 3.6 ???

 

[ac30irons]

And then I realised this … C1 + C4 are in each others spaces !!! It’s obvious I’m no expert but I’m thinking that’s my issue right there !!!

 

[Feral Feline]

Thanks. Will whip it out tonight when I get home from work and post some more pics.

Not necessary, keep it in your pants.


Glad you got the circuit problem sorted.

You can get a box-film 2µ2 for C1 and it'll have better sound and longevity than the electrolytic — too bad the foot-print doesn't reflect the box-film but the box's legs can be bent to the 'lytic-spacing.


Mark it solved, once you've checked the cap swap was indeed the problem!

 

[ac30irons]

Not necessary, keep it in your pants.


Glad you got the circuit problem sorted.

You can get a box-film 2µ2 for C1 and it'll have better sound and longevity than the electrolytic — too bad the foot-print doesn't reflect the box-film but the box's legs can be bent to the 'lytic-spacing.


Mark it solved, once you've checked the cap swap was indeed the problem!

Thanks dude, think I have some 2u2 boxes. I hate de- soldering

 

[juice886]

And then I realised this … C1 + C4 are in each others spaces !!! It’s obvious I’m no expert but I’m thinking that’s my issue right there !!!

Most likely it's not a reason for the issues you have. Make sure Q3 is not touching IC pins, that is not clear from the photo you posted. Also check Q3 pinout and connectivity between components around Q3. Q3 should have around 8-9V at the collector obviously.

 

[ac30irons]

Most likely it's not a reason for the issues you have. Make sure Q3 is not touching IC pins, that is not clear from the photo you posted. Also check Q3 pinout and connectivity between components around Q3. Q3 should have around 8-9V at the collector obviously.

So as it happens - it did not fix it !!! I reflowed everything and double checked but same problem. I’ve bypassed Q3 now and it sound fine !!! Bloody frustrating .

 

[juice886]

So as it happens - it did not fix it !!! I reflowed everything and double checked but same problem. I’ve bypassed Q3 now and it sound fine !!! Bloody frustrating .

Q3 is a buffer, not engaged in distortion.

 

[andrewsrea]

Did you measure the values of the resistors which make up the Vref for Q3? R11, R12 & R13? Additionally the polarity and solder connection of C9?

If Vref is too strong or weak, Q3 becomes an 'on-off' switch. Vref should be close to 50% of Vcc.

 

[ac30irons]

Q3 is a buffer, not engaged in distortion.

Thanks dude - it looks like this now bufferless

 

[ac30irons]

Did you measure the values of the resistors which make up the Vref for Q3? R11, R12 & R13? Additionally the polarity and solder connection of C9?

If Vref is too strong or weak, Q3 becomes an 'on-off' switch. Vref should be close to 50% of Vcc.

Hey dude, I’ve litterely checked everything I know how to check. I did not know Q3 was a buffer and can certainly live without it. I wondered why it sounded mostly the bloody same

 

[Robert]

Is the back of your tone pot insulated?

 

[ac30irons]

Is the back of your tone pot insulated?

Nope - just a bare old pot, it’s not touching the board though

 

[andrewsrea]

Hey dude, I’ve litterely checked everything I know how to check. I did not know Q3 was a buffer and can certainly live without it. I wondered why it sounded mostly the bloody same

Q3 buffers Q2 from being influenced by the impedance of the output circuit. It could (or might not) have an effect on the tone or reaction of the fuzz generated in Q2.

If you like the result, you didn't need it.