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Hi Guys,
Trying to figure out what’s going on. It’s weird- I built this schematic on perfboard (feeling confident after the expert tutelage I received on this forum following my Apollo Trem build issue involving a defective TL072) and it worked great. I had the PCB from you guys already so figured I’d go ahead and build another. Having issues with the PCB build though!
Pertinent information:
- Traced the audio path and it’s fine up until it Q1. The base gets the audio signal but it goes no further. I get no audio from the collector. I have swapped the transistor to and getting the same result.
- Checked continuity, reflowed solder in suspect areas.
- Voltage readings seem off from the references give for the v3 build. These are my readings:
- Q1 E = 1.8V, B = 0 V, C = 0 V
- Q2 E = 1.2V, B= 1.8V, C= 1.1V
- LED turns on, 9.24V measured at the source. Also tried using a battery measuring 8.88V FWIW
- Audio signal fine in bypass mode
Any ideas? Thanks, fellas!!!
-Ted
With no voltage / current on the base of Q1 the transistor won’t conduct, so no signal will flow through it
Can’t see your DC jack wiring properly are you actually getting 9. 24v on the pcb not sure what you mean by source have you taken your reading on the pcb 9v and ground pads
If that’s the case and you are getting power to the pcb I’d begin by checking the components around the transistors R3 and 4 etc
Your transistors could obviously be faulty depending on where you got them I can see you’re now using sockets for Q1 but if they were soldered in intially like Q2 they may have been damaged
Are both transistors 2N3904
Hi Billy,
I’ll trace the voltage shortly, but as I recall the voltage was getting to the board OK.
Both transistors are 2N3904. Q1 is a fresh transistor- tested in another circuit with a breadboard. I had originally soldered another 2N3904 in there but removed it and replaced with sockets while troubleshooting.
I’ll check all of the other questions and get back with results. Thanks again for the help.
Here are some photos that better show the DC Jack wiring…
Barry,
Voltage from battery is 9.00V up until R3.
The leg of R3 closest to power source is 9.00V, it drops to 1.76V on the downstream leg.
The leg of R4 closest to power source is 9.00V, it drops to 1.13V on the downstream leg.
edited*
Are you definitely taking your readings with your meter set to DC voltage
R3 and 4 as far as I can see look correct R3 looks like a 47K so not far off 51K but I can’t make out if the last band is red or orange obviously it should be orange for 47K, R4 is 22K from what I can see
Double check your ground connections sometimes with strange voltages it’s simply a poor ground connection especially with your reading on Q1 emitter which is connected to ground or you’ve simply mixed up your Transistor CBE with your initial readings which is easy to do
Definitely not getting 4.5V on the collectors. I think you were right about my mixing up CBE on the first reading.
Latest readings (SURE I got CBE right this time) are:
Q1 C = 1.71 V, B = 0, E = 0
Q2 C = 1.06, B = 1.71, E= 1.08V
Confirmed measuring DC voltage.
I’m getting continuity with ground everywhere it looks like we should have continuity per the schematic, but maybe I’ll reflow all the ground pads just in case.
Definitely not getting 4.5V on the collectors. I think you were right about my mixing up CBE on the first reading.
Latest readings (SURE I got CBE right this time) are:
Q1 C = 1.71 V, B = 0, E = 0
Q2 C = 1.06, B = 1.71, E= 1.08V
Confirmed measuring DC voltage.
Also on the resistors you are correct, I subbed a 47K for the 51K so that one is a bit lower. Also checked the 22K and verified its code. I usually multimeter test each resistor right before I put it on the board just to be safe so likely those are correct.
We’re getting continuity with ground everywhere it looks like we should have continuity per the schematic, but maybe I’ll reflow all the ground pads just in case?
Reflowed the whole PCB. Same. Going to replace R3 and then if the same will replace R4 just for the heck of it.
If I fried Q2 would that effect my voltages on Q1?
Ignore what I said regarding collector voltages
The correct voltages as you said at the start are in the V3 build doc
Q1 Emitter: 0V, Base 0,58V, Collector 1,2V
Q2 Emitter: 0,88V, Base 1,2V, Collector 2,3VSo back to the base of Q1 not getting anything there’s not a lot of components prior to it and if you get signal up to the base that indicates they are ok looking on my PC the solder joints at Q1 do look dry I don’t know whether you took the image after changing to a socket if the transistor was tested ok on your breadboard we can rule that out so I’d reflow those joints again
Q1 base needs current to operate and that would have a knock on effect check that non of the socket holes have continuity sometimes solder can pool underneath the socket where you can’t see it and cause a bridge
May have found the culprit. I haven’t had the chance to play it through an amp yet, but voltages now reading about right after replacing C2. Old C2 read +/- 10n after I took it off the board, but figured I’d replace it just to be safe. I also replaced R2 and R3, but the voltages didn’t look right until I swapped C2. Fingers crossed and will keep you posted…
Makes sense Ted could have been shorting straight to ground taking the signal with it albeit highly unusual like everything it’s still possible
Actually that may not have been it- I think it was the B500K Pinch pot. It was a brand new Alpha B500K pot, but somehow I think it was shorting out. I checked my wiring and nothing visible was touching that shouldn’t have been, but as I moved the pot it occasionally gave me audio again (infrequently). I removed it and replaced with another one to test and it works- fuzz!
I sprayed some DeOxit in the old pot and now it seems fine. Weird as it wasn’t scratchy or anything. I wonder if somehow I had damaged it or something when soldering initially, but I’ve honestly soldered quite a few pots and never had that happen. I dunno.
Maybe it was a combination of all of the above- I dunno but somehow the pedal gods smiled upon us..
For now all good!
Really appreciate the guidance- thank you!
Great Ted
Glad you got it going
P1’s in the feedback loop so could have cut off current to Q1’s base at a certain rotation
I’ve had several Alpha A100K and 500s fail on me over the last few months around 4 or 5 usually in nice simple circuits like fuzz faces and as per usual no problems in the complex circuits it had me scratching my head
When I checked the resistance across them and at either end, perfect readings most of the time then eventually they would go to infinate at one end but not all of them
Those would cut audio out when I moved them whilst testing the circuit absolute nightmare! don’t know how many times I desoldered, resoldered and checked them and everytime I wiggled a pot wire it’d cut out
I’m sure my neighbours thought I’d lost it the amount of expletives they must have heard
Circuit rage haha
HA! I wonder if that is it- I must have a bad batch, too. Maybe that wasn’t it, but it sure sounds like the same thing!
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