SOLVED Cobalt Drive problems…..SOLVED……..FINALLY!

Jeff C

Jeff C

Active member
New member here and also new to building pedals, as you will shortly see. I previously built a BYOC Reverb pedal kit successfully and it sounds great. I’ve also built from scratch a Strat, a Tele, a 59 LP, and an LP Junior. So, I wanted a blues driver pedal and thought I’d take a whack at the Cobalt Drive from PedalPCB. The directions are not as detailed as in a kit so I’ve had some difficulty. Clearly in over my head. I managed to procure the parts from the list (not without trial and error on my part) from Tayda. I mistakenly bought a switch without solder lugs so after consulting a patient, helpful friend, bought a daughter board and did my best to figure out how to marry the two - having no skills whatsoever in electronics. History major. I have managed to assemble it but I get nothing from it except static pops when I plug it in. Bypass doesn’t work. No idea what I’ve done wrong but I suspect it revolves around needing to do more with the daughter board on the switch. But what do I know? Here’s a couple of pics (the power jack is not there but I did connect it to test). And I haven’t installed the LED yet. Any and all suggestions are eagerly welcomed. You may recomemd I should just start over but I hope not….. Thank you!
855EE297-D464-47F8-880D-F0D8B9C40E15.jpeg 15E06C0D-93DB-4AE9-944D-BA1BED3416FB.jpeg
 
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Well, it’s been an interesting chapter in my saga today. (I was going to call this pedal the Blooz Ooze (long story) when I finally get it working, but given it has become my great white whale, I may call it Moby Lick 😜). Because the volume is so low, I decided to put the audio probe on every single point on the schematic. I get audio at varying levels everywhere except r3, d2 and d4. That said I had to be careful because when the probe got close to some components it would pick up sound w/o touching anything!) Audio is very loud on all the pots. Q1 and 3 have pretty good audio. Q5 source pin sounds very low. R5 is low. Q6 has audio only on gate pin. Both sides of c6 are good and loud. R13 is loud but static-y. D5 and D6 are low. After that, things get pretty static-y and low on most of the points. On the IC, I get a louder signal on pin 5, and very low response elsewhere (except nada on 4 and 8 of course). But it was here where I would most often get the low signal without touching anything. And c20 was low too. For what it’s worth, the pedal sounded pretty good through my tube amp. Gain and tone pots working well but just had to turn the guitar volume up to 11 (well, 10). I don’t want to reflow ALL my joints - suggestions on where to start first?
 
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Jeff C said:
Well, it’s been an interesting chapter in my saga today. (I was going to call this pedal the Blooz Ooze (long story) when I finally get it working, but given it has become my great white whale, I may call it Moby Lick 😜). Because the volume is so low, I decided to put the audio probe on every single point on the schematic. I get audio at varying levels everywhere except r3, d2 and d4. That said I had to be careful because when the probe got close to some components it would pick up sound w/o touching anything!) Audio is very loud on all the pots. Q1 and 3 have pretty good audio. Q5 source pin sounds very low. R5 is low. Q6 has audio only on gate pin. Both sides of c6 are good and loud. R13 is loud but static-y. D5 and D6 are low. After that, things get pretty static-y and low on most of the points. On the IC, I get a louder signal on pin 5, and very low response elsewhere (except nada on 4 and 8 of course). But it was here where I would most often get the low signal without touching anything. And c20 was low too. For what it’s worth, the pedal sounded pretty good through my tube amp. Gain and tone pots working well but just had to turn the guitar volume up to 11 (well, 10). I don’t want to reflow ALL my joints - suggestions on where to start first?
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Pin 5 is marked as NC (not connected?) on the data sheet so I’m not sure why you are getting loud signal there. How’s the volume at pin 6 and 3? That’s where it should be loudest I think. Can you tell us exactly which pot pins are loudest?
 
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Well, I used the PIN numbers per Buddy’s post above (#295), but I’ve noticed some variations in PIN numbers. I’ll check again tomorrow………. And all the pot pins seem the same volume…Loud.
 
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Jeff C said:
Well, I used the PIN numbers per Buddy’s post above (#295), but I’ve noticed some variations in PIN numbers. I’ll check again tomorrow………. And all the pot pins seem the same volume…Loud.
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All pot pins at the same volume seems suspicious. You should get no signal at pin 1 of the volume pot, maximum volume at pin 3. Pin 2 will depend on the position on the pot. Are you getting the same amount of volume from all three?
 
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R3 should have audio on the non grounded side Q5 and 6 are BJTs pins are C B E collector, base middle and emitter with the arrow

Q5 and 6 should have audio on base and collector pins

You will hear differences depending on whether it's going through an amplification stage (louder) or a tone stage (more bass or treble) as @giovanni says depending on the relevant pot position

My advice is when you come to a component that has lower than expected audio reflow the solder joints as you come to it
 
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Mcknib said:
R3 should have audio on the non grounded side Q5 and 6 are BJTs pins are C B E base middle emitter with the arrow, arrow pointing in is PNP (Points in Permanently 2N3906) and pointing out NPN (Never Points in 2N3904)

Q5 and 6 should have audio on base and collector pins

You will hear differences depending on whether it's going through an amplification stage (louder) or a tone stage (more bass or treble) as @giovanni says depending on the relevant pot position

If you read the circuit analysis I posted back in the 80s I think coulda been the 90s I'm not sure you'll be able to identify stages

Here's the link to save you going back to the 80s and those ridiculous mullets we thought looked cool at the time

Circuit Analysis : the Boss BD2 - Analog Is Not Dead

Blogs about analog electronics still exist in 2021. Here is one about how you can hack your toaster into a guitar amplifier and modify your shower into a modular synth.
www.analogisnotdead.com www.analogisnotdead.com

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My advice is when you come to a component that has lower than expected audio reflow the solder joints as you come to it
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R2 has audio on BOTH sides. Q5 and t get good, loud audio on base and collector pins. Louder on collector.
 
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giovanni said:
All pot pins at the same volume seems suspicious. You should get no signal at pin 1 of the volume pot, maximum volume at pin 3. Pin 2 will depend on the position on the pot. Are you getting the same amount of volume from all three?
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I am definitely getting signal at volume pot pin 1. Pin 2 and 3 also, but as you say volume is louder at pin 3. Tone and gain pots deliver similar volume signal on all 3 pins, except gain pot has no signal on pin 1 (well, it has that faint signal that comes when I put my probe pin near anything on the PCB).
 
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giovanni said:
Pin 5 is marked as NC (not connected?) on the data sheet so I’m not sure why you are getting loud signal there. How’s the volume at pin 6 and 3? That’s where it should be loudest I think. Can you tell us exactly which pot pins are loudest?
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Good volume on pin 1 (null), 2 (input), 3 (input), 4 (vol - ) and 5 (null!). nada on 6, 7 and 8. I know that’s weird. By far the loudest volume is on the pot pins. I also discovered that the Harry Homeowner who owned our house before us back in the 80’s did a lousy job on the basement workshop wiring because pretty much any light you turn on, especially fluorescents, causes buzz in the amp, making hearing what I need to hear correctly difficult. Moving back to the ‘music room’ upstairs……..
giovanni said:
Do you get audio at any end of R101 and R102?
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I get nada from either on both. I get audio from r13 and 15, though.
 
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Jeff C said:
Good volume on pin 1 (null), 2 (input), 3 (input), 4 (vol - ) and 5 (null!). nada on 6, 7 and 8. I know that’s weird. By far the loudest volume is on the pot pins. I also discovered that the Harry Homeowner who owned our house before us back in the 80’s did a lousy job on the basement workshop wiring because pretty much any light you turn on, especially fluorescents, causes buzz in the amp, making hearing what I need to hear correctly difficult. Moving back to the ‘music room’ upstairs……..

I get nada from either on both. I get audio from r13 and 15, though.
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If you get audio on R2 but not 101/102, that means there is something going on between the power divider (101/102) and R2 (they share a node). Maybe a short somewhere around there. Do you have the opamp installed correctly? I haven’t noticed the orientation in the pics.
 
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giovanni said:
If you get audio on R2 but not 101/102, that means there is something going on between the power divider (101/102) and R2 (they share a node). Maybe a short somewhere around there. Do you have the opamp installed correctly? I haven’t noticed the orientation in the pics.
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Yes, I have the op amp in correctly (although should have used a socket……). I get good audio from the top pin of r2. Nada from the bottom one. But volume output on the pins now varies from before. Volume on 5 and 3, but low. And I’ve lost overall output now. Only getting it with the probe. And on q3, only audio on source, nada on drain or gate. also, Q2 and 4 are quiet. Q5 audio on source and gate, but not drain. Q6 audio on gate only. Nada on Q7.
 
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Jeff C said:
Yes, I have the op amp in correctly (although should have used a socket……). I get good audio from the top pin of r2. Nada from the bottom one. But volume output on the pins now varies from before. Volume on 5 and 3, but low. And I’ve lost overall output now. Only getting it with the probe. And on q3, only audio on source, nada on drain or gate. also, Q2 and 4 are quiet. Q5 audio on source and gate, but not drain. Q6 audio on gate only. Nada on Q7.
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Ok that’s how it’s supposed to be. I thought you said you got audio on both sides of R2. I wonder why the state of the pedal seems to constantly changing. Is there anything loose or maybe intermittent contacts here and there? This makes debugging really hard because every time you take a measurement we seem to get something different.
 
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