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!
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Ok. 9v+ to the diode pin (diode is no longer there as I clipped it out…..), put the bridge in place of the missing diode. Now get 9v to C100 and about 5+v to C20. (Took me FOREVER to remove the - wire from the PCB. De-soldering cord worked pretty well on the + pad but neither it nor the solder sucker worked well at all on the - pad. Eventually got it out, though.). IC stays cool, not heating up too hot to the touch as previously. Enough for tonight. I need a glass of wine or two or three and to play my guitar loud.
 
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BuddytheReow said:
The big issue we are dealing with right now is power. That is first and foremost since the circuit won't work without power.

Secondly, those wires going to the footswitch are unclear if they are crossing since the fabric on them is blocking our view. Confirm that the metal within them are not touching.

Third, those yellow capacitors look like tantalums to me. This means that they are polarized like the electrolytic ones and need to be installed in a certain direction. This should be addressed once we get the power issue straightened out. The circuit will sound different if those yellow ones are installed backwards and we have no way of knowing which way they were installed based on the pic.

For the record @Jeff C I admire your persistence on this troubleshooting thread. 250+ threads and 3 weeks of this and it still isn't working. If I were in your shoes I would have pulled the rest of my hair out already with the amount of hours put in this and still no dice. Nothing is more frustrating than a non-working build. I don't want to discourage you from the building process so may I make a suggestion and think about your next project/build and start that up? You have already learned a lot so far in this thread and it will carry over in the next project. I'm saying this because putting something aside for a while may actually help in the long run instead of soldering/desoldering parts and potentially damaging your board. A lot of the peeps here are very knowledgeable and are helping you through this process.

In short, start a new build (potentially a less complicated circuit), take your time and focus on neatness. It will be nice to rack up a win in your book when finished and give you more confidence to go back to this project.
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Tks, Buddy. Now that I’ve found my stupid reverse voltage mistake, I think I’ll continue. I’m retired (twice!) so I have the time. I don’t work on it constantly so it’s really been kind of fun despite all the frustrations. And of course I do REALLY appreciate all the help from EVERYONE, particularly given the amateur nature of my many mistakes……
 
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Jeff C said:
Ok. 9v+ to the diode pin (diode is no longer there as I clipped it out…..), put the bridge in place of the missing diode. Now get 9v to C100 and about 5+v to C20. (Took me FOREVER to remove the - wire from the PCB. De-soldering cord worked pretty well on the + pad but neither it nor the solder sucker worked well at all on the - pad. Eventually got it out, though.). IC stays cool, not heating up too hot to the touch as previously. Enough for tonight. I need a glass of wine or two or three and to play my guitar loud.
Click to expand...
Enjoy the wine, you deserve it, Rock hard !
 
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Mcknib said:
I agree it was a saga but you learn a lot from your mistakes and keep passing it on

People like yourself @giovanni @zgrav @BuddytheReow @carlinb17 and many more keep this place one of the best forums passing on your knowledge and staying with it

Jeff's now armed with how to use a probe and lots of other debugging knowledge for future builds thanks to everyone's efforts

Who's gonna look and see if Jeff's set a record for the longest debug.......

Anyone?
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So not sure my knowledge is extensive enough to help anyone, but more sets of eyes sure helps….

Now, because you asked, I obliged:

Search criterias:
32019052-9E75-4AA0-9955-5688505C8A49.jpeg

Results:

29E46B70-4C22-45C4-84CC-8DC5B4402A0F.jpeg

So @Jeff C with 287 replies win by a landslide, unless somebody manage to post a longer thread without using the word pedal !
 
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EGRENIER said:
So not sure my knowledge is extensive enough to help anyone, but more sets of eyes sure helps….

Now, because you asked, I obliged:

Search criterias:
View attachment 26679

Results:

View attachment 26680

So @Jeff C with 287 replies win by a landslide, unless somebody manage to post a longer thread without using the word pedal !
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Yes, I got a “trophy” from PedalPCB when I hit 100 posts. 😂 Maybe they’ll send me a D100 diode as a prize…….
 
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O here’s my ‘power’ status now, referring to the power section of the schematic: 100% to the D100 pin (no actual diode there; a temporary bridge wire connects its pins); 100% to C100; 50% to C101; 100% to R101; 0% to R102; 0% to R100; the IC pins all get varying degrees of power (my measurements could be flawed given the tight space to work in); #1 gets 2.5v; 2 gets 0; 3 gets 5; 4 gets 9; 5 gets 5; 6 gets 5; 7 gets 2.5; and 8 gets 5. Is there a problem there? The IC did get very warm during that ‘testing’ but not too hot to the touch like it did when I had the power reversed.

Audio probe: a little good news there, but the pedal itself doesn’t send any audio to the amp except on bypass. With power on, I’m getting audio to gate AND Source on Q1, but not drain. But no audio to the other Q’s. R6, R2, C1 all get audio. Nothing else.
 
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Your IC voltages are off. Pin 4 should be 0 since it connects to ground and pin 7 should be close to 9v. You can see in the schematic how I figured that out. R101 and R102 work together to form a voltage divider. About 4.5v should be going to VREF

Edit: It may be worth your while to remove the IC and install a socket. With the IC removed you should check the voltages on the corresponding pads.
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BuddytheReow said:
Your IC voltages are off. Pin 4 should be 0 since it connects to ground and pin 7 should be close to 9v. You can see in the schematic how I figured that out. R101 and R102 work together to form a voltage divider. About 4.5v should be going to VREF

Edit: It may be worth your while to remove the IC and install a socket. With the IC removed you should check the voltages on the corresponding pads.
View attachment 26716
View attachment 26718
Click to expand...
Ok, I’ll give it a try…….
 
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Jeff C said:
Ok, I’ll give it a try…….
Click to expand...
DO you have an extra tl071 lying around in case this one gets damaged while removing? Sockets are your friend when it comes to opamps. My experience with sockets is that if you don't think you'll need one you'll probably have to desolder something to swap a component out and vice versa.
 
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Jeff C said:
Ok, I’ll give it a try…….
Click to expand...
Ok, moved the dang pot further out of the way to get better access. I have 0 at pins 4 and 8. 9v at 7. All tracking with you. Pins 2,3 and 6 have 5v. 1 has 2v and 5 has 3v. I do have another IC071 (TL 071CP) and now have some sockets. But if it is now tracking ok, I’d rather avoid the surgery………
 
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In drain, source, gate order: Q1: 8.6, 4.3, 4.5; Q2: 8.6; 4.8; 4.2; Q3: 9.3; 9.3; 9.2; Q4: 9.3; 4.8; 5.0; Q5: 9.3; 8.0; 9.3; Q6: 9.2; 8.5; 5.0; and Q7: 3.1; 3.8; 9.2. Takes me a little while to get a solid reading on each, bit I think those are accurate.
 
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Jeff C said:
In drain, source, gate order: Q1: 8.6, 4.3, 4.5; Q2: 8.6; 4.8; 4.2; Q3: 9.3; 9.3; 9.2; Q4: 9.3; 4.8; 5.0; Q5: 9.3; 8.0; 9.3; Q6: 9.2; 8.5; 5.0; and Q7: 3.1; 3.8; 9.2. Takes me a little while to get a solid reading on each, bit I think those are accurate.
Click to expand...
I haven’t analyzed this circuit but anything much higher than 4.5V on the drain of any of Q1-Q2 is probably bad news. Those are all common source so the drain is typically biased around 4.5V. If you see 9.3V that means you are at the power rail value so there is no way to get signal through. I’m not entirely sure what could be causing the problem. Let me take a look at the circuit.
 
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