It isn't my circuit, it's a commercial build that I'm attempting to troubleshoot. When I built my own clone of the original circuit, I had a similar issue and thought I could help out my friend, but it was not the same issue. My clone also uses the 7660 and functions properly.

Have you checked the junction I mentioned to see if the (almost) doubled voltage is there? You mentioned looking for it at pin 8, and you definitely won't find it there.

If you don't find doubled voltage at the junction where it should be, tell us what voltage you do measure there. If you're using the 1uF caps shown in the schematic instead of the 10uF recommended in the datasheet, that could easily be the problem.

I also wonder (but honestly don't know) if there's any potential for trouble connecting pin 1 to the supply voltage, when it's labeled as NC. I would guess that the pin wouldn't connect to anything internally and so the connection would be harmless, but maybe it does connect to something internally and actually needs to be left floating? If that were the case, cutting the trace to that pin might be worth a shot. You want to do some much better and more thorough troubleshooting before jumping straight to that though. First see what voltage you're actually getting and upgrade the caps if they need it.

 

Have you checked the junction I mentioned to see if the (almost) doubled voltage is there? You mentioned looking for it at pin 8, and you definitely won't find it there.

If you don't find doubled voltage at the junction where it should be, tell us what voltage you do measure there. If you're using the 1uF caps shown in the schematic instead of the 10uF recommended in the datasheet, that could easily be the problem.

I also wonder (but honestly don't know) if there's any potential for trouble connecting pin 1 to the supply voltage, when it's labeled as NC. I would guess that the pin wouldn't connect to anything internally and so the connection would be harmless, but maybe it does connect to something internally and actually needs to be left floating? If that were the case, cutting the trace to that pin might be worth a shot. You want to do some much better and more thorough troubleshooting before jumping straight to that though. First see what voltage you're actually getting and upgrade the caps if they need it.

Been traveling a bunch for work, finally got to take another look at this tonight.
At the junction you mentioned, I get 8.86V to ground. I'm curious though about the mention of 10uF caps; the label on the PCB calls out 1uF, as does the schemo and the clone that I put together, so I don't believe that value is a mistake. Would there be harm in replacing them with the larger value to see if that helps?

 

Since it's been awhile, what chip are you actually using?
EDIT: That's right you substituted the 7660 for the MAX1044. I see where the confusion is about pin #8. You should be getting 16 volts on pin 8 of IC2 only but will need to change all the caps to 10uf.
SG

 

Are you measuring the voltages unloaded or with the op amp (IC2) connected? Could be the op amp you are trying to power with this is defective and drawing too much current.

 

Since it's been awhile, what chip are you actually using?
EDIT: That's right you substituted the 7660 for the MAX1044. I see where the confusion is about pin #8. You should be getting 16 volts on pin 8 of IC2 only but will need to change all the caps to 10uf.
SG

Thanks! Hadn't occurred to me pin 8 was referring to IC2. That makes perfect sense.

 

Been traveling a bunch for work, finally got to take another look at this tonight.
At the junction you mentioned, I get 8.86V to ground. I'm curious though about the mention of 10uF caps; the label on the PCB calls out 1uF, as does the schemo and the clone that I put together, so I don't believe that value is a mistake. Would there be harm in replacing them with the larger value to see if that helps?

The 1uF value was based on using the MAX chip. The 7660 isn't identical.

The MAX chip has a feature which allows it to switch at higher frequencies, which means less risk of noise in the audio frequency bands and it also means you can use much smaller caps. In the supplied schematic, that feature is enabled, thus the smaller caps. Since you're not using that chip, you'd have to use larger caps, as described in the 7660 datasheet.

Assuming the larger caps get you the voltages you're looking for (which I believe they should,) that still leaves you with greater risk of audible power supply noise than you would've had with the MAX chip. Still, one problem at a time...

If you're willing to replace the 7660 with the MAX chip called out in the schematic, it *might* solve all your problems. If you don't want to try that, I think you should try the 10uF caps.

 

It isn't my circuit, it's a commercial build that I'm attempting to troubleshoot. When I built my own clone of the original circuit, I had a similar issue and thought I could help out my friend, but it was not the same issue. My clone also uses the 7660 and functions properly.

I forgot about this post where you mentioned another clone that worked with the 7660. So, in that one that works, are you using 10uF or 1uF caps? How about pin 1 on the 7660 - is it left floating like the datasheet recommends, or is it connected to VCC like in the MAX-chip schematic you shared here. Maybe similarities and differences in the implementations can be used to help troubleshoot.

 

Are you measuring the voltages unloaded or with the op amp (IC2) connected? Could be the op amp you are trying to power with this is defective and drawing too much current.

With the second opamp connected. I tried swapping out the TL072 with one from my own collection, that didn't help either. The 7660 was used in my clone, also with 1uF caps and it works great.
As for if pin 1 was left floating, I'll need to take a closer look at the trace and get back to you.
Thanks again for all your input.

 

Haven't heard anything in a while, just wanted to confirm that the trace on pin 1 doesn't appear to connect to anything as best as I can tell.
Thanks.

 

I don't understand your unwillingness to try 10uF caps. Datasheets give recommended values for a reason. You might be able to make things work with other values in some situations, but anytime something isn't working, step 1 should be checking datasheets and related app notes. The datasheet for the chip you're using (not the chip in the schematic) recommends 10uF caps. Why not try them?

As for having another circuit elsewhere which uses the 7660 with only 1uF caps, maybe you just got lucky. Maybe other parts of the circuit draw less current. Maybe there's some other reason it works there and not here. Who knows?

Anyway, it doesn't seem like we're seeing any obvious flaw in the overall circuit, except that you're using a different chip than specified and then using the wrong sized caps for that chip... so please, either try the MAX1044 with the current caps, or try the bigger caps that are recommended for the 7660.

*** EDIT: Sorry, that came out sounding a little mean and judgy. I don't mean it that way. I stand by the opinions, but apologize if the tone was harsh.

 

I don't understand your unwillingness to try 10uF caps. Datasheets give recommended values for a reason. You might be able to make things work with other values in some situations, but anytime something isn't working, step 1 should be checking datasheets and related app notes. The datasheet for the chip you're using (not the chip in the schematic) recommends 10uF caps. Why not try them?

As for having another circuit elsewhere which uses the 7660 with only 1uF caps, maybe you just got lucky. Maybe other parts of the circuit draw less current. Maybe there's some other reason it works there and not here. Who knows?

Anyway, it doesn't seem like we're seeing any obvious flaw in the overall circuit, except that you're using a different chip than specified and then using the wrong sized caps for that chip... so please, either try the MAX1044 with the current caps, or try the bigger caps that are recommended for the 7660.

*** EDIT: Sorry, that came out sounding a little mean and judgy. I don't mean it that way. I stand by the opinions, but apologize if the tone was harsh.

Well, as I said, this is a commercial build I'm trying to troubleshoot, not a kit or homebrew. It uses 1uF caps and a 7660. However, the kit that I built that is a similar circuit (both are Klon derivatives) also uses a 1uF and a 7660. Other Klon clones also seem to use the 1uF and a 7660, so I'm not sure that's the issue. The schemo that I posted is just what I had handy, and it implies the Max and 7660 can be interchanged without issue.
I don't friggin' know at this point. I thought I had 18V differential at the right points at first, but since I unmounted the complete pedal from the enclosure can't get that. All the grounds are good, but either I goofed in making my readings or there's something else going on, and that's what I'm hoping to nail down. I'm pretty frustrated with it at this point.

 

Well, as I said, this is a commercial build I'm trying to troubleshoot, not a kit or homebrew. It uses 1uF caps and a 7660. However, the kit that I built that is a similar circuit (both are Klon derivatives) also uses a 1uF and a 7660. Other Klon clones also seem to use the 1uF and a 7660, so I'm not sure that's the issue. The schemo that I posted is just what I had handy, and it implies the Max and 7660 can be interchanged without issue.
I don't friggin' know at this point. I thought I had 18V differential at the right points at first, but since I unmounted the complete pedal from the enclosure can't get that. All the grounds are good, but either I goofed in making my readings or there's something else going on, and that's what I'm hoping to nail down. I'm pretty frustrated with it at this point.

I can certainly understand your frustration.

Do you have an oscilloscope? Poking around with one might help. The have been a number of times when poking around with an oscilloscope revealed problems that I wasn't even looking for, but which turned out to be the underlying problem.

The most recent case was actually on a 7660 circuit. The op amp it was powering was behaving oddly, so I was trying to get a better look at the op amp's signal inputs and outputs, but when I looked at the the supply pins I found the real problem - I had somehow completely skipped the 7660 output capacitor, so instead of putting out -5VDC, it was putting out a really ugly oscillation. The funny thing is that my DMM read around -4V on that signal... I knew that seemed a little off, but not so much that I thought it was the problem. Seeing it on the scope suddenly made it obvious where my problem was.

Anyway, the point of that story wasn't that I think you've skipped a cap or anything dumb like I had done, but that scoping things can be very revealing and point you in the right direction. If you haven't already tried it, might be worth trying a scope. No advice on what to look for - just look at everything and take note of anything unexpected. Might find some useful clues.

 

There are capacitors and then there are capacitors.

1 µF is already far below the recommended value. If those capacitors have degraded, which is common with electrolytic types, the whole thing may have reached the point where there is simply no hope of proper performance. If the capacitors are ceramic of a certain type, they can drop in capacitance not due to wearout but to changes in the actual ceramic itself. If they are solid tantalum, "wearout" is unlikely.

Normally degradation in conventional aluminum electrolytics results primarily from ripple current through them and hence is a function of actually being in operation. However aluminum caps can degrade over time due to "drying out" - loss of solvent from the electrolyte because of imperfect sealing. They can also be "poisoned" by use of chlorinated solvents for PCB cleaning; some are "solvent proof", some are not.

If I had a problem like this the very first thing I would suspect would be the capacitors.