Centaur Klon Squealing & low output

[fenderguy81]

This is a Klon clone that uses 2 TL072 and 1 7660s. The pedal was working fine without issues until it just started acting up the other day. It passes signal with the switch bypassed fine. With the switch engaged, the volume drops to a faint sound and there's a loud high pitched squealing noise. I opened it up and checked around for any obvious issues, but didn't see anything. I reflowed some solder joints, chopsticked around, and also made sure all ICs were secure when I felt the 7660s and capacitors around it were getting pretty hot. Would this be from one the of eCaps failing, a failing diode/zenor diode failing IC, or? Any help would be greatly appreciated! Thanks!

[MikeA]

All the 7660 does is generate +18 and -9V for IC2 (the second op amp in the signal chain), so you've narrowed it down, as you say, to those two components and the related caps, diodes and traces.  I'd check the supply voltage into the 7660 on pin 8 (+9V), the voltage out on pin 5 (-9V or slightly lower), and the voltage into IC2 on pins 4 (-9V) and 8 (+18V.)  That should give you a clue.

[fenderguy81]

Thank you! I just checked the voltages you mentioned as well as the other pins And got the following:

IC1 TL702
1: 7v     
2: 7v
3: 6.4v
4: 0v
5: 9.42v
6: 8.84v
7: 7.20v
8: 7.20v

IC2 TL702
1: 7.97v
2: 7.18v
3: 7.11v
4: 3.0v
5: 8.06v
6: 8.11v
7: 7.30v
8: 7.26v

IC3 7660
1: 9.38
2: 5.75v
3: 0v
4: 2.44v
5: 9.39v
6: 7.78v
7: 4.36v
8: 2.89v

I haven't had a chance to look into it much more, but I'll definitely try to get back to the bench later today. Obviously pin 4 on IC2 and pin 8 on IC3 are low. Any guesses as to what could be causing this? Thanks!

[italianguy63]

Known good voltages:

Measurements taken with a regulated bench supply set at 9 volts using a Fluke model 87V meter with fresh calibration

IC1 - TL072

1 = 4.49
2 = 4.49
3 = 3.54 stable, 3.95 initial
4 = 0
5 = 4.49
6 = 4.49
7 = 4.49
8 = 9


IC2 - TL072

1 = 4.55
2 = 4.49
3 = 4.49
4 = -8.59
5 = 4.49
6 = 4.49
7 = 4.44
8 = 16.23

IC3 - ICL7660SCPA or TC1044SCPA

1 = 9
2 = 4.59
3 = 0
4 = -4.22
5 = -8.59
6 = 4.09
7 = 5.59
8 = 9

MC

[fenderguy81]

Thanks italianguy63 for the readings on a known working pedal! I'm still a beginner when it comes to this stuff, but I've been using an audio probe with a signal generator to trace the pedal to try to find the problem. To clarify, the high squeal sounds like an ambulance siren that starts high pitched and lowers as the pedal warms up. With the audio probe, I found that the signal is good up until the first potentiometer. The signal comes in fine at lug 3 and is quiet/distorted on lug 1 even with the pot all the way up. The 390p capacitor from pin 6 to pin 7 of the IC2 TL072 had a clear loud signal on the first part of the capacitor and a weak distorted sound on the other side of the cap. I tried cleaning the pot and will need to test the cap out of circuit, but I'm thinking the problem is most likely around the IC2.

[MikeA]

fenderguy81, I wonder if you're counting the IC pins the same way we are?  The pin numbers run counterclockwise, see https://aronnelson.com/diywiki/index.php/Frequently_Asked_Questions_(DIY_FAQ)#OP_AMP .

Also, if any of your pin voltages read negative rather than positive, that's relevant.  Pin 5 of IC3 and pin 4 of IC2 should read the same negative voltage (around -8 to -9V) if all is well, see italianguy63's list.

[DJPsychic]

I also just completed my first Klon build. For whatever reason the 7660 always caused a high pitched sound. I used a MAX1044 like others have suggested, and that solved the issue

[italianguy63]

I also just completed my first Klon build. For whatever reason the 7660 always caused a high pitched sound. I used a MAX1044 like others have suggested, and that solved the issue

Need to use a 7660S

[DJPsychic]

Need to use a 7660S

I've read lots of people having to use 1044 because the 7660S causes the high pitched squeal.

Curious why is 7660S required?

[idy]

the important is the "S". 7660S, or 7660SCPA. The "suffix." Makes a difference...

[italianguy63]

Need to use a 7660S

I've read lots of people having to use 1044 because the 7660S causes the high pitched squeal.

Curious why is 7660S required?

It operates at a higher frequency... too high for your ear to hear.

[bluebunny]

It operates at a higher frequency... too high for your ear to hear.

...if pins 1 and 8 are shorted together. 

[italianguy63]

It operates at a higher frequency... too high for your ear to hear.

...if pins 1 and 8 are shorted together. 

Correcto... had to look at my notes.  The "Boost" column infers that.. need to connect pin 1 and 8!

I'll post this again.  Seems charge pump questions/issues always arise!

MC

[DJPsychic]

I actually found some on the jungle site  and you were right, no noise issues. The "S" is indeed crucial.