Phase 100 - Problem - Please rescue Me!!!!!

[ilcaccillo]

Hi,
I've built a Phase 100 pedal, everything works fine except 2 of the modes produce an ugly distortion. The other modes are fine.

I replaced all the Tl072 with new ones but the problem persists.

I recorded a sound file to show the problem. Please have a listen since I need some help here to figure out what to do.

You can Download/listen to the file here:

http://www.upload-mp3.com/pfiles/52423/Phase%20100%20-%20problem.mp3

http://twin-x.com/groupdiy/displayimage.php?pos=-2956



Picture corresponding the Modes to the Sound Clips recorded

[ilcaccillo]

The Board and project are from GGG.

No modifications were made to the circuit, I respected all the components in the GGG BOM.


Schematic

http://www.generalguitargadgets.com/pdf/ggg_p100_sc.pdf

BOM

http://www.generalguitargadgets.com/pdf/ggg_p100_bom.pdf


Layout and Wiring Diagram

http://www.generalguitargadgets.com/pdf/ggg_p100_lo.pdf

[oskar]

Hi!

R1 is either cut out or switched in by the intensity switch so that could be a good place to start. It could be shorted, open or wrong value. Maybe you can tweek the value of it. R1 is providing feedback so I really would expect the filter to oscillate rather than distort if it would somehow missbehave...   
I don't think it's anything on the LFO side.

[ilcaccillo]

Thanks Oskar,
I will check R1, to see if something is wrong there.

I already checked the pcb traces and solders joints for shorts severeal time.
Everything seemed in place.

Do you have any idea of why does the distortion only occurs in Positions 2 and 4 ?
whats different in those 2 positions that could cause the distortion to occur there and not in the other 2?

[oskar]

I don't understand how the switch symbol works on the schematic but on one side you have a feedback resistor that is either in or out and on the other side you have an LFO and I don't think they should mix... So you get two different feedback settings and two different modulation depths. I would definitely try and figure out how to swap the intensity switch for two pots instead.   
Step through the switch and measure it with the DVM. Then draw up an equivalent circuit so you see for sure how the signal is routed through it.

[ilcaccillo]

thanks.

I will do some measurements over the weekend,
also tracing the circuit with and audio probe might be helpful.

Get back to you as soon as I have more info.

[ilcaccillo]

Everything seems fine with R1,
clean solder joints. An I double checked the value and is 15K, so it's correct.

Gonna check the other feedback resistors now.

[ilcaccillo]

Checked all the feedback resistors from R20 to R30.

Al solders are good, there's no shorts. All the Values for those resistors are correct.

[ilcaccillo]

Replaced all the TL072 IC's today with LM1458.

Although the clipping is less pronounced than with the TL072, it's still there.
So the problem is not from the IC's or IC type.

[lowell]

Anything ever come of this?  I'm having the same exact problem.  I've replaced all the ICs, transistors, and LFOs. 

[ilcaccillo]

Hi Lowell,
unfortunately I have nothing new to say. No one ever helped me also, so I gave up and I only use the 2 modes that are fine.

it seems that this project was put into GGG without being completelly verified, and a lot of people are having the same problems.

JD from GGG told me he was investigating this, but he never got back to me.

What I can say to you is that TL072 are not for this circuit, first thing is to change to LM1458.

if you have any more info in the meantime please tell me.

[Ummagumma]

Hi guys,

I think I've solved the problem I've got that sexy phasing.

Although I've swaped all of TL072-s for sockets and then tried NE5532(noise??), LM358(ok), 4558 (no phase?) at the end I've got them back because they give clear, no distorted phasing. And the real SOLUTION was to change 20k trim to 500k which is now around a half. R1 is 20-22k. Also I've used BC550 tranies and VTL5C3/2.

cheers