MXR Phase 90 not phasing

[JRB]

After my last failure on the phase 90 with my own layout on perfboard I decided to follow a existing one from General Guitar Gadgets. Problem is its not producing any phasing sound. I have looked at the signal with a scope as well and I can see it phase shift it just doesn't modulate even tough the LFO also seems to be working. The strange ting I noticed was as soon as I put the FETs in the sockets the voltage on the Gate gets pulled to the same voltage as the Source.

Here is the data:
Circuit:
MXR Phase 90 using the layout from General Guitar Gadgets.

Link:
http://www.generalguitargadgets.com/projects/23-phase-shifters/311-mxr-phase-90-script-logo

Modifications:
Changed the opamps to more locally available ones and what I had laying around.

Problem:
Passes signal but doesn't phase at any point on the resistor (suspect something with the FET's)

Voltages:
Supply
9,5V

IC1 TL081
1 0.2V
2 3.83V
3 2.59V
4 0V
5 0.2V
6 3.83V
7 9.5V
8 0V

IC2 TL071
1 0.15V
2 3.83V
3 3.75V
4 0V
5 0.15V
6 3.83V
7 9.5V
8 0V

IC3 TL071
1 0.15V
2 3.83V
3 3.75V
4 0V
5 0.15V
6 3.82V
7 9.5V
8 0V

IC4 TL071
1 0.15V
2 3.83V
3 3.75V
4 0V
5 0.15V
6 3.83V
7 9.5V
8 0V

IC5 TL071
1 0.19V
2 3.83V
3 3.75V
4 0V
5 0.19V
6 3.83V
7 9.5V
8 0V

IC6 TL061
1 0V
2 3.5V-4.6V
3 2.8V-4.1V
4 0V
5 0V
6 1.1V-6.6V
7 9.5V
8 0V

Q1-Q4 2N5952
G 2V-2,2V with out FETs in the sockets. 3,83V with FETs in sockets
S 3,83V
D 3,75V

Q5 2N4125
C 2,1V
B 3,2V
E 3,8V

If anyone has any suggestions I would be thank full.

[R.G.]

I have looked at the signal with a scope as well and I can see it phase shift it just doesn't modulate even tough the LFO also seems to be working.

So you can see the signal moving back and forth in time with respect to the input signal? If you trigger on the input signal and watch both input and the signal at the end of the fourth phasing opamp, it moves back and forth? Is that right?

The strange ting I noticed was as soon as I put the FETs in the sockets the voltage on the Gate gets pulled to the same voltage as the Source.

That could be a measurement error. It depends on the voltmeter impedance. Could also be a circuit flaw.

With respect to the schematic you mention, look for signal at the non-base ends of both R24 and R27. What do y ou see?

[JRB]

I have looked at the signal with a scope as well and I can see it phase shift it just doesn't modulate even tough the LFO also seems to be working.

So you can see the signal moving back and forth in time with respect to the input signal? If you trigger on the input signal and watch both input and the signal at the end of the fourth phasing opamp, it moves back and forth? Is that right?

When triggering on the input signal I see the input signal, then on the 4e opamp I see the input signal shifted 180 degrees it doesn't change overtime. This is basicly what I was getting with my own layout except that then the amplitude of the phase shifted signal was changing overtime.

With respect to the schematic you mention, look for signal at the non-base ends of both R24 and R27. What do y ou see?

Ill have a look at that when I get back home.

[JRB]

I had a look at the mixing resistors R24 R27 and they are the same as the input signal.
I also had another look at 4e phasing opamp and I gues I need my memory checked out.
On its output it has the input signal it was the 3e opamp and the 1e opamp that had the 180 degrees of phase shift on the output.

The other ting I noticed was different from my last attempt is the signal on the base of the transistor. with my previous attempt it was a flat dc line, now its a flat DC line with the top of the input signal showing on the positive side of reference at roughly 0.5V above the dc line.

[Seljer]

Double check the pinout of your JFETs

Q1-Q4 2N5952
G 2V-2,2V with out FETs in the sockets. 3,83V with FETs in sockets

Thats the part that seems iffy to me. The base voltage should be moving around with the LFO, when it is its just a matter of setting the trimmer right to get the phasing.

[JRB]

Just tried switching them around nothing changed.
I am starting to suspect the fets being broken but I tried a different set in them already that had the same thing.

[Seljer]

Try adding them in one at a time and observing the voltages (specifically the gate voltage)

[JRB]

Well the weird ting is after I posted last time I put them back around and suddenly by magic I can see a voltage moving and when I move the trim pot it changes the level of the voltage. Still no phasing doh not even when I move the trim pot.
But hey its progress.

EDIT: I forgot to mention between what voltages I can get it to move.
0.4V-0.6V on lowest pot setting
2.1V-2.3V on highest pot setting

[Andr3as]

Have you tried different zeners? That did the trick on mine... Only thing bugging me now is a ticking noise with the 22k resistor switched in.. No probs with 100k nor NC.

[JRB]

Gues Ill have to order some then used the last on on this ting Any suggestions on value's?

[Andr3as]

Try everything from 3-6V, It's a PIA to wait any longer than needed... trus me 

[JRB]

Well the zener diodes finally arrived yesterday and to my disappointment they didn't fix the problem. I am starting to suspect the FET's, so does anyone have any suggestions on how to test them to see if they still work?

EDIT:

I just tested the matched FET's I bought with the FET matcher from R.G. and they read -1,58V  to -1,60V for Ugs. So the fets seem to be working fine.

[JRB]

I just finished testing if changing R25 could possibly fix it by increasing the voltage sweep of the LFO but all this does is make the LFO leak into the audio path so that's probably not the solution.

I am really starting to get desperate cause the lack of sweep was the only thing I could think of that would be the cause of the problem.

[R.G.]

I am really starting to get desperate

At the risk of being pedantic, that one thing will keep you from seeing the problem, even if it's staring you in the face.

At this point, if it were me, I'd:
1. Take out Q1 JFET temporarily.
2. Sub in a 100K pot for Q1, hooking up one end contact and the wiper, leaving one end contact open. Actually, it would be better to use a dual pot and sub one section for each of Q1 and Q2; this will make phase shifts more visible.
3. Apply a 1kHz test sine wave to the input. Put probes on Pin 7, IC1 and Pin 6, IC2. Trigger on the input signal at IC1, pin 7.
4. Increase the level of the test signal until you notice distortion on IC1, pin 7, or until you get to 1V peak.
5. If you noticed distortion at 1V peak on the input, you have a problem with the input amplifier.
6. Turn the pot shaft back and forth. The signal at IC2, pin 6 should show a phase shift which changes at some rotations of the pot. If it does not, there is a connection/circuit error in IC2 (and/or IC3 if you did the two-section pot thing).

Mother Nature is very deterministic. She insists you follow Her Rules strictly; but if you do, She makes it work every time.

[JRB]

I'll have a look at that next weekend when I get back from my dorm.

Thanks R.G. and desperate was probably a to big of a word more like clueless on how to continue cause I exhausted all the debugging techniques I learned at school.

[R.G.]

It's sometimes hard to suppress the frustration. I found that formal schooling is often just the intro. It gives you the tools and facts, and - sometimes subversively - lets you teach yourself to learn on your own if you can. Hang in there. Many, many of these have been made to work. It's probably something so trivial or obvious that you *can't* see it.

I've been doing PCBs for over 40 years in one form or another. I've learned that I always - always - need someone else to look at it for the things I can't see because they're too simple.

[JRB]

Well it took a week longer then i expected but I made the measurements and its clipping big time.

So I measured for any wrong connections etc. the only ting I noticed was that when measuring between pin 2 and 3 of IC1 the resistance starts at 500k and keeps counting up until it go's out of the display resolution instead of just going there immediately.

[JRB]

Well I managed to get ride of the clipping by just resoldering the whole input opamp and the 5.1V zener that decided to fall out of its socket. so far still no phase shift but atleast one problem was fixed.

[Rebel_88]

Hi all, I know it is a lot of time that this post is not followed but i found an answer to this problem and so i decided to write.
On General Guitar Gadget we can find instructions to build the effect https://www.generalguitargadgets.com/pdf/ggg_p90_instruct.pdf but there are some mistakes.
The first is the use of the 5.1V Zener, this could not allow to get 5V on some pin so if we don't find 5-5.5 V on Q1,Q2,Q3,Q4 Source we should change this to a 4.7 or 5.6V Zener, for me the 5.6V worked.
The second is the biasing of the matched Q1,Q2,Q3,Q4, on the Instructions is written that it should be at 2.5V, this is not the same for all circuits, I have found that for mine the biasing should be around 3-3.7V because I have a Source voltage of 5.5V on these transistor.
So If the pcb is correct you have to bias correctly Q1,Q2,Q3,Q4.
I have created a PDF  that you could download from here http://sdvpedali.altervista.org/DIY/polarizzazione.pdf where i wrote all my voltage changing the zener. Red columns are not working effect and the green one is the correct. At first i followed the Instructions and so i biased Q1,Q2,Q3,Q4 at 2.5V and i have all voltage value in the file, but my phaser didn't work. So i changed the biasing at 3,2V ( but it was phasing between 3 and 3.7V with different sound for each voltage) and now it is working.
I hope my experience could help someone.
Bye.

[stuznu]

Hi,
I am interested in the adjustments made to solve your phaser problem. I tried downloading the pdf document you posted but the link is  no longer available.
Thanks