GGG Phase 90 not working right

[kerryandray]

Hi, all.  Happy quarantine, LOL!  Feeling thankful to have a pedal problem to occupy my time and mind 

In any case, some background...

I am not a total noob...I have successfully built a few pedals already including the GGG Mutron clone and GGG Phase 90 (which I love). I have also built several tube amps from scratch (working on a Vox AC30 right now). 

But...I admit I'm no electrical engineer.  When troubleshooting issues, I have usually been lucky enough to find an answer on the pedal (or amp) building forums to figure out how to get something working without a total understanding of the circuit.

However, this Phase 90 is not working right and I am at a loss given my not understanding the circuit well enough.  I already read a few relevant threads:

https://www.diystompboxes.com/smfforum/index.php?topic=98606.msg862327#msg862327

https://www.diystompboxes.com/smfforum/index.php?topic=111862.msg1030520#msg1030520

https://www.diystompboxes.com/smfforum/index.php?topic=102618.msg910471#msg910471


Here's what I know:

1. When I swing the trimmer control back and forth, I do get a spot where it "phases" (in that is makes a filter-y sound).  When I leave the trimmer in that spot, the sound stays static (i.e. doesn't swirl).  If I crank the speed knob back and forth, it "phases".  If I could just pay someone to twist the speed knob at the right pace, I think I'd be in business, LOL.

2.  I did temporarily changeout the 5.1 Zener (D2) for a 5.6 Zener.  It didn't seem to make it work, so I changed it back and then took voltages (see below).  I also replaced the other diode in the circuit just to make sure I hadn't accidentally put the Zener in the D1 spot and the 1n914 in the D2 spot.  So those are installed correctly.

3.  I have built this into a travel guitar I'm making that also has a GGG ITS8 circuit board (wired as a Boss SD1) and a DIY stripboard version of the Danelectro Honeytone amp in it.  I am running everything off a set of 6 AA batteries wired to be a 9v battery (I use rechargeables).  I noticed the voltage was pretty low (7.82v), so I also hooked it up to a 9v wall wart (which was putting out 9.42v).  Same behavior as before.

So...here are my readings.  Any ideas on what to do next?  Thanks in advance for any help/advice folks can offer 

Component   Pin      7.82v      9.43v
IC1               1         0.00         0.00
IC1               2         4.97         5.06
IC1               3         4.74         4.83
IC1               4         0.00         0.00
IC1               5         0.00         0.00
IC1               6         4.96         5.06
IC1               7         7.82         9.42
IC1               8         0.00         0.00
IC2               1         0.00         0.00
IC2               2         4.99         5.07
IC2               3         4.99         5.07
IC2               4         0.00         0.00
IC2               5         0.00         0.00
IC2               6         5.01         5.09
IC2               7         7.82         9.42
IC2               8         0.00         0.00
IC3               1         0.00         0.00
IC3               2         4.99         5.07
IC3               3         4.99         5.07
IC3               4         0.00         0.00
IC3               5         0.00         0.00
IC3               6         4.98         5.06
IC3               7         7.82         9.42
IC3               8         0.00         0.00
IC4               1         0.00         0.00
IC4               2         4.99         5.07
IC4               3         4.99         5.07
IC4               4         0.00         0.00
IC4               5         0.00         0.00
IC4               6         5.01         5.09
IC4               7         7.82         9.42
IC4               8         0.00         0.00
IC5               1         0.00         0.00
IC5               2         4.99         5.07
IC5               3         4.99         5.07
IC5               4         0.00         0.00
IC5               5         0.00         0.00
IC5               6         5.00         5.06
IC5               7         7.82         9.42
IC5               8         0.00         0.00
IC6               1         0.00         0.00
IC6               2         2.19         1.86
IC6               3         5.45         5.89
IC6               4         0.00         0.00
IC6               5         0.00         0.00
IC6               6         7.16         8.76
IC6               7         7.81         9.42
IC6               8         0.00         0.00
Q1               D         4.99         5.07
Q1               S         4.99         5.08
Q1               G         2.39         2.42
Q2               D         4.99         5.07
Q2               S         4.99         5.08
Q2               G         2.39         2.42
Q3               D         4.99         5.07
Q3               S         4.99         5.08
Q3               G         2.39         2.42
Q4               D         4.99         5.07
Q4               S         4.99         5.08
Q4               G         2.39         2.42
Q5               E         4.98         5.08
Q5               B         4.40         4.49
Q5               C         3.22         3.31

[Govmnt_Lacky]

First and foremost.... I am assuming this is a P90 circuit with (6) Dual op amps (4558s, TL062s, etc.)

If this is the case...... you have NO power (Vcc) going to ANY of the dual op amps. Pin 8 of all 6 of the op amps should be reading around +9VDC. All of yours read 0V

Double check that you are reading and posting the voltages correctly. Here is a pin chart for the dual op amps:



You could also link or post a schematic/layout that you are building from.....

[kerryandray]

First and foremost.... I am assuming this is a P90 circuit with (6) Dual op amps (4558s, TL062s, etc.)

If this is the case...... you have NO power (Vcc) going to ANY of the dual op amps. Pin 8 of all 6 of the op amps should be reading around +9VDC. All of yours read 0V

Double check that you are reading and posting the voltages correctly.

OK, will do.  I'll open it up later today and double check.  But I am 99% sure those are correct.  I'll post again when I've verified.  But I am going to look upstream of pin 8 on the schematic and see what's going on.  Thanks!

You could also link or post a schematic/layout that you are building from.....

I am using the General Guitar Gadgets P90 clone (exactly the design you were guessing).  I actually bought their kit with the PCB and all the parts.  Here are some links:

Overall project page: http://www.generalguitargadgets.com/effects-projects/phase-shifters/mxr-phase-90-script-logo/

Schematic: http://www.generalguitargadgets.com/pdf/ggg_p90_sc.pdf

Layout: http://www.generalguitargadgets.com/pdf/ggg_p90_lo.pdf

Bill of materials/parts list: http://www.generalguitargadgets.com/pdf/ggg_p90_bom.pdf

Additional P90 build instructions: http://www.generalguitargadgets.com/pdf/ggg_p90_instruct.pdf

Again...thanks for the reply!

Ray

[Govmnt_Lacky]

Ok. Forget about my last post. That layout is using SINGLE op amps. Like the LM741. So, it appears that you are in fact getting Vcc (on Pin 7)

Are you seeing any voltage swings on IC6 Pins 2, 3, or 6 when you measure? If the LFO is working, then one or all of those voltages should not remain stationary.

EDIT: Did you tie Lugs 1 & 2 together on the Speed pot?

[kerryandray]

Ok. Forget about my last post. That layout is using SINGLE op amps. Like the LM741. So, it appears that you are in fact getting Vcc (on Pin 7)

Are you seeing any voltage swings on IC6 Pins 2, 3, or 6 when you measure? If the LFO is working, then one or all of those voltages should not remain stationary.

EDIT: Did you tie Lugs 1 & 2 together on the Speed pot?

OK, cool.  I did notice that pin 7 had the same voltage as the power supply. 

I saw no voltage swings on any of the IC pins.  And I did tie lugs 1 & 2 together on the speed control.  Thanks!

[willienillie]

1. When I swing the trimmer control back and forth, I do get a spot where it "phases" (in that is makes a filter-y sound).  When I leave the trimmer in that spot, the sound stays static (i.e. doesn't swirl).  If I crank the speed knob back and forth, it "phases"

Your LFO isn't working.  IC6.  Same thing happened to me with my first Phase 90 build, coincidentally also the GGG pcb.  In my case a small bit of debris was shorting two pins on that opamp.  Brushed it off and all good.

[kerryandray]

1. When I swing the trimmer control back and forth, I do get a spot where it "phases" (in that is makes a filter-y sound).  When I leave the trimmer in that spot, the sound stays static (i.e. doesn't swirl).  If I crank the speed knob back and forth, it "phases"

Your LFO isn't working.  IC6.  Same thing happened to me with my first Phase 90 build, coincidentally also the GGG pcb.  In my case a small bit of debris was shorting two pins on that opamp.  Brushed it off and all good.

Oooh...fingers crossed!  I'll check in a little bit.  Thanks!

[kerryandray]

Ok. I checked the underside of IC6 and nothing appeared wrong.  But i desoldered and replaced it with a new LM741.  Nothing changed.  Still acts the same.

I also went over the back og thr PCB with a magnifying glass and found no solder bridges, bad solder joints or unsoldered pins.  I tried using the batteries and using wall power.  Any more ideas on what to check? 

[kerryandray]

Not sure it's useful info, but when i have the speed knob all the way down (as specified in the instructions for measuring voltages), I get the initial readings.  I noticed IC6 voltages change with the speed knob while others don't. 

I get the following voltage ranges on IC6 going from Speed set to low vs high:

Pin 2: 1.6v - 3.4v (which slowly falls to 3.0v)
Pin 3: 5.44v - 5.1v
Pin 6: 7.15v - 7.02v
Pin 7: 7.8v - 7.8v

[willienillie]

From the GGG instructions you linked above:



So the variation is normal, but it looks like your pin 6 is too high.  Maybe a wrong value resistor or bad cap somewhere around there.  Can you post pics of your board, both sides?

[kerryandray]

Sure thing

[duck_arse]

here's a thing - the circuit shows Q5 EMITTER connects to the SOURCE pin of all the fets. if all your fet sources are reading 5V08, why is your Q5 COLLECTOR voltage 5V08? if you've misnamed the pins in your post, just ignore me, and carry on.

[kerryandray]

here's a thing - the circuit shows Q5 EMITTER connects to the SOURCE pin of all the fets. if all your fet sources are reading 5V08, why is your Q5 COLLECTOR voltage 5V08? if you've misnamed the pins in your post, just ignore me, and carry on.

Good catch.  I mislabeled Q5.  I've fixed it above.

[kerryandray]

Ok, based on willienillie's observations that I have too high a voltage on IC6 pin 6, I replaced C8 and removed and tested the values of R19, R20 and R25.  I even removed the potentiometer and measured it.  All check out fine.  I reinstalled everything and I'm still in the same boat.  I notice pin 3 is also a bit high, which makes sense being that it's connected to pin 6. 

Any ideas?

[kerryandray]

Ok.  Found it.   I had C7 reversed...duh.  must not have noticed it was polarized during the install. 

So...if everything looks right except pin 6 on IC6 has high voltage, check tha C7 is oriented correctly   

Thanks everyone for your help/comments!

[kerryandray]

And here's a little look at the overall project which is almost 100% functional now thanks to everyone's help.  It sounds great (for what it is...sound better using a larger speaker via the speaker out jack compared to the 3" speaker in the guitar).  The only thing that isnt 100% functional is the headphone out, where the headphone volume doesn't work. 

Problem for another day.  This thing is REALLY fun to play and i can literally go anywhere without cords or anything to carry other than the guitar.  The batteries and tools fit into the upper right cavity which is held on with magnets so it's tool-less access, no screwdriver needed 


Here's some pics:

[Kevin Mitchell]

Okay, that's dope.

-KM