GGG Phase 90 Problem

[Jeeper2000]

I'm having some trouble getting my GGG Phase 90 to work.  I etched my own PCB and have installed the jumper wires and the 22k resistor mentioned in another thread.  Still nothing.  Comparing my voltages to the GGG instructions, I can see that something is way out of whack.  I've triple checked my solder joints and everything looks ok, but obviously there is a problem.  I just finished a Madbean Current Lover without a hitch, so I thought this one would be a breeze.  Wrong!  I am appealing to the knowledge of the forum to avoid more bruises to my forehead from beating it against the wall.

1.What does it do, not do, and sound like?
The bottom line is that there is no phasing at all.  I get clean sound in bypass and clean sound when the effect is engaged.  There is no audible change in the sound when the effect is engaged.  Changing the rate or the trim pot has no effect on the sound.

2.Name of the circuit = General Guitar Gadgets P90 (MXRTM Phase 90TM Replica)

3.Source of the circuit =
Instructions and GGG voltages http://generalguitargadgets.com/pdf/ggg_p90_instruct.pdf
Schematic http://generalguitargadgets.com/pdf/ggg_p90_sc.pdf
DIY PCB Jumper http://generalguitargadgets.com/pdf/ggg_p90_jumper.pdf
BOM http://generalguitargadgets.com/pdf/ggg_p90_bom.pdf

4.Any modifications to the circuit? No, built exactly the specs on the GGG BOM.

5.Any parts substitutions? No substitutions. I used 741s for my ICs, Matched 2N5952s from GGG, and a 2N4125 for Q5.  I ordered all of my components from Smallbear.

6.Positive ground to negative ground conversion? No conversion.

7. What is the out of circuit battery voltage?
I built it to run strictly on plug in power, so there is no battery clip.

Voltage at the circuit board end of the red power supply lead = 9.01v
Voltage at the circuit board end of the black ground lead = 0v

Here are my measurements:

Q1, Q2, Q3, Q4
G = 4.37
S = 4.37
D = 4.37

Q5
C = 2.54
B = 3.76
E = 4.36

IC1
P1 = 0
P2 = 4.37
P3 = 2.94
P4 = 0
P5 = 0
P6 = 4.37
P7 = 9.01
P8 = 0

IC2, IC3, IC4, IC5
P1 = 0
P2 = 4.37
P3 = 4.36
P4 = 0
P5 = 0
P6 = 4.37
P7 = 9.01
P8 = 0

IC6
P1 = 0
P2 = 4.55
P3 = 3.86
P4 = 0
P5 = 0
P6 = 4.55
P7 = 9.01
P8 = 0

D1
A = 0
K = 9.01

D2 (5.1v Zener)
A = 0v
K = 4.37

I have an electrolytic cap for C6 and a tantalum cap for C7.  Both are showing more voltage on the + side than the – side.  Also, I have an unused solder pad between R5 and R23.  I don't see anything on the build documents to show what, if anything, should go there.

Thank you all in advance for taking a look at this with me.

[Mark Hammer]

And you have attempted to set the bias for the FETs correctly?  Keep in mind that the FETs need to be biased in order to be amenable to varying their drain-source resistance with the LFO.  If not biased right, they just sit there.

[JRB]

First thing that seems strange to me is that the gate voltages aren't moving up and down.

On a side note I have tried multiple times to make my own perfboard version with the GGG building plans and I haven't managed to get any of them to work. In the end I just ordered a PCB from musikding that did work the first time I fired it up. So it could be possible some information is missing in the plans if you ask me.

[Jeeper2000]

I'll have to check the bias again when I get home tonight and see what happens.  I never noticed any phasing across the full spectrum of the trimmer, but after reading a little further about it, it seems that the window of functionality may be a little narrower than I thought.  Maybe I skipped over the sweet spot and didn't realize it.  I'll post a follow up after I test it again.

As far as problems with the GGG docs, I checked the DIY PCB layout against the photo of the board JD sells and it looks like a spot on match.  You just have to add the jumper.  I know from another thread that people have gotten the GGG Phase 90 to work by etching their own boards.  Maybe there's a breakdown between the posted schematic and the PCB layout??

[Mark Hammer]

I'll have to check the bias again when I get home tonight and see what happens.  I never noticed any phasing across the full spectrum of the trimmer, but after reading a little further about it, it seems that the window of functionality may be a little narrower than I thought.  Maybe I skipped over the sweet spot and didn't realize it.  I'll post a follow up after I test it again.

It's been known to happen. 

[armdnrdy]

First,

Make sure the JFETs are in correctly:
Here's the pinout:
http://circuits.datasheetdir.com/316/2N5952-pinout.jpg

With a voltmeter, check for oscillation at IC6 pin 6
If you have oscillation, check for oscillation at the JFET gates. Move the bias trimmer around and see if the voltage on the gates changes.

If you have oscillation at the LFO output and at the gates but no phasing, you might have to change the Zener to a higher or lower value. 4.7-5.6 volt.

Just because the JFETs are "matched" to each other doesn't mean that they're matched to the bias voltage. That is what the bias trimmer is for but even with adjustment some matched sets will still fall outside of the "stock" zener voltage.

[Jeeper2000]

I just checked the pinout for the JFETS again and they are in there correctly. I checked every setting for the trimmer and never got any phasing. I did notice that the sound does change slightly when the effect is engaged. It is very slightly muffled. I do have oscillation at Pin 6 of IC 6. However, the voltage at the gates of the JFETS never changes as I move the trimmer. All are steady at 4.37v.

[armdnrdy]

Okay,

Then check pin 2 of IC 6 for oscillation.

Check both sides of R19 and R18 report voltages.

Check both sides of R17 move Bias trimmer see if voltage changes.

[Jeeper2000]

Pin 2 of IC 6 does oscillate.

R19 = 4.55-4.57 on each side. 

R18 = 4.37 on one side, 4.55-4.57 on the other.

R17 = 4.55-4.57 and doesn't change with the trimmer.
Also, R17 is carbon film and all other resistors are metal film. Don't know if that matters, but wanting full disclosure.

[armdnrdy]

Make sure that the trimmer is properly grounded. (check solder joints)

With your meter set to resistance verify that the trimmer is oriented correctly.

[Jeeper2000]

Solder joints on the trimmer look good. It's also oriented correctly.

[armdnrdy]

Try replacing the zener with a 5.6 volt.

Your voltage reference looks low. The JFET gates should be more negative than the drain and source, and should be oscillating around 2.5 volts.

[Jeeper2000]

Will do. I'm gonna see if I can find one here locally to avoid having to order one. Just made a big order for my next project, too. Missed it by a week! Thanks for all the help.

[Jeeper2000]

Found a 5.6v zener here in town. Installed and still nothing across the entire spectrum of the trimmer. New voltages are:

Q1, Q2, Q3, Q4
G = 5.08
S = 5.08
D = 5.08

Q5
C = 3.21
B = 4.47
E = 5.08

IC1
P1 = 0
P2 = 5.08
P3 = 3.42
P4 = 0
P5 = 0
P6 = 5.08
P7 = 9.01
P8 = 0

IC2, IC3, IC4, IC5
P1 = 0
P2 = 5.09
P3 = 5.08
P4 = 0
P5 = 0
P6 = 5.09
P7 = 9.01
P8 = 0

IC6
P1 = 0
P2 = 5.10 and oscillating
P3 = 4.45
P4 = 0
P5 = 0
P6 = 5.10 and oscillating
P7 = 9.01
P8 = 0

D1
A = 0
K = 9.01

D2 (5.1v Zener)
A = 0
K = 5.08

I also picked up a 4.7 zener just in case.

[Jeeper2000]

Sorry. That last reading is on the 5.6v zener. Not 5.1v.

[armdnrdy]

I've been going through the GGG schematic and layout comparing it to other drawings of the P90. I don't see a problem with the schematic.

You've checked that you have all of the components in the right place?

Years ago I was troubleshooting a build for days. It turned out that when I punched the schematic into eagle, I forgot to change the value of one resistor when I was copying and pasting the resistors!

[Jeeper2000]

I brought it with me to work today to investigate on my lunch break.  I'm gonna check all of the values again and make sure everything is right.  I think the 5.6v zener brought my voltages closer to where the GGG measurements are.  Forgive my novice ignorance on this, but the flaw has to be in one of the components connected to the gates of Q1-Q4, right?

[DougH]

Did you match the jfets you used, or buy a matched set? That's vitally important with a phaser like this.

[Jeeper2000]

I bought a matched set from GGG.

[Jeeper2000]

I just checked every resistor, cap, and transistor again. My board looks just like the parts layout. All the resistor values are correct. I changed the 1k to the LED to a 4.7k, but that shouldn't matter. IC6 is a different brand than the other 5, but they are all 741s from Smallbear.