need help debugging Phase 45

[dfarrell]

 I have just finished building a Phase 45 using a circuit board from tonepad. I have made no changes or parts substitutions. At first, it didn't make any sound. I turned the 2n5952's around and now I get sound, but the sound I get is like a distorted noise gate. The sound gets cut off shortly after playing a note.
These are the voltages :
IC1:
1 - 8.21
2 - varies from 5.41 to 4.13
3 - varies from 4.98 to 3.42
4 - 0
5 - 3.65
6 - 7.72
7 - 3.30
8 - 8.54

IC2:
1 - 7.98
2 - 7.91
3 - 0.33
4 - 0
5 - 0.85
6 - 1.01
7 - 1.44
8 - 8.64

Q1:
1 - 0.18
2 - 0.76
3 - 0.55

Q2:
1 - 0.18
2 - 2.54
3 - 1.44

Diode
K - 0.16
A - 0

I am new at this, but I have been able to get my other builds to work. If anyone can help me here, that would be great.

[snoof]

i did not look at your voltages, but your prob sounds similar to one that I had.  if you can, try a variable DC supply.  I had a similar prob with one of my P45's in that with a reg batt or wallwart, it wouldn't work(sounded fuzzy), but with a RC batt that put out 10.3v all was well.  So to sum up, try something that will get you a volt or so more, and see what happens.  and make sure you have the trimpot dialed in right as well, the sweet spot is REAL small.  This crkt appears to be very sensitive to over/under voltage differences.

[dfarrell]

I'm thinking that I should check out the area around IC2's pins #3 and 4 and try to get those voltages steady. Does that sound right?

[slacker]

On the layout which chip is IC1? In the tonepad pdf they are both labelled IC1. If IC1 is the chip on the output side of the the board then pins 1,2 and 3 make up the LFO so they should be changing. Pin 1 should be as well so you might have a problem round there.

The real problem is pins 1,2,3 of the other opamp and pins 5,6,7 on both opamps, they should all be about 4.7volts. It looks like something is wrong with the bias voltage, the cathode of the diode should be at about 4.7 volts. Check that it is in the correct way round.

[dfarrell]

I am not getting any voltage on that side of the diode, or on the negative side of the capacitor. I have a voltage of 0.17 on the positive side. Could the capacitor be backwards? (I've checked the orientation of the cap. against the layout - and it is as shown) Or is it grounding out somewhere?

[slacker]

On the tonepad layout drawing the cathode of the zener diode (where the black line is on the diode) should be connected to the grey trace, the positive of the 100uF cap should be connected to that trace as well. The Grey trace should have 4.7 volts on it.
Check to see if you've got any shorts between the grey trace and ground (the green trace).

[dfarrell]

The voltage on  the grey trace is 0.18 volts. I can't see any solder bridges or damage to the trace anywhere. Any ideas on what else to look at?

[jimosity]

I know this is an old post, but I had the same issue and wanted to share my problem so that anyone else searching for a 'fix' could consider this as well.

Like the OP, my 'Phase 45' build (I made the PCB) was giving me a 'fuzz' tone and I was getting no phasing.   It would cut out like there was a noise gate, which is often similar to the way JFETs aren't biased right.
I did no part exchanges in my build, but then tried J201's and both TL082's and TL072's...the fuzz was consistent and there was a hum out of the unit as well, which could be controlled in pitch/sound by adjusting the trim pot.

I went thru about 30 J201's trying to match up some and couldn't get anywhere with it.
I finally (which probably should have been first) pulled out my MM and did a beep test on the traces to ensure a good contact, sure enough, there was one contact that while visibly intact, wasn't quite making good contact, so a quick retrace with a bit of solder and the circuit worked perfectly with most any of my jfets and sounds great.