Waaah. Phase 45 not phasing

[PCS]

Torchy's Phase 45 w/Mods.

LFO oscillates, LED blinks, speed pot works, plugging in JFETS causes audible change in tone, Bias pot does nothing, circuit does not phase.

I have tried 8 2N5458's from smallbear, none phase. They all change the sound but the bias pot has no audible effect. The mix pot causes a change in tone, but nothing other than that.

Any suggestions? I omit voltage readings, etc, because the LFO works and the sound is affected by the FETs, but I'll get them if necessary.

[PCS]

The IC voltages all appear to be correct. The D and S voltages on the FETS are both 3.40V. The bias knob changes the G voltage from around 3.40V to 1.8V.

[PCS]

3.40V across the 5V1 Zener. I'm really hoping the obvious answer isn't the correct one, i.e. buy a zillion more FETs and wait for them to arrive.

[Fret Wire]

I omit voltage readings, etc, because the LFO works and the sound is affected by the FETs, but I'll get them if necessary.

Post em', especially the zener voltage.

[Paul Marossy]

Uhh... did you match the FETs? That might make a difference. It is possible that out of eight, none of them pair up well.  :x

I actually used J201s in mine, and it works great even though I've been told that they're not supposed to...  :?

[PCS]

I tried matching them as per J.C. Maillet's instructions, but absolutely no phasing occurs with any FET at any location at any point on the Bias pot, despite the Bias pot adjusting the Gate voltage from anywhere around 1.2V to 3.40V depending on the FET.

[Paul Marossy]

Hmm... perhaps there is a mistake in the layout, or maybe you have a bad cap or maybe you inadvertently used a wrong cap value?

[PCS]

I don't think there is a mistake in Torchy's layout, as it has been built by many others. I cannot see any mistakes in my wiring, there are no shorts, all of the readings seem to be correct, sound comes through from the guitar, all of the caps are of the correct value and all seem to be working (although I don't have a capacitance meter). The bias pot changes the gate voltage, but the circuit won't phase with the LFO. Any other possible troubleshooting angles?

[Paul Marossy]

Checked the voltages on the opamp in the LFO section? Checked all solder joints? Have you tried using a 4.7V zener? I believe the original Phase 45 used a 4.7V zener...

[littlegreiger]

If you can, try and match the FETs using the FET matcher over at Geofex. Just search jfet and you should find it.

[PCS]

IC1:

1=3.33V
2=3.34V
3=3.2V
4=0.6mV
5=8.63V
6=3.45V
7=3.39V
8=3.39V

IC2:


1=~2.3-7.2V
2=~3.8-4.8V
3=~3.4-5.3V
4=0.5mV
5=8.57V
6=3.32V
7=3.38V
8=3.38V

Zener 5V:

a=0.5mV
k=3.38V

FET1:

D=3.38V
S=3.38V
G=~2.5-2.7V

FET2:

D=3.38V
S=3.38V
G=~2.5-2.7V


:x  :x

[PCS]

Ack, on the IC pin readings, 5 6 7 8 should actually be labeled 8 7 6 5.

[PCS]

Any suggestions? I'm getting desperate, and I don't want to give up on this pedal. I get the feeling it's something obvious...

[tungngruv]

Torchy's layout is verified, so it's not that. I was lucky enough that mine worked first time. I bought 10 trannies from Steve at SmallBear and the first two I plugged in worked but the bias had to be at the far right of rotation. Since then, I actually went through them all and did get a few pair that did work in the center of the rotation. I'll mail you a free pair that worked for me if you need them to try? It actually sounds like everything is working right, except the phase. Here are a couple things I did notice:
-the Phase is a little subtle, but very good sounding.
-the Bias knob has a sweet spot (between 12:00 and 1:00 on mine), anything outside of that = no phasing (like yours) and within the 12:00-1:00 range, there is a definite change in the phasing sound character.
-the mix knob on mine is no effect when at minimum, darker sounding phase from 11:00 to 2:00 and the high end comes in after that
-speed knob works at the last third of the pots rotation (but I haven't installed the 500K reverse log that Phillip recommends yet). Hope you get it working, it's really good sounding from a vibe "wobble" to pulsing tremelo, phase a it also get a cool filtering sound when you put it after a fuzz with the speed slowed down (think Eddie). Good luck

[PCS]

I'd be thrilled if you were to send me a pair of trannies. I guess that it must be the highly unlikely scenario that none of my transistors work in the circuit... I'll PM you my address. I'll owe the forum some Karma points.

[Paul Marossy]

Well, you could always resort to building another one. I have had to do that on a couple of things that I built - even though I could not find anything wrong with the circuit, something was wrong because it didn't work.  :x

[tungngruv]

Also, double check the bias pot, and pot wiring. Your initial description points to that. 4 trannies on the way in the morning that I know work.

[PCS]

Well, the 1 and 3 on the Bias pot were backwards and the phase/vibe switch was backwards, but neither of those helped. I'll wait for the trannies and report back.

[Paul Marossy]

It sounds like it's been narrowed down to the FETs then.  

[Fret Wire]

It sounds like it's been narrowed down to the FETs then.  

Or JFET pinout. Did you double check the pinout of jfets? What brand are they? Pinouts differ from company to company. You can look up your brand at Mouser and check the data sheets, or go to the companies web site directly.

tungngruv: The 500k rev. log pot does have a better distribution of the phase. That's what MXR originally used. I've found that whenever MXR used a 500k rev. log pot, it always is the best progressing taper to the ears.