Phase 45 ... Help, and yes I've search ... voltages inside.

[Melanhead]

Okay, I built this thing a few months ago ( torchy's layout )  and finally got around to ordering the FETs ( 2n5458 ) and built RG's fet matcher to match 'em.

Can someone please check these voltage readings ... they look okay to me but I'm probably overlooking something ...

I matched 2 FETs at - 2.030
Zener is a 5.1v

Q1

D 3.74
S 3.74
G 2.25 ( based on the bias pot half way up ... Bias goes from 1.58 to 2.87 )

Q2
D 3.74
S 3.74
G 2.25 ( based on the bias pot half way up ... Bias goes from 1.58 to 2.87 )

IC1

1 3.61
2 3.64
3 3.48
4 0
5 3.74
6 3.74
7 3.89
8 9.53

IC2

1 4.90 ( fluctuates )
2 4.84 ( fluctuates )
3 4.81 ( fluctuates )
4 0
5 3.74
6 3.74
7 3.60
8 9.53

Speed light works and all seems fine but no phase ... If the voltages are okay then I guess I'll have to get the audio probe out ...

[slacker]

The opamp voltages look ok to me. I think the problem is round the fets, the gate voltages should be going up and down in time with the LFO. Check the stuff between pin 2 of the second opamp and the fets (R15 - R19) hopefully you'll find the problem.

[barret77]

Hey Melanhead

We're in the same boat!

My problem is slightly different: voltages too low on the jfet G's - I changed the bias pot and it improved. But no phasing. I checked and recheckd connections, voltages, parts, traces, everything.
But then, something weird: Instead of using the battery, I plugged a 10.3v wall wart (it was supposed to be 9v, but I found it in the dumpster) - and now I'm getting some phasing! The project is far from being "good" or "done", but I walked one more step. Maybe you should give it a try...

[Melanhead]

The opamp voltages look ok to me. I think the problem is round the fets, the gate voltages should be going up and down in time with the LFO. Check the stuff between pin 2 of the second opamp and the fets (R15 - R19) hopefully you'll find the problem.

Thanks ... I thought the opamp was fine but bthought I'd be sure ... wasn't quite sure about the fets though ... I'll check it out ...

[Melanhead]

Hey Melanhead

We're in the same boat!

My problem is slightly different: voltages too low on the jfet G's - I changed the bias pot and it improved. But no phasing. I checked and recheckd connections, voltages, parts, traces, everything.
But then, something weird: Instead of using the battery, I plugged a 10.3v wall wart (it was supposed to be 9v, but I found it in the dumpster) - and now I'm getting some phasing! The project is far from being "good" or "done", but I walked one more step. Maybe you should give it a try...

Thanks man, but I'm using a wall wart now ... ... I'll check the mix pot like I saw in your other post as well ...

[R.G.]

The reason I put that note to put links into your posting for the schematic and layout that you're asking for help with is that it takes me a fair amount of time to track down the schemo sometimes, and the schematics and layouts vary in their part number references even if I have the schematic.

I didn't find torchy's layout yet, but I found J.C.'s schematic, so I hope I'm working from the right thing. I'm working from this schematic - http://www.lynx.bc.ca/~jc/phase45modded.gif

First: if you are using a 5.1V zener and you're only getting 3.74V on the sources of the JFETs, the zener is not zenering for some reason, possibly because some bad connection or solder thread is letting something suck all the available current from the series 10K. It's also possible that the zener is actually a 3.7V zener. solve this one first, it may fix the biasing problem.

Next, JFETs vary - a lot. It's possible that your particular JFETs simply can't be put into the phasing voltage range by your combination of biases. The schematic I'm looking at has a 100K bias adjust pot and two 47k's on either side restricting its range. Short out those 47K's. Now the 100K bias pot can vary by the entire bias voltage range. See if the bias pot can now tune in some phasing.

As for a higher voltage supply causing it work - sure that's possible if the higher voltage supply tweaks the bias in because of the restricted range. I'd prefer on my pedals to change the circuit to suit a 9V battery rather than having to use a non-standard voltage supply, but whatever works for you works for you.

[Melanhead]

thanks RG I'll check the Zener, that makes sense and the bias pot ... I'll try a few other fets as well and see what happens.

Sorry about not linking to the schematic, you're using the right one. I'm sure I read your post but my memory isn't as great as it use to be

[R.G.]

Sorry about not linking to the schematic, you're using the right one. I'm sure I read your post but my memory isn't as great as it use to be

No problem - it just takes me longer to look things up and get a reply in.