Phase 90 not phasing... (it works!!)

[gak]

hi guys
i've just built a phase 90 using tonepad's layout...
it sounds but it doesn't sweeps...
i'm using 4 BF245 matched at 5.93v... the zener i'm using is 5.1v
i've been reading a lot of topics of phase 90 debugging and build reports and everyone seems to be using fets matched at smaller values... maybe i should try another zener value for use with my fets?
turning the trimmer (used a 200k one) works like a "tone" control... i get some nice clenad sounds but no phase at all
any help would be appreciated

thanks!

gak.

[R.G.]

I'm not all that familiar with the tonepad layout, but if you have a 5.1V zener and the JFETs seem to work in the matcher at 5.9V, you can't expect them to work for phasing. You need JFETs with Vgsoff at less than the zener voltage. Your numbers suggest that your JFETs have Vgsoff too high to work with that zener.

[gak]

that's what i've just figured out after reading another post of you about this...

i've also measured voltage at the fets..
4.11v at D and S
1.61v at G

4.11v at the zener too...

there's a way to tweak voltage provided by the zener? (i think i've read a resistor can be used instead...)
i don't wanna wait until monday to buy another zener and try my phaser!

thanks for your answer r.g!

[gak]

well, i figured out i was using an almost dead battery...
with a new one, the value i get in the matcher is 7.6v... even higher... 
replaced the 5.1v zener for a 4.7v and a 3.6v in series and i wasn't getting enough voltage at the zener, so i added the 5.1v in series too...
now y measure 7.84v...
also 7.84v at FETs D and S, and 3.96v at Gate..
all DC voltages measured against ground...
i'm still getting no phase effect
i just hear the clean guitar and also the clock pops... but no phase... any suggestion?

thanks in advance...

[R.G.]

The zener voltage needs to be no higher than 5.1. The original used 3.0V. That's so the zener reference voltage is somewhere between 0V and the battery's 9V (if you have a fresh one).

You can't just keep raising the zener voltage. That makes the opamps not work. You have to get JFETs that match at voltages lower than the zener reference voltage. That's because the JFETs have to be turned nearly off to work as phase resistors, and if the Vgsoff is over the reference voltage of the zener, you can never turn them off.

[gak]

thanks for the explanation
i'll give a try to another JFETs...
i'll let you know how it works
thanks again!

[gak]

well... after all, the JFETs didn't have such high Vgsoff values... there was a bad solder joint on my fet matcher... the actual values are about 2.7v... so there's no problem with the zener voltage i think...
but it still doesn't sweep...
i've checked every trace on the PCB, continuity between every component leg, component values... surely i'm missing something, if it all were fine i think i'd have a phaser 
so... i hope you guys can help me...
here are my voltage readings...
V+ at PCB: 8.16

IC1
1: 4.38
2: 4.38
3: 2.94
4: 0.01
5: 3.26
6: keeps changing constantly
7: keeps changing constantly
8: 8.29

IC2
1: 4.36
2: 4.37
3: 4.36
4: 0.01
5: 4.36
6: 4.36
7: 4.37
8: 8.23

IC3
1: 4.36
2: 4.36
3: 4.37
4: 0.00
5: 4.36
6: 4.37
7: 4.37
8: 8.22

Q1
e: 4.36
b: 3.80
c: 2.16

D2 (Zener 5.1v)
4.36

FETs
D: 4.27
S: 4.36
G: 0.57

algo i've realized that the "tone" change i've mencioned on my first post is actually the phase shift... so that part is working... based on the changing voltages on IC1 i think the clock is working to... but not afecting the fets? well... that's all i can think... i hope someone with more knowledge can help me...
thanks!!!

[gak]

those voltages i realised i wasn't getting enough voltage at JFETs gate... so i've increased the zener value... turn the trimpot... and... yeah! it's working!!!!!!!!!!!!! 
very cool effect

thanks r.g. for your answers, they were really helpful 

[Fp-www.Tonepad.com]

Congratulations on your build.

Remember to include a link to the specific project you're troubleshooting so you can get better help:

http://www.tonepad.com/project.asp?id=7

Fp

ps: Please fill in a build report!