Phase 45: no phasing.

[dasein668]

Hi,

I'm new to effects and electronics in general (first post here!). I've successfully built a couple of fuzz circuits and decided to jump into a phase 45 circuit. Perhaps unshockingly, I'm now a little stuck...

I've been through the debugging thread here and at geofx and am still stuck. Here's what's happening, and what I do know so far:

1) this is the tonepad phase 45 circuit and layout.

2) Engaging the effect results in a very slight volume drop and what sounds like perhaps a small phase change, but no oscillation of the phase effect. The tone is slighlyt brighter than when bypassed.

3) I etched the circuit board myself--first time. Before populating the board I checked continuity on all the traces that were supposed to be connected. After populating I inspected we a magnifying glass and even checked for continuity in the couple of areas that I thought might be inadvertently shorted out. Everything seems to check out ok.

4) I substituted a matched pair of 2n5457 jfets for the specified 2n5952. I checked the pinout per the data sheet (and even tried flipping them based on the reports that some mentioned of incorrect pinout spec on the layout). I substituted .047 uf caps for the specified .05 uf. All other components are as specified.

5) Two jumpers are called for, and they are in place! (Almost missed that!)

6) power is supplied from a dc wall wart. 9.39 supplied volts.

Pin voltages are as follows:

Z1:
A: 0
K: 3.54

Q1:
G 3.54
S 3.54
D 1.50 (Adjustable from 0.81 - 3.34 depending on trimmer setting)

Q2: same as q1

IC1:
P1 3.54
P2 3.53
P3 3.54
P4 0.1 mv
P5 3.37
P6 3.54
P7 3.54
P8 9.38

IC2
P1 4.70
P2 4.69
P3 4.50
P4 0.2mv
P5 3.54
P6 3.53
P7 3.54
P8 9.38

I noted while searching the archives that pins 1-3 on ic2 are typically fluctuating in voltage--mine are rock stead at the listed values. I'm guessing that that's the root of no phase sweep...

Any suggestions would be greatly appreciated!

--Nathan

[Kipper4]

Schematic here.


http://www.tonepad.com/getFile.asp?id=70

Ic2a is the lfo.
So the voltages should fluctuate.
I'd look for a bad connection, solder bridge, value error around there.

Your 4n7 should be fine.
And the fact that it's passing audio might be a good sign.

[M.A.P]

Hi dasein668,

welcome here. There has been a long thread about a troubleshoot of an Phase45. It was not the same problem as you describe but maybe you can find some helpful infos there.

http://www.diystompboxes.com/smfforum/index.php?topic=113760.0

Hope you get your Phase45 fixed soon

Greetings from Germany
Marcus

[dasein668]

Woot! Despite an earlier check, a revisit with the continuity checker showed a solder bridge. Cleaned up and phasing! Thanks for sending me back to basics!

I'm getting a nice subtle phase with the components that I have in place. I'd say it seems a little more subtle than other phase 45s I've heard. Do you think that could be attributed to using a different jfet than spec'd?

[Kevin Mitchell]

I'm getting a nice subtle phase with the components that I have in place. I'd say it seems a little more subtle than other phase 45s I've heard. Do you think that could be attributed to using a different jfet than spec'd?

Try using a more well matched set. If you don't think that's the issue try looking into mods for the LFO. There are some tips for extending the range but you wont get much more out of it.

This is why I've been tinkering with OTA phasers - like the MF-103. A decent DIY OTA would be the Causality - version 6 if you're ever interested.

[cnspedalbuilder]

Congratulations on your fix! I spent about 10 weeks figuring out my problem (a broken 3PDT).

My kit has a trimpot (allowing you to adjust bias current?). I needed to tweak trim pot and found a sweet spot where the effect popped out. It's still very subtle. I did mine with the "univibe mod" and was very happy with that result (see GGG Phase 45 mods site).

Cheers.

[dasein668]

Try using a more well matched set. If you don't think that's the issue try looking into mods for the LFO. There are some tips for extending the range but you wont get much more out of it.

This is why I've been tinkering with OTA phasers - like the MF-103. A decent DIY OTA would be the Causality - version 6 if you're ever interested.

I used a matched pair from Small Bear. I don't have a tester but the reported numbers seem pretty close. Might be worth playing around anyway-- that's the fun, right?

I think a multi-turn trimmer might have been helpful as well, as I kept skirting by the very narrow sweet spot. I finally got it biased well and that definitely helped.

[newfish]

+1 on the multi turn trimmer.

I built a Phase 45 (from a kit I bought online) - I knew the kit would be good as I'd had a couple of drives / fuzzes from there before.

Even with the matched FETs included, I was able to have a better sounding (IMHO) pedal by using R.G.Keen's excellent (and simple!) FET matching circuit - and a multi turn 220K trimmer.