My Phase 45 won’t Phase!!

[SirHugo]

Hello all, I have recently completed a GGG phase 45 clone and it's not working correctly. It bypasses fine when on or off (though when on there is some volume drop, which I Understand is common with phase 45s). There is a tonal change when it is on but no "wooshing" if you will. I also added the "Univibe mod" and it just seems to act as a tonal switch at the moment I've triple check the components and wiring so I don think that, that is the issue, So far as I can hear the speed knob dosnt change anything, however when I multimetered it's legs they read as changing voltage and would speed up as I turned the knob. Could this be caused by not having matched JFETS? If not I'll post the multi meter readys and go from there. Thanks ahead of time JHK

[PRR]

Did you bias the JFETs?

They may like 1V or 3V of bias. There is usually a trimmer to set the gate bias for the specific JFETs you have.

Not-matching will degrade the wooosh but there should be some effect if they are all the same type.

[SirHugo]

Hmmm well that's concerning then,
Yes I tried the internal trimmer and it didn't seem to do much other
Than slightly change the tone.

[SirHugo]

I ordered a matching pair of replacement JFETS,
So hopefully that will help but in the mean time I will
Post my multi meter findings and see where we go from there as
Far as diagnosing the problem.
JHK

[duck_arse]

what part number are your fets? are they as specified or subs?

[SirHugo]

They we're the recommended 2n5952s but I ordered a matched set
Off of the GGG website that are 2N5485s.
In the instructions they offer multi meter parameters for the ICs and the Qs
All of my readings are on the money except for pin 3 in IC 2, it's not varying in voltage like it's supposed to, it's just steady at 4v.

Here at links to the build docs if that helps;
Parts layout:

http://www.generalguitargadgets.com/pdf/
Schematic:
http://www.generalguitargadgets.com/pdf/ggg_p45_sc.pdf
Mods layout (I only added the Univibe switch mod)
http://www.generalguitargadgets.com/pdf/ggg_p45_mods_lo.pdf
Maybe it's something to do with the switch? It connects partially at pin 3 of IC2.

[willienillie]

That sounds like a problem with your LFO (IC2B on the GGG).

When I completed my first Phase 90 clone, my LFO wasn't functioning.  A look with a magnifying glass revealed a tiny fragment of steel wool was shorting two pins.  Brushed that off, and it came to life.  So examine closely around IC2B and double check all component values in the LFO circuit.

You did not waste money ordering the matched pair of 2N5485s, even if JFETs aren't your biggest problem right now, the phaser will sound much better with those matched.  I used 2N5485s in all three Phase 90s I've built and they work great.  The pinout is reverse of the original 2N5952, so very easy to adapt.

[duck_arse]

I used 2N5485s in all three Phase 90s I've built and they work great.  The pinout is reverse of the original 2N5952, so very easy to adapt.

indeed, this. did you reverse the fets as per your datasheets? [because we haven't seen the photos of your work, yet ......]

[SirHugo]

I haven't, I didn't realize they were reversed,
I'll have a look at it this evening and get back to you about the
Fets and the pin 3 leg connection.
Here are a few pictures for edification.





Just FYI these are pictures before the Jfet swap.

[duck_arse]

[how much is that bird on your box worth?]

well, now I don't know anything. I'm looking at two fairchild datsheets, one for the 2N5484/5485/5486, which shows the gate pin "on the left" flat down, as you'd expect on a 2N5457. the other datasheet is for the 2N5952, and shows the gate pin "on the right", like on a BF245. the pcb and build docs shown are marked "2N5952", but have the gate pin marked [and wired] on the left.

so if you've fitted [fairchild] 2N5952's as specced, they would be backwards, but "incorrectly, unrotated, substitute" [fairchild] 2N548x's would be correct.

can someone please check this - feels like I'm missing something.

[SirHugo]

They seem to be working better flipped,
However this is relative as I'm still having issues with
The pedal, same deal, it just wont woosh, the knob isn't
Changing the sound. Pin 3 on IC2 seems clean but still
Isn't varying voltage all other pins that are supposed to, are.
As well as the terminals on the pot it's self, and the knob
Changes how fast it varies, but no sound change.
I'll post all multi meter reads this afternoon.

[willienillie]

To add to the confusion a little:

http://www.generalguitargadgets.com/pdf/ggg_p45_instruct.pdf

Toward the bottom of page 1.  Seems the board was laid out for '5485s, yet the layout and schematic say '5952.  Don't know if you have your matched pair yet, but install them IAW the board graphics.

The lack of voltage variation, though, is still an LFO issue, unrelated to the JFETs.

[SirHugo]

Well thats really odd!
ok i found time to multimeter the entire thing so here are my reads:
Resistors:
R1 3.45   3.45
R2 3.63   3.63
R3 3.45   3.63
R4 3.63   3.63
R5 3.63   3.63
R6 3.63   3.63
R7 3.63   3.63
R8 3.63   3.63
R9 3.63   3.62
R10 3.63   3.63
R11 0.00   0.00
R12 3.62   3.62
R13 3.62   3.62
R14 3.63   3.62
R15 3.62   3.63
R16 9.66   3.63
R17 3.62   3.24
R18 3.24   3.63
R19 1.38   3.63
R20 varies   varies
R21 9.66   3.65
R22 9.03   3.26
R23 0.00   3.64
R24 8.37   9.03
R25 3.25   varies
R28 0.00   0.00
R29 9.66   9.66
Capacitors:
C1 3.45   0.00
C2 3.62   3.63
C3 3.62   3.62
C4 3.63   0.00
C5 3.62   3.62
C6 3.62   3.62
C7 3.63   0.00
C8 3.22   3.62
C9 varies    varies
C10 varies    0.00
C11 9.66  0.00
C11

IC1
1 3.64  8 9.66
2 3.63  7 3.63
3 3.46  6 3.62
4 0.00  5 3.62

IC2
1 3.63 8 9.66
2 3.63 7 varies
3 3.62 6 varies
4 0.00 5 varies

Q1 3.62   3.63    3.63       
Q2 3.62   3.63    3.63

Trimmer 3.63   1.38   0.00

Speed Pot  varies   varies    varies

9v 9.66    0.00

LED 9.66    0.00

On/On switch
Up:
1 0.00    2 3.62    3 3.62
4 0.00    5 3.63    6 3.63
Down:
1 3.62     2 3.60   3 0.00
4 3.63     5 3.63   6 0.00

On Board pads:
O 0.00
9v 9.66
I 0.00
L 9.64
S3 varies
S2 varies
G 0.00

Hope this helps!
And thanks to you all for helping me thus far, its much appreciated !

[willienillie]

So now you have varying voltages at IC2B?  Maybe your LFO is working after all.

Do you have the matched JFETs installed yet?  My experience is with Phase 90s, not 45s, but there is a fairly small range of the trimmer where phasing effect happens.

[SirHugo]

I've had caring voltages on IC 2 but according to the build docs Pin 3 is supposed to vary
But it isn't. I did replace the Qs with the matched set but alas didn't help it to work.
Do any of the meter values suggest anouther problem ?
I also tried for a bit to get something with the trimmer and nothing unfortunately.

[willienillie]

Now I'm suspicious of R25 (3.9M).  You have varying voltage on one end but apparently not the other.  Maybe it's bad, poorly connected, or the wrong value.  It is obscured in the picture, but seems to be the only carbon film resistor in your build.  Likely it has a 4-band marking instead of 5-band like the metal films.  Should be orange, white, green (and gold if 5% tolerance).  If it's right, try re-soldering it.

Could be something else entirely, but that's where I would check next.

[SirHugo]

I checked R25, it's the correct value. And then reflowed the pads for it
And unfortunately no change.

[willienillie]

Well, I'm basically out of ideas.  But a few questions for clarity:

-Where you have varying voltages, does the rate change when you turn the knob?  The faster settings will confuse most digital meters, but you should see some difference between the extremes.

-You say R25 is the correct value.  Do you mean by color bands, or did you lift a leg and actually measure it?  Bad new resistors are rare, but not unheard of.

-Is there any setting of the trimmer where you can get varying voltage on the "far" end of R25?  Again, easier to detect at slower LFO speeds.

-Can you post more pictures of your board, especially the underside?

-Have you examined everything closely with a magnifying glass or jeweler's loupe?

[Rob Strand]

Try measuring the voltage on the gates then see what range of voltages you get with R26 (trimpot) set to each extreme. It might also help to measure the voltage each side of R19 with R26 (trimpot)  at each extreme.

If you are keen you could lift one end of R5 and one end of R7.  The adjust R26 (trimpot) to each extreme.   
You should be about to pass audio at one extreme and perhaps cut it off at the other.   If you get a bit of bleed through of the at the LFO don't worry.   If you get that far try finding a spot in the middle where you can get a kind of tremolo effect;  it might tremolo the lows and let the highs through.   All this means the JFET appear to be working (I'm hoping there's no diode VCA effect if the JFETs are in the wrong way).

Oh, check all your resistor values around the JFETs.  If you are out by a factor of 10 or more it could stop things working.

[duck_arse]

Mods layout (I only added the Univibe switch mod)
http://www.generalguitargadgets.com/pdf/ggg_p45_mods_lo.pdf
Maybe it's something to do with the switch? It connects partially at pin 3 of IC2

.

partially? either yes/good or partially/bad. I'd say remove those wires to the switch, and tack-solder a cap across the pads - value not important, 10nF to 100nF for the test. see if you get anything then.