Phase 45 (w/ Univibe mods) Troubleshoot

[DJPsychic]

Just finished a Phase 45 (w/ Univibe Mods), and I've obviously done something completely wrong.

I'm getting roughly 9v across both IC's 

Except 0.0v on both Pin 8's

I'm using a pair of matched 2n5952. Both read the same:

G - 3.3
S - 4.6
D - 8.8

I'm getting bypass signal, but effect engaged no sound. I spent the past few hours cleaning traces and eliminating bridges. Hard to photograph but in person I'm pretty sure there are no connections. (Some leads may appear to be touching but are just photographed on an angle)

Admittedly this is my most complicated build so there is a learning curve (excuse the mess!)

any guidance is much appreciated.

[GibsonGM]

Hi DJ,

Can you post a link to the build docs/schematic please?    Did you use TL071s instead of TL072s?  My bifocals can't resolve that lol.  The schematics I have call the Phase 45 for dual, not single, opamps...   

You can remove the ICs and measure voltages at each socket point to see what's up, too....

[DJPsychic]

Hi DJ,

Can you post a link to the build docs/schematic please?    Did you use TL071s instead of TL072s?  My bifocals can't resolve that lol.  The schematics I have call the Phase 45 for dual, not single, opamps...   

You can remove the ICs and measure voltages at each socket point to see what's up, too....

My apologies, I used this layout.

http://tagboardeffects.blogspot.com/2012/07/mxr-phase-45.html

And oops there's my first problem I was using TL071   

[GibsonGM]

Ok, it's down to voltages now.  The '71 has power applied to pin 7.   TL072, power is on pin 8.    What do you get on those sockets?  If 0 on pin 4, 9V on pin 8, you have a chance of it working.   

Just as simple builder error with the single opamps, we've all done it I gave you a like for your honesty lol

[DJPsychic]

Ok updated numbers with the TL702 (9V battery)

Both are pretty much identical:

1:  .76v         8:  .86v
2:  176mv     7:  .76v 
3:  176mv     6:  176mv
4:  .9v          5:  176mv

Q1, Q2:

G:  .4
S:  .76
D:  .76

[GibsonGM]

I meant get the voltages with the ICs removed   

Next issue: power on a TL072 is pin 8.....look closely at your pic, note where the locating dot is!   I believe you have pin 4 on the same row as 9V, which means the chips are reversed.   You have to do a 180 with the ICs...the dot will be 'upper left', and that's "pin 1".       You can confirm that this is correct by doing the voltage measurement with nothing in the socket...pin 4 should be 0, pin 9  battery voltage...remembering to plug a guitar cord into the input jack to 'turn on' the circuit! 


See if this helps.  Pin 4 VCC -  (gnd)   Pin 8, VCC+  (9V):

[DJPsychic]

Ahh right once again. I was confusing those connection dots on the layout 

Gave the chips a 180, and I am now getting signal when switched on, but no effect.

Here are the socket voltages

"Top IC"

1: 3.6   8:  9.3
2: 3.6   7:  3.6
3: 3.6   6:  3.6
4: 0      5:  3.6

"Bottom IC"

1: 3.6   8:  9
2: 3.6   7:  118 mv
3: 3.6   6:  .2 mv
4: 0      5:  59 mv

[Rob Strand]

Gave the chips a 180, and I am now getting signal when switched on, but no effect.

The bottom pin of the 150k to the right of the lower IC is going to the wrong place, currently in first PCB row but should be second row.

[DJPsychic]

Gave the chips a 180, and I am now getting signal when switched on, but no effect.

The bottom pin of the 150k to the right of the lower IC is going to the wrong place, currently in first PCB row but should be second row.

Rob good eye!

Fixed it, but still no effect when pedal engaged.

[GibsonGM]

What are the voltages now?

[DJPsychic]

"Top IC"

1: 3.6   8:  9.3
2: 3.6   7:  3.6
3: 3.6   6:  3.6
4: 0      5:  3.6

"Bottom IC"

1: 3.6   8:  0.9 v
2: 3.6   7:  1.4 v
3: 3.6   6:  1.4 v
4: 0      5:  0.9 v

[Rob Strand]

Perhaps another bug in that bottom right area of the PCB:  The 150k to the left of the top lead of the 7k5 resistor.  Top lead of the 150k is off by one should align with the 7k5 top lead.

Maybe check over that whole corner.

[DJPsychic]

Perhaps another bug in that bottom right area of the PCB:  The 150k to the left of the top lead of the 7k5 resistor.  Top lead of the 150k is off by one should align with the 7k5 top lead.

Maybe check over that whole corner.

Actually that one was fine, I did however completely miss a 150k next that 10n. Now I have effect! 

Next issue is I'm only getting effect in one position of the trimpot, or at least a very tiny window of the turn.

I currently have a 500k in there instead of the 250k. I have a 250k on order.

[duck_arse]

the tiny window is to be expected. find the window, power off, and measure the resistance of the trimpot, one end to wiper. then you want to use a smaller value trimpot, maybe 50k, and add padding resistors to the total of 500k either side. then your window will be much wider, easier to trim.

[DJPsychic]

the tiny window is to be expected. find the window, power off, and measure the resistance of the trimpot, one end to wiper. then you want to use a smaller value trimpot, maybe 50k, and add padding resistors to the total of 500k either side. then your window will be much wider, easier to trim.

excellent thank you if I understand this right:

- measure the "sweet spot"

- replace with 50k trim? or did you mean 50k lower than resistance "sweet spot"?

- then add resistance to the amount of 500k?

[DJPsychic]

And unrelated (sorry if this derails the thread) but can someone point out the 10k "intensity" resistor?

I.E. "intensity" pot via GGG mods: http://www.generalguitargadgets.com/effects-projects/phase-shifters/mxr-phase-45/

Is this the same as the "mix" pot shown here?

http://tagboardeffects.blogspot.com/2012/08/mxr-phase-45-modded.html


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[fowl]

[DJPsychic]

Thank you! 

Is this the same as the Mix knob?

I plan on adding this "intensity" pot and replacing the 3M9 as a "width" pot

[DJPsychic]

Before I hack this thing up, here's a sample of the pedal so far. It sounds pretty nice, although it does distort quite quickly. And maybe a little on the dark side. But has a nice watery swirl for sure.

Please excuse the unprofessionalism of my playing, It is bad! 

Using a tele into a blues jr, bridge PU - recorded on iPhone

https://soundcloud.com/user-809000973/psychic-vibe-test-1?si=6cc80f9323d34a09b06bdd6d209e8384

[ElectricDruid]

the tiny window is to be expected. find the window, power off, and measure the resistance of the trimpot, one end to wiper. then you want to use a smaller value trimpot, maybe 50k, and add padding resistors to the total of 500k either side. then your window will be much wider, easier to trim.

excellent thank you if I understand this right:

- measure the "sweet spot"

- replace with 50k trim? or did you mean 50k lower than resistance "sweet spot"?

- then add resistance to the amount of 500k?

An example might help:

Say the best place with the 500K trim is measured as 345K.

So we replace the trim with a 50K trim. We ideally want the sweet spot to be right in the middle of the trimmer, so 25K either way.
That would give us 345-25=320K for the resistor at the bottom end of the trimmer.
The other end would be 345+25=370, which leaves 130K to get to 500K, so we stick 130K on the top end of the trimmer.
So we'd need 320K and 130K resistors.
In practice 330K and 120K are the nearest standard values (and, usefully, one went up by ten where the other went down by ten) so we'd use those and accept that our sweet spot might not be exactly in the middle. We should still have enough room for manoeuvre, even if the final position on the trimmer finishes up being 15/35 instead of 25/25.

HTH