[Solved] Cepheid Chorus - only the LEDs work

[zipfool]

This seems like it's going to be tricky to figure out. Bypass works fine, but the 2nd LED stays lit even in bypass. When I engage the switch, both LEDs light up, but I'm not hearing any of the Chorus effect no matter how much I crank the knobs/pots.

I opted to go with the MN3207 / MN3102 IC pairing, but I suspect that my source for these was bogus (seller on EBay). I've tried 4 out of 10 of the pairs they sold me, and I'm getting the same [lack of] effect with all 4 pairs. I could keep trying out the other pairs, but I'm suspicious that all of them will be the same.

Take a look at these photos and LMK if you see anything else suspicious.

There's a few things to this build that are new to me: not sure what the trim pot is supposed to control, and I've never had to solder an onboard jumper to signify which chip combo I bought. Did I do the right thing by putting a bead of solder to connect each of the 2 sets of pads?

If I dial the trim pot up too high, the sound cuts out. Same if dial it too low. Right in the middle and I get clear sound/tone. What does this trim pot do?

 

[fig]

You have a private message @zipfool

 

[zipfool]

You have a private message @zipfool

Thanks so much! This is one of the most generous forums I've visited. Generosity FTW!

 

[Stickman393]

Thanks so much! This is one of the most generous forums I've visited. Generosity FTW!

One of us, one of us...

 

[zipfool]

Update: I'm getting a bit more of a chorus effect now that Fig sent me some verified MN3207/MN3102 ICs. I only notice the effect when I have both rate and depth turned all the way up. Even then, it's very subtle.

I have tried dialing the trim pot a bit and there's definitely a sweet spot but it's still barely noticeable.

Here are the voltages I'm getting:

TL022
3.9-4.5 fluctuating
4.35
4.0-4.5 fluctuating
0
4.35
4.35
4.2-4.5 fluctuating
8.73

MN3207
0
4.24
5.21
8.14
8.73
4.21
6.5
6.5

MN3102
8.75
4.21
0
4.23
0.28
8.38
2.87
8.14

TL072
6.01
6.0
5.9
0
6.01
6.002
6.01
8.86

Any thoughts on what I could try next?

 

[carlinb17]

Have you tried using a 4558 chip in place of the tl072? I believe it has a lower voltage draw and it’s what’s in the parts list for this build. I can grab the voltages from mine in the am for reference if you want them.

 

[zipfool]

Thanks! Yeah, I tried a 4558 today and got the same measurements.

 

[Stickman393]

I'll have to double check against my own IC voltages, but truthfully the CE-2 isn't the craziest chorus in the world. It doesn't quite go where the Julia does.

It's a more subtle beast...you won't get super whacked out sounds from that pedal.

I'd say try this: adjust the trimpot until pins 7/8 on the MN3207 are at roughly 1/2 input voltage as a starting point, and adjust by ear from there with rate at min and depth at max. Each BBD will be different, and you might have it dialed in right now...or maybe something else is going on. Hard to say without hearing/putting a scope on it.

 

[music6000]

Update: I'm getting a bit more of a chorus effect now that Fig sent me some verified MN3207/MN3102 ICs. I only notice the effect when I have both rate and depth turned all the way up. Even then, it's very subtle.

I have tried dialing the trim pot a bit and there's definitely a sweet spot but it's still barely noticeable.

Here are the voltages I'm getting:

TL022
3.9-4.5 fluctuating
4.35
4.0-4.5 fluctuating
0
4.35
4.35
4.2-4.5 fluctuating
8.73

MN3207
0
4.24
5.21
8.14
8.73
4.21
6.5
6.5

MN3102
8.75
4.21
0
4.23
0.28
8.38
2.87
8.14

TL072
6.01
6.0
5.9
0
6.01
6.002
6.01
8.86

Any thoughts on what I could try next?

Are all the voltages listed are as pictured:


1.
2.
3.
4.
5.
6.
7.
8.

 

[music6000]

If Voltages are matching pinout above, Check matching circles for continuity.
What Voltage do you get @ R22 - 150K Yellow circle?
What voltage do you get @ R22 - 150K Blue circle?
UPDATE: Can you confirm R26 = 33K - Orange, Orange, Black, Red , Brown

 

[carlinb17]

ok here are my voltages for reference if it helps

4558
4.8
4.8
4.9
0
4.8
4.8
4.8
9.1

22

Fluctuates 3-6
Fluctuates3-6
Fluctuates3-6
0
4.5
4.5
Fluctuates 3-6
8.99

 

[music6000]

If Voltages are matching pinout above, Check matching circles for continuity.
What Voltage do you get @ R22 - 150K Yellow circle?
What voltage do you get @ R22 - 150K Blue circle?
UPDATE: Can you confirm R26 = 33K - Orange, Orange, Black, Red , Brown

View attachment 15705

The Op Amp Diagram was to confirm the order of your previous Voltage readings are correct!!!
Your MN3102 has some low voltage going on, Can you test the PCB as marked above for Continuity & Voltage in Yellow & Dark Blue, both sides of R22 - 150K?

 

[music6000]

I'll have to double check against my own IC voltages, but truthfully the CE-2 isn't the craziest chorus in the world. It doesn't quite go where the Julia does.

It's a more subtle beast...you won't get super whacked out sounds from that pedal.

I'd say try this: adjust the trimpot until pins 7/8 on the MN3207 are at roughly 1/2 input voltage as a starting point, and adjust by ear from there with rate at min and depth at max. Each BBD will be different, and you might have it dialed in right now...or maybe something else is going on. Hard to say without hearing/putting a scope on it.

Have you built the PedalPCB version?

 

[Stickman393]

Have you built the PedalPCB version?

Yup...got a build report on the forum. Actually got one of the first batch, before the revision that enlarged SW1&2 and fixed the issue where r27 bypassed SW2 and connected directly to ground. It would have worked fine with a *3207, but I built it with the NTE1641, a mn3007 work alike. Spent a good couple of hours tracking that one down...

Zip, you're best off taking music6000's advice here.

 

[zipfool]

If Voltages are matching pinout above, Check matching circles for continuity.
What Voltage do you get @ R22 - 150K Yellow circle?
What voltage do you get @ R22 - 150K Blue circle?
UPDATE: Can you confirm R26 = 33K - Orange, Orange, Black, Red , Brown

View attachment 15705

Sorry for the delay. Yes, my voltage readings follow the order/numbering in your diagram.

As for continuity, yes both the Teal and the Red sets in your image have continuity (respectively).

R22:
Yellow: 8.7v
Blue: 2.9v

R26: 33k confirmed by both the stripes and double checked with a multimeter.

 

[zipfool]

I'll have to double check against my own IC voltages, but truthfully the CE-2 isn't the craziest chorus in the world. It doesn't quite go where the Julia does.

It's a more subtle beast...you won't get super whacked out sounds from that pedal.

I'd say try this: adjust the trimpot until pins 7/8 on the MN3207 are at roughly 1/2 input voltage as a starting point, and adjust by ear from there with rate at min and depth at max. Each BBD will be different, and you might have it dialed in right now...or maybe something else is going on. Hard to say without hearing/putting a scope on it.

Thanks for the suggestion of adjusting trim until legs 7/8 are roughly half voltage. I'm getting more reasonable numbers now for all the ICs:

TL022:
2-5 (fluctuating)
4.3
3.5-5 (fluctuating)
0
4.3
4.3
3.6-5 (fluctuating)
8.7

MN3207:
0
4.2
3.59
8.12
8.7
4.2
4.2
4.2

MN3102:
8.7
4.2
0
4.2
0.27
8.35
2.8
8.12

TL072:
4.3
4.3
4.3
0
4.3
4.3
4.3
8.85

I recorded a short video to give a sample of the tone I'm getting through the pedal:

0 new items by Colin Day

photos.app.goo.gl

It's almost imperceptible in the video. I can just barely hear a difference between bypass/enabled with my ears. And maybe I'm just fooling myself with that observation. Truly, this pedal shouldn't be that subtle, right!?

 

[music6000]

Thanks for the suggestion of adjusting trim until legs 7/8 are roughly half voltage. I'm getting more reasonable numbers now for all the ICs:

TL022:
2-5 (fluctuating)
4.3
3.5-5 (fluctuating)
0
4.3
4.3
3.6-5 (fluctuating)
8.7

MN3207:
0
4.2
3.59
8.12
8.7
4.2
4.2
4.2

MN3102:
8.7
4.2
0
4.2
0.27
8.35
2.8
8.12

TL072:
4.3
4.3
4.3
0
4.3
4.3
4.3
8.85

I recorded a short video to give a sample of the tone I'm getting through the pedal:

0 new items by Colin Day

photos.app.goo.gl

It's almost imperceptible in the video. I can just barely hear a difference between bypass/enabled with my ears. And maybe I'm just fooling myself with that observation. Truly, this pedal shouldn't be that subtle, right!?

No, it's not right, I have an Original Boss CE-2!
I have gone over your PCB with a fine tooth comb, Magnified it as big as the screen.
Can you tell me the Voltages at the Pads on both sides of R22 -150K marked in Yellow & Dark Blue in the Picture above.
Can you re check all your Resistor values with this Calculator
Click on Bands for 5 COLOURS:

Resistor Calculator

Resistor Calculator is an App developed by CherryJourney to help the user find the value of a resistor.

resistor.cherryjourney.pt

 

[zipfool]

For

No, it's not right, I have an Original Boss CE-2!
I have gone over your PCB with a fine tooth comb, Magnified it as big as the screen.
Can you tell me the Voltages at the Pads on both sides of R22 -150K marked in Yellow & Dark Blue in the Picture above.
Can you re check all your Resistor values with this Calculator
Click on Bands for 5 COLOURS:

Resistor Calculator

Resistor Calculator is an App developed by CherryJourney to help the user find the value of a resistor.

resistor.cherryjourney.pt

For voltages at R22, (8.7/2.9) look at my post from earlier this morning... I'll double check that all resistors are right. Thanks for the band reader tool.

 

[zipfool]

No, it's not right, I have an Original Boss CE-2!
I have gone over your PCB with a fine tooth comb, Magnified it as big as the screen.
Can you tell me the Voltages at the Pads on both sides of R22 -150K marked in Yellow & Dark Blue in the Picture above.
Can you re check all your Resistor values with this Calculator
Click on Bands for 5 COLOURS:

Resistor Calculator

Resistor Calculator is an App developed by CherryJourney to help the user find the value of a resistor.

resistor.cherryjourney.pt

I checked all the resistor colors/bands and all of them besides two matched perfectly with the image you posted above...

...but it looks like either that's an old/inaccurate image and PedalPCB updated their build docs, or the image you posted is correct and thats where I got resistor values wrong.

In your image, R34 and R35 are 12k. But in my build docs (and the PCB screenprint), those two resistors are supposed to be 47k. This is the only discrepancy I can see between your image and the current build docs, so it makes me curious what I should be using in those two spots.

I could try 12k in those two spots, but I run the risk of wearing out the pads soldering and resoldering.

 

[zipfool]

No, it's not right, I have an Original Boss CE-2!
I have gone over your PCB with a fine tooth comb, Magnified it as big as the screen.
Can you tell me the Voltages at the Pads on both sides of R22 -150K marked in Yellow & Dark Blue in the Picture above.
Can you re check all your Resistor values with this Calculator
Click on Bands for 5 COLOURS:

Resistor Calculator

Resistor Calculator is an App developed by CherryJourney to help the user find the value of a resistor.

resistor.cherryjourney.pt

I checked all the resistor colors/bands and all of them besides two matched perfectly with the image you posted above...

...but it looks like either that's an old/inaccurate image and PedalPCB updated their build docs, or the image you posted is correct and thats where I got resistor values wrong.

In your image, R34 and R35 are 12k. But in my build docs (and the PCB screenprint), those two resistors are supposed to be 47k. This is the only discrepancy I can see between your image and the current build docs, so it makes me curious what I should be using in those two spots.

I could try 12k in those two spots, but I run the risk of wearing out the pads soldering and resoldering.

 

[zipfool]

I poked around a bit more and discovered what was going wrong. It works now!

I noticed that C16 was the wrong capacitor. Swapped it out for the right one and it works great now.

0 new items by Colin Day

photos.app.goo.gl

Huge thanks to everyone who pitched in to help:

Music6000 and Stickman393 for patient wisdom taking me back to the fundamentals.

Fig for sending me a pair of MN3207/3102.

Everyone else I missed, thanks for all the help!