Help with Boss CE-2B build

[peradam]

Hi,

I'm currently working on a clone of the Boss CE-2B bass chorus based on this layout: http://tagboardeffects.blogspot.com/2014/07/boss-ce-2b.html . I've built a few other vero pedals, but this one has me stumped When I engage the effect, I only get the dry signal with the vibe switch off. If I turn on the vibe switch, I get a very very weak and distorted chorus effect that's barely audible. I tried to check for accidental solder bridges and even ran an xacto knife between the tracks just in case I missed something. I also double checked the placement of all the components, tried to replace the ICs, and played around with the trimpot.

The MN3007 and MN3101 I bought from Small Bear so I'm fairly confident they're not counterfeits.

Please let me know if there is anything I'm missing!

Voltages:

PSU: 9.78

IC1 JRC4558D
1 6.12
2 6.12
3 6.04
4 0
5 6.09
6 6.12
7 6.12
8 9.40

IC2 TL022CP
1 0.70
2 6.09
3 5.23
4 0
5 6.09
6 0.38
7 8.62
8 9.31

IC3 MN3007
1 9.47
2 4.90
3 5.33
4 0.65
5 0
6 4.85
7 5.08
8 5.08

IC4 MN3101
1 9.47
2 4.85
3 0
4 4.90
5 0.49
6 7.74
7 3.71
8 0.65

Transistors:

A)
C 9.46
B 3.87
E 4.83

B)
C 9.46
B 5.32
E 5.36

C)
C 9.46
B 6.93
E 6.45

D)
C 7.02
B 0.47
E 0

E)
C 9.46
B 5.01
E 5.38

photos of the build:

[peradam]

Update: I tried to resolder some potential cold solder joints and now I have the following readings. The problem still persists though.

IC1
5.05
5.03
4.97
0
5.02
4.99
5.03
8.66

IC2
3.4-6.5
5.03
4.6-5.5
0
5.03
3.92
4.6-5.5
8.66

IC3
8.66
4.50
4.24
0.59
0
4.45
3.95
3.99

IC4
8.66
4.45
0
4.50
0.32
7.40
3.45
0.59

[j_flanders]

The voltages (0.59V) you list for pin4(Vgg) on the bdd chip and pin 8(Vgg) on the clock chip look off...
The voltage on those pins should be 14/15 * Vdd. Around 8V, from: 14/15 * 8,66V

[peradam]

Could it be that you have IC4 (the MN3101 clock chip) in backwards?
The voltages (0.59V) you list for pin4(Vgg) on the bdd chip and pin 8(Vgg) on the clock chip also point to that.
The voltage on those pins should be 14/15 * Vdd. Around 8V, from: 14/15 * 8,66V

I'm not sure...I believe they are all oriented correctly, with the notch pointing up. That's how the layout shows them. The voltages seem in line with other successful builds such as https://www.diystompboxes.com/smfforum/index.php?topic=64074.0 too.

[Slowpoke101]

I suggest setting the bias first. I've compared your voltages against my listed voltages and yours are close.
From your pictures, the MN3101 appears to be installed correctly when referring to the tagboard layout.
To adjust the bias voltage you simply adjust the trim-pot near the MN3007 chip whilst listening to a signal going through the effect. Start by having the trim-pot set fully counter clockwise, set depth and rate to mid-range and have the vibe switch open (this removes the dry signal and you only hear what is going through the delay chip). Power up the effect and apply signal (strum a guitar or an MP3 play or looper - whatever) and slowly turn the trim-pot. Eventually you will hear a distorted signal and as you keep turning the trim-pot the signal will clean up. Keep turning the trim-pot until the distortion returns. Adjust the trim-pot to midway between the two distortion zones on the trim-pot.
Now see if everything else works.

[peradam]

I suggest setting the bias first. I've compared your voltages against my listed voltages and yours are close.
From your pictures, the MN3101 appears to be installed correctly when referring to the tagboard layout.
To adjust the bias voltage you simply adjust the trim-pot near the MN3007 chip whilst listening to a signal going through the effect. Start by having the trim-pot set fully counter clockwise, set depth and rate to mid-range and have the vibe switch open (this removes the dry signal and you only hear what is going through the delay chip). Power up the effect and apply signal (strum a guitar or an MP3 play or looper - whatever) and slowly turn the trim-pot. Eventually you will hear a distorted signal and as you keep turning the trim-pot the signal will clean up. Keep turning the trim-pot until the distortion returns. Adjust the trim-pot to midway between the two distortion zones on the trim-pot.
Now see if everything else works.

Thanks for verifying and yep that's how I've got the trimpot set currently - I can hear the wet signal with the vibe switch on, but it's so so faint. I tried an audio probe on the output pin of the MN3007 and I do hear the signal ok...is there a path I should follow with the probe? Could it be an issue with another component i.e. a bad resistor or capacitor? I did a continuity probe and all my jumpers seem ok, next I'll check to see if the resistance values all look correct.

[j_flanders]

I'm not sure...I believe they are all oriented correctly, with the notch pointing up. That's how the layout shows them. The voltages seem in line with other successful builds such as https://www.diystompboxes.com/smfforum/index.php?topic=64074.0 too.

You're right. I was wrong, getting confused because this  was coverted to using +9v on these chips instead of -15V.
Instead of 14/15*Vdd it should be 1/15*Vdd which gives around 0.57V, so your 0,59V is definitely correct.

[Slowpoke101]

I forgot to welcome you to the forum..So...Welcome and we hope that you will have fun here.

Now back to your problem.
You have audio coming out on pin 7 and 8 of the MN3007. Good - that means that the clocking chip and the BBD chip are OK. The audio passes into a filter network that is supposed to clean up any clocking noises on the delayed audio. The transistor that you have labelled "C" is involved here. So the main area of interest is as shown;



Check all the components and solder connections in the area around the transistor. Essentially audio from the MN3007 passes through the 33n capacitor near IC4, passes through several resistors and capacitors, then amplified by the transistor and then exits through the 12n capacitor to the left of the transistor. From there it goes to pin 6 of IC1 and is mixed with the dry audio if the Vibe switch is closed. You do have dry audio when the switch is closed so the rest of the circuit should be OK.
This is a very non-technical guide but it may help and is somewhat simpler than a technical essay.

[peradam]

Thanks Slowpoke! I just checked all my resistors and they all seem correct, except for one - the 330k next to the 9v/ground. It is very odd - it measured at ~12.4k when soldered into the board. I thought it might have been bad so I removed it, replaced it with a spare 330k resistor (making sure it measured correctly before soldering it in), and it does the same thing! Is this expected? I have the power disconnected and I'm measuring the two ends of the resistor with my DMM.

Checking with my audio probe, the volume of the delayed signal is ok once it passes through the 33n cap, then I guess the volume drops somewhere in between that and the transistor. If I audio probe the transistor's base and emitter, both are the very low-volume signal. I double checked the connection around there but I'll triple check as well...

[peradam]

One other thing - could it be a case of a bad potentiometer for the effect level? I have it wired like so, which I think is correct according to the layout:



and just to make sure I even bought the right one, it's this pot in 250k: http://smallbear-electronics.mybigcommerce.com/alpha-16mm-single-gang-reverse-audio-w-solder-terms/

[peradam]

Verified that my effect level potentiometer is good. When turned all the way to the right, it reads 0 ohms as expected. Still no luck getting the circuit to work though.

I found this schematic for the pedal: https://www.hobby-hour.com/electronics/s/boss-ce2b-bass-chorus.php
It looks like Q3 is the transistor you're referring to? The voltages still look ok, but when I use the audio probe on the 3 10k resistors right before it (R16,17,18 in the above schematic) it seems like that is where the volume drops (especially around R16/C11).

[peradam]

Well, I decided to scrap it and start over with a new board - was extra careful/slow this time around and it worked the first time I plugged it in! Thanks for the help all. The pedal sounds great.