Zombie Chorus help request

[fentom_lord]

Hello,
I built a Zombie Chorus recently and I was wondering if everything's ok with it. Can anyone help me interpret the voltage values? I will be following the "Debugging - What to do when it doesn't work?" instructions on this one. Here it goes

1. Zombie Chorus. It does work, but I'm not sure if it works right. When I turn both pots all the way up and then turn one of them down like a quarter turn I can hear no modulation, just buffered signal. Any changes in depth or speed take place within the last quarter of both pots' range.

2. I got the schematics here
http://www.geofex.com/PCB_layouts/Layouts/zombie.pdfI used the layout I got there. No changes.

3. I used TL072 opamps as I couldn't get 062s in my local store. I also applied the deticking mod as is suggested here
http://hammer.ampage.org/?cmd=lt&xid=&fid=&ex=&pg=4

4. No positive to negative ground conversion.
I power it with a 9V psu.

Voltages (both pots set to max values):

Power supply 8.08V

U1 pins:
1 4.79
2 4.79
3 0.89
4 0
5 4.12
6 4.71
7 4.71
8 8.08

U2 pins:
1 8.08
2 3.97 to 3.99
3 4.79
4 0
5 0
6 4.0 to 4.02
7 4.68
8 4.68

U3 pins:
1 3.95 to 4.11
2 4.01
3 3.88 to 3.94
4 0
5 4.01
6 1.35 to 1.35
7 3.83 to 3.87
8 8.08

U4 pins:
1 0
2 3.96 to 3.99
3 3.96 to 3.99
4 3.96 to 3.99
5 0
6 0.23
7 0.23
8 0
9 3.80 to 3.84
10 3.89 to 3.95
11 3.87 to 3.90
12 7.57
13 0
14 8.08
15 0
16 8.08

Can anyone help me with this one? Thanks in advance.

[Govmnt_Lacky]

I have not built this circuit yet however...... knowing about dual opamps, something DEFINITELY looks WRONG on U1 Pin 3. It should be closer to 4 to 4.5V. Also, U3 appears to be the LFO and if this is the case then it looks totally wrong.
Are you sure you used the correct values and/or tapers for the pots? Did you wire them correctly? That would take a few seconds to verify.

After that, you will need to do some debug work. Check component values, placement, and use a DMM to check for solder bridges.

[Thomeeque]

I have not built this circuit yet however...... knowing about dual opamps, something DEFINITELY looks WRONG on U1 Pin 3. It should be closer to 4 to 4.5V.

It's most probably just measuring error caused by "low" input impedance of DMM (R2 is 10M!!).. T.

[fentom_lord]

Also, U3 appears to be the LFO and if this is the case then it looks totally wrong.
Are you sure you used the correct values and/or tapers for the pots? Did you wire them correctly? That would take a few seconds to verify.

After that, you will need to do some debug work. Check component values, placement, and use a DMM to check for solder bridges.

As for the U3 being wrong, what seems wrong and what can I do about it?
When it comes to the pots or any other parts, I just printed out a list, went to a local store, gave the list to the store guy and he went around the shop and found everything one by one. When I was placing the components on the board, I checked every single one at least twice to make sure I'm putting the right thing in the right place.
I verified the pots' wiring - looks ok.
As far as solder bridges go, this was the first thing I did after having everything mounted on the board. I found one and removed it. everything else looked fine.
I'll check everything again, just to be completely sure.

[fentom_lord]

OK, I checked the whole circuit for solder bridges. Found none. I also looked through it to check component values. Everything seems to be in the right place. Maybe there's something wrong with the opamps? I'll look for possible cold solder joints, too.

[fentom_lord]

Didn't find any cold joints. Any clues?

[deadastronaut]

hi fentom lord,

i built this too, i also did the tick mod etc..i found mine wouldnt chorus on a psu, only on battery,
i put a 9v regulator in it, and it worked fine....

but yeah,i am the same i dont get much adjustment on the pots...no speed control to speak of..but i dont want it wobbly anyway..
but would be nice to have the choice.
and the the depth is pretty much the same as yours by the sound of it too....no ideason a cure apart fromchanging the pot values i guess
but im no expert....

heres mine..as you can see from the knobs..they are right up.....
http://www.youtube.com/user/100roberthenry#p/u/19/HxvZKri-5QA

[fentom_lord]

heres mine..as you can see from the knobs..they are right up.....
http://www.youtube.com/user/100roberthenry#p/u/19/HxvZKri-5QA

As a matter of fact, mine is wobblier. I'll put it in the enclosure first and then will try to record some samples and upload them somewhere.

[Valoosj]

hi fentom lord,

i built this too, i also did the tick mod etc..i found mine wouldnt chorus on a psu, only on battery,
i put a 9v regulator in it, and it worked fine....

but yeah,i am the same i dont get much adjustment on the pots...no speed control to speak of..but i dont want it wobbly anyway..
but would be nice to have the choice.
and the the depth is pretty much the same as yours by the sound of it too....no ideason a cure apart fromchanging the pot values i guess
but im no expert....

heres mine..as you can see from the knobs..they are right up.....
http://www.youtube.com/user/100roberthenry#p/u/19/HxvZKri-5QA

Robert, how did you add the pulsating led?

[merlinb]

Error

[deadastronaut]

Robert, how did you add the pulsating led?

i cant remember now , it was a while back, i just tried to look in mine but its a stuckdown and very tight in there..
and the led wire runs on the underside..arghhhhh....

i think i just connected the pos of an led to the lfo on one of the 8 pin ic's...probably with a resistor on it...

i guess you'll have to probe it  with an led to see...sorry i cant be of more help..cheers rob.

[fentom_lord]

Error

What do you mean?

[fentom_lord]

I connected R16 and the Depth pot's pin linked to it with the new Vref and I'm getting more speed control, but still no depth below 3/4 of its range.

[Mark Hammer]

This circuit really wants low-current op-amps.  TL062 will work, as will TL022 or LM358, from what I gather.  TL072 is probably asking for trouble.

[deadastronaut]

This circuit really wants low-current op-amps.  TL062 will work, as will TL022 or LM358, from what I gather.  TL072 is probably asking for trouble.

hmmm....gonna take a peek at mine again.....i may have used 072's...it was a while back now.....
its a very lush chorus though...just not much range on pots....now wheres that screwdriver?....

[Mark Hammer]

You can search through the archives and find all this info, but the peculiar way in which the Zombie uses a singular bias voltage for everything (BBD, LFO, audio path) in order to achieve its "minimalist" design, makes it not work properly with a TL072.