Chorus.

[Devius]

So I've breadboarded the zombie chorus (RG version). I couldn't get the mofo to work. I got clean signal but no chrous. I used an NTE1641 instead of the mn3007.
I've tried a few times and nada. Can anyone recommend any other good choruses?

[scuzzphut]

I built a Tonepad Corral , which is a Boss CE-2 clone.

I etched the PCB myself and spent maybe 4 hours debugging the build (it was mostly etch issues).

The chorus is thick and deep - really excellent. The mods are good too.

[Mark Hammer]

The Zombie, stock, requires use of the right op-amps in order to be biased right. And when it comes to BBDs, biasing is crucial.

[gcme93]

Rick holt's little angel with a pt2399!

It was my first pedal, and sounded beautiful after a simple debug. Nice and small too. Search the site for the thread and go with the birthday version with the lock up fix (to be certain it'll work with all pt2399s)

George

[Devius]

The Zombie, stock, requires use of the right op-amps in order to be biased right. And when it comes to BBDs, biasing is crucial.

The voltages read normal (4.5v) on u1a. u1b I got 6.5v all the way back to pins 7 and 8 on u2. I'm using tlo82s for the opamps. The lfo worked fine as well.
Pins 2,3 and 4 on u3 were around 4.5v.

[Mark Hammer]

The Zombie wants a TL062.  Trouble is that the biasing of the BBD is shared with the op-amps.  It doesn't have a separate bias source like most chorus circuits.  This is one of the reasons why so many people will recommend other chorus circuits - because hey allow one to set the bias for the BBD separate from the bias for the op-amps.

[Devius]

Would biasing the bbd on its own work?

[Mark Hammer]

Yes, and that's why some folks start suggestig other chorues.  Because by the time you've added this, that, and the other, you end up with a CE-2, Small Clone, etc.

[Devius]

What should the bias voltage be for the bbd? 4.5 voltarinos?

[Mark Hammer]

No, and therein lies the problem.  If the optimal bias voltage for the BBD was identical to what works for the op-amps, life would be wonderful.  But it's not the same.  John Hollis tried to design the most minimalist chorus he could (and this was before the PT2399 chip ever existed), and cut a number of corners.  You will note thast Vb for the Zombie is derived from a divider pair of 10k and 15k.  WTF!!   That's right.  Instead of using an equal value pair to yield 4.5V from a battery, he used 10k and 15k to produce a 5.4V Vb.

That reference/bias voltage comes into the first op-amp, and because there are no DC-blocking caps en route, it comes out the other end of IC1 and provides an audio signal to the BBD, riding on a bias voltage of +5.4V.  Having more headroom on one side of the bias point than the other is not great news for the op-amps, and not that great either for the LFO, but it's what the BBD wants.

So the bias is ideally obtained separately for the BBD and the rest of the audio path. 

[Devius]

Anyone have the schematic for the little angel with all the mods?

[gcme93]

http://www.diystompboxes.com/smfforum/index.php?topic=96277.0

Space warbler mod thread

http://www.diystompboxes.com/smfforum/index.php?topic=86297.msg791360#msg791360

Most recent schematic version

The two mods that I'm aware of:

[Devius]

Thanks man!

[Devius]

you wouldn't happen to have pin voltages would ya?

[gcme93]

IC 1          1) varition from 1.4 - 7.4 ( lo-speed ) to 2.5 - 3.5 ( hi-speed )    
               2) 4.87 V
               3)  4.77 V
               4)   0.00 V
               5)  varying 2.5 - 3.5 V
               6)       "     2.5 - 3.5 V
               7)      "     1.4 - 7.8 V
               8 )  8.56 V (normal output of my PSU )  
                                                                     
PT2399      1) 5.02 V
               2) 2.5 slight wobble
               3) 0V
               4) 0 V
               5)  2.22 - 2.5 V   (didn,t spot the small variation before )
               6)  0.75 V
               7) 0.66 V
               8 )  0.66 V
               9 - 16) all as pin 2 , i.e.minor variation around 2.5 V

Mine were all very similar to this (slightly above these if I remember right, but my battery voltage was about 9.2V rather than his 8.56

How are yours looking?

*Edit to make the 8 ) not look like

[deadastronaut]

seriously go with the tonepad chorus...i built it and its lush..

stick a vol pot on the end of it too...

it fits in a 1590b thanks to perrow and his squeezing pcb skills.

the thread says ''zombie''  but ignore that it developed into the ''tonepad chorus''...


nice build.

http://www.diystompboxes.com/smfforum/index.php?topic=97344.msg852925#msg852925

[Devius]

I have the parts for the zombie and the little angel. I've breadboarded the little angel and still debugging (motherf*#%ing not working first time c*#$sucker!)
I'll try and get it up and running, I have clean signal bypassed and some weird sounds when engaged so somethings not right.
If it doesn't work out I'll definately try the tonepad one.

[Devius]

Correction... I HAVE it working. Sounds bizarre maxed out. Add warbler switch with the vibrato on and it kind of sounds like drunk alien robots discussing interplanetary politics.
Thanks for all the info everyone.

[gcme93]

Sweet! Hit us up with sound samples if you've got the time

[Devius]

I am using linear pots so the tapers may have something to do with it. I'll get some rev logs whens I do my next small bear order.