signals coming out of Zombie Chorus parts

[ahermida]

I'm helping Davefx debug his Zombie Chorus and everything appears to be OK except that the signal never comes out of the BBD chip.  The last thing to check are the signals coming out of the 4046 (pins 2 and 3/4) and out of the LFO to pin 9 of 4046.   If you can give the the frequency range and the Vpp and DC offset for these guys and the LFO that would be great...I'm not sure Davefx will be able to sleep until we fix this pedal :-)

We swapped chips but still no luck.

Alf

[george]

what sort of opamps are you using? They need to be TL062 or TL072 or something JFET based with high input impedance or the signal to the BBD won't bias properly - remember this thing doesn't have a bias trimmer on the BBD input in the manner of other chorus designs.

The signal to the BBD needs to float on DC within a certain range if it's going to work.

hth

[Davefx]

Hey George...

Both op amps have to be? I'm using 4558's, so I will give it a try.  This thing is producing what seems to be healthy triangle waves out of the LFO... Hmm.. At this stage, I'll try anything...

Thanks, gonna try it in the morning..

Dave

[Davefx]

By God, that fixed it, George!!!!  So it must be the output impedance from the jfet opamp that does it...  I slapped in a TL072, and it went from no effect to functionality!!!  Wow!!!  It had me and Alf wanting our money back!!!  LOL!

Thanks again, George!!

[Mark Hammer]

You can thank Mike Irwin for that one.  After experiencing a similar lock-o-signal, Mike said "here, let me have a look at it".  He checked it out, and once the crack in the board was fixed, he noticed that the bias was completely off, and identified the 4558 or 5532 that was in there as the culprit.

[george]

credit where credit's due ...

I should have mentioned that I read it in one of Mark's posts ...  :oops: