Which op amp for Zombie Chorus?

[ranchak]

I did a search and I see that there are mixed opinions and reviews of which op amps to use in the Zombie Chorus. Anybody want to throw in their two cents? I want to start on this project this weekend and have everything but the op amps.

[Mark Hammer]

This has been discussed to death but if you're new to the discussion, not our fault to ask, eh?

The original schematic used a single bias voltage (Vref) to accomplish several different tasks, one of which was biasing the BBD chip.  THAT design, intended to cut several corners, relied heavily on using TL062 op-amps or else things would get "stuck".  A more fully-fleshed-out version of the circuit, with separate BBD-bias and Vref for the the op-amps and LFO, tends not to run into those problems, and other op-amps will work.  Although it only uses 4 op-amps, it is wiser to use a pair of dual op-amps than a quad.  This lets you decouple the power supplies for the chip providing the LFO and the one carying the audio signal.  That arrangement provides better immunity to LFO-clicking.

Ultimately, a TL072 for the audio path, and a TL062 or TL022 for the LFO, is probably about as decent an arrangement as you can get. The TL062 is not as good as the 72 for noise but it uses less current so the sudden drain on the power supply from the LFO will result in less audible clicking.  You don<t really care about noise specs in the LFO portion.

[ranchak]

Is this a build worth doing? Should I try a different chorus?

[oli]

Hi,

it is for sure worth building it. I recomend the "deticking" mod from http://hammer.ampage.org/?cmd=lt&xid=&fid=&ex=&pg=3

Regards,
Oli

[Mark Hammer]

Is this a build worth doing? Should I try a different chorus?

I've got a half dozen assorted chorus pedals, including a Zombie, a CE-2 clone and a Small Clone clone.  The Zombie lacks much of the lowpass filtering in the other pedals, so the tone tends to be a bit brighter with a bit more noise coming through.  If you wouldn't be able to figure out how to do the power supply decoupling and biasing on your own, then I suggest the CE-2 clone is likely the safest bet, since all of that is already worked out for you on a nice tidy layout.  They all use the same 3007 chip, so you'll have to mail order from somewhere anyways.

In general, a mod here and there can make any single one of them mimic the others.  You'll be happy with a CE-2 clone.