Problem with Tomboy's Zombie Chorus

[abysmal412]

Hi guys!!!
I'm trying to build a zombie chorus starting from tomboy's layout. It
seems sound very good, but there is an annoying "tick-tick-tick"
(excuse me, but my english is a shit!) in background, like a metronome
that increase speed when i turn the speed-pot.
I was searching for a solution on-line, but i didn't find anything. Can
you help me? Thanks! 

[Mark Hammer]

Tomboy's Zombie layout, while convenient, is problematic for the very reason yo posted.  Two of the op-amps are in the audio path, and two of them are in the LFO.  The two op-amp pairs need to be bypassed and power-smoothed separately, in order to prevent the sudden current draw from the LFO producing an audible "tick" in the audio path.  So, even though use of a quad op-amp makes layout convenient, it robs you of the opportunity to have seperate (and separately-smoothed) power for the two sub-circuits.

Personally, while I deeply appreciate the effort Tomboy went to, I would avoid using that layout, and use one which employs two 8-pin dual-opamps.  That way, you can also use an op-amp type optimized for each part of the circuit.

[abysmal412]

Oh, my god...
Ok, if there is no solution, i will prepare my third PCB for this chorus :-(
I think I can use tl072 for the two opamps. can you suggest others for each part?
Thank you very much!!!

[Mark Hammer]

TL022 or LM358 or some other equivalent is good for the LFO.  These are what many manufacturers use.

Hollis specifies TL062 because the single Vref he provides in the original circuit works for them.  But if you are building a version which provides separate Vref for the audio and LFO and separate biasing for the BBD, then there is no requirement to use TL062, and a TL072 will probably deliver better noise performance.

[solderman]

Hi
I made a PCB layout for the Zombi chorus. It was made to fit in a 1590A box but of cause can be used in any s box size. I have no "ticking" problem.

http://solderman.fatabur.se/Never%20Mind/Nevermind%20project%20file.pdf

Together with other MN3007 circuits on the same power chain there is slight high frequency whistling sound that comes from that the zombie is a "only what needed to work" circuit.
Your problem can also come from other circuits if you have a common power chain.

[abysmal412]

Hi Solderman,
thanks for your suggest :-)
I'll try to add a trimpot to adjust Vref, if it doesn't work fine I'll take your project XD
Thanks!