Author Topic: Zombie chorus with anti tick mod 1590b layout?..  (Read 75749 times)

Mark Hammer

Re: Zombie chorus with anti tick mod 1590b layout?..
« Reply #260 on: February 03, 2020, 07:25:02 PM »
Unfortunately, the Zombie has no DC-blocking cap between the input stage and the MN3007, otherwise I would say just drop the value of the cap to shave off some bass.

However, in an effort to simplify the circuit, Hollis used a single bias voltage for the audio path and LFO, such that the bias voltage applied to the input stage is shared with the BBD.  While it simplifies things and removes the need for bias trimmer and DC blocking cap, it also means you can't shape the tone of the wet path before it hits the BBD.

Ideally, you'll need to adjust the bias voltage for the op-amps and LFO such that it is V+/2, and provide a trimmer to feed the BBD with the required bias voltage.  I gather a 100k trimmer and 100k current-limiting resistor from the trimmer wiper to the BBD input pin is fairly standard.  What remains to be identified is the value of any cap between the output of the op-amp and the input pin of the BBD.  Note that the dry signal still goes from the output pin of the input stage to the mixer.  The added cap is just to trim off some bass and render the wet path a little more immune to clipping from large amplitude swings of bass.

Truth be told, many choruses sound a little nicer with some of the bass removed.  It makes the pitch wobble less obvious.  Normally I do it at the mixing stage, but for purposes of reducing clipping, you need to do it before the BBD, not after.


deadastronaut

Re: Zombie chorus with anti tick mod 1590b layout?..
« Reply #261 on: February 04, 2020, 03:11:26 AM »
cheers mark,  i did try a resistor out of the opamp and before the bbd, however that just lost all chorus effect..

didnt think to try a cap....so will give that a go.  8) back later.

update: tried it , no joy, lost all chorus, still clipped.

i even tried a seperate buffer after the opamp/before the bbd....same clipping result...

i tried a vol pot at the input, but that also cut the chorus.....

guess this chorus is for strats only by the looks of it... :icon_rolleyes:



« Last Edit: February 04, 2020, 04:24:30 AM by deadastronaut »
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Mark Hammer

Re: Zombie chorus with anti tick mod 1590b layout?..
« Reply #262 on: February 04, 2020, 07:40:21 AM »
I guess now you know why so many BBD-based devices also use companding.

Joewago

Re: Zombie chorus with anti tick mod 1590b layout?..
« Reply #263 on: April 21, 2021, 08:10:44 PM »
Have any of you seen this Stompboxology article on tremolo? I bring it up because there is a "'Clickless' Op-Amp Triangle Generator," on page 3. You add a small capacitor and a resistor to  the LFO and it basically rounds the edges of the square wave, where those hard shifts in current can sometimes cause clicking.

http://moosapotamus.net/files/stompboxology-mo-tremlo.pdf