Stereo chorus to a delay....

[Randar]

Hi, I'm a newbie here and I'd like to get some input    I was wanting to know, is it possible to change a stereo chorus to a delay format? I heard that changing out some ic chips it could be possible. Is this true?
Thanks in advance

[Mark Hammer]

It's a much bigger job than you have been led to believe.

1) Yes there ARE delay chips with more delay-time capacity that are pin for pin replaceable with those used for short delay times like chorus and flanger, but the chip best known for delay times worthy of being called echoes is NOT pin for pin compatible with what you likely have in your chorus pedal.

2) To make a delay pedal, you would need to identify the portion of the circuit which sweeps the clock up and down, and disable it, replacing it with components that would produce a fixed, but adjustable, clock rate and delay time.  Feasible, but loads of trouble and clearly well beyond your level of expertise at the moment (of course if you're willing to wait a year or two...)

3) ALL bucket-brigade-based pedals, whether chorus, echo, flanger, etc., require lowpass filtering tailored to keep both any clock whine that has leaked into the signal path, and the aliasing produced whenever you chop an audio signal up into successive "moments", at a minimum.  The form that filtering takes will depend upon the delay chip and clocking used.  If I use a 1024-stage BBD to achieve the same delay time as someone else achieves with a 256-stage chip, my clock rate will be 4x slower, and the lowpass filters will need to be set lower to compensate.  Minimum number of stages needed to produce anything you could confidently call echoes is 2048 stages, and more likely 4096.  To achieve a couple of hundred milliseconds of delay time (assuming there was a pin-for-pin compatible chip you could buy and just pop in), you would need to clock this slow enough that the filtering on your unit would undoubtedly need to be changed, either moderately (swap out a few caps to change corner frequency) or drastically (find somewhere to stick in another 3 poles of filtering).  Just to give you a sense of the possibilities, the Zombie Chorus diy project has 3 poles (18db) of lowpass filtering,  A great many analog delays have 4 times as much (6 poles before and after the BBD).

So, uh, have I talked you out of it yet? :wink:

Still, it shows evidence you are learning, which is good.  You are correct in understanding the relationship between the various BBD/time-based effects pedals, and yes, they are part of a continuum.  The leap from flanger to chorus (and back again) is considerable shorter/smaller than the leap from chorus to delay-line, though, and that's where your request sort of blows up in your face.  Keep at it though.  Discovering analogies is a big part of what will make you better at this.  Keep at it.

[Randar]

Thanks for your answer, yes it seems alot more than I can chew, I was wondering when someone w/ knowledge would answer my post. Thank you for your expertise and consideration. Know of any good delay pedal projects that are easy to build? pt-80 or rebote 2 ? or ?

[sean k]

Theres a book called "advanced projects for electric guitar" by J.Chatwin (BP 380)and published by Babani books in England (but its no longer printed so you might have to look into second hand copies) that has all your looking for and then some,flangers,chorus and analogue delay which all use MN3102 and MN3207 and a digital delay using HT8955 and I'm kind of sure that Small Bear still stocks these chips.Just checked,he does,and when you check under his IC listing for delay and reverb you'll find hints where to start looking for schematics.

[sean k]

Actually everything you want is at general guitar gadgets under effects projects/modulation and echo with all the parts at small bear electronics.

[Mark Hammer]

Just to follow up, people have generally had good things to say about Scott Swartz's projects: the PT-80 and AD-3208.  Small Bear carries parts for both.