Chorus Pedal HELP. EBS Bass Chorus/Flanger

[nandrewjackson]

A friend of mine has an EBS Bass Chorus/Flanger.  When he plays his Bass through it, it starts to "oscillate?" and "feedback".

I took apart to see if anything was visibly burnt out, bad solder joint, etc, but I have NO IDEA how a chorus pedal works.

It works fine with a guitar through a small practice amp, but when it's hooked into his bass rig (MESA 400+ and 4-10 cab) it goes berserk.

He uses either an active Ernie Ball or a passive Rickenbacher, it does the same with both basses.

Does anyone have any clues on this one?  OR does anyone know a good article on the workings of chorus pedals I could look into.  I can find lots of schematics, but I can't use that info without any explanation of what's going on in there.

The pedal was bought new and worked fine for 6+ years.
Thanks, Noah

[smackoj]

I had a pedal a few weeks back that did the same thing. I found out that the bias on the IC was not in the proper range and the gain was so high it just squaled and skreetched. If you can isolate which resistors are used to bias the transistors or op amp or jfet/mosfet, you can add some more resistance at that point and see if it calms down?

good luck,   

[nandrewjackson]

thanks, smackoj.

I'll look into that, it sounds like a good starting point.

[nandrewjackson]

I am officially giving up on this EBS Unichorus.  99% of the components are SMD and about 2 or 3 mm in size.  the board is double sided, very crowded.

There are 2 double op-amp chips, all of them being used, the chorus/flanger is MN3207 and MN3102, but with unreadable SMD resistors and caps, it's a no=go.  There are also 2 other chips on the board, one 12? pin and one 16? pin.  Very small and I tried to search online what is written on top of them, couldn't find them anywhere online.

[super&plexi]

Hi, understand your troubles, if you haven't totally given up on it yet, hit up the diy stompbox forums;Aron Nelson, tagboard effects, GEO, diystompboxes, there are tons of really helpful folks, info, ......you will be bitten by, and probably build something, I was. and if possible, can you switch op-amps?  anything socket-ed?. I have old DOD bass phaser/or whatever, and by changing 8pin dips I can get it to go wacky, or tame. I think it might have to do w/money saving in design;cheaper products can require close/custom  component      matching. maybe something drifted, or because basses can have such large hi or low varying  outputs, the input impedance/and possibe buffered input might be somewhere to look 1st. if he wants this old dod, 'cause ya can't get that one to work, let me know, I got at estate sale cheap, and love trading, or?  I warn you, those little boxes are addicting, frustrating, but I have wireless headphones, splitters for home stuff, besides  my own tubescreamers, phaseshifts, delays, envelope followers, amp sims, that I made, on my board, and around the house because I was in your predicament. good luck either way.