omnifex analog delay self-oscillates.

[william]

I'm working on a friends Omnifex 706AD Delay pedal.  It's using a BBD MN3205 chip for delay, and has three controls, rate, mix, repeate.  When the rate knob is changed from min to max the frequency of the oscillation also changes.  The amount of oscillation also seems to change depending on what its plugged into.  I'm not sure what the problem might be.  Anyone have suggestions?

[Mark Hammer]

So you're saying there is a noticeable squeal that changes as you adjust the time delay?  That's the clock that steps the 3205 through its paces.  At shortest delays it is higher in frequency and you probably don't hear it.  Most of what is in an analog delay is actually intended tomake that whine as inaudible as is possible.  While admittedly first generation delays tended to amaze people so much that they didn't notice the whine as much (the way that surface scratches and clicks tended not to bug your grandparents when listening to Jimmy Dorsey of Patti Page), by the time we got to 1978 or so, most delays had some form of whine/noise reduction circuitry in them.  If yours produces that whine in a clearly audible manner, then something needs tweaking.

[bwanasonic]

(the way that surface scratches and clicks tended not to bug your grandparents when listening to Jimmy Dorsey of Patti Page)

Mark! Whadda ya tryin' to rile the vinyl loyalists or somethin'? I keep my vinyl clean, and many bands still crank out those big black slabs.

Kerry M

[Mark Hammer]

Yeah, that's right, I'm a vinyl troll :lol:

Nah, vinyl's great, sounds great, and I've got lots of it I keep meaning to get back to, scratches and all.  The fact of the matter, and the basis of the reference, though, is that vinyl is subject to abrasion-related damage over time, and the process of mechanically transducing physical wiggles into something electronic via a coil has a propensity to acquire hiss under the best of circumstances (yup, even when you spend a fortune on keeping them clean, or doing dumb stuff like spraying your discs with cold water to keep heat-abrasion damage to a miimum and short out static charge) and some serious surface noise under the worst of circumstances.  It's not vinyl per se.  It's what happens when something electronic gets turned into something physical and then back into something electronic.  Same nuisance as occurs with spring reverb.