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FX70 Flanger Whines

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11/4/1999 3:14 AM

FX70 Flanger Whines

Hi All,

I have a DOD FX70 Stereo Flanger. It's not been used much recently but was a couple years back. The last time it was used, was in a studio. I dug it out over the weekend and noticed a rather high pitched whining which I suspect is clock bleed-through. The curious thing is that it didn't show up in the studio where things were much cleaner and quieter.

So, anybody have any idea how to go about tracing this noise down? I've down loaded the FX75 schematic from AMZ in an effort to arm myself.

Or, has anyone had this problem and know what to do?

Thanks in advance,

Dave James

11/4/1999 3:23 PM

Not sure about the innards of the FX70, but it is a common practice in circuits that use the Reticon delay chips to use the chip as a kind of two channel deal, with anti-phase clock signals being sent to each side. Then, when the signal comes out of the last stage or "bucket" of the channel, it is combined with the other side, via a trimpot which is wired as a kind of "balance" control. Since the two clock signals are of opposite polarity, when they are combined in perfect balance, they cancel each other out, in a manner that is analogous to balanced line microphones, banishing clock-whine from your output. Since the signal being carried by each clock-driven channel is IN phase, they sum appropriately. Like the roach motel, clock whine gets in, but it never gets out.

Bottom line: If there is a little trimpot at the output of the delay chip (and I say this without looking at the schematic, because the onyl one I can find at the moment is a Postscript version and I can't view it at work), then you may want to consider tweaking it since it may have drifted from its optimum setting.

Again, just a hunch, sight unseen. Better opinions might emerge from those with REAL information at their disposal.

11/4/1999 4:29 PM
Gus	Sometimes taking the effect apart and cleaning the jacks checking the solder and drying it fan sun etc. will "fix" effects that worked OK in the past. I believe what mark wrote is probably the fix.

11/4/1999 9:10 PM
Dave James	Thanks Mark & Gus Guys, Thanks for the input. Mark - I've seen the "balance" control on the FX75 schematic and now understand its purpose. Gus - I'll clean the guts when I crack it open over the weekend. If there's anyone else who'd like to comment on this situation, I'd appreciate the input. Later, Dave James

11/5/1999 12:33 AM

I had a DOD flanger that I got in a pkg deal, did the same thing, I took off the back, sprayed contact cleaner/lube into the pots and jacks, worked a plug in and out of the jacks and it still whined.
Tried the pedal a few days later, no more whine.
Guess it was just dirty.
Had a Yamaha Distortion that would do the same thing, it had PC mounted jacks, if you barely bumped the cable, whine city! I think that problem was in the jacks, and I didn't want to fool with changing them out, sold the pedal as is.
Later!
FWIW, never had that problem with any Boss, Ibanez pedals.

11/6/1999 4:35 AM
Dave James	MG - thanks for the feed back. General concensous indicates cleaning. Later, DJ

11/5/1999 3:36 PM
Mark Hammer	Re: Thanks Mark & Gus I finally looked at the FX75 schematic last night and the trimpot I was thinking of doesn't appear to be incorporated in the 75 unless the schematic is drawn wrong (don't know about the 70). That being said, you can always fiddle with it and put it back where it was if it doesn't solve the problem.

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