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Delay effect troubleshooting techniques


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10/17/2000 8:19 PM
Rob
Delay effect troubleshooting techniques
There's been a good amount of info on troubleshooting distortion, fuzz and OD effects, but I haven't been able to find much on troubleshooting delay-based effects. Can anyone point me in the right direction? I have a dead Ross Dist./Phaser, MXR Stereo Chorus, EH Small Stone and Del. Memory Man. I am having no luck with any of them. Even basic little tidbits would help. A simple walk-through of what happens to the guitar signal as it goes through would really be nice, though.  
 
Rob
 
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10/17/2000 8:35 PM
Rob
Technology of Phasers and Flangers
Just found it at GEO. Why have I never seen this before?! Sorry..
 
10/17/2000 8:58 PM
Mark Hammer

I have something sitting on blocks which goes a little more into troubleshooting BBD chips and their clock circuits. You're going to have to wait a bit longer for it though.  
 
Experience on AMPAGE has indicated, though, that a large proportion of flanger/chorus "tsuris" (Yiddish for nuisance, trouble, strife, headache) often stems from drift in the trimpot settings. The BBD's in delay-based devices often require a bias voltage for the audio signal to ride on during its journey through the delay chip, and also may require an accurate balance between two signals emerging from the delay chip to give an accurate depiction of the audio signal. In both cases, a trimpot on the board is used to set things just so, and the trimpot may be bumped or drift due to other sources over the years. Restoring optimal functioning may often involve tweaking the trimpot by ear or by scope.  
 
In other cases, the initial point at which sweep begins (whether for a phaser or flanger/chorus) may be set by a board-mounted trimpot, rather than by a chassis-mounted control, and that trimpot may be off a bit. As a result of an erroneously set starting point, the sweep may be truncated by ceiling or floor effects, and result in less than optimal sound.  
 
There are MANY other sources of effects misbehaviour for this category of effects (especially given the use of static-sensitive components in these units), beyond the usual things (bad pots or switches, torn battery leads, etc.), but drifting trimpots are a common one, and certainly more characteristic to this type of effect than to other types such as fuzzes, etc.
 
10/18/2000 1:03 PM
CJ Landry

I have repaired many delay FX and if you give us some symptoms I will pass on experiences and fixes I have seen.  
 
CJ
 
10/18/2000 6:22 PM
Jay Doyle

OK, CJ here's one, I have an old EH Memory Man, blue face, that works except for a constant "beating" that changes frequency with the delay knob, and drastically speeds up when I switch to "chorus".  
 
Should I change the power supply filter caps? I adjusted all of the trims and set them back to normal as they did nothing. It does everything it is supposed to do, except the beating is always audible and quite annoying. I'm glad I bought it for only $30.  
 
The filter caps are the only thing I can think of. The pedal is so old these electros could have dried out. Also what voltage rating should I use? 50V? 100V?  
 
Thanks for the advice,  
 
Jay Doyle
 
10/18/2000 6:50 PM
R.G.
Could be filter caps, it's certainly old enough, and I personnally would do that first.  
 
However, what you describe could also be clock noise bleeding into the audio path.  
 
Do the caps, then check back.
 
10/18/2000 6:56 PM
Jay Doyle

Thanks R.G. as always, I'll change those caps this weekend and get back to you guys. Off to NYC for a label showcase at the Lion's Den on Friday (8:00 pm if anyone is interested) so I won't have the time until I get back. Sometimes I really hate this business and all of the hoops one has to jump through to even get a chance. Sorry for the small rant.  
 
Jay Doyle
 

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