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Re: EDP Noise Problem

At 03:53 PM 9/1/2005, muman wrote:
>Hello all,
>After every loop, my EDP makes a quiet thunk sound. I have Loop IV and 
>have the
>memory maxed out. I think it's an early generation machine.
>Anyone have any suggestions?Louis Hesselt-van-Dinter

Hi Louis,

There is a trimpot in the Echoplex that may need to be adjusted in your 
unit. It is there for nulling out dc offsets at a VCA, which can cause 
thumping at the loop startpoint. Normally the trimpot is set at the 
and should not need adjusting, but maybe it got knocked out of adjustment 
somehow in your case.

I posted instructions on how to do this adjustment once long ago, it is 
here in the archives:


However, I realize those instructions need to be updated a little bit for 
Echoplexes using LoopIV. So I'll just repost it now, updated for LoopIV:

How to adjust the Echoplex dc trimpot (LoopIV version):

This requires that you actually open up the unit, and have it opened with 
the power on. *Please follow appropriate electrical safety rules!!*  If 
are not careful and you fry yourself, please don't blame me!

There's a trimpot on the PCB, near the left side, by the volume knobs. Its 
job is to trim a dc offset from a VCA. Sounds like your's is not set right 
for some reason, which would cause the thump you hear.

To set it you need to run one of the built in diagnostic tests. The test 
turns the VCA on and off at about 60Hz, so if there is an offset you can 
hear the resulting tone in an amplifier. (or see it on a scope, whichever 
way you like.)  While that test is running, you adjust the trimmer until 
the tone/waveform reaches its minimum.

To get into the trimmer test, power up the unit while holding the 
and Overdub buttons down. The display will show a version number of the 
test software at first. When you let go of the buttons, it should say 7F.

Press the parameter button so the "Switches" LED is lit (or "Keys" on 
units), then press Insert to start the trimmer test.

You should hear a ~60Hz tone in an amp. Turning the input volume off, mix 
to "loop", and the output volume up helps to hear it if it isn't obvious. 
The tone will change in volume as you adjust the trimpot. You may need a 
small screwdriver to make the adjustment, depending on the type of trimpot 
in your unit. Adjust to where the tone is at it's lowest level. (you'll 
still hear hashy noise sounds, but the 60Hz should become nearly 

After you set the trimmer, pressing parameter again will stop the test. 
Then you can turn the echoplex off and power back up normally.


hope this helps,

Kim Flint                     | Looper's Delight
kflint@loopers-delight.com    | http://www.loopers-delight.com