Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Effects => Topic started by: BrianS on April 15, 2022, 11:42:50 am
-
Try to keep this succinct:
-non-functioning 1978 EHX Echo Flanger comes into shop. Owned by a long-time user of the pedal. He's not technical.-Multiple issues found & repaired. Pedal now works.
-"Upgraded" the AC side of the power supply: New switch wired so it disconnects both legs of AC. Earth ground chassis/3 prong cord. Originally came wired with 2 prong, non-polarized cord. AC power meets a step-down/isolation transformer and goes on to the rectified/regulated DC supplies.
Current "problem": pedal is noisy...not white noise/chip noise...mains hum. Pedal is essentially unusable when amp is set to have overdrive/distortion. Think of the nastiest 60 cycle hum you can imagine. "Clean" amp settings are fine for the most part, but the hum is noticeable.
-All input and output jack signal grounds go through the chassis. I'm wondering if I made the pedal noisier by earth grounding the chassis? I know these pedals can be noisy regardless, but maybe I made it worse. These are a real pain to work on, and I'm wondering if it might be worth the effort to either put the old cord back on (or a new, polarized 2 prong cord); or reconfigure the input/output jacks so they are isolated from the chassis & move the grounds to the circuit board.
I know someone will say "try it and find out!", which is a valid response & my next step. Still, hoping someone here has actual experience with something like this.
Link to power supply circuit: https://experimentalistsanonymous.com/diy/Schematics/Flangers/Electro%20Harmonix%20Echo%20Flanger%201.jpg (https://experimentalistsanonymous.com/diy/Schematics/Flangers/Electro%20Harmonix%20Echo%20Flanger%201.jpg)
Link to signal circuit: https://experimentalistsanonymous.com/diy/Schematics/Flangers/Electro%20Harmonix%20Echo%20Flanger%202.jpg (https://experimentalistsanonymous.com/diy/Schematics/Flangers/Electro%20Harmonix%20Echo%20Flanger%202.jpg)
Any insight? Thanks!
-Brian
-
I know someone will say "try it and find out!"
Let me! Let me! Try it and see.
I would first just disconnect the power cord green wire from chassis.
-
A lot of Copicat tape echos are not grounded here in the UK and fitting a 3 wire lead is a typical upgrade, but can introduce noise through the output lead to amplifier, ideally they need a small 1:1 isolation transformer on the output cable to stop any ground loop
Maybe it would help but it is in the signal path, so may change its original sound?
-
Tried a few things; nothing helped. I could fill a page complaining about layout & design of this thing, but I'm not an engineer, just a tech, so what do I know.
There is a part in this pedal that I've never seen before, and is somewhat defective. I don't know the proper term for it, so I'll just call it a "multi-buss". It's a long, thin "wafer" that stands vertically with leads coming out the bottom. It spans the width of the circuit board; basically bisecting it. This "multi-buss" has 3 "sections: 15V supply; 7.5V supply & ground, all in parallel. I found that one section of ground was open, so jumped that with a wire. All the other sections seem to be doing their job, though. It is kind of de-laminating on one end, though.
I hate to do it, but I'm shotgunning the rest of the electrolytics. The new parts are here; just have to put them in and pray I guess...
Thanks.
-
Picture please.
-
Here's a few pics (hopefully this works):
https://photos.app.goo.gl/pubBzZJb9ZJK5DJL6 (https://photos.app.goo.gl/pubBzZJb9ZJK5DJL6)
Didn't even see the "Bussco" label on the buss until I zoomed in to take the pic!!
-
Link doesn't work.
-
Edited link...try again?
-
:thumbsup:
-
I offed the one I had a year or two ago.
Big 60/120hz hum till I realized reservoir cap post power transformer had a lifted pad.
Perhaps?