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Topic: [Revisit EP250 output issue] See Apr 20 posts on |
Jerry Overstreet
From:
Louisville Ky
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Posted 26 Apr 2021 8:05 am |
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Yeah, being the gearhead that I am, I'd like for the attenuation circuit to work. I can see how it would be useful as now I have just discovered I cannot sit the unit on my amp and run any kind of voume without howling feedback from the reverb control. I have to keep the REVERB level control or the amp volume very low to control it.
If I move it 4 or 5 feet away from the amp, it's fine and I can dime it without feedback, so maybe I need to examine the reverb pan mounting?
I think the PEAK light was coming on because I was having to run the INSTRUMENT LEVEL control wide open to get any usable volume. I'm assuming that now the output is the same as if the switch was in the 0dB position.
I'd really love to get the circuit board and switch operation examined. Any ideas? The switch works just fine out of the DELAY jack. |
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George Biner
From:
Los Angeles, CA
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Posted 26 Apr 2021 8:53 am
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Maybe you could use a piece of foam under it to isolate the vibration.
The first thing to do is inspect the resistor board and dB switch circuit and draw it out on paper. You'll have to make some assumptions about the switch internal operation and configuration. Then start probing with a VOM, checking all continuity and resistances.
Again, I could be wrong, but I don't think you're going to find an original replacement switch so it's doubtful you'll ever get it to the original form and function if the switch is bad.
_________________
Guacamole Mafia - acoustic harmony duo
Electrical engineer / amp tech in West Los Angeles -- I fix Peaveys
"Now there is a snappy sounding instrument. That f****r really sings." - Jerry Garcia |
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Fred Treece
From:
California, USA
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Jerry Overstreet
From:
Louisville Ky
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Posted 26 Apr 2021 6:28 pm
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Thank you Fred. I had not seen that photo. That one has a level meter, otherwise it's the same as mine. The reverb pan sits on about a quarter inch of hard foam.
A note about the feedback. When I tested it on the bench after I bypassed the dB circuit, the reverb did not howl. I could run the amp or the reverb control CW as much as I wanted.
It was only after I put the case top back on yesterday that I encountered the horrendous howl. Also, there was noise induced when the reverb was activated by the footswitch, which I didn't have earlier.
I pulled the case back apart today and noticed the howl and f/s noise was absent again, so I dunno if it's picking up a field from the metal somewhere.
Too dangerous to just leave the top off so I don't know if the case top needs shielding at the pan area or just what is necessary.....more tinkering to come. I just love electronics, don't you? 😖😩😬😵
[Edit:] The reverb howl is somewhat mitigated by sitting the unit on it's rubber feet rather than letting it rest on the bottom of the case. It's still there though and worse when racked in a case and sitting vertically on the floor. I also hear some electrical crackling when attempting to install the case cover with the unit powered up. I may have a grounding issue, but I have no idea how to diagnose it further than I already have done by visual and trial and error means. |
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