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Fender reverb circuit diagnostics/repair
Fender reverb circuit diagnostics/repair
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Old 3rd April 2013, 04:33 PM   #11
cancon is offline cancon  Canada
diyAudio Member
Join Date: Mar 2011
Thanks again, that's interesting.

The old pan is 4EC3C1B. I think you're right - this was a wrong replacement. I learned a lot from these two links:


So the important details from the code translate to Type 4 length (17"), 600ohm input impedance, 10k output impedance.

Delving further into the reverb domain... I notice (more often than not) that reverb circuits are noisy, commonly adding lots of hiss as you bring up the control knob. I did a quick test, unplugging the pan input did not reduce the hiss, but removing the output did...so would the pan or recovery stage be suspect?

Last edited by cancon; 3rd April 2013 at 04:51 PM.
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Old 4th April 2013, 12:02 AM   #12
Enzo is offline Enzo  United States
diyAudio Member
Join Date: Sep 2004
Location: Lansing, Michigan
Hiss is a companion to gain. The reverb recovery deals with weak signals and so has a lot of gain. That can be noisy. You can unplug the reverb cables from th baack of the amp and listen to the hiss from the circuit itself. The long wires down to the pan will pick up noise. They are shielded, but that is not 100% efective. Also, the footswitch for reverb is simple, it grounds the return signal. The reverb footswitch is a shielded cable, parallel the pan output, and in the foot pedal it simply shorts teh shield to teh signal. So unplugging the footswitch potentially reduces noise. Anothewr factor, the metal reverb pan has an open side. One might get some improvement by putting a metal cover over the open side.
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