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FDP Forum / Amp Mods, Repairs, and Projects / 1966 Super Reverb Question



Sep 19th, 2017 03:13 AM   Edit   Profile   Print Topic   Search Topic

Hi there
I have already posted this in the vintage amp section but maybe this place is better:

I have a pretty annoying problem with my Super Reverb.
The bass changes during performances. Actually it may be more than just the bass but it simply sounds like someone plugged in a low pass filter. It is quite easy to hear but since it's quite unpredictable it is not easy to fix. I have only experienced it on channel two.
What can this be. The amp has just spend a couple of weeks at the amp doctor but he only experienced it once and he couldn't reproduce it and therefore couldn't fix it.

All the best
Henrik Krogh

Contributing Member

United States

Vance Erickson
Sep 19th, 2017 11:55 AM   Edit   Profile   Print Topic   Search Topic

I had a problem that sounds almost exactly the same with my 64 Super Reverb. The bass response would intermittently disappear. Often I could get it back by thumping hard on the strings to shake the amp a little. I took it to one tech after another for years, and they all said they couldn't reproduce the problem.

I took the chassis out, hooked up to speakers and started tapping everything from the channel input upstream to the tone control for that channel, using a wooden chopstick.

I found a solder joint that would cause the bass to kick in or out when I touched it. As I recall, it was a soldee joint near the slope resistor for that tone circuit, but in your case it might be another one. I resoldered that joint, and the problem was gone for good.

Don't do this if you don't know what you're doing with a powered-up open chassis! But even if you don't, this might be guidance for a good amp tech.

Contributing Member

United States

Vance Erickson
Sep 19th, 2017 11:57 AM   Edit   Profile   Print Topic   Search Topic

I just noticed you said "low pass filter" meaning a loss of treble, not bass. It could still easily be a bad solder joint in the tone circuit.



Sep 21st, 2017 12:39 PM   Edit   Profile   Print Topic   Search Topic

I did mean a low cut so the first description is right :-)
I think I am a little less unfortunate than you. The amp seems to do it every time I use it after a few minutes. The problem is that the tech would have to stand beside me and wait for it to happen. After that I can't get the bass back again until it has been turned off for a while.



Sep 21st, 2017 01:29 PM   Edit   Profile   Print Topic   Search Topic

Low cut requires a high pass filter :-)

With the amp in its fault mode, how is the action and range of the tone controls affected?
Bear in mind the interactivity of them, check the action of each control at various settings of the other controls.



Sep 23rd, 2017 07:17 AM   Edit   Profile   Print Topic   Search Topic

It has nothing to do with the control setting. The amp starts out fine but after a few minutes the bass drops maybe 25 percent. It is only on channel two and it doesn't happen until it gets signal it seems (although that is hard to determine). It happens within a couple of minutes so there isn't any time for testing.
Over the next week I will record it everyday to see if it always reproducible and if it always follows the same pattern.

PS Low cut filter and high pass filter are the same. It's just a beast with two names.



Sep 23rd, 2017 09:12 AM   Edit   Profile   Print Topic   Search Topic

You may not have understood what I suggested to do?
After a few minutes, with the amp exhibiting the fault, report on the range and operation of the tone controls.

Contributing Member

Too Near Atlanta GA

Amp Tech Emeritus
Sep 23rd, 2017 02:54 PM   Edit   Profile   Print Topic   Search Topic

In other words, when the damned thing loses bass response, do the tone controls make any difference. I might add...though it may sound spartan...try banging on the cabinet during the the time when the amp loses bass response. Might indicate a loose connection or bad solder joint.




Bobby Roadrunner
Dec 24th, 2017 07:02 AM   Edit   Profile   Print Topic   Search Topic

Yep, when all else fails, take out the Big Hammer!!!

Contributing Member

Curled up

in the fecal position
Dec 24th, 2017 07:20 AM   Edit   Profile   Print Topic   Search Topic

All good advice!

Could be poor grounding of the tone control pots or a bad/cracked solder joint somewhere in the preamp section.

FDP Forum / Amp Mods, Repairs, and Projects / 1966 Super Reverb Question

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