Hum From Vertically Mounted Reverb Pan

[Jecarroll7]

I have two Acoustasonic non-dsp amps with identical reverb hum.

After making sure the circuit was working, playing with the wires and trying a new pan I isolated the hum to the vertically mounted pan (stock position).

I mounted the same pan flat to the cab floor and it significantly reduced the hum in both amps.

Has anyone else run into this yet?

[Enzo]

Or try mounting it where it was, but rotated 180 degrees. The OUTPUT end of a reverb pan can pick up the field around a power transformer and so needs to be as far from one as possible.

ANother ploy is to cut a sheet of thin steel to cover the open side of the pan, and screw it on to shield the sensor inside.

[Jecarroll7]

Good thoughts Enzo, maybe I missed something but I didn't detect any electrical interference, even waved some components past the transformer.

But I think you solved this in a posting in '08 (which I found after my post above) where you talked about air flow contributing to a reverb feedback loop.

The pan was sitting vertically directly behind the speakers. When mounted, there is at least a 3/16" gap between the bottom of the pan and the wood.

Since these amps are closed cab and 10+ years old as are the pans and springs, I wonder if over the years the springs lost just enough tension to be more susceptible to speaker airflow?

My guess is the correct fix would be a reverb pan bag or a new pan?

Either way I mounted both to the floor of the cab toward the rear and they sound fine. Less direct airflow in that position I guess.

Thanks for your help from the '08 posting and now.

[Bruce / Mission Amps]

Huh? You mean airflow is jiggling the springs or something?...??

[Jecarroll7]

Well let me put it this way, pretty sure it was mechanical and not electrical.

What I'm not sure about is if it was air from the speaker, cab vibration or pan vibration or all the above.

I have to believe the amp didn't leave the factory with that hum, so my guess is the reverb springs lost some of their tension with age.

Whatever the reason mounting it to the floor (center and to the back) cleaned up the hum.

[Chuck H]

Interesting. Of course it's entirely possible that the reverb pan was suffering acousical feedback in hum related frequencies!!! This sort of thing could be hard to diagnose given that hum sources are generally electronic rather than acoustic. Whether it's luck or savy I'll offer kudos for making short work of the problem. And add...

I once had the daunting task of adding built in reverb to a head type amplifier. As per Enzo's suggestion I found that pan orientation and location are everything. I did check both orientations and scooched back and forth. In the process I found a location that was dead quiet. One inch left, right, forward or back and the hum crept in. But I mounted in the quitest location and all was well. Grounding is also paramount for reverb systems. That wasn't the issue in this case. But it has been for me in the past. These experiences, for me anyway, explain why all the BF reverbs hum. This is a problem that should never have been. A lot to be known. All available here with searching. Best site of it's kind on the net.

[Enzo]

I am not sure why I might have said anything about airflow specifically. But I do consistently warn against screwing reverb pans down tight to the wood. They need to sit up off the wood and free to wiggle. Not for air flow, but for acoustic/vibrational isolation from the wood.