Bad Buzzing in SF Bandmaster Reverb

[Blues Lyne]

I have a SF Bandmaster Reverb that was Blackfaced about 12-13 years ago. Both channels are connected to the reverb, so they are in phase. I use an ABY box to switch between the two channels. It also has a Vari-Watt installed.

Lately it's buzzing really bad, but the volume of the buzz will fluctuate. Some days it's better than others. Sometimes it will change from one minute to the next. If I turn both volumes off, the buzz stops. If I have nothing plugged into the amp the buzz stops. It buzzes if anything it plugged into the amp. It's not buzz from my guitar. It does it even if the pedal board is muted (Boss tuner is the last pedal on the board and it has a mute function). It buzzes even if a calbe is plugged in, but not connected to my board or guitar. It's worse If I plug into both channels. It doesn't change depending on whether I'm touching the strings of the guitar, like some grounding issues cause. One night it seemed like it was worse if the reverb was on, but that hasn't always been the case. It seems like the switches on the ab box and my pedals tend to pop more than they used to, but that could be unrelated.

I am running the volume around 7 with the Vari-Watt turned down, but this seems like more buzz than I should get. This is buzz, not the usual white noise.

My first thought was caps, since it's been almost 15 years since it was recapped. But, if it was filter caps, would it stop if nothing was plugged into the amp, or if the volumes were turned down?

Anyway, anythoughts on where to look would be appreciated. Thanks.

[Jazz P Bass]

Input Jack

First, make sure all of the input jacks are connecting to ground when nothing is inserted.
There is a grounding tab on each jack, sometimes they stay open circuit.

[Blues Lyne]

Help me get my mind around this. This has been suggested a couple of times. Most of what I know about electronics is just what I've picked up from tinkering with amps and pedals. In other words, not a lot. So, I like to learn a bit of the "why" along the way.

Is the issue that some of the jacks that aren't being used may not be grounding? Since there is no buzz when nothing is plugged in, I'm assuming the issue isn't with the jack the cable is plugged into, but maybe there is a problem if something is plugged into one jack and one of the other jacks isn't grounding. I haven't tried plugging into the second jack in each channel, but it buzzes on either channel with I plug into the first jack.

Anyway, I'll look them over. Thanks

[Albert Kreuzer]

If the amp is quiet with nothing plugged in and the volume up, the problem is not in the amp.
Maybe a grounding issue with your house wiring? RF interference?
Have you tried the amp in a different environment?

[Blues Lyne]

I've been using it at Church mostly. We are rehearsing a new drummer, so haven't schedule many gigs. We've done a couple of outdoor gigs, but it's hard to tell if it was as bad. I'm going to bring my whole rig home next time I'm there and see if it does it at home.

[loudthud]

Sometimes there is corrosion between the jack washer and the brass plate behind the front panel. Remove, clean and re-tighten. Pots also have the same problem form time to time.

[Jazz P Bass]

Jack grounding

Quote:
"Is the issue that some of the jacks that aren't being used may not be grounding? Since there is no buzz when nothing is plugged in, I'm assuming the issue isn't with the jack the cable is plugged into, but maybe there is a problem if something is plugged into one jack and one of the other jacks isn't grounding. I haven't tried plugging into the second jack in each channel, but it buzzes on either channel with I plug into the first jack."

Sorry. I missed that about "no buzzing" if nothing is plugged in.
Probably not the jacks.
John G

[Enzo]

Well, maybe.

When nothing is plugged in, the jack is within the shielding confines of the metal chassis. If the jack relies on the chassis ground, in this condition at worst a little background hum, especially when you bring your hand near. But plug a guitar cord in, and all of a sudden there is all this cord and guitar outside the amp acting as an antenna plugged into this ungrounded jack. Boocoo noise.


Not saying this is what is happening now, but one can have poor jack grounds that only really evidence themselves when something is connected.

[Blues Lyne]

This is so wierd. At one point the buzz seemed to go away if I unplugged the reverb cables, but then came back. I tried it with just guitar-cable-amp and it buzzed. But last night, it only buzzed if it was connected to my pedal board. I unplugged my onespot and all the buzzing stopped. I'll have to bring my other amps in and try the onespot with them, because I didn't get any buzz from it when I was using my other amps previously.



I plugged in another power supply and the buzzing was gone, though there was more hum or white noise than when the pedal board wasn't plugged in. I started to unplug the power from all of my pedals to see what happened if they were all run from batteries, but realized I'd have to take the board apart to get some of the plugs out. And, some of the pedals didn't have batteries in, so I'd have to get some batteries and pretty much completely disassemble the board. So, I plugged everything back in, and now I'm getting a lot of hiss from several of the pedals that were totally quiet before.



I'll experiment with using my pedal board with different amps tomorrow at rehearsal.

[Lee_ranaldo]

it's know that those DC-ON-TAP power supplies have a constant hiss on the background.

When u say "buzz" sounds like "hum" to me

Faulty Ground Switch (if it's a 120 VAC version)
Faulty Power Cable (the ground wire must be not properly connected or internally cut)

if when it was modified into Blackface version maybe he modified the grounding scheme and something got loose

What happened to me working on a fender amp was that it had tied the cathode resistor from the reverb driver into another stage so it was buzzing randombly with a lack of volume.

Since it happens randombly i will suspect from a bad ground loop there