AC/DC powered amp

[dkevin]

Hello all,
I recently received an AC/DC powered amplifier as a "Thank you" for services rendered. It is a Peavey Companion 15 similar in design to the later Peavey Solo amp. Mine is powered by 8 ea. "D" cell batteries or by an A/C adapter. The adapter as sold by Peavey was nearly $50 and was called a "Battery Eliminator". I found an alternate that provided the specified power (12Vdc@2A..negative ground) for much less $. The amp powers up and produces sound but also has a healthy buzz. The amp is fairly quiet without the guitar cord/guitar attached. But when the instrument is plugged in the buzz becomes quite pronounced and is only slightly lessened when the strings of the guitar are contacted. I took a closer look at the battery eliminator and noticed it had a 3 wire cord and plug from the transformer to the wall source. I wonder if this cheap adapter could be modified to use a 3 wire plug as well and ground the amp chassis while it provided the 12Vdc needed by the amp. On another related topic, I use a G-Boom Bluetooth speaker for my phone/ music playback. It has an internal battery that powers the unit and is rechargeable by plugging into an adapter and wall source. Is there a way to install a similar system into this AC/DC guitar amp? A lithium battery of the same size would be much smaller and less expensive than constantly replacing the D cell batteries and the wall-wart charger could be used to power the unit or recharge the battery. Any resources you could point me towards would be greatly appreciated!

[Mike Sulzer]

One way to answer the question might be be to run a wire from the amp chassis to ground (maybe the screw on the outlet cover plate) and see if that makes a difference.

[J M Fahey]

Agree and add: not sure your problem is a grounding one.

1) what guitar pickups are you using, single or double coil?

2) what happens to buzz if guitar controls are set to 0?

3) what if you move around? Does buzz change?

4) what effect do amp controls have on buzz?
Does it disappear if all set to 0?

[Enzo]

Does this hum ONLY happen using the adaptor? In other words: on batteries is the amp nice and quiet?

The adaptor itself has a grouded mains plug, but note the power from the adaptor to the unit is only two wire. EArth ground doesn't come up the power cord.

If the power was the issue, it wouldn't care if something is connected to the input. I'd be checking for the input jack grounds.

[dkevin]

I tried the amp again with a different guitar (hb ) and different(better) cord and the buzz was less noticeable. The original guitar was a strat copy (single-coil p.u.) so it may have been part of the buzziness. I replaced the off/on switch with a Peavey rocker switch ( it had a huge paddle type switch stuffed in the hole) and tried it once more. All these trials have been with the same wall-wart 12V/2A power supply. Anyway, I tried it and found some interesting things...the buzz drops out completely when the high frequency knob is pulled and pressured gently upwards. When my fingers approach the hf knob, the hum gets louder and louder. It's like my body is acting as a ground. I am leaning toward removing all the jacks, pots and pulling the PCB to examine the connections. It's either that or hire someone full-time to pull upwards on the hf knob while I play the amp. The amp sounds pretty good for an inexpensive SS amp. I'm thinking it would be a pretty cool vacation amp...throw it in the trunk and play it at the hotel or the beach. Thank you for the advice and I'll let you know what I find inside.