Power amp troubles

[Ivellias]

Hi there,

I have 2 Ampeg B2RE's and wanted to try putting a SVP-BSP Preamp into the Power Amp In socket. Worked fine apart from an annoying loud buzzing! I initially thought that it was the pre amp, but its still humming even when the pre amp is off?! Its happening with both B2RE's. I've tried different leads, no change. When I plug into the normal input of the B2RE it works fine.

Can anyone help at all?

[Dood]

Try plugging into the effects return instead of the poweramp in. You need the volume control on the B2 in order to attenuate the gain of the poweramp, else it does a good job of amplifying the noise of the output stage on the BSB. It's a bit hard to explain, but I am familiar with the schematic lay out of most ampeg stuff and I think you'll get better results with the effects return.

[Ivellias]

[quote name='dood' post='213536' date='Jun 5 2008, 10:38 PM']Try plugging into the effects return instead of the poweramp in. You need the volume control on the B2 in order to attenuate the gain of the poweramp, else it does a good job of amplifying the noise of the output stage on the BSB. It's a bit hard to explain, but I am familiar with the schematic lay out of most ampeg stuff and I think you'll get better results with the effects return.[/quote]

Its still humming Im afraid. Whatever I plug into them, be it the pre amp or my compressor, whether plugged into to the power amp in, the effects return or even the main input it still hums. If I plug my instrument into them its ok. Tried lots of different leads. Im stuck for ideas really! Did a gig with one on saturday, with the pre amp and compressor plugged into it, and used the balanced output on it and the soundman complained about the hum. Had to DI my bass in the end.

[BassBod]

Are these rack mounted (or metal cases in contact)? Could be earth loop through the cases/rack rails? If so, look for humfrees - they can work sometimes, and only need to be used on one item.

Good luck

BB

[obbm]

Are they captive or IEC mains leads?

Have you tried different ones?

Check for an Earth/Neutral miswire in the plugs if they are not the moulded type.

[Ivellias]

Im pretty certain its an earth loop now as they are rack mounted with metal rails and when I remove one of the amps it definetly improves. Im going to try insulating them from the metal rails, if that doesn't work im going to try one of those earth loop breakers. Thanks for your help and I'll let you know how I get on!