Possible Peavey Mod??

[Shakey 1047]

I have a little "Peavey Backstage Plus" which is a great little anp but I am wondering, are there any better output transistors than the standard SJ6505 and SJ6392. I have changed the standard4558's for OPA2134'S on the input stage which has made a great difference but I am curious if there is a similar sort of mod on the output stage.
Cheers Dave.

[nashvillebill]

Bear in mind, I'm certainly not an expert like many of the guys on this Forum, but here goes. In my opinion of course.

Short answer: nope.

Long answer: I've swapped OPA2134's for some 4558's in several Peavey amps and I too have perceived an improvement. This could be coming from one or more reasons: it could be merely a placebo effect. Or, it's because the 4558 is a BJT opamp, whereas the OPA2134 is a FET. On a preamp circuit, where the opamp may be driven close to clipping, the FET could clip more smoothly. Or it could be the slightly different impedance/capacitance/internal compensation characteristics of the FET opamp interact slightly differently with the rest of the preamp circuit.

However, the output transistors serve quite a different purpose at least to my thinking. They're not buffering or being driven into clipping (usually) or acting as part of an EQ circuit. Rather, output transistors are just like a water faucet in your sink. The power supply in the amp is the water supply, the handle on a water faucet is being turned up or down by your hand, but in an amp the input signal to the output transistor is turning the valve (the power supply) up or down. Changing one water faucet to another isn't going to make the water supply come out with any more pressure than the water supply can deliver. Changing the water faucet shouldn't make the water taste any different.

[Shakey 1047]

D'you know I never thought of it like that, so I suppose subbing a 2n3055 for the 6505 wouldn't make any difference at all?? Or any other equivalent transistor.
Many thanx Dave.

[Enzo]

Go to the Schematic Request section, and one of the sticky posts is the Peavey master semiconductor guide. Download it for you records. It decodes those house numbers. For example the two you mention are just MJ15015 and MJ15016 under the skin.

No, changing those is going to do little if anything.

[Shakey 1047]

Thanks Enzo.