Help Design a Peavey Rage 158 Based Amplifier

[teemuk]

The volume potentiometer(s) trouble me. If it's not ganged then you have a serious imbalance between the two power amps. On the other hand, if it's ganged then why not use just one?

[SECONDandBOWERY]

Yes, my intent was to use a dual ganged pot.

Rock'n'Roll,
--Andy

[teemuk]

I looked the schematic more closely and it seems to have at least three identical gain circuits that have no controls. If you only switch between preamp A and B (and do not, for example, blend them) you don't have to build gain stages separately for each preamp. (Ie. Sw1 pole also to sweeper of both 1M gain set potentiometers and to "input" of both 10k gain set potentiometers. The other gain stage looks like it could use a very similar arrangement). If you figure out the switching and signal routing more thoroughly you simplify the circuit a lot. Trust me. You probably have to implement switches with more poles to succeed. Also, i already mentioned about the "master volume" potentiometer.

Edit: I'd use a mono potentiometer and put sw1 before the series 10k resistor and 33n capacitor at the sweepers of 50k potentiometers: You now now need only one 10k resistor and 33n capacitor instead of two.

[teemuk]

A thought occured to my mind... If the switching arrangement gets too complex it might be a good idea to replace it with CMOS switches and design a control arrangement for them. This has some additional benefits: The signal path will be shortened and the switch's "life" will be hugely extended. Also, it allows implementing a good foot pedal control. This could be done with discrete components too but i consider using CMOS chips as much simpler solution.

[el mo]

hi,
very late and completely unrelated to the last postings- but: would it work to "tap" the output of the small peavey by using a small transformer and just feed that signal into any large
ss-poweramp?
basically the interaction of rage-amp and speaker should be preserved like this and you can simply plug it into any cheap PA and drive a marshall cab (good for rock'n roll).

[SECONDandBOWERY]

Not a bad idea el mo.  I was actually thinking about something along those lines where I could just rehouse the peavey in a smaller case with no speaker and feed it into a reactive load and then EQ it so it sounds like it's coming out of a real speaker and then feed it into the PA and then a cabinet.  Also, if I could house the reactive dummy load, speaker sim EQ, and power amp all together with little to no knobs, then I could use it with low powered tube amps (am I allowed to say that on this forum?)!

Rock'n'Roll
--Andy

[teemuk]

This will be problematic only if you want to switch the Peavey´s speaker off while plugging to PA. But why use a transformer: Just put a high impedance voltage divider to the output (in parallel with the speaker) and buffer it's output. A high impedance (>1Meg) will be virtually "invisible" in parallel with the speaker load and the voltage divider is used to attenuate amplifier´s too high output voltage to 1-2V range - which should be suitable for most line level inputs. Then just feed the output signal from the buffer to the PA. This is the most basic form of the circuit you'll need. If you want to isolate the source from PA (to reduce hum, have balanced input etc.) you can put a 1:1 transformer to the buffer output.