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Author Topic: Peavey IP1 Preamp Schematic?  (Read 578 times)

Scott Novak

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Peavey IP1 Preamp Schematic?
« on: September 01, 2019, 06:36:19 AM »
I'm seeking a Peavey IP-1 preamp schematic.  It's about 1979 vintage. The preamp seems to be a good candidate for upgrades as the PWB already has sockets for the Op=Amp ICs.

It's using 4558s and some other op amps that don't appear to have any markings on the top or bottom.  Based on their positions on the PWB I suspect that the unmarked Op Amps are a lower noise type.

After cleaning the pots with Deoxit D5, channel 1 seems to be operating normally.  However, on channel 2 when I rotate the gain control I hear noise and when the control is rotated near maximum gain I hear what sounds similar to a high frequency oscillation.

The block diagram on the top of the preamp shows the "gain" control being part of the negative feedback loop, which may explain the behaviour of the control.  I haven't hooked up an oscilloscope to look at it yet.

Swapping out the 4558s in favor of OP-249s is a no brainer.  But please let me know if you know of any better dual Op Amps.  I've noted that the DC offsets on the OP-249s are so low that I've been able to remove electrolytic capacitors from the feedback circuits.  The electrolytic capacitors cause so much noise and DC drift that the DC offset varies less WITHOUT the capacitors.

Does anyone have any idea what type the unmarked Op-Amps might be?

Scott Novak