So I have an old Kenwood KA-3500 stereo amp that I'm thinking of converting for guitar use. I'll be modifying a lot of stuff in it to simplify operation. I've done this before on other amps that were less featured then this one.

I plan to use the stereo output to drive two seperate 12" speakers (it puts out about 40 watts rms per channel), but the input will be mono to both channels. I'm sure that folks here understand that.

My question here is: This amp has multiple different imputs including two tape inputs, phono, tuner, and Aux. I am assuming that the tape, tuner, and aux imputs are all designed to accept a 1 volt peak-to-peak signal, while the phono takes a low strength signal (like a mic or pickup). I'm trying to figure out which input to tap for the guitar (direct pickup input).

I'm guessing that the phono input would be best, but any other ideas?

Thanks guys! I've got it now and will give it a try. Some final questions: Using the variable level idea, what wattage would be best for the 47K resistor? And will there be any impedance problems between the attenuator and the line-in of most power amps? If you can advise me on that, I can take it from here.

Thanks again for the help!!

My past involved some electronics. I've built a few tube amps and done some tube repairs, but the transistor/IC stuff I'm a bit leary about. So lets see if I understand this.

Your offering TWO ways of doing this: First, leave the power amp chip connected, then run the speaker out + line to a voltage divider, and use that as a signal for the power amp. OR, run a 47K resistor (I assume from the tap-in point we discussed before) to a 10K pot and feed the power amp from that (to give a wider variety of sound (distortion).

On the first idea, I am guessing that the voltage divider idea will use the whole amp as a preamp for the new power amp....right? I like this idea, but if the speaker out goes through the voltage divider, then to ground, where do I get the signal from? I assume it goes speaker out->voltage divider->output of divider to power amp->and common grounds. Sorry, I don't know too much about voltage dividers. Everything turned up, this amp supposedly puts out 20watts rms. Not sure how much voltage that converts to, but most power amps look for 1volt peak-to-peak, which I assume is what the amp inputs to it's LM1875.

Am I getting way off track here?

Thanks! Actually, my intentions (apparently not stated very clearly in my OP), is to make this little amp a preamp only and to kill any signal to it's own power stage. I'd do this by cutting loose and then shorting pin one of the CM1875T to ground, after tapping the preamp output as you describe above. That make any difference in the way you'd do it?
Thanks.

J M Fahey, thanks for the response! Hard to follow this thing as the traces are tiny and there doesn't appear to be any schematic available, but I'll see what I can. Of the choice between the 2.2K~4.7K resistor, which might be a better choice?

I have a small Stagg BA20 amp, and I wish to tap the circuit board to create a preamp output (use this amp as a preamp). The output on these amps is driven by a CM1875T audio power amp IC. I know that pin one of this IC is the positive input, so, if I tap into that input pin and wire out to a jack on the panel (so that the board input to that pin now goes to the panel), would I then have a preamp output?

If incorrect, what should I do?  Thanks!