1 mono signal into a stereo (amp) input?

[GibsonGM]

So I'm making a tiny practice/recording amp out of an old PC powered speaker PCB I ripped up and a spare 8" guitar combo minus its own amp.  It actually sounds really good with my Strat      Only using one channel of the thing right now cuz:

It's got a stereo chip, so 2 inputs of course. I want to feed it a mono guitar signal, inserting into both channels (is this 'bridging'?).   Is there a need to use resistors to isolate the one input that will be jumped to the 2 input terminals, or anything special like that?   I understand you'd need that if mixing the OUTPUTS of 2 opamps etc, but never heard of any official good practice for jumpering the inputs.   Seems like a 'just do it' thing, but I wanted to know if that would be 'the right way'.

In the end I'll probably whip up a quick preamp and have to go from an opamp (single out) to those inputs (two in).  Thanks!

[antonis]

Try to solder a custom cable to a stereo jack and make a bridge between right & left channel..



If it doesn't work good, place 1 X 10k resistor or so between each channel and tip wire..

P.S.
I know you're lazy enough so I don't propose you a signal splitter..
http://www.muzique.com/lab/splitter.htm

[FiveseveN]

The only issue with shorting the inputs is that the preamp will see half the impedance, so you just have to make sure it can drive it.

is this 'bridging'?

Bridging means using the two poweramps in a push-pull configuration (into a single load), which means one input signal needs to be out of phase. The datasheet for your chip should provide an example if it supports it. If not, you'll need two speakers if you want to use both channels.

[GibsonGM]

Ahh, ok, I see; glad I asked.  Antonis - even easier than that, I have the PCB and am not keeping its case or the jacks, so I could do that on the board.

FiveSeven...chip is under a permanent heatsink so I think determining just what it is may be out of the question.  It's around 20 yrs old. I may just leave one side unused - it's loud enough the way it is.   It's for recording at bedroom levels anyway w/an SM57, which it already has plenty of output to do.  Haven't made a 'preamp' and it's already loud enough.  Has surprisingly good tone for such a basic circuit.   

Thanks for the info, I knew there were a couple of things to consider!   

[anotherjim]

An amp per speaker works well and if you blow one with insanely distorted power chords, the other still works.
I assume it was a PC speaker with the electronics & speaker in one box and just a speaker in another box? Do you have both speakers?

[GibsonGM]

Yes, exactly what it was...I ripped out the tiny speakers and saved them (of course), but right now am running just 1 side into an old peavey combo cab with an 8" gtr speaker in it.   I wouldn't want to keep the PC speakers, they obviously sound like ass.  I don't think this will blow, it's likely rated higher than the PC amp output.

What makes this sound really good, too....is to pop a Mosfet Boost before it, ha ha. Classic breakup...  All my big amps (tho awesome tone) are just TOO MUCH to record w/a mic in the bedroom studio, so I want to bang out this little job to fill the gap.   Just working up a preamp deal at the moment.

[ashcat_lt]

I was messing with this kind of idea a while back, and decided the best thing to do was just cascade one of the amp stages into the next.  Maybe add a volume pot and/or some filtering in between to shape things a bit.  It was getting pretty cool, but I got distracted by other things and never actually went anywhere with it.

[GibsonGM]

Hey, that's one idea, for sure.  I'll think on that one.   So far, I'm planning to make some kind of a mosfet or fet boost, maybe do clipping diodes with a lift switch, and a simple high cut.    Thing sounds like an AC30, LOL.