impedance?

[construct09]

i did not realise you had to match the impedance of your synth to , say , a guitar amp. you can damage an amp by not doing this? are we talking volume levels ? if so what would/could you use btween synth and amp?

[tim gueguen]

No, you won't damage an amp because of an impedance mismatch between an instrument input and an instrument. (Speaker connections are another matter. Attaching the wrong load to the speaker outputs of an amp can damage the amp.) I'd be far more worried about damaging a speaker by running an inappropriate signal through your amp ie a guitar amp speaker isn't going to like having synth bass tones run through it at high levels.

[tallowwaters]

+1

(moving this over to Sound Production where we've had quite a few of these threads.

[cornutt]

Impedance mismatch between instruments and amps is more of a concern when the signal source is high impedance and the amp is low impedance. An example is a guitar plugged into the line input of a home audio amp. Not only is the signal level low, but the tone sounds like c**p because the low-impedance amp input loads down the guitar's pickup coils, and all you get is the midrange.

With a synth, you typically have a low impedance output capable of delivering a pretty hot signal. If you plug that into a guitar amp, whose preamp section is designed to accommodate the puny signal level from a guitar, it's hard not to overdrive the input stage of the preamp. That part of the amp is not the part that is intended to be overdriven, and typically it results in hard clipping which doesn't sound very good.

[Projectile]

What tim and cornutt said is right. I've seen people spend way too much money tackling impedance matching issues that don't really exist. I don't know how all of these wrong ideas about impedance matching got started. The only thing you need to worry about when plugging a synthesizer into a guitar amp is the signal level. It's technically possible that you could damage an amp by running too hot of a signal into it, but it's mostly unlikely. Some guitar pedals can output a level just as hot as many synthesizers, and it generally isn't a problem, but it will overdrive an amp pretty hard. Just start with the volume all the way down and slowly turn it up until you hear clipping. It's probably going to start overdriving at a pretty low level. If it's a tube amp, then feel free to overdrive the input a bit.

Just be aware that most guitar speaker cabinets severely roll off the high frequencies, and don't generally sound quite right with anything other than guitar. Though, certain synth stuff can work great through them. As Tim already pointed out, the speakers may have trouble handling some of the bass frequencies put out by a synthesizer. Something like a resonant filter sweep down at 40Hz could easily blow a speaker, if it isn't filtered out by the amp's coupling caps along the way.