Using Guitar Pedals in a Synth Setup


The Barber Launch Pad, used at the end of the pedal chain before we go back to the mixer.

I promised in an earlier entry to write something about using guitar pedals (which expect a high impedance, instrument level input like a guitar) with synthesizers (which typically have a low impedance, line level output). Here’s something adapted from what I wrote on the Harmony Central synth forums about how we do this, if the tech stuff bores or confuses you (it definitely bores and confuses me) just go to the last paragraph which basically just tells you what you need to do to make it work:

Going in to a guitar effects pedal from an unbalanced line level synth, what you need to worry about is volume/gain. Instrument level signals (what the pedal expects to see) are lower/quieter than unbalanced line level signals (what the synth will output), so some pedals will overload if you feed them something that’s too loud. Try to err a little on the quiet side coming out of the synth by turning down the volume, while still trying to maintain a decent signal/noise ratio. A good approach is to decrease volume until you can’t hear any distortion going through the pedal, and then back off some more. How much you will have to turn down the volume depends on how hot the synth output is, some are louder than others.

As far as impedance mismatch goes when going into a pedal, my personal belief is that it doesn’t matter. Your big worry with an impedance mismatch is when you have a (relatively) high impedance signal going into a (relatively) low impedance input. Doing this will audibly affect the sound, and it is a bad thing. But, with a synth you have a low impedance output going into something designed to handle a higher impedance, the opposite situation from above and not a problem. In general, I’ve read you want to keep a ratio of at least 1:10 output:input, but the higher the ratio the better. Your mixer, for instance will have a 10k-20k ohm input impedance to handle the 600ohm impedance coming from a typical synth. Again, all guitar pedals should have an even higher input impedance than the mixer, so you are fine.

Now, you might make the argument that the pedal is still expecting a higher impedance coming in, and even though the lower impedance from the synth will result in less distortion, maybe the pedal was designed to color the sound in a particular way with that higher impedance signal. The problem with this argument is that guitars all have different impedance outputs, and pedals all have different impedance outputs, so any given pedal can’t be expecting a particular impedance value anyway. Some pedals, like the Moogerfooger phaser, have an output (1000ohm) close to what you’d expect from your synth, others like the Moogerfooger delay (5000ohm) have a higher one. What this says to me is that plugging your Mooger phaser into the next pedal in a chain is just about as “bad” as plugging your synth in to a pedal… which is to say, it isn’t bad (as long as it sounds good to you).

Going out of the pedal might be a different matter! The two pedals I mentioned above, while they both look nearly identical and might be expected to have similar tech specs, would actually have impedance ratios of 1:10 (good) and 5:10 (not good) when hooked up to a 10kohm mixer input. Two very similar pedals by the same manufacturer, but one will work well and one maybe not so well. So, at the end of your pedal chain before you hit the mixer you will want to make sure you have a low impedance output, which you can get by using a DI, or a preamp with instrument inputs, or just always use a particular pedal with a known low impedance output. Again, you always want to go from low impedance output to high impedance input. The mixer’s input impedance was designed to handle low impedance signals, so if the last pedal doesn’t have an impedance output in the 600-1000ohm range you will want to fix that. And if you don’t want to bother looking up specs for all your pedals, which trust me is time consuming and annoying, just always put something there so you don’t have to worry about it. A couple solutions for this:

Boost/buffer pedal: Barber Launch Pad
Preamp with instrument input: FMR RNP

Again, this is just my experience with pedals. I haven’t experimented with using amps (they are probably more finicky) and I don’t run balanced cables… if either of those was the case, I’d want to experiment with a re-amp device before the amp. I did try putting a re-amp between my unbalanced synth and my pedals, honestly I heard no difference and it was just a hassle, so I’ve stopped using it. Your experience may differ. I could also just be doing it wrong! I’m not an EE, I don’t understand all the impedance tech stuff at a deeper level, and most explanations I’ve seen on the subject seem to be targetted more towards EE theory and how to design a circuit rather than how to go about chaining together instruments and pedals and recording them. That said, I’ve tried a number of solutions at both ends of the pedal chain, and this one works for me…

Bottom line: watch your volume going into the pedals, and remember you always want low impedance outputs going to high impedance inputs. The place you most need to worry about impedance mismatches is at the end of the pedal chain, before you go to the mixer or back into an effects rack, because some pedals have high(er) impedance outputs. Putting something like Barber Launch Pad pictured above or a preamp at the end of the pedal chain will fix this problem, and then you don’t have to think about all the technical crap and can just make music.