11.29.06

One of the trickiest issues (and most often discussed) with amplifiers is to match the output of a Theremin to the input of the amplifier.

We often speak of audio signal levels. "level" refers to the strength of the signal.

In addition, we use the terms: input and output. In simple terms, you will connect the Theremin's OUTPUT to an amplifier's INPUT. You will use a patch cord (sometimes called a cable) to connect the Theremin's output to the amplifier's input.

Theremin (out) --> (patch cord) --> Amplifier (in)


Amplifier inputs come in three basic varieties:

1) Microphone (Mic) level

Mic Level is the weakest level -- thus a Mic-level input is designed to handle a weak signal and will be quickly overdriven by a higher level signal.

2) Instrument Level

This level is stronger than Mic Level but still relatively weak. Generally instruments such as electric guitars put out an instrument level signal.

3) Line level

This is the strongest signal level and is produced by CD players, sound modules, and keyboards.

For a single input to handle line, instrument, or Mic levels, the amplifier will feature an input trim pot. This is simply a knob that sets the input gain from Mic level thru Line level. Note that a trim control is NOT the same as the amplifier's master volume control.

Some amplifiers, rather than having trim pots, will have separate inputs for Mic, instrument, and line level signals.

So what happens if the Theremin's output and the amplifier's input is mismatched?

To run an instrument level signal to a line level input will result in a weak and noisy sound. To compensate, one has to turn up the master volume on the amp -- and increase the audible noise (hiss and hum) along with the Theremin's signal.

To run a line-level signal into a Mic or instrument level input will exceed the headroom of the input stage and cause an unpleasantly loud and distorted sound. You can turn down the master volume control to reduce the overall volume, however you would need a trim pot or an attenuating patch cord to get rid of the distortion.

If you plan to run your Theremin thru effects pedals, then a good plan is to choose effects pedals that have input trimmers (many if not most of them do). Without input trimmers, then you have to be vigilant about your signal levels across the entire effects chain. When things are mismatched, unwanted noise and distortion can accumulate from one effect to the next.

The Moog Theremins and the Theremax all work well with line-level inputs. I have read that some other Theremins produce instrument level signals (not sure if any produce Mic level, though).

When you pick out an amp, find a knowledgeable salesperson, bring in your Theremin, and you might say to them:

Hi. I need an amplifier for my electronic Theremin. I am not sure whether it puts out a line or instrument level. I'd like to find an amp that will match the output of this Theremin. Can we try some out? ... and go from there.

A well-matched system will give you the widest dynamic range and the lowest noise. Such a setup will give you the greatest enjoyment from playing.

All the best!

-- Kevin