The wattage is not as important as the speaker size and quality of the electronics.  Unless you're playing public venues, 100 watts is probably overkill for most of us.  50 to 60 amps is more than sufficient for indoor use.  A 12" speaker is probably the best compromise.  A 15" isn't necessary unless you're playing in public and/or LOVE playing the low end, but of course they cost more.

A very nice feature to have is REVERB.  I'm sure most people here would agree.

REVERB is very important to me. I got my Fender Amp from a second hand and it is perfect for what I do, and it does have a bunch of built in effects that makes the sound of a theremin so dreamy... Love it :)

It's difficult to recommend an amp because people have so many different preferences regarding how their theremin should sound. I have attended several theremin events and some of the amps I have heard used sound just dreadful to my ears, yet their owners are delighted with them.

For the record, I am delighted with my SR Technologies Jam 150 Plus and Studiospares Fortissimo 15A Sub Bass Active.

I think reverb is an important element in learning to play the theremin.

First of all, you're going to enjoy your sound more if it has a professional, sound studio "finish" to it. More importantly, with a small amount of reverb (not so much that your sound is mushy) you can hear the echo - an instant of the sound you made after you stopped playing - and that can help with pitch identification. 

Giacomo Puccini, the Italian opera composer, used to instruct his sopranos to sing as if they were floating in a glorious cloud of music.

Coalport wrote: "Giacomo Puccini, the Italian opera composer, used to instruct his sopranos to sing as if they were floating in a glorious cloud of music."

That is such a nice imagerie.... Exactly how I feel when I play the theremin :)

"Looks like Thierry posted while I was typing the above post.I'm going to throw my hat in with him.Behringer equipment does the job, and Thierry's amp sounds like a winner to me."

Yeah, for the money, IMO,Behringer is hard (impossible?) to beat.

Fred.

Thanks to everyone for the great advice -- I really appreciate it.

I think for my purposes the Behringer K450FX is ideal, especially since it has the reverb preset. Now to find a used one! :)

Reverb rules!

Delay can be cool too, especially with slow glides of pitch.

ROLAND KC-60 KEYBOARD AMP

I've had my etherwave theremin for about 9 months.
I wanted to spend about $300 on an amp and was looking for portability and about 30 watts.

After auditioning a number of bass and keyboard amps I decided to purchase a
Roland KC-60 keyboard amp.

40 watts - 10" speaker - 3 inputs - 1 XLR input - plenty loud - easy to carry, and  only $250 for a floor model.
It produces the sound that I've heard in my mind's ear when I play my etherwave.

The three band EQ and the etherwave's waveform and brightness controls allows me a wide variety of sounds.
This is the amp for me.


I auditioned (in Guitar Center and 2 other music stores) a variety of bass and keyboard amps
(Behringer, Orange, Peavey, Fender, and some others I can't remember).

The theremin always drew a crowd when I plugged it in to test these amps.
That was fun, letting folks try their first theremin.
After all of that, I decided on the Roland.

UNTIL THE ROLAND I HAVE USED:
2 guitar amps
 - Crate GFX-15 (15 watts, 8" speaker)
 - MusicMan 112 RD (60 watts, 12" speaker)
both of these sound kind of thin without an even response over the theremin's range.

1 bass amp
 - Peavey MINX 110 - (35 watts, 10" speaker)
not bad at all - even response but without the thickness and body I wanted.
This would be the one I would use if I had not bought the Roland.

1 keyboard amp
 - Peavey KB 100 (75 watts, 12" speaker
Pretty nice but WAY too big and cumbersome.

The Roland keyboard amp is an excellent choice.

I use a 40-watt Crate Acoustic amp which has a 8-in speaker, digital reverb and sounds very nicely, one reason being that it is designed to accept high input signals coming from instruments with a pre-amp.

Also a big Peavey KB/A 100 with a 15-in speaker, it's huge and heavy but it sounds so nice with its 12-in spring reverb, it also has a -12db cut on two of its 3 channels which softens the input signal.  I have used it for many gigs when a mic and instruments are required and no PA is available.

For practice I also use a small portable TVM10 10-watt Traynor amp, it is battery-operated, the sound is rather bright and it has no reverb.

Also an important aspect is the position of the amp. Most people leave it on the floor, but the sound is much better when it can be put on a stand, and tilted back  to project the sound upward.