self powered amp/ speaker for busking with theremin

Can anyone suggest a suitable battery powered speaker for busking with theremin?  I have been searching and working on this project for year or more with nothing but frustrating failure in my endeavour. At home I run my B3 pro through a talking box (gives a breathy/ human sound) with Hartke 100W keyboard amp. The tone is pure/strong. I am able to power the theremin and talking box with separate battery packs. My last hurdle is a battery/self powered amp/speaker. I have tried all types of battery powered amps but the result is a hideous growl/scratch each time. I have experimented with various noise/interference reducing plugs and boards to no avail. I've tried Roland cube,(have since learned that a theremin will not work with a guitar amp. ) I have since tried Bose, LG. as well as trying to power my entire set-up including my Hartke with a portable  AC power box but no good.  I live in Perth Western Australia,there are no theremin retailer  and I took a chance buying the B3 online, but have been pleased with it. There seems to be no expert in Perth who is able to help me with my frustrating project of being self powered. Does anyone have suggestions?  Could it perhaps be an earthing issue or something like that to do with my B3? I am not an electrical whizz but have researched as much as I can online.  I would be most grateful for ideas/ suggestions. Cheers Thuggboy Zigg.

hello zigg,

i only know of one person who busked around with a roland micro bass. check this out: busking

i think there was some discussion about how to ground battery powered gear here on t.w.

hope it might help (of some sort) and welcome to thereminworld.

As my kind Swiss friend xtheremin8 wrote already, the problem is not finding a suitable battery powered amplifier, even a "Ghetto Blaster" will do that job with the theremin connected to its "aux" input, but the problem is grounding. A theremin has to be grounded in the same way as old long wave radio receivers had to. This ist nowadays normally done by connecting the theremin to an amp which is grounded through its 3-prong wall plug. The theremin's power supply itself provides no grounding to prevent other nasty effects like noise and hum induced by so-called ground loops which are created by multiple grounding of the same device chain.

Thus, there is no battery powered amp which will solve your problem, especially not in conjunction with a B3 theremin which is much more sensitive to dirty side effects than a Moog Etherwave Standard or Plus Theremin.

I know a few people who found (sometimes with my help) working solutions :

a) Moog Etherwave Plus Theremin (modified for battery operation) + Roland Micro Bass RX Amplifier + a grounding wire/strap to link the player's ankle to the system.

b) Moog Etherwave Standard Theremin + Behringer KT-108 Amplifier + 12V->230V converter from the cigar lighter plug of a car, the latter slightly modified to use the whole car as virtual ground.

Thierry said: “A theremin has to be grounded in the same way as old long wave radio receivers had to. This ist nowadays normally done by connecting the theremin to an amp which is grounded through its 3-prong wall plug. The theremin's power supply itself provides no grounding to prevent other nasty effects like noise and hum induced by so-called ground loops which are created by multiple grounding of the same device chain.”

This is so right on, there use to be arguments around here on the importance of this subject. There is more involved than just a capacitive loop to the player. My solution if you Busk in the same place all the time is to be near a flower bed and pound in a 1 meter metal rod and leave it there until next time. On an EWS I would use a Y adapter at the audio output to have easy access to a point to connect to ground. Another method to razor blade off a piece of insulation on your ¼” cable to the battery powered amp to expose the outer shield or metal braid. Alligator clip from here to connect to the earth ground rod.

PS: If your theremin playing is mostly noise none of the above really matters.

Christopher