How about using a 500K pot as a variable divider and setting it to whatever sounds good to you?
Ethervox output goes to outer terminals of pot.
For 1/4" jack to amplifier, tip goes to wiper, shield goes to low side outer terminal.
Wow. I thought it was bad that the Etherwave Standard/Plus didn't include a standard volume knob to adjust the global signal level... and now I see that the multi-thousand-dollar Ethervox didn't include it either?
That's a feature where the $150 Burns B3 wins over all :)
I think the reason that a "standard volume knob" was not included with the EW or E-Vox probably has more to do with possible confusion over "Volume antenna" (tuning) and Volume (level) control. The assumption was probably that line-level equipment would be driven..
Many monophonic synthesisers have no output level control, including some expensive Moog models - It is assumed that the output will be taken to a mixing console or PA, not to a guitar amplifier!
I am sure that cost was not the reason for the omission - I just think that Bob did not deem it to be a useful control - He was right, and he was wrong, IMO.. Going into a mixing console, one does not want an extra stage of possible attenuation - Far better to get unattenuated signal from the instrument and deal with this at the console, as this gives best S/N ratio.. It is always best to have high drive levels from your instrument, and only have one place where these levels are attenuated or amplified.
The only reason why there is any problem is because amplifiers with the wrong input sensitivity are being connected to unattenuated theremin outputs... But where I think Bob was perhaps wrong, is that he should perhaps have taken this likelyhood into account.
The issue of attenuation is discussed here http://www.thereminworld.com/Forums/T/28571/using-a-talking-machine-with-etherwave-standardplus?Page=1
and a simple construction for both fixed and variable attenuator is shown.