Best way to lower audio output

Posted: 5/1/2009 5:28:46 PM

From: United States

Joined: 3/26/2009

I have an Etherwave Standard and have purchased a Peavy Vypyr 30 guitar amp.

The audio output needs to be lowered. Here the solution per p. 9 of “Understanding,
Customizing, and Hot-Rodding Your Etherwave,”

“To reduce the Etherwave's audio output level
so that it will not overload the input of a guitar
amplifier, remove R33 (4.7K resistor) and
replace it with a 47K resistor. “

Would it be best to make this mod or get a filter box (direct box) with a selectable
Posted: 5/1/2009 8:53:28 PM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

Why not do the mod instead of buying and worrying about lugging around all of the extra equipment? Those are the kinds of little things that always get left behind when you want to take your theremin out of the house to play.

While you're at it, why not just ADD the 47K resister beside the 4.7K plus a single-pole/double-throw (SPDT) switch so you can switch between them as needed? This type of switch (HI/LOW Output) is common on most vintage synths and keyboards.
Posted: 5/1/2009 9:11:31 PM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

BTW....I thought the Vypyr was an interesting name. However, since it is an "amp", I thought "Vampyr" would be more fitting.
Posted: 5/1/2009 9:23:04 PM

From: Asheville, NC

Joined: 1/25/2008

I did the same mod (with a switch). It works like a champ.

See my post regarding it Here ( Some helpful folks added some tips that might be worth considering.
Posted: 5/2/2009 10:04:56 AM

From: Asheville, NC

Joined: 1/25/2008

I also have a Behringer Ultra-DI 100 direct box that can attenuate a signal up to around -40dB. I think they are only about $40 if you didn't feel like soldering.
Posted: 5/2/2009 7:28:43 PM

From: Colmar, France

Joined: 12/31/2007

The possible "problem" is that guitar and bass amps have a non-linear frequency response in order to compensate the response of magnetic pickups which have much less output voltage at lower frequencies. So these amps act as a low-pass filter which risks to dull the theremin's sound...
Posted: 5/3/2009 11:36:58 AM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

"So these amps act as a low-pass filter which risks to dull the theremin's sound..."

That's not always a bad thing. Some people may prefer to have the higher frequecies attenuated a bit. That way they won't get quite so shrill.
Posted: 5/4/2009 12:41:11 PM

From: Escondido, CA

Joined: 2/6/2008

Thanks, Thierry, I forgot to mention that (frequency response tailoring)on my post to that other place that shall not be named :)

Guitar amps sometimes have a "bright" switch. That circuit switches in a treble boost filter that attempts to compensate for the roll-off from the guitar. Magnetic guitar pickups actually respond to the rate-of-change-of-flux rather than linearly responding to string vibration frequencies. This, in essence, amounts to a low-pass filter response.

But the "dull" sound probably has more to do with running the guitar amp at reduced volume (or attenuated input signal) then anything else. This effect is explained in reference sources as "loudness compensation" and those usually refer you to the "Fletcher-Munson" curves. Those graphs show the ear's frequency response at various volume levels.

Another interesting thing that can be seen from those graphs is the peak around 2-3kHz. In guitar amps and in some early hi-fi amps, they had a "presence" control which allowed you to boost the frequency response in that range. Boosting response around that point has the effect of "bringing a singer to the front".


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