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Power Soak vs Attenuators For Amps


Elias Graves

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Is there a difference? I had a guy yesterday trying to explain how they differ. I think I got it but it seems subtle. Is there really a distinction between the two approaches?

If I understood correctly, the explanation was that a power soak more accurately keeps your amp's character in place by maintaining proper ohm levels to the speaker, thus preserving more of your amp's true character.

Is this right? Am I being fed a line?

 

EG

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That said, I'm having a hell of a time figuring out if L-pads are actually okay to use with guitar amps...sounds like people tend to damage the amps only because they're running the things cranked constantly, but I dunno.

better be a heck of an L-pad to get rid of the built-up heat. And don't L-pads make impedance fluctuate?

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an attenuator by nature maintains a constant load level...where the Power Soak improved on the concept was by varying the load the same way a speaker does, based on input levels that vary with different attacks...

 

The power soak didn't compress the dynamics as much as the other attenuators...but I believe they all do the Power Soak thing now...

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If I heard the guy right, he explained that an attenuator works on the amp itself, cutting output. The power soak goes between the amp and the speaker allowing the amp to work normally but "soaking up" some of the power on the way to the speaker.
:idk:

EG

that's where they do go, either one. That said, there are two main ways of bleeding off signal between the amp's output and the speaker. One design uses some sort of L-pad circuit. The other uses an actual dummy coil of some sort. If you go to the Weber site, they give a pretty good explanation. And they have models that use either type of design.

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better be a heck of an L-pad to get rid of the built-up heat. And don't L-pads make impedance fluctuate?

As far as heat, they're rated for various power levels it seems. I'm only looking to dissipate the output of a 5W amp myself, but I gather than strictly resistive attenuation sounds awful with larger amps anyway. You have to cut a lot more signal away, after all.

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L-pads maintain the impedance for which they are rated.

 

Powersoaker is an attenuator but I believe that the design that coined that name uses a speaker motor (meaning no cone or sound) to simulate the variances that a speaker creates in use. As the voice coil moves in the magnetic field the load changes.

 

Both can be put at the output of an amp (as a matter of fact other than the FX loop that's the only place you can put one).

 

Attenuators will suck a bit of the high end off of your signal. You can put a simple high pass filter in the circuit (meaning a capacitor across the L-Pad) to compensate for much of it. The rest you can usually dial to taste with an EQ.

 

There is a simple, but very effective L-Pad attenuator that is called the Ampwell House that I use on my 5W tube amp. Cost me less than $20 to make and works like a champ. It's bolted to the bottom of my amp stand in this picture. If you want a parts list or something I'd be more than happy to hook you up.

 

01020002.jpg

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If I heard the guy right, he explained that an attenuator works on the amp itself, cutting output. The power soak goes between the amp and the speaker allowing the amp to work normally but "soaking up" some of the power on the way to the speaker.
:idk:

EG

 

An attenuator goes between the amp and speaker. It offers some resistance (by a variety of means, resistors, dummy speaker motors, etc.) and dissipates much of the heat sent to the speaker (wattage is a rating of heat dissipation). The more popular examples of these are the Marshall Powerbrake, The Weber MASS, Trainwreck/Dr. Z Airbrake, and THD Hotplate. The Powersoak, by Tom Scholtz's Rockman is an early, obsolete example (and quite troublesome). Mine is an Allessandro Muzzle.

 

The other popular option these days is power scaling, a patented deisgn now licensed by London Power (Kevin O'Conner), it allows you to lower the plate voltage (while keeping the heater voltage intact) to lower the output and headroom of an amp. Many companies now license and incorporate the design and you can by retrofit kits from Skipz Circuits or direct from London Power.

 

The old school version of power scaling is to use a variac to lower the wall current. The downside is that since variacs affect the primary winding on a power transformer (wall current), they affect both the high voltage AND filament secondaries, which isn't good.

 

There are a few other options, but these days, most of the time it comes down to attenuators, power scaling or master volumes (both old school pre-PI and the more trasnparent post-PI versions).

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