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Smooshr (Power Soak/Line Out)

Concept

The Epiphone Valve Jr head sounds really good, but even at only 5 watts, it can get painfully loud. As everyone knows, these kind of amps sound best when driven hard, so what can one do? The answer is to use a power attenuator aka power soak.

Description

The Smooshr is my standalone power soak for the Epiphone Valve Jr. head, which allows me to get power-stage distortion at reasonable (low) volume levels.

It also has a line-out feature, which it incredibly useful in that it turns the Valve Jr into another preamp.

I switch between the Valve Jr and a multi-channel guitar preamp routed into a common effects unit and power amp. The tones and colors that the Valve Jr give (clean, chimey tones, smooth, class A breakup, violin-like sustained tones, etc) nicely complement the preamp distortion of the other preamp.

I call this device the Smooshr because at extreme settings, the Valve Jr massively compresses the signal. I also think of it as compressing the harmonic content as well. Pushed hard, the Valve Jr rolls off the low and high end, emphasizing the mid-range - like a thick, buttery, Vox-like distortion. This setting is really effective for single-note, legato leads (think Cliffs of Dover).

Although the Smooshr is a passive circuit that doesn't do much to color the sound in and of itself, I still consider it a kind of effect because of how it lets you get more sounds out of your amp.

Design

The power soak portion of the Smoosher is simply a Radio Shack 20 watt power attenuator, which itself is just a multi-tapped transformer mounted to a small circuit board with a ten-position rotary selector switch that selects the desired tap. Nothing new here - lots of guys are doing this.

The line-out was my design; the only line-out schematic I've found on the web for the Valve Jr is a preamp-out, which is next to useless for me. It completely bypasses the most interesting part of the amp - the power section.

Breaking out my trusty electronics books and my calculator, I came up a simple resistive voltage divider, calibrated to convert the output of the Valve Jr (through the power attenuator section) to line level (<=2V peak-to-peak output voltage @ 200-ohm impedance @ ~1kHz). I used 10-watt power resistors (Radio Shack, again). I like the design because the parts are cheap and easy to find, and it works well, especially in conjunction with the attenuator.

All the parts are mounted inside a vented aluminum Radio Shack case, with Neutrik jacks for input, speaker out and line out. The Neutrik jacks are the black plastic ones with the chrome ferules as used on many amplifiers; they're insulated from the cabinet so that they do not share a ground.

Easy to build, sounds fantastic.

Schematic