Surprise Sound Lab : HVO - High Voltage Overdrive





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Published on Aug 26, 2013


250 internal Volts makes for a very dynamic overdrive. The HVO bites. You get three voices, gain, treble and bass control, 3 bass rolloff settings and 3 gain settings. The HVO also has a power on/off switch - that's different for an overdrive! You can use it as a clean boost, standard OD (low to high gain) or as a fairly brutal distortion box.

From Kim Hardee at Surprise Sound Lab:

"The HVO is the result of a question I asked myself -- is it possible to make a solid state pedal that sounds like a good tube amp?.

I have been dissappointed in all of the overdrive pedals that I have tried over the years. They all lacked dynamics and sounded like mush. The ones that used discrete transistors instead of opamps sounded better, and I think this is because opamps use a large amount of negative feedback, which kills dynamics. Even the pedals using discrete transistors still didn't sound as dynamic and rich as good tube amps, though. I think part of the reason for this is that they are running at a low voltage, 9V or 18V compared to at least 250V in a tube amp.

I decided to try to design a solid state pedal that mimiced a tube amp as much as possible. The unique properties of a tube amp are that the preamp gain stages use triode tubes and run at very high voltages. When over-driven the grids of the triode tubes conduct and clamp the input voltage.

The I-V characteristics of transistors are very non-linear and very different than a triode tube characteristics. After much research and thought, I eventually came up with a way to make a transistor behave much like a triode tube. Normally transistors have characteristics that are very similar to a pentode vacuum tube. By using some ideas that others came up with and a few of my own, I succeeded in making the transistors behave like triode tubes.

By using high voltage transistors and a proprietary internal power supply, I was able to run the transistor gain stages at 250V. This is about the same voltage that's used in tube amps.

When I powered up the first prototype and played a few notes, I was shocked as how much it sounded like a tube amp. All the harmonics and dynamics were there. It sounded better than any other overdrive pedal I had tried. There were still a few bugs to work out, but I had the answer to my question -- yes, it is possible to make a solid state pedal that sounds like a good tube amp.

I took about 6 months of tweaking to get the prototypes working perfectly. Most of that time was spent minimizing noise and getting the most amp-like tone.

The final results have far exceeded my expectations, and I am very excited about this pedal. I'm confident that those of you who give it a try will find that it is the best overdrive pedal you have ever heard.

The internal HVO power supply only puts out a few milliamps at 250V -- not enough to really hurt you, although you'd feel it. Also the case is fully grounded, so there's really no way to get shocked unless you open it while it's powered up. Basically, it's much less dangerous than the power supply on a typical pedalboard."

Today's recording gear:

Guitars: Smitty Custom Guitars S-Style with Brierley Rebellion Pickups; 2008 Charvel So-Cal Style 1 (USA), stock.
Amp: Laney VH-100R Clean Channel & L412 Cabinet (Greenbacks)
Cables : Providence
Mic : Violet Design 'The Amethyst' (amp) Samson Airline77 (me)
Camera : Canon 60D (me) and Sony HDR CX150 (pedal)
Soundcard : AVID Mbox Pro 3
Computer : Apple iMac 27" i7 3.4 GHz 16 GB RAM
Software : Pro Tools 10 LE, Waves CLA Guitars (slight comp over input track), Waves L3-16 Limiter (to keep levels in check at output), Apple Final Cut Pro X (video editing and Youtube compression)

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