The One With The Lightningbolt
Many gutarists swear on the sound of overdriven tube amps. Effect builders know this and therefore like to come up with designs that emulate the sound of such overdriven amps. These are generally called emulation or simulation effects. We already had two of these, the 30+ and the Miraculum. The builders and the companies like to target the most popular amp brands and so the Marshall emulation pedals are in majority. There are quite a few that simulate Fender, Vox, Orange or even Mesa Boogie sounds. The runoffgroove.com page has a dedicated series of amp emulation circuits based on JFET tube amp simulation. Two of the most exotic exemplares from this series are the Supreaux and Supreaux Deux. These simulate the sound of a less known amp brand: the Supro.
Supro amps were popular in the 1950ies and 60ies thanks to the Valco company. This company produced many cheap brands that became popular and later also collectible and highly praised, such as National-Dobro, Jet, Kay or Harmony, but even Gretsch sold their products under their own name. Strangely enough Valco never put anything on the market under their own name. For those who are interested in the Valco company’s history you can read more here. The Supro amp brand has been lately resurrected, it is worth to check their current product line.
I never had a real Supro amp, but a friend of mine have built a clone and he also has built the ROG effects. He says the Supreaux Deux is really close to the amp’s tone. I have built both versions of the ROG effects too and I personally like the sound of the simple Supreaux more, though there is not a huge difference between the two versions. It is a low/medium gain overdrive with a very distinctive character. The tone pot doesn’t do much in my opinion, I’d rather sub it with a fixed resistor with a value between 0-500kOhm and use the effect as a simple two-pot overdrive. The maximum output level is quite good, the effect can easily be used as a booster. With a clean booster in front of it the distortion level goes quite high and has a nice texture. In practice I would say that with a switchable booster in fornt this effect can cover all needs of the average blues/rock guitarist.
The Supreaux is a three-stage JFET based common source architecture circuit, with the gain pot after the first stage. The circuit itself is a simple one, the secret lies obviously in the frequency characteristic and the gain of the individual stages. The individual stages invert the phase of the signal and since there are an odd number of stages the complete effect inverts phase as well. Not a problem in itself, but might be worth to keep in mind when adding the effect into a paralel loop. A possible mod is to replace the tone pot with a fixed resistor and add a simple tone control at the end of the circuit, like a simple low pass filter as in the Rat. Optionally one of the last low pass filters can be converted to a variable filter by changing the resistor component (R9 and C10 or R6 and C11).
The Supreaux Deux is supposed to be an improved version of the original Supreaux circuit. On the Runoffgroove site it is stated to be closer to the original Supro amps. I have not heard a huge difference between the two versions. If anything then the Supreaux Deux is a bit more sterile and more cold with a hint more distortion. The tone pot doesn’t do much here either, nor the switch, I would leave these off as unnecessary parts. Here again one could add a simple low pass tone control at the end, before the Volume pot, or change the last low pass filter’s resistor component (R9) to a variable resistor. For the +18V internal conversion this circuit needs an additional IC, and a quite expensive one. In my opinion it is not worth, especially, since I prefer the older version’s sound. Also the higher voltage increases the headroom and so boosting the effect is less effective than with the Supreaux.
The build docu (Supreaux, Supreaux Deux) for both effects can be found on the Projects page as usual.
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