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THD UniValve Single Channel Guitar Amp |
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The THD Univalve is a 15-watt class A tube single ended guitar amp. This is one of the best amps out there for recording or for use as a preamp. The main idea with this amp is that you can put almost any power tube, i.e. 6L6, 6550, EL34 and others, as well as any preamp tube (12AX7, 12AT7 etc...) in the amp. In essence you can get the Fender Twin sound, or a 1970's Marshall (6550) sound, or a Mesa Boogie wound just by changing the type of tubes. The other amazing thing is that you don't have to re-bias the power tubes, the amp is self biasing. The amp comes with two 12AX7 preamp tubes, and an EL-34 power amp tube. You can check out Groove Tubes for other power output tubes for the amp. Changing the tubes is as simple as unscrewing the four thumb screws, lifting off the black tube guard, and sliding off the spring tube holder and changing the tube. Of course this should be done with the amp unplugged and allowed to cool off for a few minutes. The amp comes with a power soak that allows you to turn down the volume of the amp and still over-drive the output tube. THD calls it a Hot Plate Power Attenuator. You might be thinking WHY have a power soak on a 15 watt amp? Because it 15 class-A watts and it's louder than you think. We compared the amp to a 50-watt Marshall and the Marshall was louder but not by much. Of course the amp can't compete with say a 200 watt amp in volume. You can however plug the line output built into the back of the amp into another amp, power amp, or mixing board. Use this amp to get the great tone and then use a Monster power amp to get to ear damage level. In my studio there hasn't been a need for a louder amp and most of the guitarist that have played the amp end up using it on the recording. A single ended tube means there is only one output tube. Because of this the amp has to run in what is called Class ‘A’ mode. The thing with it being a "CLASS A" amp means that the output of the tube is always on or technically speaking the plate current flows all the time. They run a little hotter than other amps because of this. Current is always flowing because it doesn't use two separate tubes ( push-pull) where one tube would output the positive side of the signal while the other tube output the negative side. The Univalve surprisingly only has one Valve or tube which outputs the complete full range signal (Single Ended Amp). Meaning the amp's output signal is ON all the time. When the signal changes from positive to negative there is no cross-over distortion, or phase cancellation that removes many of the great sounding EVEN Harmonics. Because of this there isn't any cancellation of the EVEN HARMONICS which is what gives you that great tone and sustain. The balance between ODD and EVEN HARMONICS is what gives this amp unique sound. The amp gives you more sustain and if you like a more controllable feedback this amp does it. Upper even harmonics are accessed easier so you get more pitched/controllable feedback and sustain. FYI: Most Marshall amps for example class A/B push-pull and they make some of the best sounding amps. There are also a number of other considerations that make a great sounding tube amp and not just the power output tube class. This amp though sounds great no doubt about it :)
I've tried this amp with a few different output tubes: 6L6, 6550, and EL34. The amp had a completely different sound just by changing the output tube. I didn't change any of the preamp tubes as yet but I'm sure it would have a considerable change on the tonal sound of the amp. The amp is mono and has two large transformers, two preamp tubes, and a single power tube. There are two inputs named "Rock" and "Roll". The amp sounds it best when you plug the guitar directly into the amp. The Rock input is more sensitive and lets you over-drive the preamp tubes easier. Depending upon the Hardness level of the power tube you can use this channel and just lower the volume of the guitar to get a clean, yet hot, sound. The other input, Roll, is used for cleaner sounds as it isn't as hot as the Rock input. This is mainly for jazz and country clean sounds especially when used with the 12AX7. It has a treble and bass knob that allow for a variety of sounds. There is also an "Attitude" knob that seems to add more harmonics and treble which ends up giving you a more edgy sound. Turning this knob down gives you a sweeter and warmer tone even when over-driven. One strange thing is the NOISE REDUCTION circuit in the amp. It uses a yellow light bulb that glows brightly when you play the guitar. If the light burns out then it means that the noise reduction circuit isn't working. The noise reduction circuit and the transformer-isolated line output make this amp great for driving other larger guitar amps or power amps. It doesn't have that harsh crispy sound that you get when you use other guitar line outputs. Since its only 15 watts you can turn it up without too much problem but it does get somewhat loud, especially in a small studio. I’ve found that I like the sound of an open back speaker cabinet with two 12 inch Jensen speakers over the THD speaker cabinet. The Jensen’s are warmer sounding yet are able to breakup. As mentioned before the built-in Hot Plate Power Soak allows you to crank the amp up and still keep the volume at any level. THD put in a switch that turns off the Attenuator by bypassing it and sending the full strength signal to the speakers. NOTE: When switching between full power and using the Hot Plate you should place the amp in Standby while switching. The High Voltage/Low Voltage switch sets the tubes plate voltage. Using a different plate voltage will give you a different sound. For instance the High Voltage setting puts about 450 Volts onto the plate of the tube and gives the amp more punch and a more aggressive sound. Setting the amp to the Low Voltage setting gives you a mellower, warm, and smooth sound out of the amp. It'll also extend the life of your tubes if you're at all interested in that ;^) Another great thing about the amp is that you don't lose any sonic definition even with the amp cranked. You can play chords and you'll hear each note without a bunch of mush or sizzle. The EL34 has the Rock sound, while the 6550 has a more boxy sound that reminds me of the earlier Marshall sound. My favorite sound so far is a Hardness "3" Groove Tubes 6550-R. The types of power tubes you can use in this amp are:
The types of preamp tubes you can use are:
Features
The power tubes can be installed without re-biasing the amp. Some of the more common of these tubes are also conveniently listed next to the appropriate tube sockets on the chassis of the amplifier. Refer to our website for updates of this data.
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