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The TORPEDO III is the latest DIY design from Dsavitsk of ECP Audio. Based on the successful Torpedo planform, the Torpedo III is also of parafeed design, but differs in the unique differential amplification stage prior to the output transformers. The dual-triode tubes are configured in a long-tailed pair circuit, whose differential output is further amplified by a high-voltage differential solid-state circuit before input into the output transformers. The result is a totally unique headphone amplifier. The differential circuitry inherently rejects all commond-mode distortion. The output results in a remarkably, fatigue-free listening experience. When combined with the optional Cinemag output transformers, highs are extended and details are increased to a world-class level of performance. Details of the circuit design are described below. In addition, one of the finest papers written on the subject of parafeed circuits can be found here: The Basics of Parafeed (by Dsavitsk, of course). All tube parafeed amplifiers incorporate a vacuum tube gain stage that is AC-coupled to an output transformer. The TORPEDO IIII is no different, but the entire circuit is differential between the input/volume pot and the output transformers.
The circuit is designed to work well with most of the 12A*7 family of tubes, but is optimized for the 12AY7. Different tubes will provide different levels of gain, but some types may not perform as well as others, with high-frequency performance possibly suffering in some instances. The 12AY7 provides optimal performance and approximately 6X (15dB) gain into 300 ohm loads and 2X (6dB) into 32 ohm loads. Other tubes are shown below:
Notes on some specific tubes:12AU7 - probably has too little gain to be very useful, but if you have a particularly hot source and/or tend to listen quietly, it might be worth playing with.
12AX7 - has a higher mu (gain) than the other tubes listed, but it also has a higher plate impedance. This will result in lower gain and some high frequency loss. It might still be worth playing with, but it is probably not the ideal tube here.
12AT7 - has similar looking gain to the 12AY7. However, the circuit runs it at lower voltage and current than are idea which will result in slightly higher distortion. Subjectively, we found it to sound more tubey which some people may like.
12AZ7 - looks like another decent option, but I have not tried it.
6DJ8, 6922, 6H6, 6H31, 6N23, 6N1P, etc. are not compatible with the circuit. At the very least, if you try them you'll probably damage the tube, but there is a good chance you'll damage the amp, too. If you are in doubt about a particular tube, please ask before you try it.
Features of the TORPEDO III:
Like the TORPEDO! before it, the TORPEDO III offers the most integrated board design yet available. All connectors are PCB-mounted. Except for one small ground wire to the Alps volume pot and a safety ground, there is no other wiring required, whatsoever.
file last changed:Saturday, June 25, 2016 10:26:40 PM
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