The ECP Audio
O R P E D O
parafeed headphone amplifier
The TORPEDO! is the latest DIY design from Dsavitsk of ECP Audio. Based on a tube parafeed design, one of the finest papers written on the subject 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! is no different, but includes additional features and refinements that bring this design to a level of performance and convenience heretofore unattained.
The TORPEDO! incorporates all of the following features and more:
- The basic tube parafeed circuit,
- Onboard, PCB-mounted transformers - both power (1) and output (2). No high-voltage power wiring required!
- Solid-state, low-noise rectifiers for the tube gain stage and the tube heater power supply.
- Solid-State, LED-set CCS's (Constant Current Source) for the tube current setting
- Transistorized-LED tube bias.
- Extra long PCB to prevent magnetic coupling between the Power Transformer and output transformers.
- Switchable between high-impedance headphone output and low impedance.
- extruded TO-220 heat sink footprint for Left and Right channel CCS's and a regulated heater power supply.
- PCB-mounted IEC inlest
- PCB-mounted RCA jacks
- Onboard option for resistor power supply output or a PCB-mounted choke.
- Tube stage based on the plentiful and cheap 6J6 tubes.
- Custom wound transformers from Edcor (power, two output)
- Custom-extruded and machined enclosure from Context.
- Enclosure uses split-body construction, allowing easy removal of the lid for tube rolling
- Alps Blue Velvet stereo volume pot
- Neutrik stereo 1/4" headphone jack
- Flexible layout for parafeed capacitor position
Unlike many OTL (Output Transformer-Less) tube designs, the TORPEDO's output transformers can pair well with low-impedance Grados or high-impedance Sennheisers. There is no need for a relay-delay on the headphone connection, either - the transformer automatically blocks DC even from power-on transients. Gain has been optimized by Dsavitsk so that with either low or high-impedance headphones, normal listening levels hover around the half-volume mark of volume pot travel.
The CCS (Constant Current Sources) for the tubes are based on a transistorized solid-state design and the resulting load presented to the tubes is extremely high, meaning the PRR (Power supply Rection Ratio) is very high and almost all of the power from the tube is supplied to the headphone output. The CCS uses LED's for setting the current, resulting in low noise and accuracy. For an extended explanation of the CCS's operation and design, refer to Dsavitsk's article here.
For the lowest distortion in setting tube bias, a unique, transistorized-LED circuit sets bias. For an extended explanation of the transistor-LED bias circuit, refer to Dsavitsk's article here.
The TORPEDO! 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.