Tube Semiconductor Hybrid Amplifiers

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Tube and Semiconductor Combos – the best of both worlds

An interesting project on the web is that of a 6SN7 Mosfet audio amplifier capable of delivering 50W per channel. The article, written by Simon Brown is called Amplifier War and Peace – An Hybrid Amp

Taga HTA700B V2 SE Hybrid
Taga HTA700B V2 SE Hybrid  (Note: tube pre-amplifier stage)

I am not a big believer in that tube amplifiers are so much better than that of solid state but I do believe a properly designed amplifier using both devices can address problems, both in sound reproduction and ease of build.

What I DO like about tubes is the almost ease at which one can build a pre-amp or power amp by simple point to point wiring. This type of wiring is also notoriously the best way to build these amplifiers – easy to change layout, reduce noise,  unnecessary oscillation and to modify at a later stage.

The project, found at Audio Xpress features two 6SN7s in a current source configuration driving a complementary pair of Mosfets, IRFP140 and IRFP9140.   All aspects to the design are covered but the author does warn that it’s not for inexperienced builders. Here of course we must also make mention that the V2 is running at 300V on the anode. The power supply is well thought out. The entire project can be built on prototyping board.

Another project which caught my eye and also under Audio Xpress is that written by Stephen Moore – A Hybrid Valve MOSFET SE Amp – Complete Project.  With a smidgen of Nelson  Pass in the constant current source and gate bias circuitry we, like the above circuit, have two 6SN7s or similar acting as the voltage gain stage to drive the source follower  IRFP2907Z. (using the John Broskie Aikido amplifier approach).

Both these articles are very well written with a lot of insight and explanation as to the shortcomings of Mosfet output devices, work arounds and just as important, driving these devices with high voltage swings from tube devices.

The Taga HTA700B V2 SE Hybrid amplifier boasts the following:

  • Power Output: 2x45W RMS / 4ohm; 2x35W RMS / 6ohm; 2x26W RMS / 8ohm Class A/B
  • Vacuum Tubes: 2 x 12AX7B
  • THD: Less or equal 0.1% (at rated power)  Signal/Noise ratio: =>88dB
  • Frequency Response: 20Hz – 28kHz
  • Inputs: RCA stereo CD, USB (for computer)
  • Outputs: Stereo RCA with variable volume control
  • Connectivity Wireless: Bluetooth® v4.0
  • Bluetooth® Profiles: Advanced Audio Distribution Profile A2DP
  • Headphone Impedance: 32-320Ω
  • Headphone Output Power: 1W  160Ω
  • USB Supported Data: Asynchronous 24bit / 192kHz
  • True high-speed audio processor CM6631A
  • DAC Cirrus Logic CS4344 chip
  • Included Accessories: Bluetooth® antenna, USB cable,
  • Removable IEC Power cord
  • AC Power, Power Consumption: 230-240V 50Hz, 100 W
  • Dimensions (H x W x D): 14 x 17.7 x 27 cm
  • Weight (net): 4.2 kg / pc.



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