• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Hybrid headphone amp.....

Tube-Mosfet hybrid headphone amp

I went a little different route on my first hybrid amp, Schematic attached. I have a bunch of compactron tubes to play with.
I have another design in process that runs off of 24 V and uses the tubes heaters for the pull down device for the mosfet pull up. I figure that it will run at about a 12Volt average output voltage, so the heaters will have 12VDC with AC ripple on them, it should only be a few volts P-P. With 12AU7 tubes the output current would be around 150ma and with 12BH7's would raise it to about 300ma.
It would be non linear if used with a large swing. I figure only a couple of volts P-P the non linear effects should be minimal.


  • ha1.jpg
    96.6 KB · Views: 321


2003-02-11 9:02 am
I have a couple of these IRF 520, so I wonder..Do I have to order some 510, 610, etc., for this amp?

Yes you can use a very wide options of IRF device there. It is just that the sound quality will be slightly different with IRF520.

You want Ciss as low as IRF610 but transconductance as high as IRF510. IRF520 has higher Ciss than IRF510 (bad) but has higher transconductance (good). And because it is a source follower, usually transconductance is more important than capacitance (as long as not too high).

So I guess IRF520 wont be too far behind. But for headphone amp, expect higher high frequency noise/distortion.
I think I will build myself a new headphone amp. Found this on....
NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier, and I wonder...Is it ok to use a pair of IRF 520, instead of tne 510, who is used in this project?

Interesting design. One observation is that wall warts generally are not low ripple per-se. Additional filtering might be in order.

I don't use headphones because I wear hearing aids. If I put headphones on they whistle.

I've been wondering if anyone has designed an active filter to compensate for their hearing loss so that they can use headphones without using their hearing aids? I've searched a few times on the net, but only find hits for hearing aids and Personal Sound Amplifiers.
Tube MosFet Hybrid Head-Phone Amp

Latest Tube Mosfet headphone amp is up and working. It is configured like a simple opamp and runs on a 24V wall-wart PS. The tube heaters are the current sink for the output, so with 12AU7 tubes, 160mA, 12BH7's about 300mA. They drive 24 Ohm Sony cans with authority, the 12BH7's can bias up a small set of speakers. The LED's are part of the CCS bias and will be placed under the tubes.
The heaters are biased at 12.7V with a little AC ripple on them. Only adjustment is the CCS bias for the LTP input stage, 6mA, 3/tube and the offset adjustment for tube heater set point. So far a fun little project.


  • head_amp_10.jpg
    340.7 KB · Views: 207
  • headamp-12bh7.jpg
    474.5 KB · Views: 178
  • head_amp_5.jpg
    478.7 KB · Views: 172