1 year ago

Tagged:
headphone amps
hybrid
solid state
tubes
hi fi

More hi-fi stuff. Personal projects: tube and solid state headphone amps. On the left, a Sijosae MHHA tube/MOSFET headphone amp. It uses a 6922 (E88CC) for voltage gain, and two single-ended IRF510 MOSFET source followers to buffer the output. This was originally supposed to run at 24V with an SMPS, but I found that the circuit worked much better at 36V. The black box with the red LED is a 36V regulated linear supply that I built for the amp with a Hammond 30VAC toroid and a TREAD regulator board. The TREAD board needed a big heatsink in there because the amp draws close to 600mA of current. Inside the amp itself I had to up a lot of capacitor ratings — voltage and temperature, since the added drop across the MOSFETs means things get pretty toasty. They’re still well within their parameters but it’s a little frightening to see a heatsink at 90° C. This amp is really only useful for high-impedance phones that need a bunch of voltage drive and aren’t sensitive to output impedance (which on this amp is 47 ohms) — the Beyer DT880/600-ohm in the picture is an ideal candidate. I biased the amp using a spectrum analyzer and it does 0.04% THD, mostly 2nd and 3rd harmonic, into a 50-ohm load (0.01% into a 600-ohm load), which I think is fantastic for a tube amp. It’s almost not “tubey” enough. Frequency response is dead flat with high-impedance phones, but there was a noticeable 3dB bump at 100Hz resonance with my Senn HD595s. On the right is a homebrew design that’s all integrated. It’s like a giant CMOY on steroids. It uses a 24V SMPS split to +/-12V rails, which feed an OPA2227 gainstage, an OPA132 active ground channel, and BUF634 output buffers (inside the 2227’s feedback loop). This thing will supply up to 350mA of current and has an output impedance close to zero, and has a fairly low gain of 3. It’s great with low-impedance phones with wacky impedance curves that make them sensitive to an amp’s source impedance, like Sennheiser HD595s or demanding IEMs like the Triple.fi 10 or the ER-6i. It drives a 32-ohm load with an astounding 0.0007% THD and a noise floor too low for me to measure.

More hi-fi stuff. Personal projects: tube and solid state headphone amps.

On the left, a Sijosae MHHA tube/MOSFET headphone amp. It uses a 6922 (E88CC) for voltage gain, and two single-ended IRF510 MOSFET source followers to buffer the output. This was originally supposed to run at 24V with an SMPS, but I found that the circuit worked much better at 36V. The black box with the red LED is a 36V regulated linear supply that I built for the amp with a Hammond 30VAC toroid and a TREAD regulator board. The TREAD board needed a big heatsink in there because the amp draws close to 600mA of current. Inside the amp itself I had to up a lot of capacitor ratings — voltage and temperature, since the added drop across the MOSFETs means things get pretty toasty. They’re still well within their parameters but it’s a little frightening to see a heatsink at 90° C. This amp is really only useful for high-impedance phones that need a bunch of voltage drive and aren’t sensitive to output impedance (which on this amp is 47 ohms) — the Beyer DT880/600-ohm in the picture is an ideal candidate. I biased the amp using a spectrum analyzer and it does 0.04% THD, mostly 2nd and 3rd harmonic, into a 50-ohm load (0.01% into a 600-ohm load), which I think is fantastic for a tube amp. It’s almost not “tubey” enough. Frequency response is dead flat with high-impedance phones, but there was a noticeable 3dB bump at 100Hz resonance with my Senn HD595s.

On the right is a homebrew design that’s all integrated. It’s like a giant CMOY on steroids. It uses a 24V SMPS split to +/-12V rails, which feed an OPA2227 gainstage, an OPA132 active ground channel, and BUF634 output buffers (inside the 2227’s feedback loop). This thing will supply up to 350mA of current and has an output impedance close to zero, and has a fairly low gain of 3. It’s great with low-impedance phones with wacky impedance curves that make them sensitive to an amp’s source impedance, like Sennheiser HD595s or demanding IEMs like the Triple.fi 10 or the ER-6i. It drives a 32-ohm load with an astounding 0.0007% THD and a noise floor too low for me to measure.