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Showing another amplifier I just finished, decided to adapt my 6AS7G headphone amplifier circuit for 6336 / 6528.
Similar to the 6AS7G circuit, this is a dual-mono power supply design, each channel has its transformer/rectifier/reservoir and Maida style HV regulator. I use a 40 second time delay to allow the tube heaters to warm before soft start B+ is applied. I also included a 5V 3-pin fan header on the power supply PCB, there are two 92mm Noctua fans mounted internally directly below the power tubes for some active cooling. The 6J5 input stage is gyrator loaded and LED biased, the two stages are direct-coupled, and the 6336 or 6528 cathode followers are actively loaded. Output capacitance is 600uF per channel, ClarityCap metallized polypropylene. You might be able to spot them if you look closely.
The two sections of the 6336 or 6528 are run in parallel, each tube biases at 275mA with the components cold. Given the high current, both HV regulators and the power tube loads are mounted on external heat sinks. This amplifier is an engineer's dream in efficiency.
Here are some photos before some basic measurements.
Output Z:
6336 - 24ohm
6528 - 15ohm
THD w/ 6528:
1mW into 300ohm 0.007%
1mW into 120ohm 0.013%
1mW into 80ohm 0.029%
1mW into 32ohm 0.11%
All distortion above is pure H2. Distortion measurements were largely dependent on the quality of the 6J5, I chose one that measured well.
Frequency Response:
300ohm
32ohm
Some more pics with a new headphone release from ZMF, the Atrium.
All lit up at night.
The amp sounds great, it's the best OTL headphone amp I have heard, very happy with the result. Thanks for checking it out
Similar to the 6AS7G circuit, this is a dual-mono power supply design, each channel has its transformer/rectifier/reservoir and Maida style HV regulator. I use a 40 second time delay to allow the tube heaters to warm before soft start B+ is applied. I also included a 5V 3-pin fan header on the power supply PCB, there are two 92mm Noctua fans mounted internally directly below the power tubes for some active cooling. The 6J5 input stage is gyrator loaded and LED biased, the two stages are direct-coupled, and the 6336 or 6528 cathode followers are actively loaded. Output capacitance is 600uF per channel, ClarityCap metallized polypropylene. You might be able to spot them if you look closely.
The two sections of the 6336 or 6528 are run in parallel, each tube biases at 275mA with the components cold. Given the high current, both HV regulators and the power tube loads are mounted on external heat sinks. This amplifier is an engineer's dream in efficiency.
Here are some photos before some basic measurements.
Output Z:
6336 - 24ohm
6528 - 15ohm
THD w/ 6528:
1mW into 300ohm 0.007%
1mW into 120ohm 0.013%
1mW into 80ohm 0.029%
1mW into 32ohm 0.11%
All distortion above is pure H2. Distortion measurements were largely dependent on the quality of the 6J5, I chose one that measured well.
Frequency Response:
300ohm
32ohm
Some more pics with a new headphone release from ZMF, the Atrium.
All lit up at night.
The amp sounds great, it's the best OTL headphone amp I have heard, very happy with the result. Thanks for checking it out