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Giant 2A3 Headamp


Active Member
Forum Donor
Jan 15, 2018

Showing off another completed build. Another one for my buddy Zach of ZMF Headphones. This is a cost-no-object 2A3 headphone amplifier featuring nanocrystalline core interstage and output transformers from Monolith Magnetics. The transformers are huge given the high permeability cores, and as such the amp is huge, and heavy! But hey, this is for the ultimate tube and headphone enthusiast.

Anyway here are some high level details of the build:
- Custom mains and filament transformers from Monolith Magnetics
- Maida style B+ regulators, shunt regulated bias supply feeding the bias pots
- Rod Coleman filament regulators
- 5687 / 7044 / E182CC input stage, LED biased
- Monolith Magnetics nanocrystalline core interstage transformers
- Fixed bias 2A3 output stage
- Monolith Magnetics nanocrystalline core output transformers with 120ohm, 32ohm, and 8ohm taps
- Vintage Amphenol tube sockets
- Simpson milliammeters

Here are some basic measurements:

1mW into 32ohm 0.036% THD
1mW into 120ohm 0.0066% THD
1mW into 300ohm 0.020% THD
1W into 32ohm 0.36% THD
1W into 120ohm 0.35%
1W into 300ohm 0.21%

2A3 SET 1mW into 32ohm FR.jpg

2A3 SET 1mW into 120ohm FR.jpg

2A3 SET 1mW into 300ohm FR.jpg

The circuit.


And some pics of the final build.





That's it, thanks for checking it out!
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