• 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.

RH84 amplifier build

I'm excited to share my first ever full amplifier build: A headphone amp made from the RH84 circuit! I've built kits and restored vintage amps, but never built one from scratch like this. I chose this build because it was simple enough for a first-time build, and it presented a lot of opportunity for learning. I learned so much from this project, and it definitely set a good knowledge baseline for more involved projects down the road.

RH84 circuit: RH Amplifiers: RH84 amplifier - revision 2

I have a tendency to crave doing things in a way that makes them unique... so I made the following changes to the design:

1. Modified the power supply to use two 6AX4 damper diodes instead of a more "standard" rectifier.
2. Added volume control.
3. Added a switch to switch between pentode and triode-strapped mode for the EL84s.
4. This is a headphone-only amplifier. I listen almost exclusively to headphones, so I didn't care so much about speaker outs.

Some specs:
- OPTs: custom by electraprint with 32 and 120 ohm secondaries.
- PT: Lundahl LL2741
- Separate headphone jacks for 32 and 120 ohms.
- PSU is CLCRC.
- Miflex coupling caps.
- 12AT7 driver can be swapped out for a 12AU7 for less gain and improved noise floor at the cost of some power. Power loss not really an issue for headphones.
- Chassis is from Landfall Systems

Overall I am so pleased with how this turned out! It sounds amazing and is extremely quiet. Quiet enough for headphones. The inside is a little messy and some of the wire colors don't make sense because I ran out (like the rainbow of colors going to star-ground), but overall I'd say it's not bad.

Best combinations of outputs and headphones I've discovered so far:
- Pentode mode and 32 ohm jack with hard to drive planars (Hifiman Arya). My Arya sounds incredible with the high output power.
- Pentode or triode mode with 32 ohm jack for more sensitive high impedance dynamic headphones (ZMF).
- Triode mode with 120 ohm jack for high impedance dynamic headphones (ZMF)


Enjoy!
 

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