A while back I had been playing with the el-cheapo 6J1 china preamp.
Even after fixing up some of the many flaws, I was never really satisfied with how it sounded.
After some reading around I came across this build by Ratti3: 6J1\EF95 Hybrid Tube Preamp.
I had a box of NOS GE 5654W's that needed a suitable home, so down the rabbit hole I went.
Adapting the scheme from Ratti3's creation, I came up with the following, running off a simple 12v Wall-Wart:
The HV power supply comes from this cheap boost module:
This HV supply is filtered sufficiently to not impose much noise into the system.
The main amplification is done by a single 5532 which although is sufficient, a future iteration could benefit by having either another in parallel or a simple BJT stage.
The board design:
PCB (Don't have any pics of it populated to hand):
And in a finished case:
Measurements:
As can be seen, the THD is at 0.8%, but this amp has heaps of H2 making it lovely and warm:
All in all, a simple headphone amp with that nice warm 'tube' sound.
Thanks to @Ratti3 for posting his design that I used as a launch point.
Even after fixing up some of the many flaws, I was never really satisfied with how it sounded.
After some reading around I came across this build by Ratti3: 6J1\EF95 Hybrid Tube Preamp.
I had a box of NOS GE 5654W's that needed a suitable home, so down the rabbit hole I went.
Adapting the scheme from Ratti3's creation, I came up with the following, running off a simple 12v Wall-Wart:
The HV power supply comes from this cheap boost module:
This HV supply is filtered sufficiently to not impose much noise into the system.
The main amplification is done by a single 5532 which although is sufficient, a future iteration could benefit by having either another in parallel or a simple BJT stage.
The board design:
PCB (Don't have any pics of it populated to hand):
And in a finished case:
Measurements:
As can be seen, the THD is at 0.8%, but this amp has heaps of H2 making it lovely and warm:
All in all, a simple headphone amp with that nice warm 'tube' sound.
Thanks to @Ratti3 for posting his design that I used as a launch point.
I'd add protection diodes on the input of the opamp, 100V supply may generate some large transients at power up and power down that will sail through a 1µF capacitor...
Frying the opamp might make H3!!
Frying the opamp might make H3!!
Good advice!
I did make sure that the 1uF were rated for above that voltage knowing that I'd have full HV on one side of the cap until the tube starts conducting, but it definitely wouldn't hurt to have more protection on the opamp side.
Fried opamp H3 sounds nasty... 😳
I did make sure that the 1uF were rated for above that voltage knowing that I'd have full HV on one side of the cap until the tube starts conducting, but it definitely wouldn't hurt to have more protection on the opamp side.
Fried opamp H3 sounds nasty... 😳