With my first SS amp in the crapper after a transistor failure and the bugger being more unobtanium than fancy tubes, I cobbled up a simple headphone amp for high impedance loads 300Ω and up. Only parts I had on hand, nothing to be bought.
The spud idea came to be because of a parafeed preamp 5000:500 transformer I decided to use as input as voltage gain 1:3.1, with hot-ish source output and 1ohm output impedance. The near zero miller of a cathode follower 6AS7G will be inconsequential and volume knob sits at 2 o'clock.
The twist is in the biasing, a 40H 50mA choke with 550Ω DCR, which delivers 27.5V of bias when the tube has around 105V at the plate. The values were eyeballed from the curves, trial and error with PSUD gave the me the right combinations of psu components to get the desired voltage.
A tube rectifier would be nice but I stuck with a SiC bridge for now, choke input and split rails. DC heating just because I always had some random occasional hash noise with the 6080 family and I'd like to see if this fixes it. That and I had a 6.3V LDO board doing nothing.
As simple as it gets, the mains transformer is a sowter 150V, input choke is a finement 12H followed by a 32H 432Ω one. The high DCR is just to lower B+ to the desired amount, if I go for a low drop tube rectifier I'll have to use a different one.
It looks better in person.
The output tube is on a socket saver just to protected the flimsy 3d printer mounts from heat. Output caps are meant to be topside for easy cap rolling,Jensen oils installed for now. The holidays will be filled with cap/tube rolling experiments. This thing should make a really good buffer for a VFET build.
Can't hear the noise floor and the sound is very smooth and pleasing. The case is a DIY from other projects but the bottlehead badge has to stay in honor of the company who got me hooked on OTL amps.
The spud idea came to be because of a parafeed preamp 5000:500 transformer I decided to use as input as voltage gain 1:3.1, with hot-ish source output and 1ohm output impedance. The near zero miller of a cathode follower 6AS7G will be inconsequential and volume knob sits at 2 o'clock.
The twist is in the biasing, a 40H 50mA choke with 550Ω DCR, which delivers 27.5V of bias when the tube has around 105V at the plate. The values were eyeballed from the curves, trial and error with PSUD gave the me the right combinations of psu components to get the desired voltage.
A tube rectifier would be nice but I stuck with a SiC bridge for now, choke input and split rails. DC heating just because I always had some random occasional hash noise with the 6080 family and I'd like to see if this fixes it. That and I had a 6.3V LDO board doing nothing.
As simple as it gets, the mains transformer is a sowter 150V, input choke is a finement 12H followed by a 32H 432Ω one. The high DCR is just to lower B+ to the desired amount, if I go for a low drop tube rectifier I'll have to use a different one.
It looks better in person.
The output tube is on a socket saver just to protected the flimsy 3d printer mounts from heat. Output caps are meant to be topside for easy cap rolling,Jensen oils installed for now. The holidays will be filled with cap/tube rolling experiments. This thing should make a really good buffer for a VFET build.
Can't hear the noise floor and the sound is very smooth and pleasing. The case is a DIY from other projects but the bottlehead badge has to stay in honor of the company who got me hooked on OTL amps.
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Looks very well. But I'm worried about its wheight. All these iron, copper and caps may sum several kilogrames. Difficult to carry in the pocket 🙂
Spud cathode follower AVC parafeed SET?
I enjoyed this amp more than I thought, so much that I went blind into uncharted territories for me.
Ditched the step up transformer for an audio note 1:1 input transformer fed directly from the dac, 3.5V RMS in SE.
A 10uF audio note copper foil blocking cap and tribute AVC at the output volume adjust and drive high impedance headphones, namely HD650s. The AVC needs to do around 17dB of reduction so my knob is between 2 and 3 for preferred listening levels.
Those wago connectors are really nice for fast prototyping and I can't really hear a negative impact, or my hearing sucks.
Simulations show the following response and I have to say, it doesn't sound bad, not bad at all.
I enjoyed this amp more than I thought, so much that I went blind into uncharted territories for me.
Ditched the step up transformer for an audio note 1:1 input transformer fed directly from the dac, 3.5V RMS in SE.
A 10uF audio note copper foil blocking cap and tribute AVC at the output volume adjust and drive high impedance headphones, namely HD650s. The AVC needs to do around 17dB of reduction so my knob is between 2 and 3 for preferred listening levels.
Those wago connectors are really nice for fast prototyping and I can't really hear a negative impact, or my hearing sucks.
Simulations show the following response and I have to say, it doesn't sound bad, not bad at all.