At present, with some 2.7 mA cathode current, the output impedance is about 670 ohms.
If the cathode current is increased to 8 mA, the output impedance will be some 400 ohms.
This can be done by reducing the cathode resistor to 15k.
^ That's a good one too. I have one similar built up with a baffle step compensation circuit sandwiched between the triode and mosfet, and a single triode (rather than dfferential) per channel. Very handy. With enough heatsinking and mosfet idle current, you can even drive small speakers with it 🙂
The *small*-signal impedance is several hundred ohms, as said.
> power my 300 ohms headphones.
The *large*-signal output is 125V behind 47k, or 2.6mA, at high THD.
This looks like 0.8V peak or 0.56Vrms in 300 Ohms. 1 milliWatt.
Yes, I have used headphone amps this small. I have wanted larger.
The cathode 47k resistor could be reduced below 20k for more power.
There are other ways to do this. Usually involving a much bigger bottle than the faithful 6SN7.
so does 6AS7G/6N3S/6080 🙂
I think a transformer is the best solution here, either way. My flea amplifier could do it just fine, so long as you source a decent transformer.
Small signal and low powered dual triodes are not what I would choose for OTL use at all. A transformer makes the main isusues disappear.
I think a transformer is the best solution here, either way. My flea amplifier could do it just fine, so long as you source a decent transformer.
Small signal and low powered dual triodes are not what I would choose for OTL use at all. A transformer makes the main isusues disappear.
I use the Ultrapath with 6sn7 and the OPT from Electraprint. Nice and simple. Also good start-up-close-down feature. No oomphs etc from the speaker
I'm not sure I understand what's good about that Blue Velvet circuit. With only 4.5k ohm plate loads, those 6SN7s are being loaded down heavily. I put the circuit into LTspice and it looks like the distortion would be quite high at 1V rms (typical line level) out into normal loads. Am I missing something?