[KWS]

6AS7 Headphone Amplifier
Hi,i just got my HD650 last week and want to build a cheap good amp to drive it nicely.I have searched for the circuit on the internet and found 2 circuit which is somehow close to my preference.Also,i found the tube amp Darkvoice 336 also use this tube combination.So wanna get some advice for building this amp.
1.Can i simply replace the ECC88 by the 6sn7 without changing the value of the plate resistor or increasing the B+ voltage?
2.Or replace the input stage of the pic1 by that of the pic2?
3.Is it really nessesary to have 680uf output cap. for high impedance CAN like HD650?As i just found that the darkvoice only use 51uf for the output cap.

 

[n_maher]

I'd humbly suggest doing a trafo coupled output rather than cap coupled. One of these days I'll get around to posting the schematic for the Menace Lite. Follow the link in my sig, skip to the last few pages of the thread.

 

[nikongod]

Quote:

Originally Posted by KWS /img/forum/go_quote.gif 1.Can i simply replace the ECC88 by the 6sn7 without changing the value of the plate resistor or increasing the B+ voltage?

Sure you can!

You will however need to adjust the cathode resistor so that the plate voltage with the 6sn7 is the same as the 6DJ8

The 6DJ8 is not a bad tube, probably the best noval-bottle double-triode, why not just use it? At the risk of listening to the schematic, the 6dj8 works better at lower voltages than the 6sn7. OTOH, the n_maher menace TC and singlepower extreme sounded very good with the 6sn7 at lowish voltages so I'm happy to be wrong.

OOH! I would also tweak the cathode resistors on the output stage. They can be changed to smaller values to increase the idle current of the 6as7. Dunno how important it actually is, but its the popular tweak to that circuit.
Quote:

3.Is it really nessesary to have 680uf output cap. for high impedance CAN like HD650?As i just found that the darkvoice only use 51uf for the output cap.

50-100uf is plenty for high impedance headphones.


A parafeed transformer or autoformer run using the "high impedance headphone" OTL output would also make this work great for low impedance headphones. It could be added later if its ever necessary.
Quote:

Originally Posted by n_maher /img/forum/go_quote.gif One of these days I'll get around to posting the schematic for the Menace Lite.