Stabilizing difference amplifiers for headphone applications

raduschka

Member
2011-01-10 5:31 am
Hi Michael,
I have just read the article, but I'm not savvy enough to implement any of what it suggests :-( Also, i have just started a new thread, that is not posted yet. Do you think you might find a minute to help me figure out what i can do to turn a decware amp into a headphone amp? If so, here's the dilemma: I built a PTP 2watt/channel SET amp ( Steve Deckert's zen1, or SE84) with tube rectification (5uG4). I have a Minitorii so I would like to use the zen as a headphone amp, however it produces an unpleasant hum, even after drastic improvement through increased C1 and C2 capacitance. The part where I am lost is the resistance that I assume i have to add in series with my headphones. I have tried various resistors in series (headphone out is tapped from speaker posts). 100 ohm -still too much hum, 330 ohm and certain input tubes - I can live with the level of hum. My headphones (AKG k712pro [IMGDEAD]https://flic.kr/p/FBLZPu[/IMGDEAD]) have a sensitivity of 105 dB SPL/V
Max. Input Power 200 mW
Rated Impedance 62 Ohms.
Does this sound feasible? Am I doing something wrong? Can I add resistance? Am I frying the amp?
So far sound and headroom are excellent, but I can tell the extra resistance degrades the dynamics. At least that's my impression. Could I perhaps increase C2 capacitance until I get rid of the noise completely and revert to 100ohm resistors? Should I get hd650 headphones instead (those are rated at 300ohm and will be less sensitive to hum presumably)

Thank you very much for taking the time.

Radu Chrstian Barca

pics date from before I installed the heaphone jack

[IMGDEAD]https://flic.kr/p/nQS8KX[/IMGDEAD]
[IMGDEAD]https://www.flickr.com/photos/[email protected]/14316270855/in/dateposted-public/[/IMGDEAD]