I am new here, this is my first post.
As for Intros, I live in the Detroit area. Like to tinker with tube audio as a hobby. Not an expert by any means.
I own two KOSS A-1220 headphone amps. Each share the same model number, yet have completely different internals: One uses just a single 12AU7, while the other has a 12AT7 and a pair of 6AQ5A's. I have searched the forums and found one or two threads about this amp, but nothing that addresses my problem....
I have recapped each of them and they sound 'ok'. The problem I am having is that there is little to no bass present (in each unit). And there is a slight hum in the background. The hum does not raise when the volume knob, and is still present when the preamp tube is removed.
HOWEVER, my first goal is to find a way to adjust the EQ circuit and get more low end. *please note that neither of these units have tone controls.
From what I have read online, you can sometimes adjust filter caps and resistors to get different tone, correct?
Here is a link with a scan of the schematic (for the single tube version). Does anyone have any suggestions on what I can do to get a better sound?
Edited by tachyhon - 2/1/13 at 8:54pm