Kingston
Well-known member
I wanted to knit and not design anything. I also needed the end of all headphone amps so I never have to build one again. I chose this one: http://sjostromaudio.com/pages/index.php/hifi-projects/129-qrv08-headphone-amp
In the end I could not justify building just a headphone amp so I tacked along a balanced passive (5k) attenuator for a separate XLR pass-through I/O. Sometime later I might add led metering so consider that single orange led a placeholder.
The end result is a simplified monitor controller with the ultimate headphone amp. No distortion and can melt any pair of headphones if required. Headphone amp inputs can be selected between balanced with transformer (from the XLR inputs) or separate unbalanced RCA input with or without transformer. This should have been done with a 2-deck 4-pole switch, but I could not get one on short notice so the inputs are unnecessarily selected separately for left and right. Headphone amp has a 100k input attenuator, by the way.
I still need to match input levels to the headphone amp so there is some additional attenuation needed for some of the input selectors but other than that it's done. A sharp-eyed person might notice the 4-deck Elma attenuator is built "backwards". I soldered all the four decks inverted so the attenuator would have worked the wrong way around. Luckily Elma rotaries can be configured backwards like this, losing the dust guards.
In the end I could not justify building just a headphone amp so I tacked along a balanced passive (5k) attenuator for a separate XLR pass-through I/O. Sometime later I might add led metering so consider that single orange led a placeholder.
The end result is a simplified monitor controller with the ultimate headphone amp. No distortion and can melt any pair of headphones if required. Headphone amp inputs can be selected between balanced with transformer (from the XLR inputs) or separate unbalanced RCA input with or without transformer. This should have been done with a 2-deck 4-pole switch, but I could not get one on short notice so the inputs are unnecessarily selected separately for left and right. Headphone amp has a 100k input attenuator, by the way.
I still need to match input levels to the headphone amp so there is some additional attenuation needed for some of the input selectors but other than that it's done. A sharp-eyed person might notice the 4-deck Elma attenuator is built "backwards". I soldered all the four decks inverted so the attenuator would have worked the wrong way around. Luckily Elma rotaries can be configured backwards like this, losing the dust guards.
