Pro Audio Design Forum

Hi - Glad you got the bias adjusted.

Regarding the pot - I'm also using a dual cheap Alps 10K log and aren't having any issues. I'm wondering if it's possible that you have the wiper and top track connections reversed: In that configuration when the pot was taken to "0" the output of the THAT1240 would be shorted to ground by the wiper and it would have the rotation characteristics you mentioned. I'd double-check that just to be sure.

The output to feed the top track of the pot from the 1240 is labeled "O".
The wiper connection which feeds the DRV134 input is "I."

mediatechnology wrote:The output to feed the top track of the pot from the 1240 is labeled "O" the wiper which feeds the DRV134 is "I."

Hehe, I thought the opposite in haste and not checking the PCB. Thanks! Sounds very good. Now three more and then see if the PSU holds up. I'm hoping I could get away with standard LM317 PSU.

You might be able to crank the idle current down on all of them.

I chose 250 mA so that it could drive 32R loads with 0R build-out at very high level.
So depending on the sensitivity and impedance of the phones and whether or not you're using a build-out resistor (not required but good for short-circuit protection) you might be able to reduce Iq without a distortion penalty.

In line driver amp applications of this design I think Roger is using around 50 mA Iq.

Yello! Here is my headamp x 4 box. Works fine at least at the moment Have to run it some more hours to see if the PSU regulators stay on. The regulator heatsinks are a hack of two small ones, not sure if they are enough... Still have to drill some more holes on top panel, this thing heats up! Also, have to measure temperatures if I find proper tool for that.

Each amp has a switch to select source which selects either the input of the amp in question or the previous input. The switch is between input (THAT) chip and the pot. This way the signal can be chained to all four. Or just two / two etc. Worst case the first input chip drives all four pots and it seems to be fine (cannot hear a change when switching). Balanced inputs on the back panel, one stereo unbalanced input on the front that goes directly to the first channels switch. About 3mV DC on the pot from input chips.

Thanks mr. Wayne for a good project!

Best,
Teemu

Awesome build thanks for sharing!
Cool to see all those board stacked.

I do agree that the regulator heatsinks could be a little bigger.

Hi,
I'd like to learn about this DCAO before I build, in the input, if I feed with unbalanced signal, can I just use I and G and skipped the 124X, R19, and R22?

Thank You.

I'd like to learn about this DCAO before I build, in the input, if I feed with unbalanced signal, can I just use I and G and skipped the 124X, R19, and R22?

Yes you can.

Hi,
I see in the BOM in the first page:

8 Resistor, 470R 0.25W CF
2 Resistor, 4K7 0.25W CF
4 Resistor, 10R 0.25W CF

is CF means Carbon Film? And is that any problem if subtituted with metal film type?

Thank You.

Metal film is fine.
None of the resistors specified as CF are actually passing audio however.

Thank You Wayne, I'm ordering small number parts from Mouser for another project and even I didn't buy the DCAO board yet, I decide to buy some parts from the DCAO BOM for preparation