Parallel TDA1541A DAC Noise

[pftrvlr]

I got this parallel tda1541a DAC off ebay and have been playing with it for three weeks now. The DAC uses two parallel tda1541a chips. The I/V is a discrete current mirror circuit. Outputs from two tda1541a are wired directly to the I/V input

The DAC is working all fine with a single tda1541 in either of the socket. But when both tda1541 are plugged in, I can heard apparent noise/distortion - especially in the quieter music passages. The noise is not present when it is not playing music or it is between the gap of tracks. I switched different tda1541 chips in and out, some particular matches of tda1541 produce less noise, however it can not eliminate the noise completely.

This has led me to wonder if the I/V circuit is sensitive to matches of the tda1541a chips. Or two tda1541a may be in contention for bias current? Anybody has similar experience? Maybe each tda1541 need to be biased separately?

[SoNic_real_one]

My guess: each output has a nominal current. Parallel them on the same load (that's 1/2 of the single version one) and one of them will be forced to output more current while the other less - because of the inherent small diffecences.
You should build different I/V stages and parallel the outputs.
If you kept the same I/V load, then both of them will be out of the nominal current range.