mosfet i/v conversion from D1 with pcm1704

[schiller]

Has anyone tried the IRF610 stage from D1 with pcm1794 chips? (single ended, one per channel)

Schematic (for the tda1543):



It is direct coupled to the dac output, sould i bias the fet for 0v voltage at the source??

I have found in related threads that it has a low ac input impedance. I must get something wrong here, because i can't find any low impedance path to ground.

Any info would be very much appreciated,
thanks in advance

Konstantinos

[bwaslo]

your url link is pointing to the wrong thing.

[schiller]

Sorry, this is the link for schematic:

http://www.diyaudio.com/forums/attac...amp=1083004784

[bwaslo]

I have not worked with the circuit, but the schematic shows the input being at the source terminal of the MOSFET. That will be a low impedance point, as the FET will "try" to keep the source at a fixed voltage offset from the gate.

[Tim_wolf]

The PCM1794 is a stereo DAC with differential current outputs which are usually connected to inverting amplifiers and then a differential to single-ended amplifier. The TDA1543 is a single-ended output DAC; it operates at 5V with the output current sunk to 0V.

The circuit you've referenced is a basically a common gate amplifier, and it depends on a stable gate voltage to generate a constant bias current. This means temperature compensating the biasing for Q1, getting rid of the -30V supply at the source of Q1 (through the 3.3K resistor, because of the TDA1543 output level), and then setting the biasing so the signal stays in the (small) linear mode of Q1. This idea needs some more work...why not just use an op amp?