D1 to drive an F4

[oon_the_kid]

Hi,

I am wondering if it might be possible to modify the D1 to directly drive an F4. I kinda like the idea that I/V conversion is done on a resistor. At the moment I think the output is approximately aproximately 3Vp-p on a +/- 1mA input. I was thinking of increasing the supply voltage to +-60V or more. Use a 15K ohm resistor, to have a higher gain. Reduce the bias current to 2mA by increasing the 3.3K resistor to about 16K. Should be able to achieve achieve a voltage swing of 30Vp-p on a +/- 1mA. This should be high enough an F4.

I would like to hear your comments on what you think of such a modification.

Thanks.

Oon

[Zen Mod]

2mA of bias is good for ..... phono stage ?

[Itsmee]

Originally Posted by oon_the_kid

Hi,

I am wondering if it might be possible to modify the D1 to directly drive an F4.
Oon

I like the idea. I haven't checked your proposed mods for the D1, but if it works, 2mA would be technically enough, although i would be tempted to increase it to a minimum of 10mA and replace the 47K in the F4 with 100k.

[oon_the_kid]

Originally Posted by Itsmee

I like the idea. I haven't checked your proposed mods for the D1, but if it works, 2mA would be technically enough, although i would be tempted to increase it to a minimum of 10mA and replace the 47K in the F4 with 100k.

Well the issue with the circuit is this. While the AC current signal actually forms a out voltage across the resistor (1.5K), so does the DC signal. So if you multiply the 10mA across 1.5K, it would form 15Volts below positive rail (30V) which will be quite nice. Giving it good headroom for the voltage swing (since the voltage cannot swing below the intended Iout ). So if you want to increase the gain, it can be achieved by increasing the resistance, you need to deal with the DC part as well which means you would need to decrease the bias current or raise the supply voltage or both.... alternatively get a DAC with very high Iout, or parellel a few DAC chips...

So hence for my case I increased the resistance 10X, doubled the supply voltage, reduce bias current 5X to compensate for it. And I would definitely like to replace the resistor at F4 with 200K or so (need to account for the volume pot in between). On a different note, if we were to use the buffer stage in the D1 circuit, we could bypass the first stage of F4 or if we use the first stage of F4, we could bypass the buffer of the D1.

BTW, this has to do with my other posting on power DACs on this forum...

Oon