• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Grid choke as I/V?

I have a DAC that uses a resistor (~200R) as the I/V. This resistor doubles as a grid leak and the signal is fed to the grid of a tube. Overall, this works surprisingly well.

But, it occurs to me that it might work better with a grid choke instead -- high Z, low DCR. Anyone have any thoughts? All of the grid chokes I have seen have much too high DCR, so I think it would need to be a custom part of some sort, or maybe just a low H hammond. Also, the particular DAC chip (AD1865N-K) has no DC on the Iout if that changes what will work well.

Attached is what I am thinking. If you replace the choke with a resistor, it is what I am currently using.
 

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  • chokeiv.jpg
    chokeiv.jpg
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For a current output Dac, the load must have a much lower Z than the source.

An inductor has a very high Z, and would create extra distortion.

What I have seen people do is use a step up transformer to lower the effective load resistance while maintaining output.

I like the way you think. Keep at it. :)

Doug