Simple Resistor For IV Converter AD1865 DAC

On my previous DAC built, the another ultimate DAC build here is basically an oversampling AD1865 DAC using CDX1144, then the current signal from DAC will going to the replaceable module called the IV & LPF combo module. This DAC is including a simple headphone amplifier that was initially built for experimenting various type of IV and LPF, then by using a headphone, I can carefully study how those modules effect to the sound quality.

But I never did it anyway:)

So I think, this is the first time I open it up again since the very first time built. Right now I will testing one simple method of DAC IV converter using only a resistor per channel.

I am really curious how the sound quality with it.

The working principal to convert from current to voltage is as simple as implementing the ohm law.

Using a resistor from each channel DAC output, in this case the pin 4 for I out right channel and pin 21 for I out left channel goes to the ground.

This method is actually common in most vacuum tube output DAC, which the IV converter is using a resistor per channel, than because the signal is so weak, then the vacuum tube back it up to certain level that power amplifier can drive. Typically is 2 volt.

But in this test, I only using a resistor per channel as an IV converter, without any gain stage, then goes to a simple L-C LPF using series 220uH inductor and 10nF capacitor to ground.

And this is the previously IV and LPF combo module using op-amps. It using a socket pins that's makes this experimenting proses become easier.

For the IV converter resistor, I tried various value resistors from 330 ohm to 100 ohm.

I found that the higher the value, more loud the signal output. But it has some drawbacks.

The sound with higher resistor value more rough and bass dominated, while smaller value give more smoothness in overall frequency band.

I end up with using 240 ohm resistor per channel as an IV converter. This gives me the balance between the loudness and the smoothness of the sound quality.

The resistors I using in this test is Susumu thin film resistor.

I fixed the layout by directly soldered to the main board.

And this is how I did it.

I evaluate this method for a week, with many songs I played. I can assure that using this simple resistor as an DAC IV converter give more pronounce in the mid-range. It is more forward and warm sounding but a little bit raw, un-polished sound.

The smoothness is gone, the dynamic a little bit bottle up, and the frequency range is more limited because now only using as simple L-C LPF only.

Nothing perfect I guess. Using op-amps is more reliable and give a smooth sounding experience, while using simple resistor as an IV converter also gives more pronounce in the mid-range.

After all it is a good example for experimenting a new things in this DAC world.

Cheers.

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