Filburt Posted May 8, 2008 Report Share Posted May 8, 2008 Current out DACs really want to see as close to a dead short on the output as you can get, sub 1 ohm. A resistor large enough to get the required output voltage isn't going to be close to that Most opamps can't get that low even with feedback and rise as freq. goes up because of feedback/group bandwidth. The THS403x was going to be my next choice for opamp to try, but I built a discrete current steering I/V which I love. No more opamps for me. I sort of regard passive i/v as the common fallacy of simple is better that seems to float around in audiophilia. No more complicated than necessary (standard razor principle) might make sense, but simplicity for simplicity's sake seems unwise to me. As you note, these chips are designed to have a near-zero impedance on their output. You're right that op-amps can't provide that into the MHz range; not even close. The feedback factor drops into oblivion by that point. Although, an old revision of the AD8055 used to have about 70dB of OLG to 2MHz (see - http://www.jancorver.org/info/atv/baseband/files/AD8055.pdf). Current steering i/v seems to be the way to go. luvdunhill - I can barely read the charts on that article. The distortion doesn't look particularly low to me, though. They also probably have to gain the signal quite a bit to get line-level output, which just means you throw in distortion from the VAS (in this case, resulting in what seems to be a lot of odd-order products). Might be worth trying to install a current steering i/v and see how you feel about it. Quote Link to comment Share on other sites More sharing options...
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