Passive I/V? Don't know about that. Attached below is a copy of the TDA1387 data sheet. On page 4 there is a diagram showing opamp I/V as the suggested output topology. Many manufacturers follow the data sheet application circuit if one is shown. I don't necessarily have a problem with that if it is well implemented.
Of course, if the manufacturer uses inappropriate opamps, and or poor layout, and or doesn't use a ground plane, and or uses poor power supplies then those things might be expected to have have an effect on the sound some people wouldn't like. Given we are talking about low cost dacs, something like that very well might be the case here. Only way to know would be to take a look inside and see what's there.
Also, another thing to consider is that dacs outputs often have some RF mixed in at a low level with the audio. That may consist of large clock pulses in the case of older dacs like this one. Even if the audio makes it through the I/V opamp okay, there may still be too much RF mixed in with the audio for some downstream components such as headphone amps, power amps, preamps, etc. In those cases what may be needed is additional filtering after the I/V opamp, not necessarily a passive I/V. Even with a passive I/V there may still be RF present that can have an effect on downstream equipment. Sometimes it can be hard to tell if that's causing a problem or not. If sound quality is not great, someone needs to know how to investigate and find out what the problem is, and if its reasonably fixable.
Of course, if the manufacturer uses inappropriate opamps, and or poor layout, and or doesn't use a ground plane, and or uses poor power supplies then those things might be expected to have have an effect on the sound some people wouldn't like. Given we are talking about low cost dacs, something like that very well might be the case here. Only way to know would be to take a look inside and see what's there.
Also, another thing to consider is that dacs outputs often have some RF mixed in at a low level with the audio. That may consist of large clock pulses in the case of older dacs like this one. Even if the audio makes it through the I/V opamp okay, there may still be too much RF mixed in with the audio for some downstream components such as headphone amps, power amps, preamps, etc. In those cases what may be needed is additional filtering after the I/V opamp, not necessarily a passive I/V. Even with a passive I/V there may still be RF present that can have an effect on downstream equipment. Sometimes it can be hard to tell if that's causing a problem or not. If sound quality is not great, someone needs to know how to investigate and find out what the problem is, and if its reasonably fixable.
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The Nobsound TDA1387 sounds fantastic. I prefer it to DS DACs at any price point (USD 1000+). I just want the Lee DACs to sound similar.
+1 for the phidecca dac, if you can do diy it is a great sounding dac. You can get the board assembled from Richard for a nominal fee and then it's a matter of chosing the right power supplies and input. I found the jlsounds usb to i2s board to sound better than a Wolfson based spdif to coax/optical front end I tried.
He bought from Nitin at Anode Acoustics. I shipped Nitin finished boards and Nitin supplied power supplies and all casework.
