sluggoaudio
New Head-Fier
- Joined
- Jan 26, 2009
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Hello all: I've just received my V-DAC, and I've been following this thread. One mistake that's being made is that C's 55, 60, 155 and 160 are definitely 220 pF, NOT 22 pf. Just to be sure, I pulled one out and measured it. Dutchamps got it right in a previous post.
If you go to the TI website and search for the DSD1792 datasheet, you'll see their recommended design for the I to V and the output stages (they call them measurement circuits). If you calculate the rolloffs for the V-DAC, you come up with 86.8 KHz for the I to V and 185 KHz for the output, which is very close to the reference design. If you use 22 pF caps, you have a rolloff 10 times higher (1.8 MHz). This will let a lot of trash through the output and is probably why things don't sound right. If you can order from Digikey in the USA, their Panasonic P series polypropylene caps are excellent replacements for the 220 pF's as well as the 3900 pF's. The only drawback is that they have a $25 minimum order.
A question: for those using the 4562 for the output: has anyone measured the dc offset? If it's significantly less than 1 mV, you can almost certainly replace the output caps (C 3 and 4) with jumpers.
Thanks in advance.
If you go to the TI website and search for the DSD1792 datasheet, you'll see their recommended design for the I to V and the output stages (they call them measurement circuits). If you calculate the rolloffs for the V-DAC, you come up with 86.8 KHz for the I to V and 185 KHz for the output, which is very close to the reference design. If you use 22 pF caps, you have a rolloff 10 times higher (1.8 MHz). This will let a lot of trash through the output and is probably why things don't sound right. If you can order from Digikey in the USA, their Panasonic P series polypropylene caps are excellent replacements for the 220 pF's as well as the 3900 pF's. The only drawback is that they have a $25 minimum order.
A question: for those using the 4562 for the output: has anyone measured the dc offset? If it's significantly less than 1 mV, you can almost certainly replace the output caps (C 3 and 4) with jumpers.
Thanks in advance.