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Old 26th April 2009, 10:02 PM   #1
Glenn2 is offline Glenn2  United Kingdom
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Default Zapfilter2 and current-output dacs

Hi,

Can anybody who has hooked up an LC Audio Zapfilter2 to a current-output DAC please tell me what sort of output level you get and which DAC chip it was? (RMS)

I'm trying to find out if a PCM1794 will be too hot for it.

I can go with PCM1798 instead for half the output current, at the expense of worse digital filter performance, I'm led to believe.

Thanks in advance.

Glenn
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Old 26th April 2009, 10:38 PM   #2
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The Zapfilter is quite strong and will give almost double the output when hooked up "current" to an of the shelf cd players current dac output bypassing it's i/v and output stage.
With your PCM1794 that you plan to use it is possible to lower this gain by changing "Iref" resistor (pin 20) of the PCM1794 from 10k to 15k or even 20k this lowers the output of the dac this was I did with the PCM1955 except with it, it went from 2.7k to 5.6k

Cheers George
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Old 26th April 2009, 11:10 PM   #3
Glenn2 is offline Glenn2  United Kingdom
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Excellent info, thanks.

I actually have a spare Zapfilter2 (as you do), and after my current disillusionment with the new Dacmagic (ebay here I come) I have two new ideas for getting music off my PC:

1) A Squeezedac: The Squeezebox 'receiver' outputs I2S to its Wolfson DAC, not left-justified like the SB3. I could sent this to one of Twisted Pear's COD boards (PCM1794) and then to the Zapfilter, all in the same box. (Could also be done with TP OPUS, but same DAC as Cambridge.)

2) Re-box a Musical Fidelity V-DAC. They are 129 in Blighty at the moment. It has SRC4392 receiver/ASRC combo, DSD1792, and a bog-standard 6 op-amp output stage with the -V supply being inverted from the the +V supply of the wall-wart. There's a USB input too, which doesn't interest me. I could just replace the output stage with the Zap.
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Old 7th June 2009, 08:13 PM   #4
champ04 is offline champ04  United States
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George, are you using a zapfilter on your X64.4?
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Old 8th June 2009, 03:18 AM   #5
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Quote:
Originally posted by champ04
George, are you using a zapfilter on your X64.4?

Yes and it sounds magnificent, but I had to put 100ohms in series from the output of the dacs to the input of the Zap because the output from the 4 x dacs was to high for the zap, the 100ohms drop the 0db output of the zap from 9v to 7v @ 0db, if left at 9v it will soft clip the zap at 0db.
Cheers George
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