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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Re: some notes... posted by Thorsten on November 3, 1999 at 08:47:29:
Thorsten offers some good advice but I would add the Sowter can and should be used with a resistor on the DAC output as the application notes show to keep the impedance low on the DAC output especially at high frequencies. The value they chose is 25 ohms which combined with the output resistance of 47K would end up about 21 ohms. This is still a bit high in my experience. Most of the commonly used current output DACs are designed for a virtual ground on the output and would not meet linearity spec with the resulting 42mV peak compliance voltage (PCM63) or 25mV peak (PCM1704). I have found the sound of a DAC (PCM1704) using a resistor for I/V conversion to significantly improve all the way down to 10 ohms which is difficult to implement without a transformer because a gain of about 300 would be required and noise can be a problem.You might want to try a circuit with the PCM1704 (+/-1.2mA) terminated with a good quality 10 ohm resistor across the Sowter input. This would give you close to 170 mV peak out to your gain stage and would keep the voltage on the DAC output below 10mV peak.
I have not used the Sowter or any other transformer for this function but I have used resistor I/V convertors, single transistor convertors and opamp convertors. My current D/A convertor uses the single transistor zero feedback variety with a dynamic impedance around 3 ohms on the DAC output. The Sowter still seems a bit pricey at around 70 British pounds for a pair but it sounds as though you are aware of this. Good luck and keep us posted of your progress if you decide to use the transformer.
Dave
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Follow Ups
- Re: some notes... - Dave Ingels 11:40:09 11/03/99 (0)
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