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Old 8th November 2006, 09:28 PM   #11
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Default Re: Re: Re: DC offset

Quote:
Originally posted by cviller
I'm confident that your D1 design, even with my home etched pcb, can sound much nicer - I just have to get the right chip and circuit in front.
One of the special parts of the D1 was the clock PLL, and one
of the reasons we discontinued the D1 was the unavailability
of the parts for it.
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Old 8th November 2006, 10:06 PM   #12
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Default Re: Re: Re: DC offset

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Originally posted by cviller

I think that the pcm1730 chip I used could have been fried or perhaps just evil, but I'm currently trying to make up my mind if I should move on to ad1955 or have another go at pcm1730 I think I have one or two left.

If you have a scope and have eliminated the power supply as a noise source for your scratches I'd look at the vref out of the DAC with a scope. The datasheet doesn't mention that this voltage varies a lot, but perhaps it does, even varying with the signal. The sample circuit they show is immune to either slow or fast changes in vref out which makes me wonder. If you see variation on a scope then you might have your answer to your noise source and would have to create some sort of circuit to make the gate voltage follow the vref changes.

Just pure speculation on my part, I don't know how those vref voltage outs are supposed to behave.

Rob
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Old 11th November 2006, 04:12 PM   #13
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Default Re: Re: Re: Re: DC offset

Quote:
Originally posted by Nelson Pass


One of the special parts of the D1 was the clock PLL, and one
of the reasons we discontinued the D1 was the unavailability
of the parts for it.
I can feel another project emerging on my todo list!
I'm not sure however if reclocking is worth it, if I use pcm1798.

Quote:
Originally posted by relder

If you have a scope and have eliminated the power supply as a noise source for your scratches I'd look at the vref out of the DAC with a scope. The datasheet doesn't mention that this voltage varies a lot, but perhaps it does, even varying with the signal. The sample circuit they show is immune to either slow or fast changes in vref out which makes me wonder. If you see variation on a scope then you might have your answer to your noise source and would have to create some sort of circuit to make the gate voltage follow the vref changes.
Interesting ideas - sounds like something to investigate. I don't have access to a reliable scope, but maybe santa will bring me a picoscope... that would be nice, but I think it is out of his price range.

The upper 6 bits are treated different from the lower 18bits in pcm1730, so I it makes sense that the scratches were triggered by high digital numbers. Some cd's were much worse than others. I don't have the board any more because I needed some parts for my pcm1798 attempt, but I will redo it in the near future.
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