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Old 8th August 2006, 09:55 PM   #11
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Quote:
Originally posted by lohk
On all fotos of different versions of that DAC I can clearly see several crystal devices.
I think he meant "Crystal" aka "Cirrus Logic" as opposed to "crystal" devices. Clearly the manual shows a couple of VCXOs and an XO for the JISCO (asychronous reclocking?) in the diagram.
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Old 28th August 2006, 01:01 PM   #12
Charles is offline Charles  Germany
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Default Re: Altmann Attraction DAC

Quote:
Anyone care to speculate what makes it special?
Hi everyone,

to answer your questions:

On the Attraction DAC I use the TDA1543 because it is R2R and because it can be used with a single-ended power supply.

As you already know, the Attraction DAC is designed to be powered by a Optima Red Top 12V car battery which eliminates the need of wall powered (noisy) supplies.

I use active I/V conversion 1 OPA134 per channel, and 4 OPA134 per channel as output buffer. The DAC can power a speaker directly

The output level is as high as it possibly gets with a 12V supply, so it is about -3.5 Volts to +3.5 Volts full scale (which btw. seemed to be enough to overdrive DUC's preamp).

The input (spdif) receiver is custom. I programmed it into a Xilinx device. It has a switchable JISCO option and all DACs come with the UPCI (ultra-precision PLL) which synchronously reclocks the data.

There is 2 custom made VCXOs for the frequency generation and tuning and one custom XO for the JISCO function.

All features programmed into the Xilinx, which was really fun, but no walk in the park, btw

The Attraction DAC runs up to 192kHz on spdif input. It uses neither upsampling nor oversampling. Just straight conversion.

So above the more obvious stuff. But why is it so damn good ?

Okay, the pcb is flat on the bottom, which means that all through-hole solderjoints have to be flat.

There is no housing and the high-quality RCA jacks are not connected via wire, but directly soldered to the pcb.

Then this pcb is screwed on a spruce board which is the reason the pcb-bottom has to be flat.

Mounting to the spruce board adds body to the sound (which otherwise is not there).

Then there are a couple of other tricks I apply with the DAC which I better not mention here, in order to prevent some avalanche-kind of response

However, now you have something to play with ...

Fun

Charles

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Old 28th August 2006, 09:41 PM   #13
lohk is offline lohk  Europe
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Thanks, Charles, to your answer here - highly appreciateted!

Spruce: I also do that occasionally - mostly because I am too lazy to make a proper case - but why not! But we should not forget to use some layes of C37

DAC: Can you explain how the TDA1543 can take a SR of 192kHz?
And: You do have to explain to us your "tricks", but please tell us a bit more, will you?
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Old 28th August 2006, 10:05 PM   #14
lohk is offline lohk  Europe
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corr: a TDA1543 can obviously take 192kHz sample rate, in 16bit resolution

( - should have read the specs before asking - )
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Old 29th August 2006, 02:15 AM   #15
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Charles, have you experimented powering the OPA134s with a separate battery? Would be easy to implement and probably would further improve performance.
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Old 29th August 2006, 05:13 AM   #16
adhoc is offline adhoc  Australia
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I understand most of the tech stuff going on here... but a spruce board for "adding body" to the sound?
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Old 29th August 2006, 10:19 AM   #17
Charles is offline Charles  Germany
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Quote:
Originally posted by lohk
Thanks, Charles, to your answer here - highly appreciateted!

Spruce: I also do that occasionally - mostly because I am too lazy to make a proper case - but why not! But we should not forget to use some layers of C37

You do have to explain to us your "tricks", but please tell us a bit more, will you?
Your intuition goes into the right direction

Quote:
Originally posted by serengetiplains
Charles, have you experimented powering the OPA134s with a separate battery? Would be easy to implement and probably would further improve performance.
I think it would mess up performance.

However, the OPAs get the pure battery current, then comes the DAC (regulated) and then comes the digital section (regulated separately). Ground plane separation plays an important role too among other things.

I think if anyone of you would spend 5..10 years of his life tweaking with DAC issues - add a portion of luck - add an extra portion of ignorance - you would all come to quite similar results ...

Charles
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Old 20th October 2006, 07:31 AM   #18
Will is offline Will  Malaysia
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Quote:
Originally posted by Charles


Your intuition goes into the right direction



I think it would mess up performance.

However, the OPAs get the pure battery current, then comes the DAC (regulated) and then comes the digital section (regulated separately). Ground plane separation plays an important role too among other things.

I think if anyone of you would spend 5..10 years of his life tweaking with DAC issues - add a portion of luck - add an extra portion of ignorance - you would all come to quite similar results ...

Charles

Charles,
If I may ask how do you make a dual supply for the op-amp with a single 12vdc ?
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Old 20th October 2006, 10:24 AM   #19
Charles is offline Charles  Germany
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Quote:
Originally posted by Will



Charles,
If I may ask how do you make a dual supply for the op-amp with a single 12vdc ?

Hi Will,

I feed the signal at 6V, just about in the middle.

That's the reason that the Attraction DAC has coupling caps at its output.

Charles
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