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Clocks and the Alpha DAC


Mike in MD
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Hi,

 

I got a very nice reply from Berkeley Audio, which I have copied here:

 

"Thank you for your interest in the Alpha DAC.

 

Regarding the Alpha DAC not having a word clock input, I understand your concern. It's interesting that clocking is perhaps the area of the Alpha DAC's design we spent the most time and effort on.

 

We learned from development of the Pacific Microsonics Model Two that the most critical clock in an audio system is the conversion clock - the internal clock in the ADC or DAC. That clock needs to be extremely stable and have as little jitter as possible. Ideally, the clock in an ADC or DAC should not have to lock to an external clock at all, whether it is derived from a digital signal stream or a separate word clock.

 

That is why there is a "Master" mode for the Model Two that makes the internal conversion clock a master clock output to lock external signal sources to, such as DAW's or transports. That way the signal source locks to the conversion clock for lowest conversion jitter, not the other way around.

 

In designing the Alpha DAC we spent a long time developing a sophisticated proprietary system with extremely transparent audio quality that allows the Alpha DAC's conversion clock to operate virtually as a master clock for the DAC in high isolation from the incoming clock signal. This also allows the Alpha DAC to lock very quickly to different input sampling frequencies (very important with music servers and something the Model Two can't do) and eliminates the need for a separate word clock input.

 

The Alpha DAC design also provides excellent jitter isolation, although to extract all of the information in high resolution signals such as 24-bit 176.4 kHz or 192 kHz recordings, the signal source also needs to have extremely low jitter. That is because input signal jitter components form "side-bands" that inject energy into the signal grounds of the DAC. Even though the Alpha DAC has extremely high input signal isolation the amount of information in a 24-bit 192kHz signal requires microvolt analog accuracy to reproduce and the less jitter "noise" the input signal carries the better.

 

We recommend the Lynx Studio Technology AES16 IO card for music servers because it has very good re-clocking and low intrinsic jitter. In our experience if the AES16 is installed in a good hardware platform, like the Zalman TNN 300, an external clock doesn't improve performance. Of course, results may vary with different systems and hardware.

 

I hope I have answered your questions.

 

Best regards,

 

Michael Ritter

Berkeley Audio Design, LLC

 

The following is my original (semi-grouchy) post:

 

Hi All,

 

Last weekend we had a discussion about clocks and DACs in the thread "Which Front End?"

 

I have been very interested in the Berkeley Alpha DAC, and mentioned in the discussion that the Alpha DAC does not have a clock input, which maybe they should have included for $5k. So on Sunday, last weekend (12/21), I sent an email to Berkeley Audio asking them if they would comment on the exclusion of the clock input. Maybe they would explain how it is not necessary for the Alpha DAC.

 

Anyway, they have not sent me any answer.

 

Should I be annoyed ???

 

Mike

 

 

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It is the holidays after all. They may respond later.

 

The truth is that very few DAC's have internal clocks (other than upsampling clocks) and for even the ones that do, the customers rarely take advantage of it. Like I said in the other posts, you are limited to the jitter of that clock if you use it. Just because it's in close proximity to the D/A chip does not make it lower jitter. The choice of clock and the design is what achieves low clock jitter, internal or external.

 

Steve N.

Empirical Audio

 

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  • 1 month later...

I have been using the Big Ben clocking Custom Sonos into Accustic Arts tube Dac. Then I purchased the OCX to be connected to a Rubidium Word clock. But the OCX sounded much more digital and less musical then the Big Ben. Returned the OCX. I am going to buy the Lynx and connect to the Big Ben clock for HD music.

 

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