[time-nuts] Sound cards

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Jan 9 16:56:19 EST 2009


John Ackermann N8UR wrote:
> Rex said the following on 01/09/2009 06:37 AM:
>> Maybe I lost track and missed something, but I don't think I ever saw 
>> more on the subject of specific high-end sound cards that might be 
>> useful for nutty measurements.
>> I'd be interested to hear what any of the group has to share about 
>> relative merits of current sound cards that can be interfaced for 
>> measurements like what was being discussed in that earlier thread. (And 
>> some before and since.)
>>  From my own point of view, I'd most like to hear about any that are 
>> external -- connected by USB or 1394, rather than an internal card. This 
>> makes it more portable and easier to move between different PC's.
> [Shameless Plug]
> One very interesting possibility is the HPSDR (High Performance Software 
> Defined Radio) boards called Ozy and Janus.  Together with a passive 
> backplane called Atlas, they provide an extremely high performance 
> ADC/DAC that supports sampling to 192k and output via USB.  The system 
> was designed for use as the interface between a PC and an SDR and 
> special attention was paid to low noise and flat frequency response.  I 
> am not certain, but I *think* that the inputs are DC coupled.
Not according to the circuit schematic.
The input coupling is 10uF + 10K with a corresponding low frequency 3dB
cutoff of 1.6Hz.
Default inputs are single ended, balanced inputs are accessible via a
pair of headers.
Input full scale is that of the AKM5394 ADC chip (1.7Vrms nominal).
There is a small dc offset between the differential inputs to the
AKM5394 to eliminate an idle tone related spurious output.

> The two boards, assembled and tested, run about $320, with a discount 
> for TAPR members.  The backplane is a fairly simple kit (lots of 
> connector pins to solder, but not much complexity) that sells for $28, 
> also with a discount for TAPR members.  Bare boards, but not kits, for 
> Ozy and Janus are also available for the adventurous.
> I'm not aware of anyone using this system for T&F work, but it has some 
> interesting possibilities.
> [/Shameless Plug]
> John
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