EZDAC and Multiple Sources??

[TedS]

Hi everyone,

I was wondering if anyone has thought about using this DAC with
multiple sources? I'd like to build one to use with two sources. The
CS8416 can handle up to 4 sources in hardware mode, but I'm not sure
if the PCB allows for that many connections. Anyone thought about
this or have any ideas?

Thanks,
Ted

[cyclebrain]

I built mine with two inputs and looked into the multiple inputs
available at the receiver but decided that it was easier just to mount
a relay right at the input connectors and control it with a front
panel switch.

[TedS]

Hi cyclebrain,

That sounds like a simpler and attractive approach. My only concern
was whether or not this messes up the 75-ohm characteristic impedance
of the spdif line. I had read that putting "source selector" switches
in coax spdif lines can negatively impact the characteristic impedance
and cause "reflections" on the lines. But is this not a problem if
you implement the switch after the 75-ohm termination at the
enclosure?

Thanks,
Ted

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[TedS]

Hi guys,

I read up on this some more, and it looks like the relay may be fine,
if terminated properly with the 75 ohm resistor. I assume that's what
you've done, cyclebrain. What type of relay did you use?

I'm still curious as to how hard it would be to use the MUX capability
of the CS8416. I'd have to get a second transformer and 75-ohm
resistor, and I'd have to make connections to pins 3, 10 and/or 11
instead of soldering them to the PCB tracks. Pin 3 would go to the
second input +, and pin 10 or 11 would be switched hi or low to select
input 0 or 1. How hard could that be? I think I'll probably order
parts to do it either way (relay or MUX) and decide once I get my
hands on it.

Hey Evan, got any EZDUAL and EZDAC boards right now? I'm about ready
to pull the trigger on this project!

Ted

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[cyclebrain]

I used a Potter Brumfield DPDT 24VDC relay and powered it from the
negative EZ-PSU supply since it was less loaded than the positive
side. The loading of the SPDIF line is provided by the input
transformer T1 and my switch is placed prior the the transformer. The
reflections caused by impedance mismatches is a very real problem and
is caused by any connector or device in the path of a signal. Even
traces on a P.C. board can create impedance mismatches and
reflections. To me, and I know I will get plenty of flack for this,
the data rate is so low that slight mismatches caused by a relay or a
panel connector will not be a problem. Also the ratio of the mismatch
relative to the load is a good measure of importance.