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Old 14th January 2009, 07:50 AM   #1
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Default DIY DAC with input switchingon a budget?

Hi all.

I have a 3 sources with optical digital outputs that I want to use with a reasonable DAC. The sources are a sky TV digibox, Pioneer DVD payer and Sony PS2. They aren't priority sources but If I can find a DIY DAC at a good price I expect it might provide slightly better sound quality into my Amp.

Is there a good DAC with optical switchable inputs available in kit form?

Any advive would be greatly appreciated.

Rgds
Mike.
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Old 14th January 2009, 08:41 AM   #2
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You could use this in front of any diy dac:

http://www.twistedpearaudio.com/digital/cs8416mux.aspx

Although, you would have to convert the Optical signals to Spdif first, which is not much of a problem, I believe.
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Old 15th January 2009, 02:27 PM   #3
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Cheers.

Bit pricey for what I intend to use it for though.

I would even consider a secondhand one but I need at least 3 optical inputs, unless its an easy mod to convert from coax to optical and vice versa?

There's a couple of cheap DIY ones on eBay:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=004

http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=019
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Old 15th January 2009, 06:08 PM   #4
jitter is offline jitter  Netherlands
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Maybe you can multiply the optical input of one of these DACs by DIYing yourself a switch with multiple optical in and one optical out.

I'm thinking about building a switch for my low priority devices (DVDplayer, HDDrecorder, digital TV decoder) to use them on the optical input of my DAC. That way the electrical inputs remain free for HQ audio equipment.
I have some ideas of how to build one. I think of combining several optical and electrical inputs with one optical output. But right now it's no more than ideas...
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Old 15th January 2009, 09:31 PM   #5
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That sounds like the kind of thing I need too.

I have no idea how to switch optical though, isn't it done with fiber optics?

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Old 16th January 2009, 02:29 AM   #6
Cliff45 is offline Cliff45  United States
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It may be a long shot, but is this something that would work? It's not "industrial grade", from the looks of it, and it's not priced as such, either:

Nyrius SW100 Digital Audio Optical Toslink 3-Way Selector Switch for Fiber Optic Home Theater Connections

http://www.amazon.com/Nyrius-SW100-D.../dp/B000812QC6

It also looks like "Cables-To-Go" has something similar:

Cables-To-Go "Digital Explorer" Optical Switch


I would have thought that you would have to implement something like this by using three separate S/PDIF-Toslink receivers which convert the optical signal to electrical, then use a MOSFET-type switch to connect the desired input to the output(s). I guess you could do this a whole bunch of different ways, though....


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Old 16th January 2009, 05:05 AM   #7
jitter is offline jitter  Netherlands
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Quote:
Originally posted by mikesnowdon
That sounds like the kind of thing I need too.

I have no idea how to switch optical though, isn't it done with fiber optics?

Mike.
The optical switches that Cliff45 linked to indeed seem to work with optics as I dont think there's any AC adapter. If you're going fully optical, this might be a simple yet effective way to do it. But keep total fibre cable length short, especially when using plastic fiber cable (almost all of the cheaper ones). Glass fibre cable is better.

Quote:
Originally posted by Cliff45
[B]It may be a long shot, but is this something that would work? It's not "industrial grade", from the looks of it, and it's not priced as such, either:

Nyrius SW100 Digital Audio Optical Toslink 3-Way Selector Switch for Fiber Optic Home Theater Connections

http://www.amazon.com/Nyrius-SW100-D.../dp/B000812QC6

It also looks like "Cables-To-Go" has something similar:

Cables-To-Go "Digital Explorer" Optical Switch
These look fine for use in non critical sources, just as Mike intends.

Quote:
I would have thought that you would have to implement something like this by using three separate S/PDIF-Toslink receivers which convert the optical signal to electrical, then use a MOSFET-type switch to connect the desired input to the output(s). I guess you could do this a whole bunch of different ways, though....
That's the idea I have because I want a switch with multiple inputs of both optical and coaxial. But someone already DIYed just that, look here.

Mike, if you can read schematics, you can recognise the circuits needed for optical -> coax and vice versa.
I'm going yo build this, but without the use of a microprocessor. That looses some functionality (display) but I won't need a programmer or processor.
The multiplexer (74HCT251) has eight selectable inputs that can be selected by a combination of low and high signals on s0, s1 and s2. I can make it a lot easier by limiting the inputs to 4 by connecting s2 to GND permanently. To be continued...
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Old 16th January 2009, 01:14 PM   #8
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This looks ideal.

Like you suggest a simpler version should be doable for me. The switches on Amazon look ok but I'd rather have something all-in-on box with a simple rotary switch on the front. If you go ahead with this please keep me posted, it will be easier for me if I can follow someone building a similar thing.
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Old 17th January 2009, 02:38 PM   #9
jitter is offline jitter  Netherlands
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Today I breadboarded part of the circuit to test if my approach to switching between channels will work. Answer: it will.

In the attachment you can see how I was originally planning to switch between channels. Using some pull up resistors combined with pull down transistors driven by a 2 pole 4 position rotary switch to select between channels.

Explanation about the switch: 2 pole switch with 4 positions (just like in a switch box to connect 4 stereo sources to one input on a stereo amp). Both poles per position are "coded" as in the truth table next to the schematics (note that the transistor inverts the logical signal: H base means L collector as the emitter is connected to GND).
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Old 17th January 2009, 02:41 PM   #10
jitter is offline jitter  Netherlands
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But then I thought: this can be much simpler using the same switch but ditching the transistors and resistors.

Unless someone can come up with a reason why the first idea would be better, I'm going for this one instead.

Without the transistors, the "coding" of the switch does not need to be reversed.

Edit: I just noticed I forgot to connect pin 7 to ground in the schematics. Without it, there'll be no output.
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