Can I switch between two input receivers? - diyAudio
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Old 9th July 2005, 07:01 PM   #1
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Default Can I switch between two input receivers?

How do I do this? A new diy twin tda1541a dac is on the way (partially assembled tube-lover's kit). His design makes use of cs8412 digital receiver. In addition to a spdif BNC input, I want to modify this dac to add a USB interface using pcm2706 digital receiver. This IC is capable of receiving USB (and spdif) and outputing I2S to the twin tda1541a IC's (which are capable of accepting i2s input).

I would build a small daughterboard with the 2706 interface with separate battery power supply so that it is not bus powered (total of about 7 parts for this board). This interface has been built by other diy'r.

So if I want both BNC spdif input socket and usb input socket on DAC, how do I best accomplish this? Here are possible options

a) Only use the 2706 digital receiver; both for spdif input and usb input. It would send i2s to the tda1541a's. But I would need some type of switch to do this? Also, would I have to de-solder the cs8412 IC that comes installed on the dac pcb?

b) Use both the cs8412 (for spdif interface) and the 2706 board (only for usb). How would I do this if I want both 8412 and 2706 to send i2s signal to tda1541a's? Can tda1541a receive two I2s signals? If this configuration is possible, how do I switch between spdif and usb inputs?

I am concerned about taking the cs8412 out of the design: (1) because most of these tda1541 dacs use this receiver; and they must use it for good reason and (2) I am paying for the part and attendent caps, power supply etc.

How best can I accomplish my goal of adding the usb interface?

Here's photo of dac pcb...


:confused:
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Old 10th July 2005, 04:41 AM   #2
gmarsh is offline gmarsh  Canada
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74HC257 quad 2:1 MUX.
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Old 12th July 2005, 05:08 AM   #3
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Default So the mux goes...

Do both i2s signals out of the 8412 and pcm2706 go into the mux, which then feeds the tda1541's?
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Old 12th July 2005, 12:53 PM   #4
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Also, is the spdif (cs8412) or i2s (pcm2706) chosen by a manual switch or is it automatically detected by which ever input is receiving the signal?
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Old 12th July 2005, 01:05 PM   #5
dddac is offline dddac  Germany
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I have done this already and use small gold contact subminirelais to switch between both I2S outputs and feed to the DAC input....... I did not want to add extra logic in the "signal path"

Even more simple is just a 3 pole switch :-)

doede
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Old 12th July 2005, 03:26 PM   #6
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Default Hi Doede, Like This....?

I've heard wonderful things about your impressive dddac. As a novice DIY, I would appreciate any feedback on whether I am on the right path in terms of your recommendation for using a sub mini relay. I found this one:

Magnecraft PC Board Relays DPDT SUBMINIATURE 6V

http://www.magnecraft.com/products/e...pg10-11_W7.pdf

Do the i2s outs of both the 8412 and pcm2706 DIR's terminate into this subminiature relay, which then passes the i2s signal onto the dac i2s input?

Also, does this subminirelay require a manual switch, or does it just auto detect which DIR has current flowing through it and then pass the I2s out from the "active" DIR?

Any input is much appreciated!
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Old 14th July 2005, 09:00 PM   #7
dddac is offline dddac  Germany
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I am not sure HOW critical it all is, but these relais seems ok to me... I am using similar ones I can get locally ...

Basically both receivers work in parallel and "terminate" in the relais. I do the switching by hand between both inputs with a 1 pole switch on the front panel. The position which normally would be used most, is that the position were the relais is in rest and current flows. Of course, you could look for some clever circuit, based on the USB receiver or so, that indicates which one is "on air"...

good luck !
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Old 15th July 2005, 02:41 PM   #8
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Default Thank you

Thank you, Doede. Problem solved. I'll try to implement this sub mini relay.
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Old 21st August 2005, 02:00 AM   #9
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Me, I've got a more complicated scheme: I want to switch signals from 3 inputs with independant selection modes.(3 different EIAJ, MUX OB/TWC, SPDIF...) You should look at the PNG to understand what I mean. I also want to remotely switch inputs, so a mechanical switch is not an option.

Note: In the PNG, I don't repeat the complete EIAJtoI2S and SPDIF converter each times, that's why I need to switch off inputs, in case one input uses the same mode as an other.

Relays would have been a good option in this case but the only problem is that if I need 5x 1$ DPDT relay for each inputs I will end with 15$ of relays, which is a bit too much.

I just found a post talking about using a 74F157. Is there a better choice? Will it affect jitter? Is there an other 74 series(HC,F...) I should use?
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Old 21st August 2005, 07:34 AM   #10
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can you list your sending and receiving devices?
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