Can I switch between two input receivers?

[riotubes]

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...

 

[gmarsh]

74HC257 quad 2:1 MUX.

 

[riotubes]

So the mux goes...

Do both i2s signals out of the 8412 and pcm2706 go into the mux, which then feeds the tda1541's?

 

[riotubes]

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?

 

[dddac]

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
www.dddac.de

 

[riotubes]

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/e104_sec6_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!

 

[dddac]

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 !

 

[riotubes]

Thank you

Thank you, Doede. Problem solved. I'll try to implement this sub mini relay.

 

[DragonMaster]

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?

 

[rfbrw]

can you list your sending and receiving devices?

 

[DragonMaster]

The receiver would be a TDA1541A, and the inputs should be something like Video Game(SPDIF), CD Player(EIAJ), DVD Player(Still don't have one)

 

[rfbrw]

Given your sources, I can't see where all the complexity comes from.

 

[DragonMaster]

I'll think a bit more to see if I still use the mode selecting scheme, but is a 74xx157 good for this task?

EDIT: Is it worth paying 15$ of relays instead of ~5$ of ICs?

 

[rfbrw]

Both options will work well. BTW why the need to alter the input format on the TDA1541A?

 

[DragonMaster]

If I put the switch in the MUX mode(direct from jacks to TDA1541A, I can switch between OB and TWC depending on the source.

 

[rfbrw]

If I put the switch in the MUX mode(direct from jacks to TDA1541A, I can switch between OB and TWC depending on the source.

This may seem like a daft question but do you have any OB sources?

 

[DragonMaster]

No, maybe I could remove it since OB sources don't seem pretty popular. The D/F in my CDP separates the DATA in two channels for the integrated DAC. I still have to see if a D/F would be really useful or not.

 

[rfbrw]

With all the switching going on, it will be a lot cheaper to use IC's but for ultimate isolation T switches would be best. BTW, unless you are using one of the earlier digtal filters i.e the DF1700/SM5813 and before, you will have to convert the output of the filter into OB from TWC.

 

[DragonMaster]

The D/F is a Sony CXA???? so I guess it's not really a good choice for a D/F. I'll remove the I2S mode switch to keep only the most popular formats; I²S, EIAJ and SPDIF.

I think I'll use jumpers for mode selection and ICs for input selection. Does it seem OK like this?

 

[rfbrw]

Seems reasonable but when you have a settled idea of what you want to do, it may be possible to simplify things.