Digital Audio Input Selector ?????

soundNERD · 2003-10-08 2:15 am

Really? It is complicated? I guess I didn't know what to expect for a digital selector and was expeciting on something much more complicated. Since I haven't built it yet, I like the idea of the 74HC125. I have a board I pulled out of an old scanner with 5 buttons. all the buttons share a common ground, then have a seperate + wire. 4 of them control inputs, and the other will run some logic to close and release a relay upon pressing of the button, then open it on the press of the button again (if anybody can help me with that it would be great also. I originally tried a 4011, which i was told would work, but in simulation in circuitmaker, it only would close, and not open the relay. I would like to use the 4011 since I have it but can't get it to work.) The remaining 4 buttons will select between the 4 inputs. every L output and every R output of the selector will be tied together to run into 1 amp per channel. LEDs would be great to indicate selected inputs. I really haven't done too much with logic, and if anybody can help that would be great. A schematic would also be great also.

Thanks for any help, Mike

OliverD · 2003-10-09 1:11 am

The circuit you posted contained logic for the push buttons and LEDs which is why it looks more complicated than my suggestion. If you insist on push buttons instead of a simple rotary switch, you will need two or three more chips. The circuit you posted looks ok. The best solution to your problems is probably a GAL. No HF noise and only one chip to control the buffers.

KostasTheGreat · 2003-12-28 8:53 pm

what about this ? http://www.rdlnet.com/ruspx4.htm

or this?

http://www.trianglecables.com/os-3pt.html

OliverD · 2003-12-29 4:03 am

This is a DIY site.

Ryssen · 2003-12-30 11:58 pm

A simple and yet very good solution is to use relais to switch the inputs. Make sure all inputs are terminated properly, even if not selected. To avoid

If I use a relay to switch betwen 2 inputs,how do I terminate?
75 ohms in parallel or in series?

fmak · 2003-12-31 8:09 am

jackinnj said:
a wonderful selector, easily programmed and dirt cheap due to the TELCOM BUST in the US:

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How much is it, and what is the model no please. Can't see from your photo.

:xeye:

jackinnj · 2003-12-31 12:45 pm

fmak said:
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How much is it, and what is the model no please. Can't see from your photo.

The HP3488a goes for around $50 on EBay -- look for one with relay cards: The PCB inside is gold plated and the device can be programmed using HPIB, or from the front panel:

OliverD · 2004-01-01 2:52 pm

ryssen said:
If I use a relay to switch betwen 2 inputs,how do I terminate?
75 ohms in parallel or in series?

You need a 75 Ohms resistor from "hot" to GND for each input, no matter if it's selected or not. You can solder the resistor directly to the input jack.

fmak · 2004-01-05 11:07 am

jackinnj said:
The HP3488a goes for around $50 on EBay -- look for one with relay cards: The PCB inside is gold plated and the device can be programmed using HPIB, or from the front panel:

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Just found one. $60 for the unit and 35 for two cards, one SPST and one DT. Can't find user manual in the Agilent site though. Can anyone help?

I guess I shall have to terminate with 75R instead of 50R by changing resistor and sockets etc.

promitheus · 2004-01-06 8:46 pm

I just noiced that Nelson Pass in the D1 DAC uses normal Relays to select the digital inputs.
That´s the easiest solution I have seen so far.

rfbrw · 2004-01-06 9:02 pm

There is a schematic for the Stax Talent BD1 dac floating around the net. It includes a 3port input selector. For new designs there are multiple input SPDIF rx's.

fmak · 2004-01-06 9:04 pm

rfbrw said:
There is a schematic for the Stax Talent BD1 dac floating around the net. It includes a 3port input selector. For new designs there are multiple input SPDIF rx's.

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Can you pl post the url for this?

Cobra2 · 2004-01-06 9:13 pm

Input selector active switch for SPDIF digital audio COAX (Cinch) DIY kit

A cheap sollution?
http://www.bmm-electronics.com/Product.asp?Product_ID=4

Arne K

rfbrw · 2004-01-07 12:49 am

Stax Talent BD1 schematic. http://asd123asd.hp.infoseek.co.jp/DAC-BD1-1.pdf

fmak · 2004-02-07 7:12 pm

jackinnj said:
a wonderful selector, easily programmed and dirt cheap due to the TELCOM BUST in the US:

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The HP3488A is truly wonderful. Bought one on ebay.de for e60 and cards cost about e15. The HP44472A VHF card costs more (e110) and can be modified for 75 Ohm BNCs. At once you have a digital and analogue switching unit of great flexibility and performance at a great price. You can control by computer too, but control from the front panel is simple.

Giorgio · 2004-02-08 9:14 pm

Here there is another possible solution.

http://www.tnt-audio.com/clinica/tnt1541_e.html

Giorgio

Devil_H@ck · 2004-02-08 9:54 pm

Or use an IC specially designed for this function:
- TI BB MPC508: 8 mono inputs - 1 output -> so you need 2 chips for stereo
- TI BB MPC509: 4 stereo inputs -> 2 output -> only one chip for 4 inputs

More info:
- MPC508: http://focus.ti.com/docs/prod/folders/print/mpc508.html
- MPC509: http://focus.ti.com/docs/prod/folders/print/mpc509.html

If you need more inputs check out the MPC506 & MPC507. The MPC506 allows for 16 mono inputs, the MPC507 for 8 stereo inputs.

I have 2 MPC506's lying in my room, but I need to make a PS first before I can test them.

fmak · 2004-02-08 10:15 pm

Devil_H@ck said:
Or use an IC specially designed for this function:
- TI BB MPC508: 8 mono inputs - 1 output -> so you need 2 chips for stereo
- TI BB MPC509: 4 stereo inputs -> 2 output -> only one chip for 4 inputs

More ---------------------------------------------------------------

The beauty of the 3488A is that it works even with the unit switched off on the VHF card. Yes, this makes a difference to the sound even with the high degree of isolation of the inputs.

Devil_H@ck · 2004-02-09 7:23 pm

fmak said:
The beauty of the 3488A is that it works even with the unit switched off on the VHF card. Yes, this makes a difference to the sound even with the high degree of isolation of the inputs.

Sorry, but I don't get what you mean. Do you mean that the 3488A works when it's powered down? Power consumption doesn't seem to be an isue and the MPC's don't need that much power anyway.

Or am I really missing your point here

?

fmak · 2004-02-09 7:30 pm

Devil_H@ck said:
Sorry, but I don't get what you mean. Do you mean that the 3488A works when it's powered down? Power consumption doesn't seem to be an isue and the MPC's don't need that much power anyway.

Or am I really missing your point here ?

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The VHF switch on the 3488A reamins latched to the active input even if the power is switched off. This seems to make a slight difference to the sound even though the ps of the unit is far away from the connectors. Semiconductor switches presumably are non latching. Not a power issue.

Digital Audio Input Selector ?????

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