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Old 24th July 2007, 01:42 AM   #1
takeda is offline takeda  Greece
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Default Input Analog Multiplexer [Please Help]

Hello everybody,

First of all i have search the forum and didn't find a solution.

What i want is an input multiplexer for my diy amp.
The input stage before the power amp is

Click the image to open in full size.

where the buffer is used to match impedance for pga2310.

I have tried ADG409 (http://www.analog.com/UploadedFiles/...ADG408_409.pdf) without success. (Just hooked it up no extra parts, resistors filters or anything except the decoupling capacitors)

The problem was HUGE crosstalk plus noise when changing channels. Also some spikes could be heard from the speakers from time to time.

I also have MPC507 (diffential analog multiplexer) but I haven't tried out that yet.

Please give me any recommendations, circuitry corrections, how to hook the multiplexer or anything to help me out.

In case needed, my amp lookes very well grounded, analog star for analog grounds and bus connection to digital ground (with a low pass filter).

PS. One of the multiplexer inputs will be a DIY dac , another one a digital radio module and the others, typical unbalanced analog RCA source like in consumer dvd players.

Available analog bipolar power supply voltage is +15,-15
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Old 25th July 2007, 01:34 AM   #2
takeda is offline takeda  Greece
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What should I write a title to get some views and some help?

hot chicks + free pizza and beer?
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Old 25th July 2007, 02:16 AM   #3
Leolabs is offline Leolabs  Malaysia
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Dont have to.

Have u try the Dallas/Maxim website???They do produce some good multiplexers.
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Old 25th July 2007, 11:26 AM   #4
takeda is offline takeda  Greece
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i'check it out, thank you!
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Old 25th July 2007, 11:41 AM   #5
AndrewT is offline AndrewT  Scotland
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multiplexer and complaining about crosstalk.

What are you expecting the first section to do? Give us a brief.

A multiplexer usually on digital signals (but also on analogue) can mix together differing inputs such that a de-multiplxer can separate out the original signals without any loss.
Is this what you really require?
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Old 25th July 2007, 11:59 AM   #6
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Quote:
Originally posted by AndrewT
mutliplexer and complaining about crosstalk.

What are you expecting the first section to do? Give us a brief.

A multiplexer usually on digital signals (but also on analogue) can mix together differing inputs such that a de-multiplxer can separate out the original signals without any loss.
Is this what you really require?
Andrew,

I think he wants source selection.

Jan Didden
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Old 26th July 2007, 02:10 AM   #7
takeda is offline takeda  Greece
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Yes, source selection.

Sorry for the missunderstanding..
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Old 26th July 2007, 03:28 AM   #8
anatech is offline anatech  Canada
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Hi takeda,
Would you consider using signal relays to do your switching? They will sound much better with lower crosstalk. Terminate each source with a 100K resistor and also the "out" side with another 100K resistor. This will help the crosstalk some.

Then you only need to switch the coils using 12 V relays and a resistor. I would suggest a separate rectifier and supply for this. Also a separate ground return path. Let the entire thing float if you can. Optocouplers would work here.

Normally an IC input selector gives the sound a bit of a "grainy" character in my experience.

-Chris
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Old 26th July 2007, 08:40 AM   #9
AndrewT is offline AndrewT  Scotland
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or just a 4pole 3way rotary switch.
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Old 26th July 2007, 08:18 PM   #10
anatech is offline anatech  Canada
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Hi Andrew,
Quote:
or just a 4pole 3way rotary switch.
LOL!
I almost posted that, but after looking at his circuit I though he may have wanted remote control.

-Chris
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