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Old 2nd December 2013, 10:20 PM   #1
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Default The best way to build input channel switcher?

Hi! I'm finishing up my amplifier project, and I'm going to add four AUX inputs at the back.

I know that you will get some noise if you just have a switch, and don't turn down the volume, so I'm going to add a digital potentiometer that's controlled by an Arduino MCU. When I'm changing the channel (by using a remote control or pressing a soft switch) the volume is turned down to 0, the input source is changed, and then restored to the main volume.

The question is what is the most efficient way to do this? of course you can use eight relays, but I've heard something about MUX and deMUX. I'm not familiar with these, and I don't know if these will affect the sound in any way.

I want something that is (cheap), reliable, and high quality that doesn't destroy the pure gainclone sound.

What you you guys use to change the input channel?

Last edited by hansibull; 3rd December 2013 at 10:05 PM.
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Old 3rd December 2013, 02:10 PM   #2
DF96 is offline DF96  England
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A switch.

Switching noise comes if the switch sees some DC. Coupling caps and ground leak resistors prevent that.
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Old 3rd December 2013, 04:17 PM   #3
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Quote:
Originally Posted by DF96 View Post
A switch.

Switching noise comes if the switch sees some DC. Coupling caps and ground leak resistors prevent that.
Hi,

Do you mean to use caps and leak resistors specifically for switch? I'm also looking for a switch solution for two MM level inputs.

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Old 3rd December 2013, 04:20 PM   #4
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for an example (schematic and arduino code) search for lcduino or amb delta-2.

yes, you have to cap-block relays as you switch or any dc present will be a click.
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Old 3rd December 2013, 04:55 PM   #5
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The best and only way to have clean inputs and noise free is to use relays and farther more shunt to ground the source that is not selected . Via resistor of 600R if you like ( done mine directly shorting the sources with no probs so far ( 5 years running 24/7 )

Now days i designed a toggle switch or a push button to control a 4017 and every time you push 4017 jumps to the next source .

I am planing an integrated amplifier that only features one knob in the front :

Click CW to power on , increase volume CW ,and push the same button to cyclic select a source .

Neat ha ?
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Old 3rd December 2013, 05:37 PM   #6
DF96 is offline DF96  England
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Quote:
Do you mean to use caps and leak resistors specifically for switch?
If they are not already present then yes. Note that relays don't actually change anything - you still have contacts to make and break. Making a contact between two things at different potentials will cause a click.

Unselected sources can be shunted to ground via resistors - just like the selected source! 1M may do the trick, but a smaller value may be needed if electrolytic caps are used.
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Old 3rd December 2013, 09:52 PM   #7
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Quote:
Originally Posted by east electronics View Post
The best and only way to have clean inputs and noise free is to use relays and farther more shunt to ground the source that is not selected . Via resistor of 600R if you like ( done mine directly shorting the sources with no probs so far ( 5 years running 24/7 )
I actually have a relay module with eight separate relays that will give me 4 input sources. Do you mean that the resistor should be connected to the other terminal on the relay, like this fancy illustration?

Click the image to open in full size.
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Old 3rd December 2013, 10:21 PM   #8
ahaja is offline ahaja  Poland
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If you want to switch grounds also then you'll hear noise.
I use in my amp AZ850 - one for one source, switching only signals.
There is no any noise even when I turn phono pre with 30mV DC on the output.
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Old 3rd December 2013, 10:22 PM   #9
ahaja is offline ahaja  Poland
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Here is correct link: https://picasaweb.google.com/1154538...07913638363714
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Old 3rd December 2013, 10:25 PM   #10
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Switches or simple electronics (i.e. without a clock signal) driving quality relays with correct termination is the way to go. If you like noise from switched PSUs and clock signals from an MCU you could use an Arduino. Features, features and more features but less sound quality. Even the best digital potentiometer can not compete with LDR based volume control or stepped attenuators of known quality. You know the cheap Ebay stepped attenuators ? Really very good for a low price.

Keep it analog if it needs to be good or excellent. Make it digital if you want a pc or Ipad to control the amp and sound quality is not important. Don't forget to implement a very bright shining blue LED to light the room in that case

Check the Rudi Ratlos VCPre design here ! Best of both worlds...
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Last edited by jean-paul; 3rd December 2013 at 10:32 PM.
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