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Old 13th February 2004, 06:28 PM   #1
wxn is offline wxn  Lithuania
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Default Audio input selector

Hello everyone!
I thought that a channel selector would be a great addition to my preamp. The first thing I considered was a mechanical rotary switch. But it would be kind of awkward to use and very unpleasant aesthetically.
Now I'm thinking of a solid state logic circuit along with some switch like TDA1029 or CD4066. Something like this:
http://www.javed007.co.uk/007/New%20...20Selector.htm
With the only exception that I'de like to have four buttons instead of one, one for each input. The problem is that I can't find such circuit and my personal skills at triggers and similar stuff are very modest.
If anyone of you has such a circuit or can help in any other way, I'd very appreciate that.
Thank you in advance.
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Old 18th February 2004, 09:28 AM   #2
wxn is offline wxn  Lithuania
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Well, don't you people have any suggestions about this? I really need some help here
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Old 18th February 2004, 10:15 AM   #3
dhaen is offline dhaen  Europe
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Hi,

For selectiion logic, the 74c922 keyboard encoder is simple and effective.
It's output is in BCD, so you'll need a binary to decimal (or octal) decoder chip.
This will give you a logic level for each button. You can use this to drive relays or analogue switches for the signal selection.

edit: Not BCD but 4 bit binary
You'll only need the lower 2 bits.
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Old 18th February 2004, 01:01 PM   #4
wxn is offline wxn  Lithuania
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Ok, this is all neat, but I only want to control 3-4 buttons, not 16. Also, more of a problem is to maintain the last pressed button signal, any ideas how to achieve this? I've seen such things implemented with triggers in commercial amps.
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Old 18th February 2004, 01:15 PM   #5
dhaen is offline dhaen  Europe
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Quote:
a problem is to maintain the last pressed button signal
Th '922 has a latch which stores this.
It also has a DAV (data available) signal which I've used before as a mute, for totally silent switching.

Yes it's a bit wasteful using only 3 or 4 out of 16, but it's such an easy chip to use.

There are lots of other solutions. If you wait a few days, others will post their ideas.
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Old 18th February 2004, 01:49 PM   #6
wxn is offline wxn  Lithuania
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Another problem with this approach is that this chip costs a little more than 10$, which is quite a lot for me, especially when I can achieve similar results with simple (and cheap) logic devices. And sure, I can wait a few days
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Old 18th February 2004, 02:08 PM   #7
moamps is offline moamps  Croatia
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Hi,

look here.
input switching

Regards
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Old 19th February 2004, 10:39 AM   #8
wxn is offline wxn  Lithuania
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Thanks a lot, moamps! I wonder how couldn't I find it earlier
Ok, now another question: what's better for commutation, relays or switches like cd4066 and tda1029?
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Old 19th February 2004, 11:14 AM   #9
dhaen is offline dhaen  Europe
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Moamps elegant solution again

For switching. relays provide lowest distortion.
For analogue switches, do not consider the 4066. It's decades old and a poor performer.
A cheap, good analogue switch is the DG211 or DG212. The final performance depends a lot on how you use it. I'll post a schematic tomorrow if you are interested.

Or maybe Moamps has a better idea
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Old 19th February 2004, 11:32 AM   #10
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I started building a channel selector for 2 to 8 inputs, switched by relays and controlled with rotary encoder. The number of channels to choose between is user programmable, last channel is remebered when shut down, and on power up there is a delay. Its based on my relay volume control. I need more relays to build one. The software should allready work.
http://home.tu-clausthal.de/~tpa/selector/index.html
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