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Old 27th November 2012, 08:48 AM   #1
diarav is offline diarav  India
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Default Need help: Input selector control for 6 channels

Hi All,

I am building a 6 channel amp for home theatre. This will also be capable of playing music from 2 channel sources like iPod, other external sources.

I am planning to implement a simple source selectr using a 2 pole rotary switch. The L/R channels will be selected from the rotary switch.

My concern is the remaining 4 channels from the DVD which must be activated and sent through only when the source selected is DVD. I am looking for ideas where I can perhaps compare the input and output signals and if they are identical/similar, then get the four channels active else they are disconnected from the amp. But I am not an expert in electronics and only a part time hobbyist, I would appreciate pointers to any circuits that might help me here.

I do understand that the best way is to switch off the DVD when not in use, but atleast as a user it would good to have it implemented clean.
Thanks in advance.
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Old 27th November 2012, 09:32 AM   #2
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When you say "planning to implement" does that mean you haven't obtained parts yet?
(Just the pic with no description shouts, "Houston, we have a problem.")
You could use the rotary positions to switch relays.
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Old 27th November 2012, 11:08 AM   #3
diarav is offline diarav  India
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Quote:
Originally Posted by sofaspud View Post
When you say "planning to implement" does that mean you haven't obtained parts yet?
(Just the pic with no description shouts, "Houston, we have a problem.")
You could use the rotary positions to switch relays.
First of all thanks for your response.

I have already built the 6 power amps using LM3886, power supply and they are working fine. In the pic below I have only tried to isolate the issue I am trying to address. All other parts of my amp are nearly ready. I tried building an input selector using CD4066 and found issues (mostly cross talk) - not sure if the chips were bad. I decided to go with a mechanical selector option. I am keeping the relay as a last option, and I intend using the 2 pole rotary since it is simple.
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Old 27th November 2012, 11:31 AM   #4
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And finding that it isn't quite so simple after all? Aside from relays or a 6-pole switch, the only other thing I can think of is adapting an Auto-On circuit (the kind often found in active subwoofers) for the extra channels. I'm not even sure that would work, and it's really just solid-state switching. From what I recall of CD4066 performance, it isn't that great for this application. There may be more modern alternatives with improved specs.
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Old 27th November 2012, 07:54 PM   #5
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Check out BuildAnAmp.com. They have a remote control kit that will provide switching for six channels, as well as passive line level attenuation using an Analog Devices AD5206 attenuator. It will give you manual or remote control switching and/or attenuation.
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Old 27th November 2012, 11:33 PM   #6
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I could suggest the lcduino from amb.org (ob disc: I worked on the design). it can do up to 8 relay selected inputs and its controller code is open so you could create special mappings that 'know' about 5.1 audio vs 2.0 audio. it could then do various special things with extra relays. the inputs are name-able on the lcd display and the code is arduino-based so its not hard or expensive to change things if you want.
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Old 28th November 2012, 12:40 AM   #7
diarav is offline diarav  India
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sofaspud, Wayne, linuxworks,

Thanks for your inputs. I will look into it.
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Old 29th November 2012, 07:23 AM   #8
diarav is offline diarav  India
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Hi All,

I had a look at the suggestion and they seem to be pointing to readily available solutions. I was more keen on looking a something more simpler.

With some bit of thinking, I added a few more elements to my block diagram. If someone can let me know if this approach can work.

What I am trying is to connect the output of say the left channel to the +ve of the OpAmp and the left channel of the DVD input to the -ve. If both signals dont match, that is if the output from the rotary switch is from a different source other than DVD, we should have some signal at OpAmp output which is further rectified. If both signals match we should have zero output at OpAmp output. With this logic I am hoping to control the analogue switch for the four channels.

While I am still experimenting, I would appreciate any inputs to suggest if I am in the right direction and any ideas to supplement the same.

Thanks in advance.
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