simple 2 input selector switch for audio amp - diyAudio
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Old 9th March 2008, 12:14 AM   #1
gychang is offline gychang  United States
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Default simple 2 input selector switch for audio amp

I am a newbie but can solder.

I want to add a toggle switch to my t-amp clone to be able to select 2 RCA input. (I need to play files from PC and use a CD player, getting tired of swapping RCA inputs).

Will this switch work?
http://www.partsexpress.com/pe/pshow...1&ctab=15#Tabs

thanks,

gychang
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Old 9th March 2008, 03:47 AM   #2
gootee is offline gootee  United States
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I didn't look at the link you posted. But in the photo you attached, the switch had only two pins. That would be a single-pole single-throw (SPST) switch.

Since you should switch both the signal and the ground conductor, for each input, you will want a switch with six terminals, so that one pair is connected to your system's input and the switch can select one of the other two pairs at a time. That would be a double-pole double-throw (DPDT) switch. You will probably want a two-position 'on-on' type.
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Old 9th March 2008, 03:54 AM   #3
gychang is offline gychang  United States
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Quote:
Originally posted by gootee

Since you should switch both the signal and the ground conductor, for each input, you will want a switch with six terminals, so that one pair is connected to your system's input and the switch can select one of the other two pairs at a time. That would be a double-pole double-throw (DPDT) switch. You will probably want a two-position 'on-on' type.

thanks.

will this work? looks to be DPDT.
http://www.partsexpress.com/pe/showd...number=060-338

gychang
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Old 9th March 2008, 05:32 AM   #4
gootee is offline gootee  United States
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That should work. The two center terminals will go to your system. The switch will connect either of the two outer pairs to the center pair. Note that when the switch's actuator is pushed to the left, as in the photo at the link, then the pair of terminals on the right is selected.

Of course, the 'purists' might suggest something similar but with gold or silver-rhodium plated contacts, etc etc.

You might want to consider whether or not you will ever want to switch between more than two inputs. If so, a two-pole rotary switch, with more than two positions, might make later expansion a little easier.
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Old 9th March 2008, 06:52 AM   #5
OzMikeH is offline OzMikeH  Australia
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Don't forget there are two channels Tom.

Greg, you can use the DPDT switch, but connect your grounds together and use the switch wired to the center conductors of your inputs.

so looking at the bottom of the switch, if we pretend the numbers are terminals:

1 2
3 4
5 6


1= input 1 Right channel center pin of RCA socket.
2= input 1 Left center pin
3= Amplifier Right input
4= amplifier Left input
5= input 2 right
6= input 2 left.

use shielded cable and insulated RCA sockets.
Connect the shields of cables 1 3 and 5 together near the switch, and solder the amplifier end of the cable 3 shield at the amplifier end. the socket ends of the shields of cables 1 and 5 are connected to the RCA socket shield. (outer)

do the same sort of thing for the left channel.
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Old 9th March 2008, 05:56 PM   #6
gootee is offline gootee  United States
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Quote:
Originally posted by OzMikeH
Don't forget there are two channels Tom.
DOH!!

Are there any potential ground-loop problems created, when connecting the grounds of the different sources together in order to switch only the signal leads?

I wonder if maybe a nice 4P3T rotary switch might be better (and I happen to have some spare new/unused ones).

Otherwise, would it be better for him to look for a 4-pole 2-throw toggle or slide switch, instead? Or, he could use a simpler switch and some small relays...

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Old 12th March 2008, 03:49 AM   #7
OzMikeH is offline OzMikeH  Australia
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usually not, most integrated amps have the grounds all bussed together. If it was a common problem then most amps would switch ground as well.

you have to be careful with relays, most are intended for switching power and can be terrible at extremely low current and a few millivolts. I suggest an array of reed relays if you do so, ot at lease something that is sold as a signal relay.
The same with switches, try to get one with high quality self wiping contacts. You might have trouble with a cheap DPDT from an auto parts store.
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