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Old 20th September 2010, 06:17 PM   #1
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Default Multiple RCA Inputs - need switch help

I plan 4 input sources on my SSE. The RCA sockets I ordered are of the uninsulated type so the board to chassis ground should be taken care of (will ground the IEC to one of the neg. RCA tabs).

I need help ordering a proper rotary switch for selecting the input. Here is where my inexperience with electronics has me handicapped. I went so far as to look up switches on Wiki but I'm still stumped as to what I should be looking for.

Anyone have a mouser or digikey part # for a quality switch?
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Old 20th September 2010, 06:33 PM   #2
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It's pretty simple.
You need a double pole, 4 throw rotary switch. Something like this:
Digi-Key - 71BF36-02-2-04N-ND (Manufacturer - 71BF36-02-2-04N)
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Old 20th September 2010, 10:34 PM   #3
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Many thanks Frank. I soldered most of the resistors and caps onto the board today, still waiting for a couple things but at least they are not back ordered.
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Old 30th October 2010, 04:02 AM   #4
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Quote:
Originally Posted by Frank Berry View Post
It's pretty simple.
You need a double pole, 4 throw rotary switch. Something like this:
Digi-Key - 71BF36-02-2-04N-ND (Manufacturer - 71BF36-02-2-04N)
Hello,
I use the 6 position 2 pole version of this switch to switch among up to 3 inputs. I ground the even number positions 2, 4 and 6 to reduce cross talk. Yes it is 2 pole and I do switch the ground. Only one input is grounded at a time.
SR2511F-0304-19R0B-E9-N-W Alpha (Taiwan) Rotary Switches
Less than $3 a pop and a solid switch.
I would recommend the insulated RCA and not using the case for a grounding path. This and switching the ground makes for less problem with grounding loops.
IMHO
DT
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Old 30th October 2010, 02:40 PM   #5
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Originally Posted by DualTriode View Post
SR2511F-0304-19R0B-E9-N-W Alpha (Taiwan) Rotary Switches
Less than $3 a pop and a solid switch.
I use those as well and would recommend it. No need to spend more that a few dollars for a selector.
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Old 23rd November 2010, 11:23 AM   #6
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Thanks guys. Got busy with a full range build that side tracked my simple se project. My understanding of electronics is limited (but growing) so your input and advice is much appreciated.
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Old 2nd January 2011, 09:48 PM   #7
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This post confused me a bit. Wouldn't you need to pass the rca ground through the switch? So for a stereo select, you would need a 4 pole switch? This was my understanding at least.

Also, would any of you know if adding a third function to a stereo input select is feasable? The implementation I have in mind is to toggle an integrated phono preamp on when the phono input is selected. So, basically rig up the mains to a third (or sixth) pole? The mains are around 2a.

Any ideas? Has anyone done something like this?
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Old 3rd January 2011, 02:47 PM   #8
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I would get an appropriate rotary switch with an extra pole and use a relay to control power to the phono preamp. My preamp works similarly. Choose a relay coil voltage that will work with a low voltage pole that you have available, such as a 5V coil for use with a 6.3V heater winding (you'd add a small series resistor). Just be wary not to use a 6.3V winding that has been lifted to a high DC potential by the amp/preamp that you are going to put this switch into.

As to the RCA ground, no you don't need to switch that. They would all get tied together somewhere.
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Old 3rd January 2011, 04:03 PM   #9
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Originally Posted by tylervanbach View Post
This post confused me a bit. Wouldn't you need to pass the rca ground through the switch? So for a stereo select, you would need a 4 pole switch? This was my understanding at least.

Also, would any of you know if adding a third function to a stereo input select is feasable? The implementation I have in mind is to toggle an integrated phono preamp on when the phono input is selected. So, basically rig up the mains to a third (or sixth) pole? The mains are around 2a.

Any ideas? Has anyone done something like this?
Generally if you are switching ground as well as hot, most people would use a 3-pole since both L+R grounds could be switched with the single pole. You could use a 4-pole but generally it's not necessary, thus less expensive.

As for your second question, is this a passive preamp with an active phono stage? If it were me, I'd just have a regular power switch deal with either both the phono and active section at the same time (if it's an active preamp), or just the (active) phono section alone (if it's a passive preamp). That leaves the selector switch to just deal with line level signals, which the output of the phono preamp would be. I prefer non-shorting rotary switches for line level input selection.

So,:
phono jack -> phono preamp -> position X on input switch -> line level preamp, and:
other input jacks -> positions Y, Z, etc on input switch -> line level preamp.

Power switch controls either active preamp + phono preamp or just phono preamp alone.

This eliminates some issues that you probably would have crop up with your idea, in particular the number of poles you need for the rotary switch (= expensive) and the quality of the rotary switch where your power switching requirements are higher than your audio switching requirements, meaning your entire switch would have to be rated for the higher power current (also = expensive). You may also find your choice of switch becomes narrow to the point where you are buying a more expensive switch than you could otherwise find without the extra requirements. Finally there could be turn-on thumps that your idea would introduce as the phono section is powered up and phono audio is selected at the same moment in time.

Suitably rated power switches alone are not particularly expensive in comparison to rotary switches, so it would almost certainly be less expensive to separate the functions into two dedicated, properly rated switches.

There is also the issue of routing power + audio so close together which should be avoided where possible for sound quality or potential noise reasons.

There may also be safety issues that would be best addressed by separating the two functions.

There are other solutions, such as the use of relays, but broadly speaking simpler is better in my opinion.
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Last edited by Johnny2Bad; 3rd January 2011 at 04:31 PM.
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Old 3rd January 2011, 05:04 PM   #10
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Thanks for the replies, they have been very helpful! To clarify, this switch is for an integrated tube amp which has an active pre but I am also adding an active (tube) phono pre.

The phono pre uses a 9v dc 2a walwart for its power. So that is what I am referring to as the "mains". I was under the impression that high voltage AC was what you needed to worry about, rather than low voltage/low current DC? If this is the case, then I think I will just forge ahead with my original idea, taking into consideration rknize's comments about switching the RCA grounds. However, It will be easier and certainly much cheaper to seperate the mains from the line input switch. The switch I need (a 4p3t, preferably 4 deck) varies from $10 to $70 so we shall see.
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