[skyskraper]

Hi Guys,

I'm fairly new at this electronics stuff and I wanted to build a stereo input selector box controlled by a rotary switch. However I'm slightly confused when it comes to rotary switches though. Do I need a 2 Pole switch for stereo or a four pole?

thanks

SS

 

[skyskraper]

i forgot to clarify, the inputs would be from line level rca connections leading to a single stereo pair of line level rca outs.

 

[Megaptera]

It depends on if you want to keep the grounds apart or not. There are three channels you have coming in with a stereo connection, whatever the type of jack: left, right, and two grounds that you tie together into one. With a two-pole switch, what you would have to do is tie all the grounds together, which can sometimes have a noticeable effect on the sound -- noise from one source's ground channel will bleed into all the ground channels.

Using a four-pole switch is a little cleaner, because you can switch the ground as well. This is the method I would use. What I would do in this case is keep the grounds apart until they get to the switch, and then tie them together after the switch. The cheapest 4p6t rotary I've found is a Taiwan Alpha switch on Mouser -- it's only a couple dollars, so it's a pretty cheap way to figure out if that's a solution that will work for you.

 

[skyskraper]

thanks for that. id preffer to keep the sound quality up so i'll go try that avenue first

also, i need to lubricate a slide pot i have (controls the tempo on my technics turntables) would i be better off going for a lithium or a silicon based grease?

 

[tangent]

I agree with Megaptera, with the addition that you should be able to find a 3-pole version of the switch, which will give you one more throw than a 4-pole. (It's common for poles x throws to equal 12 in rotary switches.)

 

[Megaptera]

Quote:

Originally Posted by tangent you should be able to find a 3-pole version of the switch, which will give you one more throw than a 4-pole.

I had entirely forgotten about 3p4t rotaries somehow. The switch I mentioned has two decks, each with two pairs of six throws, so you can think of it as a 2x2p6t; now that 3p4ts have re-entered my personal universe, I'd recommend one of them unless you really need the extra two throws.

Quote:

Originally Posted by skyskraper would i be better off going for a lithium or a silicon based grease?

I must confess complete and utter ignorance in this topic. This will not stop me from giving you advice anyway.

I would guess that it's not too critical. The only factors I can think of are how well the grease handles heat and friction (both probably do more than a good enough job for the pot), and how electrically conductive they are. Pure silicon isn't very conductive, but it may be enough to cause a short if it gets in the wrong place (and the grease might be a silicon compound); some lithium grease is conductive too. Odds are you could apply either one carefully enough to avoid shorting the pot, so unless someone with more grease-perience has an opinion, I guess it's your call. Another option would be something like WD40, which isn't conductive.

 

[skyskraper]

cheers tangent and mega

i would preffer to have the extra throws, i guess i'll just have to get one of each and see which works best

with the 3 pole switch i would sum the grounds on the third pole right?

im hesitant to try wd40 out because ive always been under the impression it can destroy the carbon tracks of some slide pots? maybe ive just been preached the wrong information! anyway's id preffer something a bit thicker because ive already put tuner spray in and whilst it's improved the performance, it still hasnt gotten to the level i want (ie: oem performance).

ill just email one of the mg chemicals reps down under

 

[tangent]

Quote:

with the 3 pole switch i would sum the grounds on the third pole right?

I think you've got the right idea, but I wouldn't say it that way. You're not "summing" anything. Each source's input ground will go to the third leg in each set, and the output ground will be connected to the third common lug. So, each input ground will be connected to the output ground in turn as you turn the shaft.

Be sure to use isolated input jacks if you're using a metal case to hold this. Otherwise, you're tying all the grounds together anyway.

Quote:

im hesitant to try wd40 out

I class that as a solvent, not a lubricant, nevermind what it says on the can. A true lubricant doesn't evaporate.

I stayed silent on this question because I don't know what kind of grease is used. Perhaps you can call the applications engineering department of ALPS or Bourns. Alternately, some TV or audio repair shops may be able to advise, but they may be closedmouthed if they consider this a trade secret.

 

[Megaptera]

Quote:

Originally Posted by skyskraper with the 3 pole switch i would sum the grounds on the third pole right?

Yup. You should have two ground wires (per input) before the switch (either tied together at the solder tab or before it) and one ground wire leaving it. Some RCA jacks, like Cardas, will have a removeable ring with a solder tab for the ground connection -- they might be big enough to actually solder together with a single wire, which is a much cleaner way of doing things.

Quote:

Originally Posted by skyskraper im hesitant to try wd40 out because ive always been under the impression it can destroy the carbon tracks of some slide pots?

Oh, maybe. I haven't heard that, but probably better to play it safe.

You know, another possibility is just finding a new slide pot with the same value and size.

 

[skyskraper]

thanks again for the help

ive been talking to the aussie rep from mg chemicals and he's going to find out what they would reccomend for my application. i know a lot of people who service technics 1200 put cailube360 in to the faders but its just so damn pricey down under and im sure there are other similar products on the market that do the same job at a lower price.

 

[Megaptera]

Great -- be sure to post your results, since it seems like this is not an area where Head-Fiers are overstocked with experience

 

[Garbz]

just to be confusing does this really make that much of a difference? I mean some of the finest amplifiers tie the grounds together directly after input don't they?

Would the benefits really be worth the extra wiring? And the ability to use s 2p6t switch

 

[tangent]

I look at it the inverse way: because I have never needed more than 4 poles, I figure I might as well use a 4P3T and switch the grounds. It prevents any possibility of problems. That's engineering.

 

[Megaptera]

For what it's worth, I built an input/output selector using a Radio Shack RCA board and two DPDT switches, and the grounds were tied together. Overall it added a very slight fuzziness to the sound, though I don't know if I would explicitely put the blame on the ground or the RCA board. (I've used the switches plenty of times with no problems.) It might not be a bad idea to tie the grounds, but it's a good idea not to

 

[skyskraper]

well i got my response. carbon conductive grease is the one to be used if its ABSOLUTELY necessary to use grease. coz of the fact that if it crosses the track it will short the circuit and the fader response will be compromised.

the lubrication i require is for the mechanical aspect of the fader. it just moves too freely with aerosol based contact cleaners.

the mg tech reccomended using pure liquid contact cleaner in pen form or in liquid form applied with a swab for lubricating the tracks

so there you go.

with regards to the switch, im just gonna grab one of each 4p3t, 3p4t, and 2p6t. and see how we go. it seems on their top of the line mp2016a dj mixer, rane ties uses a 4p6t switch, im hoping to be able to track one of those down myself in oz. although it may be a bit of a challenge considering our much reduced market, there is an alpha distributor in my city, they dont list it in their catalog but it cant hurt to ask