Selector Switch

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#5
Tromperie said:
There are a few threads about selection switches. Did you do a search before asking?

As I've said before, you could use a cheap single pole, four position switch and use relays, normal or miniature, close to the inputs panel.
Click to expand...

I actually did research a bit on switching on here and happen to read the thread where you discuss relays, which I did not fully understand. I am a beginner and have started to research on how relays work, which is interesting.

For this project, I was looking for advice on what brands make quality rotary switches. I ordered the Grayhill 71B30-01-4-03N. I hope it's the right switch I need and is good quality.

I will investigate further into relays and start to learn the basic building blocks of electronics.

Thanks to both of you for the information.
 
#6
You didn't say what it is you are switching... that is a rather important detail, no?

Assuming you want to switch line level analog signals, than you need to think about contact contamination over time and other issues with low current low voltage signals (e.g. audio). One solution you might consider that is actually THE perfect application of the technology is to use LED-LDR devices (e.g. a "Vactrol") in combination with an inverting amplifier, with the Vactrols in series with each line that needs to be switched. You can have a 1k feedback resistor if you select your op-amp carefully. The Vactrol will have 1-10M Ohm "off" resistance, which gives you a factor of 1000-10000 attenuation of signals that are "off". The same Vactrol can have an "on" resistance of a few hundred Ohms (this needs to be trimmed up to 1k with an additional series resistor) giving you a gain of 1 in the on position. The advantages of using this approach include:
* noiseless switching
* the ability to fade in or out
* immune to the "contact contamination" mechanical contact switches can develop
* easy to integrate into LED signaling (e.g. "what input am I using???)
Once you use a switching system that actually fades the signal in or out instead of an instantaneous switchover you won't want to go back.

I attached a figure taken from a PE Vactrol app note. This circuit is actually for a maxtrix switcher, that is multiple inputs can be switched onto multiple outputs. Your circuit would be simpler, with only one amplifier section and one output.
 

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#7
If you use series and shunt Vactrols, you can get the off attenuation to be much higher. You'd basically add a Vactrol to ground at the node between the series Vactrol and the summing resistor. You'll have to do some rigging to generate the complementary LED drive, but that's not so bad. And, you do need to use 2x the number of Vactrols, but you can get very high off isolation that way.
 
#8
CharlieLaub said:
You didn't say what it is you are switching... that is a rather important detail, no?

Assuming you want to switch line level analog signals, than you need to think about contact contamination over time and other issues with low current low voltage signals (e.g. audio). One solution you might consider that is actually THE perfect application of the technology is to use LED-LDR devices (e.g. a "Vactrol") in combination with an inverting amplifier, with the Vactrols in series with each line that needs to be switched. You can have a 1k feedback resistor if you select your op-amp carefully. The Vactrol will have 1-10M Ohm "off" resistance, which gives you a factor of 1000-10000 attenuation of signals that are "off". The same Vactrol can have an "on" resistance of a few hundred Ohms (this needs to be trimmed up to 1k with an additional series resistor) giving you a gain of 1 in the on position. The advantages of using this approach include:
* noiseless switching
* the ability to fade in or out
* immune to the "contact contamination" mechanical contact switches can develop
* easy to integrate into LED signaling (e.g. "what input am I using???)
Once you use a switching system that actually fades the signal in or out instead of an instantaneous switchover you won't want to go back.

I attached a figure taken from a PE Vactrol app note. This circuit is actually for a maxtrix switcher, that is multiple inputs can be switched onto multiple outputs. Your circuit would be simpler, with only one amplifier section and one output.
Click to expand...

I am using it in a AVC line stage. I will see how the Grayhill switch turns out. Hopefully, in the future I will play with relays and see how those work.

Thanks for the info.
 
#13
#14
Charlie & Co.:

CharlieLaub said:
You didn't say what it is you are switching... that is a rather important detail, no?

Assuming you want to switch line level analog signals, than you need to think about contact contamination over time and other issues with low current low voltage signals (e.g. audio). One solution you might consider that is actually THE perfect application of the technology is to use LED-LDR devices (e.g. a "Vactrol") in combination with an inverting amplifier, with the Vactrols in series with each line that needs to be switched. You can have a 1k feedback resistor if you select your op-amp carefully. The Vactrol will have 1-10M Ohm "off" resistance, which gives you a factor of 1000-10000 attenuation of signals that are "off". The same Vactrol can have an "on" resistance of a few hundred Ohms (this needs to be trimmed up to 1k with an additional series resistor) giving you a gain of 1 in the on position. The advantages of using this approach include:
* noiseless switching
* the ability to fade in or out
* immune to the "contact contamination" mechanical contact switches can develop
* easy to integrate into LED signaling (e.g. "what input am I using???)
Once you use a switching system that actually fades the signal in or out instead of an instantaneous switchover you won't want to go back.

I attached a figure taken from a PE Vactrol app note. This circuit is actually for a maxtrix switcher, that is multiple inputs can be switched onto multiple outputs. Your circuit would be simpler, with only one amplifier section and one output.
Click to expand...

I confess this is way over my head (yes, my head is fairly low to the ground) but it does seem that a source selection pcb/kit might make a great group buy project or, perhaps even better, a nice addition to the store.

Just sayin'...

Regards,
Scott
 
#16
Hi,

Lorlin make pretty good selector switches, especially for the price. They are make in the UK and can have gold plated contacts.

Lorlin CK series Datasheet
http://www.lorlin.co.uk/PDF/CK.pdf

A quick look at the datasheet, you should check this yourself, shows 3 pole 4 position with gold plated contacts:

Model CK1952 - for PCBs
Model CK1577 - with solder tag

I'm not sure how you will go getting the gold plated ones in the US. Newark sell the silver plated versions but a quick search failed to find the gold plated versions.

Regards,
Rob
 
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