Help needed finding a small DPST switch - confused! - diyAudio
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Old 28th March 2011, 02:22 PM   #1
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Default Help needed finding a small DPST switch - confused!

Hello,

Sorry, this is really basic. I'm looking for a small low-current ON-OFF switch for two channels of audio - I thought this was a DPST switch, but can't seem to find what I'm looking for at all, leading me to think I'm barking up the wrong tree.

Can anybody help me please?

Cheers!
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Old 28th March 2011, 04:17 PM   #2
rknize is offline rknize  United States
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So you want to switch two channels on and off, not switch between two channels? That sounds like a DPST to me. At DPDT switch, which is more common, will also work fine; just don't use the extra pole in the "off" position.
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Old 28th March 2011, 04:42 PM   #3
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Thanks Russ,

Correct, I was looking for switches for UL/triode mode and cathode feedback on/off for the Simple SE, and assumed it wouldn't be a problem to obtain DPST toggles switches to do this - but was drawing a blank (apart from some large, high-current ones). I guess I'll use DPDT switches with the centre position redundant then, if that is common practice...I appreciate the help.

Mark
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Old 28th March 2011, 05:20 PM   #4
DF96 is offline DF96  England
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Centre position? Most toggle switches only have two positions. Just a few have an additional centre position.

For UL/triode switching you need DPDT, and check that the switch will handle the voltage. Most mains switches will be OK, unless you have unusually high HT.
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Old 28th March 2011, 06:09 PM   #5
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Quote:
Originally Posted by DF96 View Post
Centre position? Most toggle switches only have two positions. Just a few have an additional centre position.
I assumed that by definition all DPDThrow switches would have three positions i.e. on-off-on. Is this wrong?

I have ordered a set of DPDT switches rated at 2A, 250VAC. I plan to use them for cathode resistor swap, cathode feedback on/off and triode/UL switching. Obviously there's no problem with current ratings here, but have I underspecified the voltage? B+ will be 450V max.

Help much appreciated before I give myself a shock!

Mark
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Old 28th March 2011, 06:21 PM   #6
DF96 is offline DF96  England
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No, most DPDT are on one side, or on the other side. If you want a centre-off position then you have to choose a switch which includes that - most don't. Some of these will switch the two poles separately, so the centre position will have one pole one way and the other pole the other way - you need to read the catalogue or datasheet carefully.

Strictly speaking, 250V AC is only good up to 350V DC but most switches will have a safety margin. Best to do the switching while the amp is switched off.
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Old 28th March 2011, 10:34 PM   #7
tomchr is offline tomchr  United States
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A DPDT switch is most commonly an ON-ON switch. I.e. you flip it one way and one pair of switches is on. You flip it the other way and the other pair of switches is on. If you leave the second pair of switch poles disconnected, you'll have a DPST switch.

There are some DPDT switches that have a center position. Those are commonly referred to as ON-OFF-ON switches. They work like any other DPDT switch except for the center position where both switch pairs are off.

~Tom
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Old 29th March 2011, 01:34 AM   #8
ArtG is offline ArtG  United States
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When you order switches, there is one other consideration to keep in mind. There is a DPDT switch with a temporary position that could be easily confused with a regular one. It is usually listed as ON-OFF-(ON).
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Old 29th March 2011, 03:27 AM   #9
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Another consideration when buying switches is the two different nomenclatures of the contact "logic". First one is "Break before make", Second is "Make before break". This refers to the 'logic' of the contacts..........If this is confusing, a contact cannot be instant....as NOTHING exists that is instant.There is a time factor as you flip the switch whereby the First version will break the first contact before engaging the second contact "Break before make". The second will bridge all three contacts before disengaging the first set of contacts "Make before break". Some circuits cannot stand to be open in the first case, nor can some circuits be bridged in the second instance.


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Old 29th March 2011, 10:59 AM   #10
DF96 is offline DF96  England
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I think it would be unusual for a toggle switch to be MBB. This issue normally only relates to rotary switches.
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