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!
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!
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.
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
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
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.
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.
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
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.
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.
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
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
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).
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.
________________________________________________________Rick..........
________________________________________________________Rick..........
I think it would be unusual for a toggle switch to be MBB. This issue normally only relates to rotary switches.
Hey, Mark, check out Maplin. I bought some little toggle switches from them for this very task. 
http://www.maplin.co.uk/sub-miniature-toggle-switches-2341
http://www.maplin.co.uk/sub-miniature-toggle-switches-2341
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Thanks for the guidance everyone - I hadn't appreciated many of the subtleties but know what I need now.
My only remaining concern is the voltage. The switches will be:
1) Bias change, 60V or so
2) UL/triode, unknown voltage
3) Cathode feedback, unknown voltage.
For the unknown voltages I'm taking the worst case that it has the whole B+ to cope with, which at 450V is beyond the capabilities of the switch (250V * 1.4 = 350V). So I'm hoping that the voltages in 2) and 3) above are nowhere near the 450V B+, but hoping isn't really good enough is it.
payitforwardeddie - I have ordered identical spec ones off eBay and found you could buy packs of five significantly cheaper than Maplin. Glad to hear you've been using them successfully for the same purpose. What is your B+?
My only remaining concern is the voltage. The switches will be:
1) Bias change, 60V or so
2) UL/triode, unknown voltage
3) Cathode feedback, unknown voltage.
For the unknown voltages I'm taking the worst case that it has the whole B+ to cope with, which at 450V is beyond the capabilities of the switch (250V * 1.4 = 350V). So I'm hoping that the voltages in 2) and 3) above are nowhere near the 450V B+, but hoping isn't really good enough is it.
payitforwardeddie - I have ordered identical spec ones off eBay and found you could buy packs of five significantly cheaper than Maplin. Glad to hear you've been using them successfully for the same purpose. What is your B+?
Voltage will only be an issue for the triode/UL switch, which will carry full HT. You should be OK as long as you don't switch with the power on - which you should not do for another reason anyway, as g2 will be left unconnected momentarily as you switch.
Why are you doing this? Most amps need variable bias supply, not a switched one. Feedback should be none or enough (with a huge change in gain), not none or insufficient (with a small change in gain). We would not want you to harm yourself or a perfectly good amp!
Why are you doing this? Most amps need variable bias supply, not a switched one. Feedback should be none or enough (with a huge change in gain), not none or insufficient (with a small change in gain). We would not want you to harm yourself or a perfectly good amp!
Thank you, I hadn't considered this and would have happily switched while the amp was on to make an easier comparison on the affect on sound. Will power down now!
The amp has a variable bias, via a cathode resistor. The value of the cathode resistor in this design needs to be changed in order to optimise the idle current for different valves. For example, I will use 810R for the EL34 and 560R for the KT88 and don't want to resolder everytime I swap valves, so will wire another resistor in parallel with the primary one in order to achieve two different total resistances depending on whether this second resistor is switched into the circuit or not. Hope that makes sense!
As for the feedback, 'I don't know' is the answer; I'm merely following the (very detailed) instructions for this particular amp (Simple SE). It seems to work well for a couple of hundred others who've built it so that's good enough for me until I learn more.
As you can no doubt tell, I'm new to this, hence the silly questions such as 'wot is a switch'. Thank you for your help and patience - it's great fun!
440 volts. Mount the switch on insulating material in case it fails short circuit to its body. And see comment below.
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