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Old 15th October 2014, 01:10 AM   #1
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Default Need Help Finding Switches

Hey guys, sorry, it seems like whenever I post here I am asking for help.
Well, I have pretty much completed my Headphone Amp Design, and am putting together a BOM.

To switch between OTL and Transformer Coupled, I need to have a switch with 6 Poles, Double Throw. It works like this (one channel described)

One pole switches between connecting B+ to top of transformer or plate resistor
One pole switches between off of unconnected to B+ to Cathode Followers (for OTL)
One pole switches between off or unconnected and taking output from plate to the cathode followers.

So I need 3 poles with two "options" for each, for each channel. That's 6 Pole Double Throw if I'm correct.

I can't seem to locate one of these anywhere, so that's why I'm posting.


I also need a simple switch to toggle on/off my cathode bypass cap and another to toggle on/off my negative feedback. I think these can be SPST but I can't seem to find one of these I like either.

Obviously it's important that they are audio grade and not garbage.

Any help is appreciated, thanks guys!!!
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Old 15th October 2014, 01:33 AM   #2
rayma is offline rayma  United States
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Join Date: Apr 2011
Location: Upper midwest
Quote:
Originally Posted by dutchgfx View Post
To switch between OTL and Transformer Coupled, I need to have a switch with 6 Poles, Double Throw.
One pole switches between off of unconnected to B+ to Cathode Followers (for OTL)
One pole switches betwen off or unconnected and taking output from plate to the cathode followers.
So I need 3 poles with two "options" for each, for each channel. That's 6 Pole Double Throw if I'm correct.
I can't seem to locate one of these anywhere, so that's why I'm posting.
You cannot switch live high voltage DC with ordinary switches. Notice that most common AC switches are rated at 32 VDC.
Please don't try to do this, it would be very dangerous.

Last edited by rayma; 15th October 2014 at 01:49 AM.
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Old 15th October 2014, 02:17 AM   #3
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I am not switching live. It will be while the amp is off. I'm not that incompetent haha but thanks
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Old 15th October 2014, 02:26 AM   #4
Enzo is offline Enzo  United States
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Location: Lansing, Michigan
And instead of looking for some crazy switch, just use a couple relays controlled by a simple switch.
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Old 15th October 2014, 02:53 AM   #5
rayma is offline rayma  United States
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Quote:
Originally Posted by Enzo View Post
And instead of looking for some crazy switch, just use a couple relays controlled by a simple switch.
Same problem, and the relays can explode if operated with HVDC. Too risky.
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Old 15th October 2014, 02:56 AM   #6
rayma is offline rayma  United States
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Quote:
Originally Posted by dutchgfx View Post
I am not switching live. It will be while the amp is off. I'm not that incompetent haha but thanks
I still wouldn't do this, but the AC switch rating would have to be greater than 0.7 times the highest DC voltage connected to it.
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Old 15th October 2014, 04:31 AM   #7
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How would I activate a relay or a series of relays to function as I described? I have never used relays before
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Old 15th October 2014, 04:42 AM   #8
Vasquo is offline Vasquo  United States
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6PDT | Mouser Electronics, Inc.

6PDT
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Old 15th October 2014, 06:03 AM   #9
mirlo is offline mirlo  United States
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I'm not sure I'm interpreting your descriptions of the switch connections correctly. Are you trying to use the same tubes for the followers in OTL mode as the transformer coupled mode and trafo* coupled mode?

If not, then you might be able to switch the output jack between CF and transformer and rather than switching B+, use the switch to manipulate bias and filament to turn off one or the other set of tubes.

If so, then do you really need to switch B+ or can you connect the trafo primary between B+ and the plate and simply short out the primary in CF mode along with switching the output... this way there is never a high dc voltage to break or connect, but there is still the problem of isolation for the high side switch. In that case would you consider using a semiconductor switch, which can be controlled with a low voltage circuit controlled at groundish levels?
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Old 15th October 2014, 12:32 PM   #10
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I think if I use 2 3PDT Relays controlled by some DC Supply then I'll be golden. I might use a battery but I'm afraid it will die mid-listening and break something
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