Impedance selector switch for headphone transformers

[rjuly]

I am looking for some advice on choosing a rotary selector switch to switch between the three output impedances options for a pair of Sowter 8665 headphone output transformers. The circuits for the three configurations of three secondaries for each channel look like this:


Does it matter if I go with 6 poles x 2 decks, or is 1 deck with 12 poles functionaly identical? I believe the switch should be 3 (or more) way. Any thoughts, or advice as to which switches would be ideal will be gratefully received.

- Richard

 

[abbey road d enfer]

Does it matter if I go with 6 poles x 2 decks, or is 1 deck with 12 poles functionaly identical? I believe the switch should be 3 (or more) way. Any thoughts, or advice as to which switches would be ideal will be gratefully received.

You need 3 positions, that's all, but you need 6 poles. I don't think it exists in single deck. That is gonna be quite expensive.
I would suggest you use relays and some simple diode logic, or tune down your expectations.

 

[rjuly]

You need 3 positions, that's all, but you need 6 poles. I don't think it exists in single deck. That is gonna be quite expensive.
I would suggest you use relays and some simple diode logic, or tune down your expectations.

Yes, 3 positions - thank you. 6 poles, that's per channel, right? I will look into diode logic - thanks for that.
- Richard

 

[moamps]

4 pole, 3 positions for a channel would be enough.

 

[abbey road d enfer]

4 pole, 3 positions for a channel would be enough.

It takes some cleverness I don't have.

 

[moamps]

It takes some cleverness I don't have.

One coil is always connected at one end to say + output, and the other is always connected at one end to say - output so two poles less are needed.

 

[Bo Deadly]

Another way to word it would be to say that if you have all secondaries in series, you need one set of poles to switch the 1st and 2nd windings from series to parallel and then another set of poles to switch the 1st||2nd and 3rd windings from series to parallel.

A fun exercise might be to see if it can be done with an ON-ON-ON toggle (and preferrably so that the impedances are in order).

 

[abbey road d enfer]

That is a lot of thinking...

 

[moamps]

It can be optimized a bit more.

 

[rjuly]

I was in the midst of groping my way towards something like this - very nice! When you say it can be optimized, I take it that would be a version that uses relays perhaps? This looks like what you mentioned - a four pole, three way switch. This is a great help. Thanks to everyone who has commented - my projects would not be possible without this community!

- Richard

 

[john12ax7]

For the actual switch Grayhill is one option that comes to mind. You should be able to find 3 pos 4 pole and 2 deck (for stereo).

 

[rjuly]

For the actual switch Grayhill is one option that comes to mind. You should be able to find 3 pos 4 pole and 2 deck (for stereo).

Yes indeed, something like this looks good:
https://www.mouser.co.uk/ProductDetail/706-44A30-02-4-03S- quite pricey though, at around £70 VAT incl.
I thought perhaps to see what could be done with a network of relays to achieve the same result at a lower cost.
- Richard

 

[Tubetec]

Could you use jumper plugs and a small patch matrix in such a way that the three impedences are possible ?

How about bringing each secondary winding out to 4mm binding posts or sockets , so 6 per channel , now you can add wire links to configure the secondary load .

Would three stereo jacks with switched normalised contacts be able to select the secondary arrangement depending on which jack is used ?

A switch is convenient and idiot proof ,but the cost is high, configuring the secondaries manually with a few jumpers only takes a few moments more than flicking a switch , its set and forget and not something that needs to be adjusted on the fly .

Adding the complexity and cost of a switch or relays is a pain , I'd go the old fashioned way , you could use the bannana plugs below to make links bewteen chassis mounting 4mm sockets .

 

[Tubetec]

These guys do better quality than average the Ebay Chinese stuff at a very good price including reputable brands like Hirshmann and Staubli , 10 euro delivery charge in Europe

https://www.buerklin.com/en/Connect...elevance&GRID_OR_LIST=list&pageSize=20&page=1

 

[moamps]

It seems to me that the cheapest would be to use relays. 8 dpdt relays needed for stereo version, one BBM "1 of 3" switch and two 1N4001 diodes.

 

[rjuly]

A switch is convenient and idiot proof ,but the cost is high..

Yep! idiot proof - that’s the one for me. Although expensive, it should also be more durable and fail-safe.

Many thanks to everyone who contributed, and particularly to @moamps for the switch schematic.

I think I will be incorporating a relay network into the solo bus circuitry of my project, and this discussion has got me thinking about that now…

- Richard