S&B TX-103 wiring 3-position ratio switch advice needed

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marknoir

Hello John

May be you remember, we were talking about my humming transformers :-) I couldn't get rid of the hum completely in my set-up, and I also use cartridges requiring different gain. So I decided to move the trannies from your pretty cans into a simple steel case. I want to add a rotary (a-la Music First) switch, 3-position for gain selection. I saw that some of your MU transformers had a two-position switch incorporated in them. I wonder how difficult of a task this would be? Perhaps two positions would be sufficient? I don't know much about poles, sets etc in rotary switches, so your help would be greatly appreciated...

John Chapman

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Re: S&B TX-103 wiring 3-position ratio switch advice needed
« Reply #1 on: 5 Nov 2014, 05:00 pm »
Hello!

3 position rotary is possible - but adds a bit more switching in the signal path so unless you really need all 3 ratios then toggles are cleaner.  By far the most common ratios are 1:10 and 1:20. 1:5 was seldom used - only with those phono stages that were kinda in between MM gain (usually 40 to 45db or so) and mc gain (usually 60 to 70db or so). Some ARC stages had around 55db or so of gain and so I recall doing a couple 1:5's for them specifically.

From the cartridges point of view (loading) 1:10 gives about 470 ohms load and 1:20 about 120 ohms load. Since most MC carts want to see a load lower than 470 ohms using those 2 ratios should cover off most carts you'd play with.

For wiring this page by S&B has the info for each ratio:


http://www.stevens-billington.co.uk/page103.htm


Thanks!

John

marknoir

Re: S&B TX-103 wiring 3-position ratio switch advice needed
« Reply #2 on: 5 Nov 2014, 05:33 pm »
Thank you for reply John

I figured you mean ratios of 1:10 and 1:20? :-)

I agree. I use AT OC-9ML Mk II and Carnegie I, both around .25mV, and Denon DL-S1 and DL304, around .17mV. I'm just confused as to how exactly to wire the switches, be it a toggle or a rotary. For example, rotaries come with two, or four or more poles, they have two or up to ten decks... And if a toggle, how many layers do I need? Confusing :-) I guess I'm a bit thick.

Rgds

Mark

John Chapman

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Re: S&B TX-103 wiring 3-position ratio switch advice needed
« Reply #3 on: 6 Nov 2014, 11:27 pm »
Hello!

Not thick - it is a bit of a mind bender..... Basically you must connect the primaries all in parallel for 1:20 and in series parallel for the 1:10 ratio.  For a toggle I used to use a 4 pole double throw toggle - one for each step-up transformer giving 4 poles of switching per step-up. May still have some hiding here so e-mail me directly and I can get you the info needed of what to buy and where, etc....

Thansk!

John