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Old 10th April 2009, 06:40 PM   #1
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Default Phono input selector switch

I would like to hear thoughts about designing and building a phono input selector switch.

I have lots of turntables, and would like to be able to listen to them all without disconnection and reconnecting cables, or owning 10 different phono pre-amps.

I am using an Art Audio Vinyl Reference, and would like to build a switch with maybe 6-8 sets of inputs, and one output.

What would be a suitable switch/ selector, and where could this be sourced?

Am I incorrect in thinking that this could be constructed by using high quality RCAs, high quality wire, a switch (the mystery switch) and an enclosure.

The Vinyl Reference has a mute switch which does not seem like it would be a hassle to use when switching between inputs to avoid any switching noise.

Any links to similar projects, experiences, or thoughts on this
would be appreciated.
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Old 10th April 2009, 06:56 PM   #2
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Default Re: Phono input selector switch

Just don't do it. You have a pretty nice phono pre and it will be a pity to spoil its sound. All components at these low levels are painfully audible, especially switches.
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Old 10th April 2009, 07:11 PM   #3
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If you absolutely have to do it use a Shallco switch and make sure you switch both signal and ground. WBT sockets and some nice thin solid core silver wire. I like DH Labs but i am not such an expert on wire. Screen the casing rather than use screened wire.
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Old 10th April 2009, 07:57 PM   #4
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use a pre-preamp for each.
that way you can separate input capacitance for each
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Old 10th April 2009, 10:25 PM   #5
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Part of the intention is to be able to have a reference standard for comparisons between different turntable set-ups, and plinths.

I am hoping, that with the correct switch, the degradation of the signal can be kept in the neighborhood of say, the difference between a 1m phono cable, and a 2m cable.

I am guessing that you are suggesting to switch the ground as well to avoid any un-necessary ground connections to reduce possible problems?

Switching of impedence can still be done via the inputs on the back of the Vinyl Reference.
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Old 11th April 2009, 12:13 AM   #6
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errr.... uhhh... capacitance......
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Old 11th April 2009, 02:17 AM   #7
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Mercury whetted relays are the ne plus ultra if you have to switch -- but note that Texas Instruments has a lot of very low noise opamps with an "enable" feature. I am sure that the other guys have similar devices, but the TI units are the only ones I've actually employed.
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Old 11th April 2009, 08:51 AM   #8
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Quote:
Originally posted by Woodsong Audio
errr.... uhhh... capacitance......
You probably use MC carts so capacitance is of no importance. I would avoid any relays in the signal path as ime they are annoyingly audible. No experience with mercury wetted types but have read enough negative opinions not to be keen to try them. You should be able to make a reasonably good switcher for about $500 which certainly beats buying seven preamps. The most critical part will be the switch. Shallco are absolutely great for line level switching but i have no experience with those at uV levels. Probably still the best choice.
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Old 11th April 2009, 05:58 PM   #9
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My advice would be to do a few simple tests to see if you (or anybody) can actually hear the difference a switch (or several switches) will make. Then decide if expensive alternatives need to be followed.

Electrons (fortunately) don't read high-end audio magazines, and generally can't tell the difference between a good clean switch contact (relay or manual) and any other solid connection- especially at audio frequencies.

Just my opinion, of course.

Cheers
John
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Old 13th April 2009, 03:56 PM   #10
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They can be a bit fusty if you are using a phenolic switch wafer.

The only problems I have seen discussed wrt mercury wetted relays is that they are large and need to be mounted correctly. Contact resistance is very low, they don't chatter and are hermetically sealed. Otherwise the concern on Hg is well warranted -- that's why you should avoid the use of CFL's.
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