Phono input selector switch

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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.
 
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.
 
Woodsong Audio said:
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.
 
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
 
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.
 
Thank you for the thoughts..

I will test different switches, including some basic options, trying to find a switch that sounds bad for reference . I will be calling Shallco today, and have been able to narrow my search already. Also, picked up some old school NOS Russian Mil-spec rotary switches, 5 pole, 8 throw. These were very inexpensive, silver plated copper contacts.

In looking at RCA options... I see the top line WBT s are platinum plated. My uneducated gut response is a question about dis-similar metals if using with non-platinum plated connectors. Any thoughts on dis-similar metals in electrical connections?

This switch box will be built, I will report on it's functionality. Probably be a couple of months to finish, as I will be out for the month of May for some much needed vacation.

This morning I had thoughts of a crossfader input switch. When playing music during social gatherings (and the 1200s are not running ;) ) I love the rich texture of quality vinyl playback, and love immersing people with the sounds, I just do not like the silence between songs. A very simple crossfader switch would solve this, although that is a totally different can of worms, and will probably prove to be impractical at the moment.


Thank you
 
Woodsong Audio said:
Any thoughts on dis-similar metals in electrical connections?

I wouldn't worry about dissimilar metals in this case. Generally this causes problems when there is a conducting liquid (think salt water) around to get chemical reactions going between the metals via the electrolyte.
Switches like the rotary ones you mention are designed to 'scrape' clean the contacting surfaces as they are 'exercised'', so there is generally a good clean metal-to-metal contact. There is some argument made for softer (like silver) metals in switch contacts for similar reasons, as I recall.

I'm happy to hear about your planned tests- if you find a reasonably-priced solution to the switching, you will have more money to spend on other audio projects!

I've had good luck using inexpensive e-Switches with silver contacts for 2-way input switching (and other switch applications). Mouser p/n 612-100-F1111 E-switch p/n 100DP1T1B1M1QEH
e-Switch spec sheet
As I recall, similar switches were recommended by Eric Kingsbury (Poindexter) at audiotropic.net, though I may be 'mis-remembering' this.

Cheers
John
 
I don't have experience with this, but I'm sure that others do. Would a digital switch like this one be a good implementation?

http://twistedpearaudio.com/control/darwin.aspx

That way the switch wouldn't be in the signal path. Would a buffer help, something like a Pass B1? The B1 would give you two inputs and one output, and would buffer the signal without amplifying it, but would the output from the carts be too low for it to be effective?

Again, I don't have any answers or concrete suggestions, just ideas that might not be ideal. It would be interesting to hear responses about the digital switch, not that boards are in stock. I think there are other digital switch options out there though.

Do you DIY your cables? If so, perhaps hard wiring them on the switch input end might be the best way, and certainly much less expensive then using good RCAs. You could also try Lemo connectors, which are a better design. The Redel Lemo connectors are recommended by Allen Wright (they're plastic). They are available from Mouser and cost much less than high end RCA's ($13 or so each)

I look forward to hearing about your explorations.

Aaron.
 
orpheus said:
Would a digital switch like this one be a good implementation?

http://twistedpearaudio.com/control/darwin.aspx



I have no idea why you refer to this as a "digital switch" as these are merely relays. The audibity will depend greatly upon the relays used and i would not even consider using a non-latching relay in phono level switching.

The fact that the signal does not pass through the switch but instead passes through the relays is quite humorous.
 
With the very small signals you are looking at you want a switch that has very low initial contact resistnce. (The shallco switches are excellent in this respect).

Electrons need a low contact resistance to get across the switch. Cheaper switches will need a small current to flow to break down the oxide layer on the surface of the switch. So you may find that the sound will initially be a bit scratchy as the oxide layer is broken down then improves. I have seen this with relay contacts which often have a minimum current specified to break down the oxide layer. I would guess with switches actually wiping the surface of the contact, with a well designed switch this is less of a problem.

Dissimilar metals do create a voltage, this is how thermocouples work. However to create a voltage you need a temperature differential beween two dissimilar metal contacts. So long as all of the contacts are at broadly the same temperture and assuming you don't introduce strong thermocouple metals (such as constantine or Chromel) you are unlikely to see problems from this source. Platinum - Rodium is a thermocouple junction so if you are going to use platimum coated contacts ensure that rodium is not used in the wire you connect to it (very unlikely).

A more likely problem is noise pick up, I would use twisted pair conductors and possibly an overall screen, however this may introduce too much capacitance. A screening metal case for the switch would also be a good idea and keep the paths as short as possible.

Best of luck.
Andy.
 
analog_sa said:



I have no idea why you refer to this as a "digital switch" as these are merely relays. The audibity will depend greatly upon the relays used and i would not even consider using a non-latching relay in phono level switching.

The fact that the signal does not pass through the switch but instead passes through the relays is quite humorous.


Thank you for correcting me, I am certainly not an expert. I had thought that these switches were better implemented than pole switches, but I still have a lot to learn.

How does Manley make their switch? I have known people to use that for phono signals with good results. It isn't cheap though, but if it could be reverse engineered, I'm sure it would be much less expensive to build than to buy.


Thank you for taking the time to share your knowledge with me.

Aaron.
 
Project underway again....

Shallco 5-pole, 8 throw switch in hand. Some kind of cryoed thin solid silver wire with teflon tubing for sleeving.

Now for the final details.....

I think I will be using Cardas RCAs, because I can source them affordably.

What recommendations do you all have for an enclosure? I have been looking online, and am having little success, but can find something eventually.. Where to buy? material?

What about a wooden enclosure with aluminum plates for the face, and the I/O in back. Any thoughts about how size could effect quality?

What about shielding? Can this be the box? What about a wood box with the Stillpoints ERS fabric, Copper plate? Anything? what to do??

I have been making some phono cables lately with good success, and am thinking of wiring directly to the switch, a short lead that inputs the phono pre...


Thank you in advance for your thoughts and recommendations..


Cheers!
 
I would avoid silver plated contacts. Yes, they are supposed to be self cleaning with repeated use, but in the real world with contaminants in the air, silver contacts will oxidize with a very hard to clean "gunk" layer that may be resistant to low current signals. I have experienced this with rotary switches in HP instruments (distortion analyzers). Gold, rhodium, and platinum based contacts should be less prone to oxidation.
 
Switching Low Level Signals

Recently I completed a preamp design which supports two phono inputs. I used dry circuit reed relays for all signal switching, including the low level phono inputs. The relays are hermetically sealed, and the contacts operate in an inert gas environment. Both sides of the contacts are the same metal, so there should not be any problems with dissimilar metal potentials. So far I have been happy with the results.
 
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