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Phono switching with relays.
Phono switching with relays.
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Old 12th February 2018, 08:55 AM   #51
cliffforrest is offline cliffforrest  United Kingdom
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Phono switching with relays.
+1 to Kevin in #46

Were you with the big “T” in Boston?
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Old 12th February 2018, 02:48 PM   #52
Hans Polak is offline Hans Polak  Netherlands
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What I found is that reed relays are more than 10 times as expensive as for instance the miniature dpdt IM relays from TE connectivity costing less than 2,- from Farnell.
Both can be operated over more than 1Mio times, some reed relays even over 100 Mio times, but I dont expect Bill going to switch that often.

Hans
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Old 12th February 2018, 02:59 PM   #53
billshurv is offline billshurv  United Kingdom
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Phono switching with relays.
Even if I played 100 records a day and switched inputs for each record I wouldn't hit 1million cycles before I died. I think that has some safe margin in it
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Old 12th February 2018, 03:31 PM   #54
Koifarm is offline Koifarm  Netherlands
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On the picture switch PCB i use for gain set(MC/MM), Cload,Rload and input select(3 input). Still using rotary switches to control relais. Goal is to control the pcb with arduino.
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Old 13th February 2018, 03:32 AM   #55
Hiten is offline Hiten  India
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Quote:
Originally Posted by billshurv View Post
Generally not good practice to have unpowered circuits hanging in parallel with powered ones. I would not consider that as an option. Once you have gone through the phono pre you will be in the 0.5v range so any relay will do the job fine. Before as several people have mentioned, it's a case of picking the right relay.
OK. Got that.
Regards.
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Old 13th February 2018, 09:40 AM   #56
Monte McGuire is offline Monte McGuire
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Phono switching with relays.
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Originally Posted by Hans Polak View Post
Magnetic contacts, lots of distortion, what else have we missed.
I wonder that a small Relay can be criticized to such a degree.

What about the contacts on the Cart itself, neighbouring to very strong magnets.
And what about all the Cinch or Din connectors in the line.

The whole matter is grossly overestimated, and every gold-plated miniature relay or the somewhat larger reed relay can do a perfect job.
There are two types of relays: reed relays, in which the signal passes through a magnetically permeable reed, and 'armature' relays, in which a magnetic motor moves an armature and contacts, which carries the signal but is not ferromagnetic. It is not logically sound to confuse the two with each other.

Gold is never used on reed relays, since it is too soft, and reed relays can be made hermetic, with only the contacts inside of the glass envelope, This allows the use of platinum type contacts such as palladium or ruthenium, metals which are electrically and mechanically preferable to gold, but behave very poorly when exposed to organic substances from the air, or polymer vapors from its own coil varnish or plastic housing, as in a non-hermetic armature relay.

So, if you find that gold contact relays do not have this problem, then you're right - they're armature relays, not reed relays, so they do not pass the signal through magnetically soft materials. Two completely different technologies. Passing an AC current through a magnetically soft conductor can distort the AC signal from the field created by the signal current acting upon the magnetically permeable conductor itself. It's not a static field that causes problems, like that from magnets inside of a phono cartridge, but the signal induced magnetic field acting on the magnetically soft conductor that causes problems. Passing the signal through a non-magnetic armature of beryllium copper for example will not have these problems at all.

This effect depends on the magnitude of the current as well. With low phono cartridge currents, this effect will probably not be a problem. However, not all switching tasks are extremely low current. So, that too needs to be taken into account.

If you want a good armature relay, the Teledyne 712 is a fine hermetic, gold over silver contact DPDT relay. They're pricey, but small, and perform well. Why gold in a hermetic relay? The actuating coil, insulated with polymers, is inside of the hermetic case, so any polymer vapors emitted from the heated coil cannot be exposed to a platinum type contact like Pd or Ru, or they turn into a carbon gunk that destroys the contacts. They draw about 3/8W per coil, and switch rapidly and reliably. It's a DPDT switch too, so only one coil does the equivalent of four reed relays, simplifying logic and making them more cost competitive (or maybe 'not quite as outrageously priced'). A fine choice for any line level switching need.
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Old 13th February 2018, 10:07 AM   #57
billshurv is offline billshurv  United Kingdom
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Phono switching with relays.
Just to horrify the relay worriers I worked out how many contacts the signal has to go through in my preferred set up. It's 4, but as the phono stages are balanced, actually 8 (4 in each leg). Let the wails and gnashing of teeth commence
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Old 13th February 2018, 11:09 AM   #58
Hans Polak is offline Hans Polak  Netherlands
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Thanks Monte for your contribution.
However the Teledyne 712 being a very nice sealed relay, is no longer in production.
For a new design not a good starting point.


Hans
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Old 13th February 2018, 12:45 PM   #59
kevinkr is offline kevinkr  United States
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Phono switching with relays.
Quote:
Originally Posted by cliffforrest View Post
+1 to Kevin in #46

Were you with the big T in Boston?
I worked for Practical Engineering and after that gig did a few years at the big T aka Teradyne.. Alas the Harrison Ave offices in Boston were gone by the time I worked for them and I had to commute from the southern fringe of Boston to North Reading, a nightmarish 27 mile commute that could at that time take north of 2 hours. My commute today is further and worse over the same road, but I work from home 60% of the time on average.
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Old 13th February 2018, 12:51 PM   #60
kevinkr is offline kevinkr  United States
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Phono switching with relays.
In general I agree with Monte's comments, the current levels present in this application IMLE will not likely result in meaningful or measurable degradations in waveform fidelity.

His recommendation of the teledyne relay is a good one, to which I can add certain families of Panasonic relays as well.

His point about the metallurgy is an important one. The other important thing is purchase relays that are intended for switching low currents, I learned this the hard way with a relay that otherwise seemed highly suitable.
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