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Magnetic vs physical contacts...

losthobos

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Can anyone please tell me the advantages/disadvantages between the midi systems that are either magnetic contact or physical contact...
Considering installing midi to run a hammond simulator and want to get right first time if i do decide to follow this whim
Thanks
 

JIM D.

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The older design physical contacts only triggered one function - open contact & closed contact. They also in time require cleaning
of the contact points

The newer designed magnetic
switches can perform more than one function depending on the distance the magnet travels by the receiving post.
The magnets can be easily replaced or repositioned and require no wear or cleaning to operate.

Retrofitting an old midi installation with the new magnetic type is costly because of the labor required & parts (magnets & new midi
trigger boards).
 
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losthobos

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Thanks Jim, its the older physical system some one local is able to fit for £350 which I thought was very reasonable... Just straight midi lead out 3 channel and no boxes/gadgets/lights etx making the accordion look like a thunderbirds/joe90 machine...
Given the attributes of the ferrofish hammond unit i don't think i need anything more than each switch being either on or off but i may be mistaken
Thanks again
All knowledge gratefully received
 

Ventura

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organ modules are better controlled with simple on-off switching.. in fact i use a midi filter to remove all bellows and touch velocity data from the FR3 i use as the controller over my Virtual Cordovox rack system

the disadvantage of spring contacts is they are harder to adjust/finesse so that the *on* moment is the same for each key ( and that adjustment has more tendency to drift over time with usage ) and that spring type contacts exhibit "bounce" irregularities in the on waveform ( you can see this on a scope ) which can (and sometimes do) interfere with reliable Midi functioning.. an extra line of cmos gates are sometimes added to smooth this out

solid state switching has the disadvantage of magnets being dislodged in transit, as they are typically glued on to the action somewhere, which is an occasional problem particularly if you travel a lot and your box is subject to baggage handlers

the small transistor looking solid state switches are very reliable, easily positioned and final adjusted once mounted, never need cleaning or servicing and exhibit zero waveform bounce

a third switch sometimes used are magnet actuated reed switches encapsulated in a vacuum ( glass shell )
which interface more readily with older Midi board designs (that were engineered with physical switching in mind)

some reed switches of poor material design can become stuck in the "on" position if their paired magnet is too powerful

magnets should be mounted in uniform polarity as much as possible (though that can be time consuming to determine sometimes)
 

losthobos

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Thankyou Ventura.... Exactly the detailed info i was hoping for... Appreciated 😊
 

Alan Sharkis

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I have an acoustic accordion with midi. The system has Hall effect switches. If one goes out of alignment I can fix it. If two or three go out, I’m stuck, because they usually go in the “always-on direction. To make it worse, the installation has a bundle of wires in a position where they can easily bump into those detectors if the accordion gets bumped, and the wires are too short to be rerouted. Needless to say, I’m very careful with this accordion. If I have to transport it, it’s always in a hard case with foam blocks around it to absorb shock and prevent it from moving inside the case. But this type of midi is still a lot more reliable than the contact type.

I recall reading somewhere that there were some midi systems for accordion that employed optical detection but it didn’t work out too well. I wonder why.
 

Ventura

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hi Alan

there was a switching module available for awhile that had the optical setup encapsulated on opposite sides of a plastic channel, which merely needed something (anything) to break the light path in the channel (like the arm of an accordion action)

i think maybe the utah fellow used these for awhile before his system added velocity capability

of course they were not made or meant for midi accordion use, so when the burroughs or other computer dinosaur they WERE designed for died they probably were around for us until the allparts liquidators sold them through
 

Alan Sharkis

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I took a sabbatical for study in the 1982-1983 year and some of the courses I took involved a Burroughs mainframe, so your mention of that brings back memories. Computer hardware in those days included some very weird contraptions by today’s standards, so the optical switches you described don’t really surprise me. And, as you pointed out, they were never really meant to be used in accordions.
 

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