DIYAPASON-L Digest #942 - Sunday, January 18, 2004
 
Re: Relay/Wiring Problems - Help!!!
  by "Larry Chace" <RLC1@etnainstruments.com>
Re: [Residence Organs]  Reservoir Releathering: Choice of Leather
  by "Larry Chace" <RLC1@etnainstruments.com>
Re: [Residence Organs]  Re: Relay/Wiring Problems - Help!!!
  by "Mike Gettelman" <mike3247@earthlink.net>
 

(back) Subject: Re: Relay/Wiring Problems - Help!!! From: "Larry Chace" <RLC1@etnainstruments.com> Date: Sun, 18 Jan 2004 11:39:54 -0500   Steve Durham raised a question about the ability of his Moller keyboard contacts to handle the load of 5 chest magnets. From his note, I'm assuming that the chest is straight, such that all 5 magnets for a given note will be wired in parellel and without the use of any intervening elements except for the Reisner switches that will turn the ranks on and off.   Indeed, the current load for those 5 magnets will approach 1 amp (more or less, depending on the magnet's resistance and the applied voltage), and = it is safe to say that the little Moller key contacts won't be happy with = that load. In addition, there is the concert about inductive flyback voltages produced when the magnets are de-energized. Steve's note didn't mention whether or not he is putting diodes across the magnets to squelch that flyback voltage. Without them, the contacts will be burned all the = faster.   A solution would be two-fold. First, install diodes across the magnets, = if they aren't already there or if they aren't provided "otherwise". Second, fit each key with its own high-current switch to handle the aggregate = load. That switch can be of several forms. It can be the traditional (Reisner, for example) note relay that has a single magnet (operated by the key) and multiple independent contact wires that are all energized from a common "wiper". The use of these items will remove the need for the "fan-out" diodes that Steve mentioned.   The switch can also be a simple relay (SPST, Normally-open) that, again, = is fired by the key and whose single output leads to the "fan-out" diodes. = If the 5 ranks aren't unified, by the way, then the fan-out diodes aren't necessary at all.   The switch can also be a solid-state device, such as the ULN2004 or UDN2982,which house 7 or 8 power transistors and flyback diodes in a = single package. You can wire the inputs together and drive them from the key contacts. The individual outputs would then each run to a chest magnet. You'd need 61 of them for each keyboard. The ULN2004 pulls its output = down to ground, so the chest magnets' common wire would be positive. The UDN2982 pulls its outputs up, so the chest common would be negative.   Or, you an use standard power transistors (like the TIP series) to produce the high-current switch.   If the Reisner switches are alread ganged together, and if the chest is staight, then the outputs of those solid-state devices can be wired in parallel and connect via a single wire (each) to the Reisner buss wires.   "It all depends..." ;-)   Larry Chace          
(back) Subject: Re: [Residence Organs] Reservoir Releathering: Choice of Leather From: "Larry Chace" <RLC1@etnainstruments.com> Date: Sun, 18 Jan 2004 11:49:37 -0500   Keith Zimmerman asked for advice about reservoir releathering. Quite a = few years ago now, my organ builder friend Cullie Mowers helped me through = that process. We used the Audsley book (actually, one of the original full-sized editions!) and followed his instructions, ignoring the parts about the second set of ribs (with much relief). The results were very good.   We did "cheat" and use the pre-made corner gusset sets that Organ Supply sells. We also used fish glue, which was actually a good idea in that I was slow enough at it that the glue's slower setting time was not problem and actually let me re-position things as necessary.   You do want to be sure that the to-be-glued wooden parts are nice and bare when you glue them, so you may want to hold off on shellacing them until after the leather work is done.   Since Keith has several to do, he has the advantage of being able to use one as a sample while working on another.   Larry Chace        
(back) Subject: Re: [Residence Organs] Re: Relay/Wiring Problems - Help!!! From: "Mike Gettelman" <mike3247@earthlink.net> Date: Sun, 18 Jan 2004 12:23:51 -0500       Larry Chace wrote: (snip)   > > The switch can also be a solid-state device, such as the ULN2004 or > UDN2982,which house 7 or 8 power transistors and flyback diodes in a = single > package. You can wire the inputs together and drive them from the key > contacts. The individual outputs would then each run to a chest magnet. > You'd need 61 of them for each keyboard.   Sounds like this elegant solution (which runs about $360 a keyboard) = supplies all the necessary keying signal needs for the organ in a reliable and = modular package which also provides a standardized digital output to feed a = processor. Even those of us using more historic switching equipment beyond the key contacts right now will benefit by the reliability of the solid state = switch, and the knowledge that we are ready to add processing equipment at a later = date without any further keyboard modifications. Sounds like the way to go if disassembly of your keyboards in in your future. Mike