Allan 505B Ground Question

[Slim Jerkins]

I've been given (for the price of delivery) an old 505B console for a midi project. All electronics have been stripped except for the capture system. After a little lubrication and exercise the handful of sluggish tabs now work perfectly.

I have re-wired the keyboards and pedals to work with the Artisan serial midi input boards that I have had from a previous project. These boards look for +5V on key closure. Since I want to keep the Allen capture system, I had to purchase a new input board to handle the stop tab closures going to ground.

The concern I have (before marrying all the components) is the ground reference. The artisan equipment runs off of a small 5V DC power supply. When metering the 5V power supply ground to chassis ground I measure no potential - as I would expect. On the Allen capture power supply I notice two grounds; "M" ground and "N" ground. The stop rail frame is connected to "M" ground. I measure about 24V AC from "M" ground to chassis ground with the voltmeter. "N" ground to chassis ground shows no potential. I'm a little reluctant to connect the "M" ground of the Allen system to the same reference as the Artisan 5V ground.

If anyone can shed some light here I would be very appreciative!

thanks,

Bill S.

[Admin]

According to the schematic, M and N GND are connected together so should be at the same potential. Don't confuse the N GND terminals with the N1 - N4 terminals.

Also there should be two contacts on each tab. One goes to the stop array board and, if memory serves, is negative with respect to ground. The other goes to the DM capture board and is a +5 vdc with respect to ground.

Here is a plug 'n play solution I have for MIDI stop control and capture memory that works with your 505 and I sell:
http://www.ebay.com/itm/201731913242...84.m1555.l2649