M2 => M3 (amp question)

[geldo79]

Hi,

I want to upgrade my 1953 M2 to an M3. Besides a new matching transformer and the percussion switches,
I need to replace the AO-14 amp with an AO-29. But I don't exactly know
what type of AO-29 I can use. There are often H-AO-29 amps from M-1xx organs on ebay etc. . I think I can not use
these !? In addition, there is an EM-Speaker inside the M2, so I think I also have consider this....am I right?
Can anyone tell me what exact type number I need for my project?

Greetings from Germany,

Christian

[enor]

If you want to keep the EM speaker, you need an AO-29 from an early M-3. If you change for a PM speaker, you can use any later AO-29, including those from the M-100. Or even an AO-67 from a late M-100.

[geldo79]

Ok...but what is an early AO-29? How can I easily find out if it is the EM version?

[enor]

Ok...but what is an early AO-29? How can I easily find out if it is the EM version?

Preamp code letters J and higher (the preamp code might look something like "AO-29-1J" or similar) are the later permanent magnet version. A "code letter" lower than a J at the end of the code (that is, up until and including I) means it is an earlier version for the field coil (EM) speaker. M-100 amps have no code letter, instead they can be called something like "AO-29-13" or similar. These are easily spotted by the black transformers ... they are also permanent magnet versions.

[geldo79]

Ah...Ok. Thank you. That helped.

[Twiggybush]

I'm curious how percussion can be added to a M2. Would not the M2 be missing an extra key contact? To bad your not around my area. There are many M3's available for very little or free.

[enor]

Triggering perc would indeed be a problem. Short of replacing the top manual with an M-3 one, the most reasonable approach would be to use the 2' drawbar as a trigger, but then of course you wouldn't have any perc on the topmost 6 keys. Maybe not so bad (but not exactly like an M-3)

[Wes]

I wonder how hard it would be to design a solid-state circuit that closed a DC latch whenever audio signal was present. An op-amp with a ton of gain into a transistor that feeds the percussion terminal with ground? Then you could tap any full-length busbar. The 16' would probably be the easiest to get working right.

[geldo79]

My plan is to first do an upper foldback mod on the M2. That should upgrade the upper manual to an M3 upper Manual (with foldback B-)). The percussion triggering should not be any problem then.