[sdiy] Hammondparts

[Glen]

At 01:42 AM 8/25/04 , Rönnberg Niklas wrote:

>On this page he can by a substitue for $39.95, but he insists on building
>one. Does any of you any schematics or information to his help?

It would certainly be easiest for your friend to simply buy this part. Try
to convince your friend of this.


However, if you really want to pursue building something...

This chip is not really a full "top octave" by itself, since it only
handles 6 notes of the scale. There is a companion chip that handles 7
other notes of the scale, which is used along with this chip. One idea is
to replace BOTH these chips with a true top octave chip (a single chip that
produces 13 notes.) It's up to you to figure out if the new TOG chip will
run off the original power supply voltages, whether it needs any sort of
input or output translation, etc. The advantages of the 13 note chips is
outlined on the web page you referenced earlier.

Another route to take is to use a processor to generate the 13 notes that
used to be generated by this pair of chips. Once again, you have to make
sure about possible voltage level translations, etc.

You could always bypass the top-octave chips and build 13 oscillators,
along with a simple output buffer stage for each oscillator that makes sure
the output levels will work with the organ's circuitry, and that the organ
circuitry won't "load down" the oscillators and detune them. Then, the
pitches could then actually be tuned to perfection, instead of the
compromises made by the top-octave chips.   :)  

Personally, I think I like the 13 oscillator method best, if you decide on
pursuing a DIY project.

There is also another possibility. You might be lucky and eventually find a
used organ for sale that doesn't cost much more than this part does.  :)
Look in thrift stores, classified ads in newspapers, eBay, etc.


later,
Glen