QRe: [sdiy] Reprinting Electronotes

[Ian Fritz]

At 01:13 PM 12/14/2002, Seb Francis wrote:
>Paul Schreiber wrote:
>
> > This may be lost on a younger generation that "just wants to hook stuff 
> up and make funny
> > noises". Sadly, most folk seem to be content with that.
>
>Perhaps a bit of a sweeping generalisation.  I wasn't even alive at the 
>time when EN started, so I guess I'm one of these "younger 
>generation".  But personally (although I like to hook stuff up and make 
>funny noises just as much as the next person), I love to understand how 
>the stuff actually works - not least so I can make my own creations 
>tailored to the "funny noises" I want to make.
>
>However, there must be very few of us who don't "just hook stuff up".  Who 
>needs to consider the theory of how elecrons work in a transistor, to use 
>an opamp in the design of a synth module?  There are certainly advantages 
>in knowing things right down to the minutest level of detail, but for me 
>life's too short - I have too much music to make to spend my whole life 
>studying electronics.  No one person can do/understand everything .. we 
>all stand on the shoulders of previous knowledge.

I wouldn't want to make it a sweeping generalization either.

But if someone wants to make a filter bank, well, jeeze, that's a really 
simple thing to figure out how to do.  Most of the relevant non-obvious 
information has been posted (for free!!!) on this thread.

Here's what you do:

1.  Pick out a good low noise opamp.

2.  Search the web or some textbook for opamp bandpass circuits.  There are 
zillions around.

3.  Pick a circuit and use the textbook equations to design a set of 
filters with Q of 25 and frequencies spaced at a ratio of 2.1^(1/5).

4.  Design a mixer (or just a summer) circuit to combine all the outputs.

5.  Add some feedback to vary the Q.  (Either locally, in sub-banks or 
globally. You get to choose!)

6.  Build it and tweak up all the frequencies.

That's it.

If someone just rips off the old EN circuits then they don't learn anything 
and they give up the possibility of customizing the unit for their own 
needs.  It's really sad that anyone would want to go that route for such a 
simple device.

   Ian