[sdiy] Understanding Analog Computer Schematics?

[Grant Richter]

The least expensive, but quite capable, analog computer that I know  
of is in current production.

The Lab Electronics Model X3 "Analog Computer Trainer"

http://www.labelectronics.com/index.php? 
page=shop.product_details&flypage=flypage.tpl&product_id=43&category_id= 
13&option=com_virtuemart&Itemid=53

You should look at their other stuff too. Lab Electronics is located  
in India and is a husband and wife operation (or was).

I bought mine 12 years ago for US$325.00, I don't know what current  
pricing is. They are very hackable.

There are 4 integrators on board. They have 1 meg 1% input resistors.  
I just replaced one of the three on each integrator with a Vactrol to  
make it variable, and added a switch to switch to switch in a 1000 pF  
cap alternative to the 1 uF mylar film cap which it ships with. It  
handles standard synthesizer voltages of course. The integrators have  
nice voltage monitoring LEDs to tell you when the output is outside  
of +/- 10 volts.

Instant filter play box. I used it to develop the Wiard Boogie filter.

The build quality isn't military, but adequate, and they use very  
good components (metal film res. and mylar caps).