2040

[Joachim Verghese]

First of all, thanks to Juergen for a wonderful 2040 schematic.
(http://www.synthfool.com/diy/jh2040.gif)

> Can the BC550Cs be replaced by transistors from CA3086s?
> /JB

I did some experimentation using transistor arrays for the
gain cells in a 2040-like filter a year back, or so. I used
Elantec EN2016 (NPN) and EP2015 (PNP) arrays, but the results
weren't that spectacular. The transistors in these arrays
aren't very well Vbe-matched (5 mV), which means that you'll
end up with a substantial amount of CV feedthrough at the output.

Desicrete devices can fairly easily be matched to 2 or 1 mV,
hence you'll have better CV rejection.

CA3086 or 3046 arrays could of course be used for the gain
cell NPNs, but these aren't any better than the Elantec arrays.

To summarise then, some pros and cons:

CA30x6 Arrays
-------------
+ ease of use (no selection needed)
+ excellent thermal coupling
+ low cost, good availability

- average performance (matching, noise, linearity...)
- complicated layout


EP2015/EN2016/MAT0x Arrays
--------------------------
+ ease of use
+ excellent thermal coupling
+ high performance (MAT0x devices)

- expensive, not easily obtainable


Discrete "audio" transistors
----------------------------
+ high performance
+ simple layout
+ serviceability
+ low cost

- requires matching
- thermal coupling somewhat difficult to arrange (heatsinks/epoxy..)


Well, that's about all I can think of right now.

-joachim