[sdiy] tube ladder

[René Schmitz]

At 13:54 24.06.02 -0400, media.nai at rcn.com wrote:
>At 11:51 AM +1000 06/23/02, Paul Perry wrote:
>>
>>With the classic Moog ladder, it is important to have at least
>>the top & bottom pair of transistors matched (I don't know why,
>>unless it is to null out 'unfiltered' signal).
>>So that might be a problem, if you have to match some of the
>>pentodes as well....
>
>My half-baked idea is more like a tube OTA ladder filter -- like the SSM
>and Roland chips.

The matching in the moog ladder is only important to cancel the standing
current. 
(I.e. control voltage rejection)  If you can tolerate a lower rejection
ratio its 
ok to use unpaired tubes. Or if your changes are slow enough... Erics VCA
essentially 
does this, the control voltage is passed by a filter to prevent excessive
clicking.

Cheers,
 René


-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159