ARP Filter Chronology, was Re: Surface mount synths??

[Joachim Verghese]

On Thu, 11 Jul 1996, Sean Costello wrote:

> The ARP terminology has me confused.  Here's all I know about the ARP filter
> modules:
> 
> 4012 - Moog ladder filter copy, used in early 2600, Pro-Soloist, and
> (debatedly) the white-faced Odyssey.

Yes, the 4012 was the original 2600 filter, but it's very unlikely that
it appeared in any other models. There's a statement by Tim Smith in the
"Vintage Synthesizers" book according to which the white-face Odyssey
had the 4012. This is inaccurate (according to Tim himself). 

> 4023 - SEM-type state variable, used in white-faced Odyssey.

Correct. And some early black/gold ones too.

> 4035 - never heard of it before.

4-pole ladder filter which appeared in some black/gold Odysseys in 1974
or 1975. Very similar to the Pro-Soloist's 4034.

> 4072/4075 - 4-pole filter (probably the one covered in US Pat. No.
> 4,011,466), using LM3900 and 4 PNP transistor differential pairs. 

Correct. The 4072 is a modified 4075, to make it compatible with the
2600 gain structure and CV polarity.

BTW, this topic has appeared numerous times on both DIY and AH,
so you may want to check the archives.

Hope this helps.

-joachim