Hi James,
I may be mistaken, but I think the diodes are being used as voltage controlled resistors. They and the associated capacitors form a series of RC pairs that form the poles of the filter.
This technique started out using transistors in the venerable Moog filter, but Dr Bob patented the heck out of that. After Arp got sued for using it, they and other folks (EMS for instance) started using diodes instead.
Here is an amazingly detailed analysis of the whole subject - just get some popcorn and some advil and have a look:
http://www.timstinchcombe.co.uk/synth/Moog_ladder_tf.pdf
Best Wishes
Gary
I may be mistaken, but I think the diodes are being used as voltage controlled resistors. They and the associated capacitors form a series of RC pairs that form the poles of the filter.
This technique started out using transistors in the venerable Moog filter, but Dr Bob patented the heck out of that. After Arp got sued for using it, they and other folks (EMS for instance) started using diodes instead.
Here is an amazingly detailed analysis of the whole subject - just get some popcorn and some advil and have a look:
http://www.timstinchcombe.co.uk/synth/Moog_ladder_tf.pdf
Best Wishes
Gary
--- In cgs_synth@yahoogroups.com, James Elliott <johans121@...> wrote:
>
> I'm sure these are dumb questions but I'll ask anyway.
>
> 1) What are the purpose of the diodes in this filter? That said, I have two REV
> 1 boards that I am finally getting around to finishing, and I was just wondering
> why the extra 2 diodes were added in the new revision. After looking at the
> schematics for both revisions it seems easy enough to add the two extra diodes
> on my older boards but I don't know what I would be getting out of it.
>
> 2) What exactly does the trimmer do on the newest revision? Again, it seems easy
> enough to incorporate it into my build, but I would like to know what I'd be
> getting out of it.
>
> Thanks,
> Jim
>
>
>
>
>
> ________________________________
> From: James Elliott <johans121@...>
> To: cgs_synth@yahoogroups.com
> Sent: Fri, May 27, 2011 11:26:23 PM
> Subject: Re: [cgs_synth] Re: subosc/harmonic sequencer (iffy response)
>
>
> Excellent demo!!
>
> ________________________________
> From: drryle <dryle@...>
> To: cgs_synth@yahoogroups.com
> Sent: Fri, May 27, 2011 1:37:38 PM
> Subject: [cgs_synth] Re: subosc/harmonic sequencer (iffy response)
>
> Here is the CGS1 in MU panelling. This module is magical!
>
> http://www.youtube.com/watch?v=Le2_k5FWNww&feature=channel_video_title
>
> [Non-text portions of this message have been removed]
>
>
>
>
> [Non-text portions of this message have been removed]
>