Avatar

Please consider registering
Guest

sp_LogInOut Log In sp_Registration Register

Register | Lost password?
Advanced Search

— Forum Scope —




— Match —





— Forum Options —





Minimum search word length is 3 characters - maximum search word length is 84 characters

sp_Feed sp_TopicIcon
VA Diode Ladder Filter
No permission to create posts
July 20, 2013
2:21 am
Avatar
W Pirkle
Admin
Forum Posts: 247
Member Since:
January 29, 2017
sp_UserOfflineSmall Offline

Hi All

I have uploaded my derivation for the VA Diode Ladder Filter on the App Notes page, complete with sample RackAFX project and analysis:

http://www.willpirkle.com/proj.....notes/#AN5

The filter works as expected (matches the theoretical response) and self-oscillates nicely. I created this Topic for any questions or comments you may have; feel free to post them here.

- Will

September 7, 2018
4:01 pm
Avatar
drvenkman
Member
Members
Forum Posts: 7
Member Since:
August 27, 2018
sp_UserOfflineSmall Offline

Great stuff, Will.

Any clues as to how you would form the highpass of this filter?

PS: when testing this filter I noticed the cutoff freq was "off" by about half an octave. For me, multiplying the small g by 1.5 corrected this, but that seemed like kind of a hack. Not sure, but perhaps it is just my code.

September 7, 2018
6:24 pm
Avatar
W Pirkle
Admin
Forum Posts: 247
Member Since:
January 29, 2017
sp_UserOfflineSmall Offline

The error in the cutoff is known and is present in the analog design too, AFAIK. So it is part of the "character" of the filter... 

There isn't a way to make a HPF from the structure that I know of. But, there is a connection with the Moog ladder filter as the diode version was supposedly designed to circumvent Moog's patent, and it does also consist of series 1st order LPF blocks. Oberheim derived the "variations" for the other versions of it from a global H(s) transfer function (aka the Oberheim Variations in the Synth book). But the leapfrog structure with the crossed feedback paths would complicate any derivation that I could see. (let me know if you figure it out)

- Will 

September 8, 2018
3:03 am
Avatar
drvenkman
Member
Members
Forum Posts: 7
Member Since:
August 27, 2018
sp_UserOfflineSmall Offline

Interesting! Thanks for the explanation.

Forum Timezone: America/New_York

Most Users Ever Online: 36

Currently Online:
6 Guest(s)

Currently Browsing this Page:
1 Guest(s)

Top Posters:

Skyler: 48

Derek: 46

Peter: 41

Frodson: 40

clau_ste: 39

Gwen: 32

JimmyM: 30

TheSmile: 27

EZB: 24

lppier: 23

Member Stats:

Guest Posters: 1

Members: 522

Moderators: 1

Admins: 4

Forum Stats:

Groups: 11

Forums: 31

Topics: 545

Posts: 2134

Newest Members:

Bill, hill william, NAUN_SONAR, sufy, Diane, Richard, drvenkman, venkman, Jfx, drorh

Moderators: W Pirkle: 247

Administrators: Tom: 67, JD Young: 80, Will Pirkle: 0, W Pirkle: 247