electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Articles  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links  |  Store
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
 Forum index » DIY Hardware and Software » Developers' Corner
New 2-pole high-pass filter with SMOOTH resonance!
Post new topic   Reply to topic Moderators: DrJustice
Page 1 of 1 [5 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
Hashtag Octothorpe



Joined: Jun 11, 2017
Posts: 50
Location: Grand Rapids MI

PostPosted: Sat May 18, 2019 6:33 pm    Post subject: New 2-pole high-pass filter with SMOOTH resonance! Reply with quote  Mark this post and the followings unread

Hi!

A couple years ago I was told that sending a kick drum through a high-pass VCF allows you to tune the kick to your preference, so I started looking for a nice design. The cleanest design I got to work was a Polyfusion four-pole high-pass filter. The schematic (GORGEOUSLY drawn by Ron Folkman who I met!!!) is floating around. It's a sweet filter, but being a 4-pole, it's got a steep cutoff, and I felt like a softer cutoff would be nice. Also, it's got voltage-controlled resonance, which is a hassle.

So I cut the filter in half, eliminated the resonance CV, simplified a few things, used op-amps instead of the FETs for buffering, built, hacked, tweaked, etc. etc. and finally got THIS VCF, which has incredible properties that I love. One of my favorites is that it can self-oscillate down into infrasound.

So here's the schematic! I hope somebody can use it and build it. CC license etc. I know people will want to hear sound clips so I... I'll try to make some recordings.


IMAG0021.JPG
 Description:
Oh... any PNP transistor should do, but I use 2N3906 in my builds.
 Filesize:  780.62 KB
 Viewed:  131 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

IMAG0021.JPG


Back to top
View user's profile Send private message
AlanP



Joined: Mar 11, 2014
Posts: 633
Location: New Zealand
Audio files: 35

PostPosted: Sat May 18, 2019 10:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

That is cool. Would a tap to get lowpass be possible?

Also, why opamp buffers? Any reason you aren't using the darlington buffers in the LM13700?
Back to top
View user's profile Send private message
Hashtag Octothorpe



Joined: Jun 11, 2017
Posts: 50
Location: Grand Rapids MI

PostPosted: Sun May 19, 2019 1:05 am    Post subject: Reply with quote  Mark this post and the followings unread

I always use op amps instead of the buffers on the LM13700, maybe because I don't..... I have no formal education in electronics, so I don't really understand transistors in the same way I understand the higher level stuff that's going on with an op amp. (This may show with this design, like I'm not sure the 220nF cap and 100K filter is actually necessary, and I feel like the CV portion is needlessly complex.)

I'm led to believe that op amps are quieter and have less distortion????

I think you could inject a signal near the end of the filter to get a low-pass. I did build a version that sends the output through an inverting buffer in to where the signal is inserted in this version. It works okay (same very nice controllable resonance) but some of the blocked frequencies do get through.

Next one I build I will *totally* experiment with making it a low pass.
Back to top
View user's profile Send private message
PHOBoS



Joined: Jan 14, 2010
Posts: 4584
Location: Moon Base
Audio files: 635

PostPosted: Sun May 19, 2019 4:31 am    Post subject: Reply with quote  Mark this post and the followings unread

I love the handdrawn annotated schematic love

I think one difficulty with using transistors instead of opamps can be an added DC offset.
Also they can only sink OR source, an opamp can generally do both. So I prefer opamps aswell.

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider
Back to top
View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger
ixtern



Joined: Jun 25, 2018
Posts: 132
Location: Poland

PostPosted: Mon May 20, 2019 5:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Hashtag Octothorpe wrote:
I always use op amps instead of the buffers on the LM13700, maybe because I don't.....

Not using output buffers in LM13700 has additional advantage: in such circuit you can use LM13700 or LM13600 or NE5517 or AK317 without any changes.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: DrJustice
Page 1 of 1 [5 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software » Developers' Corner
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
e-m mkii

Please support our site. If you click through and buy from
our affiliate partners, we earn a small commission.


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use