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 
Live streaming at radio.electro-music.com

  host / artist show at your time
  EdisonRex Edison's Electronic Review
Please visit the chat
 Forum index » DIY Hardware and Software » fonik's place
fixing weird resonance behaviour?
Post new topic   Reply to topic Moderators: fonik
Page 1 of 1 [8 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
wackelpeter



Joined: May 05, 2013
Posts: 46
Location: germany
Audio files: 6

PostPosted: Wed Mar 05, 2014 1:21 pm    Post subject: fixing weird resonance behaviour? Reply with quote  Mark this post and the followings unread

first of all hello to all and thanks to all those who left their schematics public so that someone with very limited knowledge in electronics may also can try to build one of these modules.

Well, i'm not working on a modular System at all i just put a few modules in a old metal briefcase to have some more effects or modifying sources for my analog gear...

so far i have built a +/-15 V power supply... regulating that down to 12/9/5 V +/- too
the VC LFO from Fonitronik, the Wasp clone, Steiner Parker filter, simple AR Env. VCA, coloured White noise, Bandpass Filter from Ken Stone, two clock dividers, etc.

at least i have finished the korg 770ish style VCF and the Moog Ladder filter from the 1900 series but both don't work to my satisfaction when i increase the resonance... for the first time there's not much audible Variation but then they are really fast self oscillating in high frequency range... the self oscillation starts a bit abruptly for my taste and in the range before self oscillation there's not really much of an audible harshness or more edgy behaviour of the filter to hear...
makes no difference if i use logarhythmic or linear pot's
the steiner parker VCf worked in a similar behaviour first and then i read that this can be fixed to some extend by using 2 diodes parallel and in opposite direction to each other...
is the part with that 6 diodes something similar? should i maybe increase or reduce the amount of them to get an better resonance tracking? or changing the cap size before the Output where one wiper of the resonance pots is?
btw. i would like to ask if the 770 VCF is supposed to be driven at 15 or 1
2 Volts... had run it at 15 Volts...

any help would be nice and when i'm ready with these i still have to fix an error in my EMS Diode VCF where always one of the Transistors blew away...

first had Problems with these 2 aforementioned filters too... on the Transistor ladder i forgot to cut one stripe between the base of two Transistors and at the 770 board there was a bad solderpoint at the Feedback resistor of the opamp... well these failures fixed i'm only unhappy with the resonance...

thanks in advance for your help.

p.s. having again a look at the schematics of the korg 770 filter my next assumptions would be changing the 2K2 resistor betwenn gnd an Center wiper of resonance pot or the 100k resistor in the Feedback Loop of the op amp, but this would rather change the gain of the op amp as getting a smoother Transition before self oscillation i guess...
Back to top
View user's profile Send private message
wackelpeter



Joined: May 05, 2013
Posts: 46
Location: germany
Audio files: 6

PostPosted: Thu Mar 06, 2014 3:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

okay korg 770ish style filter resonance fixed just reduced that one resistor going from resonance pot center wiper to gound from 2,2k to 1,5k now that's nearly starting with a lower pitched hum and then finally reaching full oscillation at high frequency...

also equaled output levels of all 3 filter modes as bandpass was much louder as the other 2 by increasing their Input resistor to ground from 47 ohms to 270 ohms... still tracks well and levels are fine when switching between modes...

hmmm... looking at the transistor ladder filter schematics (VCF2 - 3522) i don't really know where to start with... just changing value of R18 (10k) doesn't reflect the behaviour only delays the Point where it starts when turning resonance pot on... maybe experimenting with R13 to ground (2,2k) or any other useful advice?
Back to top
View user's profile Send private message
wackelpeter



Joined: May 05, 2013
Posts: 46
Location: germany
Audio files: 6

PostPosted: Mon Mar 31, 2014 10:26 am    Post subject: Reply with quote  Mark this post and the followings unread

well, so far the resonance behaviour is almost fixed...

Now i'm a bit unhappy with the Output volume of the Transistor ladder filter (VCF2 - 3522) from fonik's/Matthias' site... it's only half as loud as the 3 other filters i've built so far (steiner, Wasp, that Korg 770ish Thing) pushed up the volume a bit with reducing the Input resistors for signal input to 47K...
but don't want to reduce them too much...
next tried to increase the feedback resistor (470K originally) in the Output stage... just a small increasing of it turns into selfoscillation of the filter with resonance pot fully down... next tried some different cap values paralleling the resistor...
with more than 1nf or so it worked and selfoscillation only occured with resonance turned on...
but that sounds not as good as before...
tried further to put instead of caps some pairs of parallel reversed diodes... best result i got with 2 diodes (4 and 6 sounded awful) but again it didn't left me that satisfied as with the original design...

does anyone have any hints how to tweak the output volume else without affecting the overall filter behaviour much?

thank you in advance helpful advice...

cheers bastian
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3759
Location: Germany
Audio files: 23

PostPosted: Fri Apr 25, 2014 3:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

raise R16/R17? you may have to raise R18 as well to get the resonance in bounds...
_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
wackelpeter



Joined: May 05, 2013
Posts: 46
Location: germany
Audio files: 6

PostPosted: Mon Apr 28, 2014 9:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Matthias,

thanks for your reply... had already fiddled with the mentioned resistors 16/17 but just played with just one of them... totally ignored that it could be Logical that both have the same value and could correspond with each other... Smile have know because i'm lacking 680k used 820k and the Output is as expected nearly the double... luckily we have build it with the level pot...

well that worked and as you suggested the fixed resonance resistor should be raised too... so far i'm not sure if i should use 22, 20 or 18K as when too much resonance occurs the filter sounded not as good what's a matter of taste... think i'll go for 22k with just slight ringing with full resonance... sounds best to me...

Again thank you and be prepared for further noob questions... Razz
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3759
Location: Germany
Audio files: 23

PostPosted: Mon Apr 28, 2014 10:02 am    Post subject: Reply with quote  Mark this post and the followings unread

wackelpeter wrote:
...totally ignored that it could be Logical that both have the same value and could correspond with each other...

...

Again thank you and be prepared for further noob questions...


google the "golden rules" for opamps. it helpes me a lot to get my head around op amp circuits.

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
wackelpeter



Joined: May 05, 2013
Posts: 46
Location: germany
Audio files: 6

PostPosted: Mon Apr 28, 2014 10:17 am    Post subject: Reply with quote  Mark this post and the followings unread

have already downloaded the "op amps for everyone" pdf by TI...
pretty much sites to read (464pg) and i'm afraid to print them all...

will have a look at those golden rules too... hopefully just a few sites less to read... Very Happy

anyway thanks again and have a nice week.

cheers bastian
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3759
Location: Germany
Audio files: 23

PostPosted: Mon Apr 28, 2014 12:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

much less:

Two "golden rules" of ideal OpAmp:
1.The output attempts to do whatever is necessary to make the voltage difference between the inputs zero.
(This rule, which applies only to closed-loop amplifier circuits, means that the feedback sent from the output to the input causes the two input voltages to become the same.)
2.The input draws no current.
(This rule means that the input terminals look at the voltage placed across them but don’t allow any current to flow into the op amp.)
(from dummies.com)

and especially the 1st one explains a lot. just apply it to the inverting and the non-inverting set-up.

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic Moderators: fonik
Page 1 of 1 [8 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 » fonik's place
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