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
Please visit the chat
 Forum index » DIY Hardware and Software » PAIA Equipment
PAIA2720-3B VC Bandpass Filter_Augmentations
Post new topic   Reply to topic
Page 1 of 1 [12 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
gasboss775



Joined: Jan 02, 2016
Posts: 193
Location: Scotland

PostPosted: Tue May 16, 2017 6:40 am    Post subject: PAIA2720-3B VC Bandpass Filter_Augmentations Reply with quote  Mark this post and the followings unread

I tried out the PAIA 2720-3B VC Bandpass Filter on the breadboard. I wasn't initially that impressed with its range. However I swapped the diode for a red led and drove it from an exponential current source, the result was a great increase in the range of the filter. I also changed the way in which the Q control was implemented, resulting in, in my opinion a more natural control contour.

I also made a second version with a simpler current source using just one NPN transistor. The results were still very impressive.

The most interesting characteristic of these filters is the way they behave when overdriven. With high Q settings, the LED becomes modulated by the very signal that it is controlling and things freak out somewhat, the LED flickers too in response to the large signal swing!

The original is included for comparison.


PAIA 2720-3B_LED_ExpoCurrentSource_Version.jpg
 Description:
 Filesize:  288.89 KB
 Viewed:  215 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

PAIA 2720-3B_LED_ExpoCurrentSource_Version.jpg



PAIA2720_3B_LED_Simple_CurrentSource_Version.jpg
 Description:
 Filesize:  212.14 KB
 Viewed:  200 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

PAIA2720_3B_LED_Simple_CurrentSource_Version.jpg



paia_2720_3b_vc_bpf_Disrete_Design.gif
 Description:
 Filesize:  11.33 KB
 Viewed:  185 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

paia_2720_3b_vc_bpf_Disrete_Design.gif


Back to top
View user's profile Send private message
gasboss775



Joined: Jan 02, 2016
Posts: 193
Location: Scotland

PostPosted: Wed May 17, 2017 5:38 am    Post subject: Reply with quote  Mark this post and the followings unread

I tried out the PAiA 2720-3L Lowpass filter. Again it worked better with LEDs instead of diodes and a current source to drive the LEDs. I chained two Lowpass filter sections together to make a 4 pole filter. It was quite good but would really benefit from having a Q / resonance control. I'm going to have to figure out if this can be done.
Back to top
View user's profile Send private message
gasboss775



Joined: Jan 02, 2016
Posts: 193
Location: Scotland

PostPosted: Sat May 20, 2017 5:20 am    Post subject: Better Current Source Version Reply with quote  Mark this post and the followings unread

This version of the 2720-3B bandpass filter has a linear current source that doesn't have any tempco problems.


1495219802500.jpg
 Description:
 Filesize:  93.87 KB
 Viewed:  187 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

1495219802500.jpg


Back to top
View user's profile Send private message
gasboss775



Joined: Jan 02, 2016
Posts: 193
Location: Scotland

PostPosted: Sun May 21, 2017 3:39 am    Post subject: Reply with quote  Mark this post and the followings unread

I was just trying out the circuit from my last post again and it would seem that 68K is a better choice for R12 as it allows the filter to be completely closed.
I suspect that there might need to be a bit of experimentation with some of the resistor values to accommodate different LED's. Specifically, R9 & R12.

Last edited by gasboss775 on Sun May 21, 2017 7:15 am; edited 1 time in total
Back to top
View user's profile Send private message
gasboss775



Joined: Jan 02, 2016
Posts: 193
Location: Scotland

PostPosted: Sun May 21, 2017 7:14 am    Post subject: Reply with quote  Mark this post and the followings unread

I built 2 of the PAiA 2720-3B bandpass VCFs and designed a little two transistor mixer and output stage with 10 V peak to peak maximum output.

The sinewave generators represent the 2 filters, the 10K resistor on the right represents the output load.


2Ch Discrete transistor mixer for dual VCF.png
 Description:
 Filesize:  48.18 KB
 Viewed:  161 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

2Ch Discrete transistor mixer for dual VCF.png


Back to top
View user's profile Send private message
n.d



Joined: Dec 15, 2011
Posts: 49
Location: Argentina

PostPosted: Fri Feb 16, 2018 6:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice work!
Back to top
View user's profile Send private message
gasboss775



Joined: Jan 02, 2016
Posts: 193
Location: Scotland

PostPosted: Fri Mar 09, 2018 12:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

n.d wrote:
Nice work!


Thanks dude.

I have experienced some problems with instability ( it bursts into oscillation ) that seem to be somewhat related to circuit layout ( I've only ever built it on a breadboard )
I did find that putting a 100n ( 0.1uF ) capacitor between the collector or Q2 and ground helped a bit. Does anyone else have any suggestions about making this behave. I was thinking of using either an FET optocoupler or a vactrol instead of the diode to tune the filter in order to avoid the circuit using the same ground as the control signal.
Back to top
View user's profile Send private message
Fernando



Joined: Dec 30, 2006
Posts: 233
Location: Barcelona & Emporda, Spain

PostPosted: Mon Aug 27, 2018 11:26 am    Post subject: Reply with quote  Mark this post and the followings unread

very nice gasboss!

I always think about trying the most simple PAiA circuits.

Well for the twin T filter (2720-3b) I'd try with a photocell instead of the diode and a circuit to control the LED. Or a real vactrol instead of a DIY one. But DIY you can use a more adequate range for the photocell and have less work fine-tuning it's right resistance range.

There are many schematics for vactrol CV around from other circuits (Buchla LPG, etc.) but I'd try something much simpler first, the simplest possible.
Try this: http://thesquarewaveparade.com/images/VtoR.jpg (second option, with offset)
And read here: http://www.electro-music.com/forum/topic-37628.html

_________________
Fer

.
Back to top
View user's profile Send private message
gasboss775



Joined: Jan 02, 2016
Posts: 193
Location: Scotland

PostPosted: Mon Sep 17, 2018 9:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Fernando wrote:
very nice gasboss!


Thanks for the complement Fernando!

Quote:
I always think about trying the most simple PAiA circuits.

Well for the twin T filter (2720-3b) I'd try with a photocell instead of the diode and a circuit to control the LED. Or a real vactrol instead of a DIY one. But DIY you can use a more adequate range for the photocell and have less work fine-tuning it's right resistance range.

There are many schematics for vactrol CV around from other circuits (Buchla LPG, etc.) but I'd try something much simpler first, the simplest possible.
Try this: http://thesquarewaveparade.com/images/VtoR.jpg (second option, with offset)
And read here: http://www.electro-music.com/forum/topic-37628.html


I have several vactrols and have been meaning to try them out in this circuit. Using a diode or LED have their own charms due to the distortion generated when the filter is driven with a strong signal. I do like vactrol based filters though, they have a dynamic character of their own.

Last edited by gasboss775 on Mon Sep 17, 2018 3:15 pm; edited 1 time in total
Back to top
View user's profile Send private message
Fernando



Joined: Dec 30, 2006
Posts: 233
Location: Barcelona & Emporda, Spain

PostPosted: Mon Sep 17, 2018 10:04 am    Post subject: Reply with quote  Mark this post and the followings unread

gasboss775 wrote:
Using a diode or LED have their own charms due to the distortion generated when the filter is driven with a strong signal..


that's interesting

I would try with a chain of Ge diodes then

_________________
Fer

.
Back to top
View user's profile Send private message
gasboss775



Joined: Jan 02, 2016
Posts: 193
Location: Scotland

PostPosted: Tue Sep 18, 2018 1:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, Ge diodes sound like a good idea, never tried them at the time.
Back to top
View user's profile Send private message
AlanP



Joined: Mar 11, 2014
Posts: 511
Location: New Zealand
Audio files: 31

PostPosted: Tue Sep 18, 2018 10:21 am    Post subject: Reply with quote  Mark this post and the followings unread

My experience of clipping diodes in pedals is that Ge diodes have a "softer" sound than Si diodes. You need a couple in series to match the Fv of silicon, though.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic
Page 1 of 1 [12 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 » PAIA Equipment
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