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
OTA - Operational Transconductance Amplifiers
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 1 [6 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
Sethkaine



Joined: Sep 26, 2015
Posts: 16
Location: Suisse

PostPosted: Mon Sep 28, 2015 3:00 am    Post subject: OTA - Operational Transconductance Amplifiers
Subject description: I want to know everything about OTA
Reply with quote  Mark this post and the followings unread

Hi OTA Lovers,

I will talk about OTA - Operational Transconductance Amplifiers.
I have build the VCO-1 from Thomas Henry. Without the 2k thermistor but with 2x 1k in series around the expo converter transistors.
I have breadboarded the Thomas Henry VCF-1 without the PNP expo converter for now. But with one 100k pot to -/+ 12v center tap binded with 22k to each two OTA from LM13700. For now the VFC-1 sound nicely with a touch of resonance as I like.

ref. here:
http://www.birthofasynth.com/Thomas_Henry/Pages/VCO-1.html
http://www.birthofasynth.com/Thomas_Henry/Pages/VCF-1.html

My questions :
1. I want to know if with a different expo (like the one from R. Schmitz) the VCF will sound the same ?

2. Someone has already build the NPN expo converter from René Schmitz ?
ref. here:
http://schmitzbits.de/expo_tutorial/index.html

_________________
my youtube channel - https://www.youtube.com/user/SethKaine/videos
my paper mix - https://paper.fiftythree.com/1865071
Back to top
View user's profile Send private message
m.o



Joined: Jul 05, 2014
Posts: 44
Location: Sweden

PostPosted: Mon Sep 28, 2015 1:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
1. I want to know if with a different expo (like the one from R. Schmitz) the VCF will sound the same ?


The (static) sound itself would be the same, what might differ slightly is the response to CV (you might hear a difference when applying an envelope), but in theory: expo is expo...

Quote:
2. Someone has already build the NPN expo converter from René Schmitz ?
ref. here:
http://schmitzbits.de/expo_tutorial/index.html

Yes you'll find if you study other VCOs (sawtooth type) that this is pretty much a standard configuration.
(And if you rearrange the components slightly in the TH design you'll see it's also is similar).
NPN configurations like this will 'sink' current into the collector of the output transistor, while PNP configs such as the one in TH VCO 'sources' (pushes out) current - different directions.

The expo in the TH VCO needs a positive current to control the 3080 (OTA), which in turn emits a positive or negative current at it's output depending on the state of it's +/- inputs - this output current 'size' is what is controlled by the expo (it's the same mA amount wether it's positive or negative).
This current is what makes the op-amp IC3a to charge/discharge the C3 capacitor at a steady rate.
Back to top
View user's profile Send private message
Sethkaine



Joined: Sep 26, 2015
Posts: 16
Location: Suisse

PostPosted: Sat Oct 03, 2015 1:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

thank you for your very interesting explication. I will study it closer and make tests.
_________________
my youtube channel - https://www.youtube.com/user/SethKaine/videos
my paper mix - https://paper.fiftythree.com/1865071
Back to top
View user's profile Send private message
PHOBoS



Joined: Jan 14, 2010
Posts: 3543
Location: Moon Base
Audio files: 534

PostPosted: Sun Oct 04, 2015 6:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Just came across this on my harddrive, maybe it's useful.


UsingOTAs2.pdf
 Description:
Understanding and using 'OTA' op-amp ICs by Ray Marston

Download
 Filename:  UsingOTAs2.pdf
 Filesize:  608.96 KB
 Downloaded:  145 Time(s)


_________________
"My perf, it's full of holes!"
http://phobos.000space.com/ http://www.acidtrash.com/ Stickney Synthyards
Back to top
View user's profile Send private message Visit poster's website AIM Address Yahoo Messenger MSN Messenger
L´Andratté



Joined: Sep 23, 2012
Posts: 123
Location: Hamburg, Germany
Audio files: 5

PostPosted: Tue Oct 06, 2015 9:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Mucho gracias, Phobos!
Back to top
View user's profile Send private message
bugbrand



Joined: Nov 27, 2005
Posts: 845
Location: Bristol, UK
Audio files: 1
G2 patch files: 1

PostPosted: Wed Oct 14, 2015 5:57 am    Post subject: Reply with quote  Mark this post and the followings unread

For people interested in OTAs, this could be an interesting/useful doc, recently published::

Minimizing distortion in OTAs

http://www.openmusiclabs.com/files/otadist.pdf

_________________
http://www.bugbrand.co.uk
http://www.bugbrand.blogspot.com
Back to top
View user's profile Send private message Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 1 [6 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
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