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
Simple VCA with bonus S&H/Glide on one piece of stripboard
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 2 of 2 [38 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Goto page: Previous 1, 2
Author Message
nicolas3141



Joined: May 25, 2007
Posts: 138
Location: Christchurch, New Zealand

PostPosted: Sun Nov 04, 2012 5:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

To make it sample as quickly as possible, reduce R103 to 10k or even 4.7K (don't go any lower than 4.7k or you might blow up the 13700) and use a TL074 or similar for IC1d (R106/107/108 will not be necessary) which will then allow you to significantly reduce C101. A smaller C101 will reduce the hold time before you notice sag, but you could experiment with different values between 1n and 50n to find a good compromise. Those 3 changes will improve the high freq performance dramatically.
R103 --> 10k
IC1 --> TL074
C101 --> 10n (experiment a bit with this value and let us know what you find)
And of course make sure P101 is right round at the fastest setting possible.
Back to top
View user's profile Send private message
Bogus Noise



Joined: Jun 03, 2009
Posts: 59
Location: Sheffield

PostPosted: Mon Nov 05, 2012 12:35 am    Post subject: Reply with quote  Mark this post and the followings unread

That's great advice, thanks Smile

I will test it out this week and report back. I already have a dual glide module and will be using this mostly as a sample and hold so shouldn't need to compromise too much, but I'll post up how things go regarding the glide response as well.

_________________
Circuit Bent Sonic Absurdity:

www.bogus-noise.co.uk
http://www.youtube.com/user/BogusNoise
Back to top
View user's profile Send private message Visit poster's website
Bogus Noise



Joined: Jun 03, 2009
Posts: 59
Location: Sheffield

PostPosted: Tue Nov 06, 2012 9:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, have given it a bit of a test. 10k and 10nf capacitor works well at high sampling rates, but drifts quite a bit if there's say a second or so for each cycle. I changed to a 100nf, still drifts a bit. It's more noticable on higher voltages (both + and -), the closer it is to 0v the longer it holds. It's good enough for the moment but when I get a chance I'll experiment with some more values to try and get the performance at higher voltages to be a bit more stable.

I'm also thinking about about adding a gate to trigger circuit on the input, could be a handy extra!

_________________
Circuit Bent Sonic Absurdity:

www.bogus-noise.co.uk
http://www.youtube.com/user/BogusNoise
Back to top
View user's profile Send private message Visit poster's website
mrand



Joined: Mar 30, 2014
Posts: 21
Location: Ottawa

PostPosted: Sun Mar 30, 2014 8:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi there,

I've been using this VCA circuit (thanks Nicolas!) for a few little projects, my first synth circuits, really, and am quite happy with it. But it must have shortcomings, since it's so wee... can anyone let me know what they are?
Back to top
View user's profile Send private message
nicolas3141



Joined: May 25, 2007
Posts: 138
Location: Christchurch, New Zealand

PostPosted: Sun Mar 30, 2014 11:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

The main improvement a more sophisticated circuit would offer is the option of a log/expo response. This one is linear only, which is what you want sometimes, but not all the time. A good VCA offers both options. In terms of a linear VCA this one should sound as good as any other.

Nicolas
Back to top
View user's profile Send private message
mrand



Joined: Mar 30, 2014
Posts: 21
Location: Ottawa

PostPosted: Mon Mar 31, 2014 6:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks, Nicolas.
A thought: Given that VCAs are frequently used to dynamically attenuate audio signals, using an EG with expo curves, wouldn't it make sense to pepper a great number of these simple, low cost, VCAs throughout one's (modular) synthesizer? (Most of the synths I've used dont seem to have enough VCAs.) Is there a reason this isn't common practice? Or maybe it is. Sorry if this is off topic.
Back to top
View user's profile Send private message
mrand



Joined: Mar 30, 2014
Posts: 21
Location: Ottawa

PostPosted: Mon Mar 31, 2014 7:52 am    Post subject: Reply with quote  Mark this post and the followings unread

I've done some more reading, and pretty much answered myself with "yes, good idea". I guess I just I wonder why people don't piggyback these on other circuits, all over the place, just for the convenience of having one nearby.
Back to top
View user's profile Send private message
bubzy



Joined: Oct 27, 2010
Posts: 539
Location: United Kingdom
Audio files: 50

PostPosted: Mon Mar 31, 2014 9:34 am    Post subject: Reply with quote  Mark this post and the followings unread

likely parts cost, to get a "good" VCA(linear/log&other fancy bits) you are looking at getting a nice OTA chip or perhaps even a purpose built VCA chip, while they are not bank-breakers, they can soon add up if you put them "all over the place"

but it is true, theres never enough VCA's
or VCO's
or LFO's
or ADSR's
or.......

*walks off mumbling*

_________________
_Richard_ Smile
Back to top
View user's profile Send private message
mrand



Joined: Mar 30, 2014
Posts: 21
Location: Ottawa

PostPosted: Mon Mar 31, 2014 9:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Okay, "nice OTA chip" might be the answer to my question. I'm sourcing from tayda, so all the parts for the simple Nicolas VCA are coming to three or four dollars. Granted, at least two jacks and possible inclusion of a pot will up the price, but is there something I should know about the ~$2 Lm13700s I'm using?
Thanks!
Back to top
View user's profile Send private message
bubzy



Joined: Oct 27, 2010
Posts: 539
Location: United Kingdom
Audio files: 50

PostPosted: Mon Mar 31, 2014 11:45 am    Post subject: Reply with quote  Mark this post and the followings unread

oh heh, I didn't look at the design, the lm13700 are nice ones Very Happy
_________________
_Richard_ Smile
Back to top
View user's profile Send private message
mrand



Joined: Mar 30, 2014
Posts: 21
Location: Ottawa

PostPosted: Mon Mar 31, 2014 1:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

So maybe this sdiy stuff can quite inexpensive, after all Smile

Thanks for your help.
Back to top
View user's profile Send private message
nicolas3141



Joined: May 25, 2007
Posts: 138
Location: Christchurch, New Zealand

PostPosted: Mon Mar 31, 2014 6:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

My experience is that generally the component cost for most circuits is pretty affordable. Where things get expensive tends to be more on the front panel - sockets, pots, switches, knobs, etc

Nicolas
Back to top
View user's profile Send private message
bubzy



Joined: Oct 27, 2010
Posts: 539
Location: United Kingdom
Audio files: 50

PostPosted: Mon Mar 31, 2014 11:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

nicolas3141 wrote:
My experience is that generally the component cost for most circuits is pretty affordable. Where things get expensive tends to be more on the front panel - sockets, pots, switches, knobs, etc

Nicolas


+1

_________________
_Richard_ Smile
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 2 of 2 [38 Posts]
View unread posts
View new posts in the last week
Goto page: Previous 1, 2
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