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nicolas3141
Joined: May 25, 2007 Posts: 185 Location: Christchurch, New Zealand
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Posted: Sun Nov 04, 2012 5:15 pm Post subject:
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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. |
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Bogus Noise
Joined: Jun 03, 2009 Posts: 65 Location: Sheffield
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Posted: Mon Nov 05, 2012 12:35 am Post subject:
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That's great advice, thanks
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 |
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Bogus Noise
Joined: Jun 03, 2009 Posts: 65 Location: Sheffield
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Posted: Tue Nov 06, 2012 9:52 am Post subject:
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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 |
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mrand
Joined: Mar 30, 2014 Posts: 56 Location: Yukon and London Ontario
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Posted: Sun Mar 30, 2014 8:37 pm Post subject:
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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? |
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nicolas3141
Joined: May 25, 2007 Posts: 185 Location: Christchurch, New Zealand
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Posted: Sun Mar 30, 2014 11:20 pm Post subject:
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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 |
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mrand
Joined: Mar 30, 2014 Posts: 56 Location: Yukon and London Ontario
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Posted: Mon Mar 31, 2014 6:05 am Post subject:
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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. |
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mrand
Joined: Mar 30, 2014 Posts: 56 Location: Yukon and London Ontario
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Posted: Mon Mar 31, 2014 7:52 am Post subject:
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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. |
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bubzy
Joined: Oct 27, 2010 Posts: 594 Location: United Kingdom
Audio files: 64
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Posted: Mon Mar 31, 2014 9:34 am Post subject:
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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_ |
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mrand
Joined: Mar 30, 2014 Posts: 56 Location: Yukon and London Ontario
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Posted: Mon Mar 31, 2014 9:55 am Post subject:
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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! |
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bubzy
Joined: Oct 27, 2010 Posts: 594 Location: United Kingdom
Audio files: 64
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Posted: Mon Mar 31, 2014 11:45 am Post subject:
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oh heh, I didn't look at the design, the lm13700 are nice ones _________________ _Richard_ |
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mrand
Joined: Mar 30, 2014 Posts: 56 Location: Yukon and London Ontario
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Posted: Mon Mar 31, 2014 1:21 pm Post subject:
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So maybe this sdiy stuff can quite inexpensive, after all
Thanks for your help. |
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nicolas3141
Joined: May 25, 2007 Posts: 185 Location: Christchurch, New Zealand
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Posted: Mon Mar 31, 2014 6:17 pm Post subject:
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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 |
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bubzy
Joined: Oct 27, 2010 Posts: 594 Location: United Kingdom
Audio files: 64
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Posted: Mon Mar 31, 2014 11:12 pm Post subject:
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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_ |
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did_poutrator
Joined: Jul 02, 2007 Posts: 6 Location: toulouse
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Posted: Thu May 07, 2015 3:59 am Post subject:
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hello, I just finished the VCA part, it works well and I was wondering if it's possible to add an LED before or after Q1?
I have not tested yet and I prefer to ask first.
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[LM324>------|Q1
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led
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R
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gnd
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could this work? |
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nicolas3141
Joined: May 25, 2007 Posts: 185 Location: Christchurch, New Zealand
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Posted: Thu May 07, 2015 12:41 pm Post subject:
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Yes, or between IC1a and IC1b. The voltage in both places will usually be negative so the led will have point away from ground.
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[LM324>------[LM324>
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led
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^
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R
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gnd
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Or after Q1 you could add an led (no resistor) in series with Q1 collector. This will limit the headroom (so probably not such a good idea after all) and you will have to use a high efficiency led, but it would start glowing with any CV. Whereas the led+R to ground will only start glowing with more than 1-2 V of CV (blue/white is worse than red/yellow in this regard) |
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killingzoe
Joined: Jun 14, 2016 Posts: 1 Location: berlin
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eeling
Joined: Apr 29, 2019 Posts: 2 Location: United Kingdom
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Posted: Fri Jun 07, 2019 11:52 am Post subject:
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Can anyone doodle me up a diagram of the wiring?? |
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eeling
Joined: Apr 29, 2019 Posts: 2 Location: United Kingdom
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Posted: Wed Jun 26, 2019 8:52 am Post subject:
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Glide side working totally fine, VCA side making not a hiss nor peep with audio, cv, etc. Where should I begin looking for issues? |
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tinfoilcat
Joined: Apr 16, 2019 Posts: 8 Location: Stockholm, Sweden
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Posted: Fri Jul 05, 2019 7:11 pm Post subject:
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eeling: I guess you are the one I responded to on Reddit, hope it helped!
I noticed an error in the stripboard layout, pin 5 should not be bridged to the V+ pin! The 10K resistor should be between pin 2 and V+. The schematic is correct. I made a video showing mine and talking a bit about the design: https://www.youtube.com/watch?v=NdxPAccjdoU
I want to thank Nicholas for the awesome designs that he shared!
And one more caveat: Don't be like me, remember to connect the output pin (5 or 12) to the buffer input (pin 7 or 9) if you are building the simpler VCA from this thread. |
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