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commathe
Joined: Jul 26, 2013 Posts: 153 Location: Beijing
Audio files: 5
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Posted: Fri Jul 26, 2013 5:23 pm Post subject:
40106 oscilator stability? |
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Hey everyone. I've been a long time lurker here and I've decided to bite the bullet and stop making stompboxes and start on a Lunetta style modular.
Breadboarding away last night though I came across a weird phenomenon. When I ran the 40106 on 4.5v it behaved very well and all 6 oscillators were very stable. On 9v however they wobbled really irregularly between two close pitches. What could have been causing this? I actually really liked the effect and when I build a module I kind of like the idea of being able to make an oscillator less stable at the turn of a dial.
Is it possible that the resistors I used to sum the signals together weren't big/high enough to hold back the current under 9v but were under 4.5v? |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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Posted: Sat Jul 27, 2013 2:39 am Post subject:
Re: 40106 oscilator stability? |
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interesting, you might be right about the resistors. I don't know what value you used but if they are low then it could cause some instability.
and/or maybe you used a 9V battery that was a bit empty.
If you want to create instabillity you can do this by adding a starve pot, which will let you limit the current, causing irregular behaviour. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
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commathe
Joined: Jul 26, 2013 Posts: 153 Location: Beijing
Audio files: 5
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Posted: Sat Jul 27, 2013 2:45 am Post subject:
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The resistors were 100k and the battery was new. Running them off 4.5v was actually off the same battery. I have a power module thingy I made so I didn't have to do voltage dividers every time that I wanted to use an op amp!
I tried voltage starving too, but the results were different. Very fun in a different way. I have a 100uf cap on my power module which meant that I got some very fun effects from unplugging the battery. |
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Cynosure
Site Admin
Joined: Dec 11, 2010 Posts: 966 Location: Toronto, Ontario - Canada
Audio files: 82
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Posted: Sat Jul 27, 2013 9:34 am Post subject:
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Here are several pieces of advice:
1. Always run CMOS chips from a power regular if possible. Running them directly from a battery can cause stability issues, especially as the battery power gets low.
2. Always use bypass caps on EVERY chip. Use a 0.1uF cap and plug it is as close as possible to the Vdd and Vss pins. This will smooth out any power fluctuations in the power supply that is being delivered to the chip.
3. Choose your oscillator caps wisely. Some are better suited than others for oscillators. http://www.analogrules.com/capacitors.html _________________ JacobWatters.com |
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commathe
Joined: Jul 26, 2013 Posts: 153 Location: Beijing
Audio files: 5
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Posted: Sun Jul 28, 2013 2:27 am Post subject:
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Thanks for the advice! Though to clarify, do you mean that I should join Vdd to Vss with a cap - or rather that I should use a two caps (one for Vdd and one for Vss)? |
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Cynosure
Site Admin
Joined: Dec 11, 2010 Posts: 966 Location: Toronto, Ontario - Canada
Audio files: 82
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Posted: Sun Jul 28, 2013 9:50 am Post subject:
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You should join Vdd and Vss with a cap that is as close to the Vdd pin as possible. _________________ JacobWatters.com |
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commathe
Joined: Jul 26, 2013 Posts: 153 Location: Beijing
Audio files: 5
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Posted: Sun Jul 28, 2013 7:32 pm Post subject:
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Awesome, thanks! |
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Cynosure
Site Admin
Joined: Dec 11, 2010 Posts: 966 Location: Toronto, Ontario - Canada
Audio files: 82
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JingleJoe
Joined: Nov 10, 2011 Posts: 878 Location: Lancashire, England
Audio files: 14
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Posted: Tue Aug 06, 2013 3:12 am Post subject:
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I've found that even on a good power supply the oscillators can interfere with each other within the IC.
My thinking would be don't use a 40106 for precise stability. general stability, probably good but with multiple oscs on the IC you can have frequency locking problems if the feedback resistance is low. _________________ As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"
Green Dungeon Alchemist Laboratories |
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