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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
40106 oscilator stability?
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commathe



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PostPosted: Fri Jul 26, 2013 5:23 pm    Post subject: 40106 oscilator stability? Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sat Jul 27, 2013 2:39 am    Post subject: Re: 40106 oscilator stability? Reply with quote  Mark this post and the followings unread

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.

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commathe



Joined: Jul 26, 2013
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PostPosted: Sat Jul 27, 2013 2:45 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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PostPosted: Sat Jul 27, 2013 9:34 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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commathe



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PostPosted: Sun Jul 28, 2013 2:27 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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PostPosted: Sun Jul 28, 2013 9:50 am    Post subject: Reply with quote  Mark this post and the followings unread

You should join Vdd and Vss with a cap that is as close to the Vdd pin as possible.
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commathe



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PostPosted: Sun Jul 28, 2013 7:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

Awesome, thanks!
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Cynosure
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PostPosted: Sun Jul 28, 2013 7:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

You're welcome. More info on bypass caps here:

http://www.seattlerobotics.org/encoder/jun97/basics.html

You should use them on every IC.
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JingleJoe



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PostPosted: Tue Aug 06, 2013 3:12 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

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