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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Changing pots values
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jean bender



Joined: Feb 21, 2010
Posts: 139
Location: france

PostPosted: Tue Mar 29, 2011 7:29 am    Post subject: Changing pots values Reply with quote  Mark this post and the followings unread

hi everybody..

Most of schematics use pots which have values between 100k and 1meg.

I've got a huge stock of 50k pots, and i think it should be stupid to not use them, and buying other pots.

My question is : What should i do when i'm building an osc, for exemple, in order to have a "normal" response ?

yesterday i tried to make some osc from a 4093. It was working, but when i changed my pots for 1meg ones, for exemple, the coarse was much better with them than with 50k.

At the moment, i'm looking after typical osc : 0.1uf caps, 10k res with the pot in feedback loop...

I don"t think that i have to change caps values, since it's them which give the general pitch. Maybe using a bigger resistance ? In parallel of the pot ?

thanks for any trick !

cordially !

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slacker



Joined: Nov 18, 2007
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PostPosted: Tue Mar 29, 2011 10:06 am    Post subject: Reply with quote  Mark this post and the followings unread

The frequency of these oscillators is roughly 1/(resistance x capacitance) so if you make the resistance smaller you need to make the capacitor larger by the same amount to keep the same frequency.

If a design uses a 1Meg pot and a 0.1uF cap and you want to use a 50k pot you'd need to make the cap 20 times bigger, so you could use a 2.2uF cap. If there's a resistor in the feedback loop as well as the pot you need to make this 20 time smaller so something like 470 Ohm.
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jean bender



Joined: Feb 21, 2010
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PostPosted: Tue Mar 29, 2011 11:22 am    Post subject: Reply with quote  Mark this post and the followings unread

ok thanks, i think it will help me a lot !!

Where can i find some knowledge about the way to build osc like these ? i mean, this math theory ?

Well, thanks for all !!

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Kabzoer



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PostPosted: Thu Mar 31, 2011 4:33 am    Post subject: Reply with quote  Mark this post and the followings unread

http://www.datasheetcatalog.org/datasheets/270/108596_DS.pdf
i think the datsheet has the schematic, with formula, at page 3.
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jean bender



Joined: Feb 21, 2010
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PostPosted: Thu Mar 31, 2011 4:59 am    Post subject: Reply with quote  Mark this post and the followings unread

You're right !!

I oftently should look at these datasheets... lots of interesting things in these documents !

Wink

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Glitch-Militia



Joined: Apr 25, 2011
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PostPosted: Wed Apr 27, 2011 12:59 am    Post subject: Reply with quote  Mark this post and the followings unread

I have a question regarding this as well.

I have recently "slaughtered" a few large mixers for parts, thus I have about [1000] pots, mainly 10 KΩ logarithmic and linear.

Is it possible to use the linear 10 KΩ in the Baby10 sequencer instead of the 100KΩ and how would I do this ?
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tjookum



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PostPosted: Wed Apr 27, 2011 6:25 am    Post subject: Reply with quote  Mark this post and the followings unread

nice find!

And yeah, if you are using the potentiometers as a voltage divider to generate a control voltage from each step you can use any pot you like. I do recommend >10K just to be on the safe side.

A voltage divider works with the ratio of the resistance between pin1 and the wiper and pin2 and the wiper. Basically if the pot is turned 1/10th it means that the ratio is 1:9 and it will let 10% of the signal go through. Try ading a voltage divider as a volume control to a simple audio circuit, you will find that the value doesn't matter.

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Glitch-Militia



Joined: Apr 25, 2011
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PostPosted: Thu Apr 28, 2011 12:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks tjookum for an informative post.
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Glitch-Militia



Joined: Apr 25, 2011
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PostPosted: Fri May 06, 2011 12:40 am    Post subject: Reply with quote  Mark this post and the followings unread

tjookum wrote:
nice find!


As icing on the cake i also pulled:

2 x MN3005 BBD's

2 x MN3207 BBD's + 2 x MN3102

2 x NE570N Compandors

M5207L01 Dual VCA

Not counting the ridiculus amount of op-amps.

And I'm not even halfway checking the circuit boards for rare / expensive / interesting chips.
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tjookum



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PostPosted: Sat May 07, 2011 4:48 am    Post subject: Reply with quote  Mark this post and the followings unread

stop making the rest of us feel jealous Laughing .

One tip, never trow a board away unless you either stripped it bare of are sure that all the leftover components are useless. I stripped my share of boards and I've trown away very usefull parts because I just didn't know what they were.

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Psyingo



Joined: Jun 11, 2009
Posts: 248
Location: Canada

PostPosted: Sat May 07, 2011 8:17 am    Post subject: Reply with quote  Mark this post and the followings unread

tjookum wrote:
stop making the rest of us feel jealous Laughing .

One tip, never trow a board away unless you either stripped it bare of are sure that all the leftover components are useless. I stripped my share of boards and I've trown away very usefull parts because I just didn't know what they were.


and the addition to that tip:
always check the chip numbers for datasheets while you pillage those boards.

http://www.datasheetarchive.com is your friend.
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Glitch-Militia



Joined: Apr 25, 2011
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PostPosted: Sun May 08, 2011 7:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Psyingo wrote:


and the addition to that tip:
always check the chip numbers for datasheets while you pillage those boards.

http://www.datasheetarchive.com is your friend.


Uhmm yeah that's what I'm doing. No need stating the obvious.

I also forgot the 3-400 DPDT's
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-minus-



Joined: Oct 26, 2008
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PostPosted: Sun May 08, 2011 1:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Glitch-Militia wrote:

Uhmm yeah that's what I'm doing. No need stating the obvious.

I also forgot the 3-400 DPDT's


Wow! Shocked With all those pots you could build a pretty huge mixer! Idea
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