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 Forum index » DIY Hardware and Software
Quick question about Baby 8 sequencer
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mubase



Joined: Mar 24, 2011
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PostPosted: Mon Jun 17, 2013 5:19 am    Post subject: Quick question about Baby 8 sequencer
Subject description: can i use....
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Hi. Very Happy

A kwikie...
I'm building another baby 8 sequencer on stripboard as per my design here:
http://electro-music.com/forum/topic-50071.html

Can I use 10K pots instead of the 100Ks for the step CV outputs?
Will it make a huge difference?

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johncronan



Joined: Feb 24, 2013
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PostPosted: Mon Jun 17, 2013 7:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

I can't tell for sure without a schematic, but if those pots are just setting a voltage (ie, the outsides are connected to power rails but the wiper goes into the circuit) then ordinarily it can't hurt to make them stiffer. You will use more power though. -John
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bubzy



Joined: Oct 27, 2010
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PostPosted: Tue Jun 18, 2013 12:23 am    Post subject: Reply with quote  Mark this post and the followings unread

what john said.

you will draw more current per output, you can fix this by putting a resistor in series with the input to the potentiometers.

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johncronan



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PostPosted: Tue Jun 18, 2013 12:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Just one little niggle about adding the resistance back in in series... I don't know about this particular case, but I wouldn't say this as a general principle. I mean ordinarily you're looking at a high impedance in the following stage, right? So you're going to have the V^2/R for each pot and that will predominate as far as the power goes. If the pot resistance is fixed, then could this power really be reduced without sacrificing range?
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bubzy



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PostPosted: Tue Jun 18, 2013 1:10 am    Post subject: Reply with quote  Mark this post and the followings unread

seems ok to me Smile just breadboarded it and there is no voltage drop when adding a resistor in series.

remember you measure voltage across a resistor, if you use a 1m or a 1k resistor the voltage will be the same.

therefore the range should not be affected by this.

also, you should be buffering after this stage anyway.

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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Tue Jun 18, 2013 4:10 am    Post subject: Reply with quote  Mark this post and the followings unread

scratch could you draw that out for me bubzy ?
The way I see it,. using a 10K instead of a 100K will increase the current draw by 10X (stll not very high though).
Putting a resistor in series would create a voltage divider together with the pot. So the voltage across the pot will be
lower and the range smaller.

Unless you mean adding a resistor to the wiper of the pot which would have no (or hardly) any influence on the current
through the pot which will still be 10x as high with a 10K compared to a 100K.

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elmegil



Joined: Mar 20, 2012
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PostPosted: Tue Jun 18, 2013 5:23 am    Post subject: Reply with quote  Mark this post and the followings unread

A resistor in series is going to change your voltage range because it will shift the voltage divider.
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bubzy



Joined: Oct 27, 2010
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PostPosted: Tue Jun 18, 2013 9:13 am    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
scratch could you draw that out for me bubzy


yup. to recreate my incredible circuit, you just grab any old resistor off the bench and write a reply to someones comment.
then later on after it has been questioned, you go upstairs and measure the resistance of said resistor.. then you realise it was 300 ohms.

ill just go and hide now Very Happy

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stewpye



Joined: Apr 30, 2009
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PostPosted: Fri Jun 21, 2013 12:23 am    Post subject: Reply with quote  Mark this post and the followings unread

The best thing to do is check the 4017 datasheet.
If you are running led's from the 4017 output they will be sinking most of the current so changing the post to 10k won't make too much difference. The maximum output voltage will be a little bit lower as it drops with increased output current. We'd really need to know what resistor values you are using for the LED's to determine the impact of changing the pot value.

Stew.
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