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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Simple Low pass resonant filter for your lunetta
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efabric



Joined: Jan 05, 2012
Posts: 19
Location: Caen, France

PostPosted: Mon Mar 26, 2012 7:30 am    Post subject: Simple Low pass resonant filter for your lunetta Reply with quote  Mark this post and the followings unread

Hello,

I found a long time ago this schematic on the squarewaveparade website :
http://thesquarewaveparade.com/images/srlpf.jpg

It's a 1 opamp low pass filter.

I'm not sure, but I think therr's a little mistake in the In and Out jacks ground. Don't the input and output must be decoupled with capacitors ?
The virtual ground in the power supply (4,5v) is directly linked to the ground output and input.

I think it's false no ?
Thank you.

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Last edited by efabric on Tue Mar 27, 2012 12:33 am; edited 1 time in total
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Psyingo



Joined: Jun 11, 2009
Posts: 247
Location: Canada

PostPosted: Mon Mar 26, 2012 9:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Yep, that's a classic sallen-key filter. Replace the dual gang pot with two vatrols for simple voltage control. That's my favorite filter topology.
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richardc64



Joined: Jun 01, 2006
Posts: 609
Location: NYC
Audio files: 25

PostPosted: Mon Mar 26, 2012 10:30 am    Post subject: Re: Simple Low pass resonant filter for your lunetta Reply with quote  Mark this post and the followings unread

efabric wrote:
The virtual ground in the power supply (4,5v) is diretly linked to the ground output and input.

It's fine, as long as the 9V that powers it isn't used to also power something that expects -9V to be ground -- in other words, single-supply.

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efabric



Joined: Jan 05, 2012
Posts: 19
Location: Caen, France

PostPosted: Tue Mar 27, 2012 1:05 am    Post subject: Reply with quote  Mark this post and the followings unread

It's a little bit strange...

I'm planning to build my modular lunetta with various units : 5v CMOS and ?V opamp based analog circuits.

What is the good way for everything to work together ?

I have a nice working radial transformer regulated 10V power supply in my bench, and 5V regulators in my spare parts.

Do you thik I can use this 0V, +10V and +5V to power up my opamps ?
Can I use the same +5V to power the CMOS modules and the virtual ground of the opamps ? Is there a risk of parasitic digital noise in the analog path ?

Can you show me a diagram with the interconnections and the decoupling stages ?

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