Help me understand filter design

veracohr · 10th December 2006, 10:07 PM

I'm not really sure if this is the right forum for this question. Sorry if it isn't, this is my first post.

I'm trying to build a phono preamp. I found a design online and built it, and it turned out to be highly distorted. Perhaps it was meant for a different kind of cartridge (don't ask me what I have, I don't know.)

So I searched around some more, but I decided that I'd rather try to design my own. It's kind of an in-over-my-head situation, but if I wanted to do it the easy way I'd just buy one.

The problem I'm having is with the RIAA filter network. There's a lot of examples online, and they pretty much all seem to be different. But I found a couple pages that explain things well enough for me to understand, and the book I've got (The Art of Electronics) helps too. But it seems about impossible to find explanations on how to make the zero points of the filter. Lots of information about the pole frequencies and how to calculate component values to get those poles, but I find almost nothing about how to zero the slope (that's probably the wrong terminology).

Can anyone point me to a good reference for understanding and designing filter poles and zeros? It's not enough for me to do a paint-by-number project. I want to understand what I'm doing.

moamps · 10th December 2006, 10:52 PM

You may wish to download this book. It has many useful things on filter design.
http://focus.ti.com/lit/an/slod006b/slod006b.pdf

This site offers a plenty of info on RIAA:
http://platenspeler.com/uk_index.php..._html/menu.txt

Regards,
Milan

andy_c · 10th December 2006, 11:09 PM

Quote:

Originally posted by veracohr
Can anyone point me to a good reference for understanding and designing filter poles and zeros? It's not enough for me to do a paint-by-number project. I want to understand what I'm doing.

If you click on my www link, there's a page there that gets into a lot of detail about the design equations for a specific type of active RIAA equalization using a single op-amp and feedback network. The equations for setting its poles and zeros are there, as well as how to set the nominal gain at 1 kHz.

mikeks · 11th December 2006, 12:08 AM

Excellent work, Andy!

andy_c · 11th December 2006, 04:38 PM

Thank you Mike.

veracohr · 11th December 2006, 10:30 PM

Thanks, I'll check those out soon.

10th December 2006, 10:07 PM	#1
veracohr diyAudio Member Join Date: Dec 2006	Help me understand filter design I'm not really sure if this is the right forum for this question. Sorry if it isn't, this is my first post. I'm trying to build a phono preamp. I found a design online and built it, and it turned out to be highly distorted. Perhaps it was meant for a different kind of cartridge (don't ask me what I have, I don't know.) So I searched around some more, but I decided that I'd rather try to design my own. It's kind of an in-over-my-head situation, but if I wanted to do it the easy way I'd just buy one. The problem I'm having is with the RIAA filter network. There's a lot of examples online, and they pretty much all seem to be different. But I found a couple pages that explain things well enough for me to understand, and the book I've got (The Art of Electronics) helps too. But it seems about impossible to find explanations on how to make the zero points of the filter. Lots of information about the pole frequencies and how to calculate component values to get those poles, but I find almost nothing about how to zero the slope (that's probably the wrong terminology). Can anyone point me to a good reference for understanding and designing filter poles and zeros? It's not enough for me to do a paint-by-number project. I want to understand what I'm doing.

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10th December 2006, 10:52 PM	#2
moamps diyAudio Member Join Date: Oct 2002 Location: Croatia	You may wish to download this book. It has many useful things on filter design. http://focus.ti.com/lit/an/slod006b/slod006b.pdf This site offers a plenty of info on RIAA: http://platenspeler.com/uk_index.php..._html/menu.txt Regards, Milan

11th December 2006, 12:08 AM	#4
mikeks Account Disabled Join Date: Jun 2004 Location: Animal farm	Excellent work, Andy!

11th December 2006, 04:38 PM	#5
andy_c Banned Join Date: Apr 2003	Thank you Mike.

11th December 2006, 10:30 PM	#6
veracohr diyAudio Member Join Date: Dec 2006	Thanks, I'll check those out soon.

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