new EQ for tuning floor monitors

Here is a schematic of the EQ that I'm building for my small FOH rig.


The bottom circuit has a "Q" adjustment.

The design was pulled from the "Art of Electronics" and various web sources. It is a bootstrapped bridged differentiator. It will be a 1RU box 2 channels of 8 sweepable bands. I made an Excel spreadsheet to calculate what the freq. ranges will be. This is a cut only EQ. Also when using the Q control as Q is increased maximum attenuation is decreased. Q should have a range of 0.3 to near 50. Changing C4, C5 and C6 will change the overall freq. range. All the caps must be the same value and preferably 2% for best performance.

I know most people here won't need this kind of EQ but some might find it interesting.

cheers,
James

This topology seems to be usefull, but not well known. I consider it for a passive notch filter for distortion measurements. Can you post the "various web resources" you have for this design? I wasn't able to unearth too much of this, thanks.

Samuel

[quote author="Samuel Groner"]This topology seems to be usefull, but not well known. I consider it for a passive notch filter for distortion measurements. Can you post the "various web resources" you have for this design? I wasn't able to unearth too much of this, thanks.

Samuel[/quote]

You're right, there isn't much out there. Here's what I've got.

http://www.geofex.com/Article_Folders/EQs/paramet.htm
(look at the bottom of the page)

http://members.shaw.ca/roma/nine.html

http://home.pacbell.net/lengal/ip/60hzfilt.pdf

http://www.national.com/ms/LB/LB-5.pdf

http://www.discovercircuits.com/A/a-filter-notch.htm
This last page has a bunch of good articles. Though not all of them are about this particular topology. All of the online info I came across refers only to the bootstrapped twin T and not the bridged differentiator. I got that from pages 280 and 281 of the Art of Electronics.

I still have no idea how to calculate for the Q of the circuit in either of the variants I posted. But I did discover using my spreadsheet calculator that the "freq. adj." pot needs to be a reverse log taper. I have my spreadsheet set up so that when you enter values for C, RV1, R2A, R2B, and degree of rotation of RV1 it will calculate the value of R1 and give the frequency. As I played around with the degree value I noticed that at the bottom of the range the freq. changed very little but as I approached the top the freq. changed much more for the same percent of rotation. Now, that being said my sheet treats the pot as a linear taper and I have no idea as to how I can set it up to be a rev log function. If you would like to have a copy of this spreadsheet pm me and I'll send it your way.

cheers,
James

Hey bigugly, i have been trying to PM you, but your inbox is full!

Sansamps use such for the midscoop.