Simple passive mid frequency cut eq. Anyone?

Hi,

I'd like to make a simple passive mid frequency "cutter" to use when I track drums. I have a Great River MP2-NV that often end up on bassdrum and snare. Would be nice to have a simple curcuit to plug into the insert of my MP2-NV just to take out some mids.

I have read some great information on this site about passive eq's. From that I've come to that it should be possible for a newbie like myself to track down a few inductors and start to experiment a little.

But of course, all help will be appreciated. :roll:

Thanks

Richard

Check out the manual for the White 4220 octave-band EQ. It shows a good straightforward implementation of a cut-only EQ.

http://www.whiteinstruments.com/discontinued.htm

It doesn't give component values, but those can be calculated easily enough.

Am I right in assuming that you want to cut in the 200Hz-400Hz region? How much cut do you need? The values of inductor and capacitor, as well the values of the pot and shunting resistor, are determined by the center frequency, bandwidth, amount of cut desired and driving and load impedances. (White's </= 1k source and 10K load arrangement works well with most modern equipment).

How does it work? A parallel resonant circuit has a high impedance at its resonant frequency, but a low impedance to signals at other frequencies. The parallel resonant circuit forms the upper leg of a frequency-dependent voltage divider; the load impedance provides the lower leg. The pot and resistor across the resonant circuit control both the bandwidth of the circuit and the amount of signal that's allowed to "bypass" the frequency-selective circuit, thus controlling the amount of cut.

The cool thing about this simple arrangement is that frequencies outside the "cut" range pass through with little attenuation.

Thanks,

This is great!

You are right about the 200Hz-400Hz region. Sometimes I take out a lot. :grin:

I'll do some calculating tomorrow.

Thanks again


Richard

I almost never use any eq in recording - especially drums, where any eq-ing of a mic induces a massive phase shift relative to the other mics. i normally use at least 16 mics on the average kit, and I like to keep my phase coherent . . . . Anyhows, should you want a nice passive eq, I cannot recomend the Helios highly enough, for just about anything. The schemo is available here

http://www.danalexanderaudio.com/recorder.html


You could use just about anything for the gain make-up. I use mine every day. btw.



Andy P

http://www.groupdiy.com/index.php?topic=2534&postdays=0&postorder=asc&start=60#img_3819

All the way down you will find CJ´s Pultek with mid cut mod.

And take a look at the Pultec MEQ5 EQ section:

http://www.gyraf.dk/gy_pd/pultec/meq5.gif

Jakob E.

I think you guys are getting carried away; look at the original post again. He's talking about maybe one band, perhaps sweepable or switchable, cut-only. A one-section version of the White will do this with minimum insertion loss at frequencies outside the cut band--so "gain makeup" is not needed. The other EQs you guys are suggesting are unnecessarily complicated for the task at hand, and all introduce insertion loss across the band and require an additional amplifier in the path.

[quote author="gyraf"]And take a look at the Pultec MEQ5 EQ section:

http://www.gyraf.dk/gy_pd/pultec/meq5.gif

Jakob E.[/quote]


That mid cut section looks interesting, but I'd like all the steps to be between 200Hz and 700Hz. That is if I can find an inductor that is tapped in that sort of way.


Thanks again to all


Richard