[Russtafarian]

I want to build a line level 24db per octave passive high pass filter to insert between my preamp and the amp driving the mid panels and tweeters of my VMPS RM30s.  Getting the caps and resistors is easy, but I'm clueless when it comes to inductors.

Any recommendations on what inductors I should use for this application and where to get them?  Depending on the crossover point I decide on, I'll need values in the range of 1 to 3 H.  Thanks.

Russ

[Speedskater]

1 to 3 Henry is an absolutely huge value!  You missed the "u" or "m" in front of the "H".  A 24dB per octave passive filter is a very difficult construction project most likely doomed to failure.  A critical piece of needed date is the input impedance of the amplifier. 

[JimJ]

Why not go active?

[richidoo]

http://sound.westhost.com/projects-3.htm

http://sound.westhost.com/project09.htm

Line level filter can be done without an inductor. To insure sufficient drive current to the amplifier, an active buffer stage may be necessary after the filter.

[Davey]

1 to 3 Henry is an absolutely huge value!  You missed the "u" or "m" in front of the "H".  A 24dB per octave passive filter is a very difficult construction project most likely doomed to failure.  A critical piece of needed date is the input impedance of the amplifier.

Nope, 1-3 Henrys would be about correct for a typical line-level crossover using inductors. 
In fact, Phil Marchand has a crossover in his selection just like this:

http://www.marchandelec.com/ftp/xm46man.pdf

I would suggest Googling for pot core bobbins and you should be able to find some appropriate inductors.

Cheers,

Dave.

[Scottdazzle]

Russ,

I went the passive route with my 30's too.  Roger Modjeski (Music Reference) made me a low pass "pot in a box" to insert between my preamp and the power amps.  The box uses two 1st order filters -- 1 at 280 Hz and 1 at 140 Hz to protect the tweeters & mids.  The pot control lets me balance the output to the tweeter/mid amp relative to the bass amp.  I rely on the coil in the speaker to control the woofer output since the bass amp operates full-range.  I am now considering these
http://store.hlabs.com/pk4/store.pl?view_product=9
to limit the input to the bass amp.

I'm sure your effort will be rewarded.  My approach is only a half-step to an active crossover, but it sounds better than a single amp with the built-in crossover active full-range.

Good luck!

Scott

[Russtafarian]

Thanks for the feedback folks.  Been off-line over the holiday, so I haven't been able to respond until now.

To answer the question "why not go active?", I am... for the bass.  I use an active analog pro sound crossover for stereo subs and for high and low passing the RM30 woofers.  What I want to avoid is running the mid/highs through the crossover since the opamp based unit noticeably colors and diminishes the sound.  Below 300Hz, using the active unit is a reasonable compromise because the gain in woofer control, and blending driver outputs to the room more than make up for the unit's coloration.  Above 300Hz, where all I need is a high pass filter, the sound quality of the active unit is not acceptable.

Davey, I tried searching for the kind of inductors used by Marchand and couldn't come up with anything.  Maybe I'll get the inductors and crossover boards directly from Marchand.

Scott, sounds like we're on the same trajectory regarding the RM30s.  Are the "pot in a box" filters in series to protect both Mid/Tweeter or is one filter for the midpanels and the other for the tweeter?

Right now I do have a 400Hz 1st order filter on the input of the Mid/Tweeter amp.  Since I removed the speaker's cap-coil high pass filter, the 1st order filter keeps the bass out of those midrange panels.  The link to those hlabs filters gave me the idea of using multiple 1st order filters to get a steeper crossover slope.  I'll have to experiment with that.

Thanks again.

Russ

[Scottdazzle]

Russ,

The "pot in the box xo" only crosses over at 280 Hz.  The VMPS crossover still handles the 6.9kHz crossover from the mids to the tweeter.  My speaker uses Auricaps which I assume are pretty good.   

Scott