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Old 8th April 2003, 12:50 AM   #1
Thunau is offline Thunau  United States
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Default Help needed with sourcing active crossover parts

Hi,
I recently started to visit here again after I got disqusted with Madisound board (for the n-th time, I might add). It's really refreshing to see civility and competence in a forum. I think I'll spend more time here from now on.

I noticed that the Pass Zen amp is enjoying a renessance. I have the original circuit board and propably will attempt to build it after some more pressing speaker projects are out of the way.

Right now my mind is on finishing of the active crossover for a 3 way Dynaudio 24W100/BG Neo8/Viva XT25 loudspeaker. I have two 3 way LR24 circuit boards from Elliot Sound in Australia. They are laid out for dual opamps. I have a tube of 5532's that I would like to incorporate in this project.
I should say that I'm using lspCAD pro and justMLS with calibrated B&K 4006 to measure and design.
My question is, when starting an active crossover project in lspCAD one is asked to enter constant values for key caps and resistors around which the rest is computed (given a target transfer function). The default values are 10k Ohm for LP and 10nF for HP filters. I would imagine that different opamps will perform optimally with different caps and resistors given the same transfer function. What are good starting values for 5532's? I'm shooting for crossover points at 600-800Hz and 3500-4000Hz and no higher than 2nd order slopes. Hopefuly I can achieve 1st order acoustic slopes at least in the mid/high section.
Also, what is a good brand (and source) of caps and resistors in this application?
Thanks in advance.
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Old 8th April 2003, 04:08 AM   #2
paulb is offline paulb  Canada
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Walt Jung suggests a higher opamp input impedance for these filters than you get with the NE5532. So I would think the lower the R, the better. However, I think that 10K is low enough.
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Old 8th April 2003, 04:34 AM   #3
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I am using Burr Brown (OK, Texas Instruments) OPA-2134 dual op-amps in my active crossover, and I like their sound a lot. (although with unity gain, most all modern op-amps are quite good) they also work well for active filters.

I would think that 10K sould be a good choice for any op-amp. I am crossing from panel to bass module at 160 Hz and with my cap choice, I am using 15K SIP resistor packs. You should be fine with the 10K values.

hope that helps,
Sheldon
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Old 8th April 2003, 04:36 AM   #4
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PS. This place kicks the living crap out of the mad-board.

The loudspeaker section alone has more breadth and depth than the mad-board will ever have. Then there's all the other sections...


Sheldon
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Old 8th April 2003, 01:12 PM   #5
bknauss is offline bknauss  United States
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Are you reffering to Madisound? I never found any real good in depth conversations over there. Just "will speaker X sound good?". Plus it was almost a carbon copy of the Parts Express forum.

Anyway, love this site. Caters to the people with some decent knowledge of electronics!
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Old 8th April 2003, 11:09 PM   #6
Thunau is offline Thunau  United States
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Thanks guys.
So, what is a good default cap value? The smaller the better?
And also, what's a good type/brand to use?
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Old 9th April 2003, 03:48 AM   #7
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I will probably be tarred and feathered for my choice:

I used 0.047 uF panasonic polyprop caps. they are 2% units and are cheap and to my ears sound good. I worked from the caps to the resistors. You only have a couple cap values in any given range. But over that same range (say 2x) you have a huge number of resistors. So I picked cap values, and then picked resistor values to achieve my desired crossover points. I was looking for a crossover point from about 40 Hz to about 500 Hz. So that's why my cap values seem huge to you.

I designed my crossover board to take SIP resistor packs. I then installed gold plated, machined pin, SIP sockets. I then set my crossover points by plunking in the appropriate SIP resistor packs in the sockets. The high pass uses two SIPs per channel and the bass uses one per.

Sheldon
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Old 10th April 2003, 05:05 PM   #8
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Default caps

some values I've found useful (at 1600 hz) are .0068 and 20kish resistors up to 3x that.
The 0068's are easily available at digi-key in panasonic polypros. I'd also get a pack of 0033's, to keep around. For the lower frequencies, of course, some higher values (probably simply 100nf) will be needed.
IT DOES NO GOOD WHATSOEVER TO DIS. OTHER FOLKS AT OTHER BOARDS! There are many, many people of good will willing to share their time (and materials) who hang out there!
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Old 11th April 2003, 10:15 PM   #9
Thunau is offline Thunau  United States
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"some values I've found useful (at 1600 hz) are .0068 and 20kish resistors up to 3x that.
The 0068's are easily available at digi-key in panasonic polypros. I'd also get a pack of 0033's, to keep around. For the lower frequencies, of course, some higher values (probably simply 100nf) will be needed."

Thanks for the recommendation. The whole reaseon for me asking this question is that I often see posts like;" 5532NE is a great opamp if the circuit is designed properly around it." I guess my question is then: " what makes a circuit designed for 5532 opamp good?" is it the choice of resistors and caps, or something else? If I plug in 5k as a starting value for resistors and compute the caps to get my crossover slopes, will it sound any different than 20k as a starting value? How about 100k, 1k, 63 Ohm? Do I need to do something to the feedback loop to achieve optimal performance?


"IT DOES NO GOOD WHATSOEVER TO DIS. OTHER FOLKS AT OTHER BOARDS! There are many, many people of good will willing to share their time (and materials) who hang out there!"

No need to shout. I din't dis anybody personally. There are many folks on Mad board who I respect a lot. But it seems that things get out of hand very easilly over there. Trolling is ever occurring and egos get out of hand. I still read it and sometimes post, but I find this forum to be a more friendly place, with good advise more common.
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