Quick, simple question about crossovers

[VolumetricSteve]

If you are going to rebuild the crossover, I would use polypropylene caps. Electrolytic caps are a bad idea in crossovers. You can get non polarizing electrolytic types, but I still would not use them.

That's interesting, why do you suggest polypropylene? Why are electrolytic caps a bad idea in crossovers?

These must be non-polarizing, they don't appear to be marked with a cathode or anode, only the PCB has symbols on it indicating polarity.

I went out and got some 63/37 Rosin-Core stuff, that should do it I think.

Before I go out and buy anything else, Is it possible to just take (for example) the 50V 18uF cap, in there and replace it with a polypropylene one that was also rated 50V 18uF? Or does the fact that it's polypropylene mean that I need to apply some formula to find the right characteristics in order to replace a different type of capacitor? (in my case, Electrolytic)

I'm guessing not, but I like to ask questions first, shoot later.....also I can't go back to the store until tomorrow.

Also, here's this:

My speaker drivers are shown by the 4 Ohm resistors pointing inward of the schematic.

Tweeter response:
http://i49.tinypic.com/23sahqf.jpg

Woofer response:
http://i48.tinypic.com/29mwsk4.jpg

All together now:
http://i46.tinypic.com/1z9kt4.jpg

Given what the manual for the speakers says, I think those readings are indicating that the crossover is doing its job...surprisingly well.

Nothing much below 200Hz, 200-2.3KHz goes to the Woofer, 2.3KHz-20KHz go to the Tweeter.

 

[TLS Guy]

That's interesting, why do you suggest polypropylene? Why are electrolytic caps a bad idea in crossovers?

These must be non-polarizing, they don't appear to be marked with a cathode or anode, only the PCB has symbols on it indicating polarity.

I went out and got some 63/37 Rosin-Core stuff, that should do it I think.

Before I go out and buy anything else, Is it possible to just take (for example) the 50V 18uF cap, in there and replace it with a polypropylene one that was also rated 50V 18uF? Or does the fact that it's polypropylene mean that I need to apply some formula to find the right characteristics in order to replace a different type of capacitor? (in my case, Electrolytic)

I'm guessing not, but I like to ask questions first, shoot later.....also I can't go back to the store until tomorrow.

Also, here's this:

My speaker drivers are shown by the 4 Ohm resistors pointing inward of the schematic.

Tweeter response:
http://i49.tinypic.com/23sahqf.jpg

Woofer response:
http://i48.tinypic.com/29mwsk4.jpg

All together now:
http://i46.tinypic.com/1z9kt4.jpg

Given what the manual for the speakers says, I think those readings are indicating that the crossover is doing its job...surprisingly well.

Nothing much below 200Hz, 200-2.3KHz goes to the Woofer, 2.3KHz-20KHz go to the Tweeter.

That crossover is first order to the woofer, with a zobel and additional impedance compensation. The high pass to the tweeter is second order with an unusual L-pad configuration.

electrolytic caps have linearity problems, and values change over time. Good quality crossover do not use electrolytic caps.

 

[VolumetricSteve]

So I've constructed another crossover out of parts I salvaged from the system's main board and soldered into a little board I got at radio shack....so far it sounds ok, it freaks out a bit under heavy load but it's also not amplified yet, also, I had my soldering iron out for quite some time, I'd be surprised if I didn't cause heat damage to the caps. No real matter, I was banking on getting polypropylene ones anyway.....but some questions about that:

Where is the best place to get them? DigiKey doesn't seem to have exactly what I'm looking for.

Do they have to be exactly "polypropylene" or can they be Metalized Polypropylene Film too?

Most importantly, is there a place online where I can just get a hand-full of them? I find a lot of places sell by lots of hundreds or thousands.


Another note on the way my crossover sounds: I've been listening to it carefully now for a few hours, did some test with only the twetter, and only the woofer, they both sound "ok" the crossover is clearly sending the right frequencies to the right drivers, however, sometimes the sound seems a bit....wet...or really it sounds like a capacitor is discharging tiny bursts of static into the sound path...is it likely it's some other part of the crossover, or is it a pretty clear diagnosis of electrolytic cap + too much heat upon installation? Also, for it to produce that particular kind of distortion, there has to be a LOT of stress, like a full range of vocals plus a really deep and strong beat, plus a lot of sharp, precise high range tones. (which is another reason I'm leaning towards damaged caps)

cheers

 

[TLS Guy]

So I've constructed another crossover out of parts I salvaged from the system's main board and soldered into a little board I got at radio shack....so far it sounds ok, it freaks out a bit under heavy load but it's also not amplified yet, also, I had my soldering iron out for quite some time, I'd be surprised if I didn't cause heat damage to the caps. No real matter, I was banking on getting polypropylene ones anyway.....but some questions about that:

Where is the best place to get them? DigiKey doesn't seem to have exactly what I'm looking for.

Do they have to be exactly "polypropylene" or can they be Metalized Polypropylene Film too?

Most importantly, is there a place online where I can just get a hand-full of them? I find a lot of places sell by lots of hundreds or thousands.


Another note on the way my crossover sounds: I've been listening to it carefully now for a few hours, did some test with only the twetter, and only the woofer, they both sound "ok" the crossover is clearly sending the right frequencies to the right drivers, however, sometimes the sound seems a bit....wet...or really it sounds like a capacitor is discharging tiny bursts of static into the sound path...is it likely it's some other part of the crossover, or is it a pretty clear diagnosis of electrolytic cap + too much heat upon installation? Also, for it to produce that particular kind of distortion, there has to be a LOT of stress, like a full range of vocals plus a really deep and strong beat, plus a lot of sharp, precise high range tones. (which is another reason I'm leaning towards damaged caps)

cheers

You have to use expensive high grade caps for crossovers like Solen caps.

I get my crossover parts from Madisound

I really can't speculate on your problems. May be your circuit is stressing the amp severely and causing damage. It really will be impossible to help you with this long range.

 

[VolumetricSteve]

Yeah, the sound issue is something I'll just have to work out, I'm willing to bet it's a lot of things, the distinct lack of any real amp (basically what TLS guy suggested) crappy caps, poor handling, etc

The site TLS guy showed me seems pretty nice, the caps I'd need, the set of four wouldn't be too horribly expensive, and I might give those a shot sometime soon (because I'd want to improve both crossovers equally)

Some of those capacitors are just nuts, Mundorf....just....Mundorf...


so for those of you still out there, I consider the matter of the recreation of that crossover to be completed for design purposes. - I'll go back through the thread and hit the "thanks" button where appropriate.

I only have two general crossover questions remaining at this point in time:

if you have a 40uF cap, and a 7uF cap, you put them in parallel to combine the values into 47uF, right?

When using inductors on a crossover, should they be kept apart from eachother, or does their proximity to one another not effect the output?

Additionally, I am curious to hear what folks have to say about op amps, setting them up, powering them, enclosures, volume knobs, and everything else that goes into building a halfway decent chip-amp.

I'd like to get my hands on two OPA627s, but they're pretty far out of my price range unless someone knows of a place that gives out samples. I'm also guessing that particular chip is superfluous for my immediate needs. (i'm assuming my cabinet/crossover/drivers aren't good enough to really warrant the need of such a high end chip)

or even more basic, if someone knows of a tutorial or guide that goes over the basics to building something like this:
http://diyaudioprojects.com/Chip/Nanoo/

Or maybe you built your own from scratch and think it's the coolest thing since sliced bread. I want to know about it.

I'd be thrilled to read whatever looks good.

One thing I've seen so far that makes me particularly nervous is the amount of voltage being used for some of these chip-amp power supplies, outputting like 25 or 35 volts. I don't have a feel for what kinds of AC voltages exist in most audio signals, say for example in normal cheap desktop speakers, the junky kind that would come with a new computer. What kinds of voltages would someone expect to see there? What would be horribly unusual, but realistic/possible?

Thanks again to everyone pitching in.

 

[TLS Guy]

Yeah, the sound issue is something I'll just have to work out, I'm willing to bet it's a lot of things, the distinct lack of any real amp (basically what TLS guy suggested) crappy caps, poor handling, etc

The site TLS guy showed me seems pretty nice, the caps I'd need, the set of four wouldn't be too horribly expensive, and I might give those a shot sometime soon (because I'd want to improve both crossovers equally)

Some of those capacitors are just nuts, Mundorf....just....Mundorf...


so for those of you still out there, I consider the matter of the recreation of that crossover to be completed for design purposes. - I'll go back through the thread and hit the "thanks" button where appropriate.

I only have two general crossover questions remaining at this point in time:

if you have a 40uF cap, and a 7uF cap, you put them in parallel to combine the values into 47uF, right?

When using inductors on a crossover, should they be kept apart from eachother, or does their proximity to one another not effect the output?

Additionally, I am curious to hear what folks have to say about op amps, setting them up, powering them, enclosures, volume knobs, and everything else that goes into building a halfway decent chip-amp.

I'd like to get my hands on two OPA627s, but they're pretty far out of my price range unless someone knows of a place that gives out samples. I'm also guessing that particular chip is superfluous for my immediate needs. (i'm assuming my cabinet/crossover/drivers aren't good enough to really warrant the need of such a high end chip)

or even more basic, if someone knows of a tutorial or guide that goes over the basics to building something like this:
http://diyaudioprojects.com/Chip/Nanoo/

Or maybe you built your own from scratch and think it's the coolest thing since sliced bread. I want to know about it.

I'd be thrilled to read whatever looks good.

One thing I've seen so far that makes me particularly nervous is the amount of voltage being used for some of these chip-amp power supplies, outputting like 25 or 35 volts. I don't have a feel for what kinds of AC voltages exist in most audio signals, say for example in normal cheap desktop speakers, the junky kind that would come with a new computer. What kinds of voltages would someone expect to see there? What would be horribly unusual, but realistic/possible?

Thanks again to everyone pitching in.

Yes in parallel caps you add the values. In series you sum the reciprocals.

Yes, you need to keep inductors apart and put them at right angles. OP amps are preamp chips and not for powering speakers.

There are IC power amps, but they are not something you want. Discrete transistor output stages are better.

Hypex have some good and interesting class D amp modules that are suitable for making active speakers.

As to voltage you have to have enough volts to produce the power. It takes 65 volts to deliver 100 watts at 4 ohms and 90 volts to deliver 100 watts at 8 ohms. Supply rail voltages in the map will need to be a little above those numbers.

Quite honestly a forum like this is not a place to get your education. You need to research some text books, or better yet enroll at University.

 

[Swerd]

TLS Guy has answered most of your questions. I'll add a little more info.

Polypropylene caps and metalized polypropylene caps are terms that seem to be used interchangeably. Madisound is a good source. Another is Parts Express. I am told that the Dayton MPP caps sold by PE and the Bennic MPP caps sold by Madisound are made by the same manufacturer in Taiwan. They seem to be very good.

Yes inductor coils generate an electro-magnetic field and you should follow some general practices about locating them on a crossover board. See this link. Scroll down to the diagram.

You also might find the tips in this link helpful.

 

[VolumetricSteve]

http://www.troelsgravesen.dk/coils.htm

that link was both educational and entertaining, I must have laughed for five minutes at "Never do this"

The other links were also very helpful, just not as amusingly worded.

I agree that this forum most likely isn't the best source for the information I need, I'm ok with textbooks, I'm not ok with university. I've done 4 years of that, I'm set for a while. I'm actually more than ok with textbooks.

I'm open to any and all suggestions there, too.

Thanks all around.