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Old 12th February 2010, 05:51 AM   #1
jaste is offline jaste  Sweden
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Default wtb: Active crossover pcb's for two way project

I want to split my Seas L18rnx and my Vifa XT25 actively and needs pcb's!
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Old 12th February 2010, 11:08 PM   #2
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Default Marchand XM-1

Quote:
Originally Posted by jaste View Post
I want to split my Seas L18rnx and my Vifa XT25 actively and needs pcb's!
The Marchand Electronics XM-1 would work nicely for this purpose. You will need to implement baffle step somehow as well, but that might be as easy as a resistor and cap modification to the input to create a frequency dependent voltage divider...

Here are some links to the XM-1:
product: XM1 Electronic Crossover Network
manual: http://www.marchandelec.com/ftp/xm1man.pdf

-Charlie
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Old 13th February 2010, 12:08 AM   #3
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I haven't used but interesting reading
Linkwitz-Riley Electronic Crossover
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Old 13th February 2010, 12:19 AM   #4
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Have you considered making them yourself? All in all PCBs are not that hard to make and an active crossover is decent as a first project to ease you into board design - through hole parts are rather large so you can use thickish traces, normally you don't need to use any gain at all, and if you do it's only minimal, so a perfect layout isn't required for acceptable performance.

The freeware version of Eagle should allow you to make boards large enough for each channel. So you'd need two of them. You'll have to learn how to use the program, it's not hard, but it will take a bit of time to get used to.

Linkwitzlab contains all the circuit diagrams you will need for this.

If this was me making them I'd make them like so.

First you need an input buffer, Linkwitz details how to build one of these. You're going to want the input impedance to be around 50-100k, so it's easy to drive. R in his buffer picture sets the input impedance. C in relation to R sets the frequency the 1st order highpass makes, blocking any DC. It's worth setting the frequency perhaps to 20-30 hz, this will help reduce the low frequency content sent to the woofer. Obviously it's not going to give much useful output at the frequencies, so any signal around here is just wasted power and cone excursion. It will also protect the woofer from any cone flapping/damage if some really low frequency is sent it's way.

For the woofer circuit you're going to want -

A shelving low pass to compensate for bafflestep. Linkwitz describes how to calculate values for the circuit.

A notch filter to kill the resonance from the L18s bell like qualities. Again Linkwitz describes how to implement one of these. But please bare in mind you absolutely need an opamp after the notch filter circuit. So in other words you have to place another buffer after the notch filter circuit, but this time it doesn't really need the C or R in his first diagram.

A 24 dB/oct Linkwitz-Riley low pass filter. This is obvious and to do it right you need to measure your system.

Place the low pass filter last in the chain, this will help to reduce any hiss that the other stages might have happened to create.

The tweeter circuit will be fairly simple. You're going to want a 24 dB/oct Linkwitz-Riley highpass filter followed by two-three delay stages. Linkwitz again describes how to calculate the delay requirement, this is only a rough calculation mind you and measurement should be used to fine tune the system. Finally the tweeter will require a variable gain stage, this should be version A and should be the last thing in the circuit, with the high pass before it and the delay stages before that.

Keep most resistor values below around 50k and scale the capacitors based on that. The resistor to ground in the notch filter may require a larger size. Using 5nF film caps should be good for the low/high pass sections and delay stages. If you want you can use trim pots for the resistors as this allows you to easily alter xover frequencies etc. In fact I recommend you use trim pots, especially on the delay stages because they usually require fine tuning to get right. Also decouple each opamp power pin to ground with a 0.1uF cap. A X7R ceramic will do fine for decoupling, to keep costs down and also to save on board space. I like using 1206 surface mount style caps for bypassing as they really help you save on space and keep the boards less cluttered.

Texas Instruments data sheets for opamps are quite useful in explaining how to best use their devices.

This may sound like a lot but once you've broken it all down, it's simply a combination of several very simple things.

I've been thinking about adding a section to the wiki on how to make PCBs because it seems like one of those things that every DIYer should be confident in doing. Being able to easily fabricate your own PCBs opens up a lot of possibilities and also gives you far more options of what you could do next!
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Old 15th February 2010, 09:07 PM   #5
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Join Date: Feb 2010
Default Digital Crossover or Active crossover?

Do you have an old computer laying around. Get a multichannel sound-card with assignable ASIO routing and make it yourself. Full digital active amplification with the added bonus of room correction and can even store your music/ movies on the pc. These can be built for any budget. Very cool. click this page.

or this page

Speaker crossover, how to build the best possible crossover affordably

hope it helps! mikal
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Old 15th February 2010, 10:05 PM   #6
jaste is offline jaste  Sweden
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Join Date: Dec 2005
Location: Stockholm
Hi all!
I have been sketching on a pvb in eagle light but I feel I'm stacking the projects and just want to get things done! But maybe I should give eagle light a little more time and get the thumb out of my... thanks for everything! Kepp an eye out for my eagle questions!
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Old 15th February 2010, 10:16 PM   #7
40 watt is offline 40 watt  Canada
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Quote:
Originally Posted by 5th element View Post
Have you considered making them yourself? All in all PCBs are not that hard to make and an active crossover is decent as a first project to ease you into board design - through hole parts are rather large so you can use thickish traces, normally you don't need to use any gain at all, and if you do it's only minimal, so a perfect layout isn't required for acceptable performance.

The freeware version of Eagle should allow you to make boards large enough for each channel. So you'd need two of them. You'll have to learn how to use the program, it's not hard, but it will take a bit of time to get used to.

Linkwitzlab contains all the circuit diagrams you will need for this.

If this was me making them I'd make them like so.

First you need an input buffer, Linkwitz details how to build one of these. You're going to want the input impedance to be around 50-100k, so it's easy to drive. R in his buffer picture sets the input impedance. C in relation to R sets the frequency the 1st order highpass makes, blocking any DC. It's worth setting the frequency perhaps to 20-30 hz, this will help reduce the low frequency content sent to the woofer. Obviously it's not going to give much useful output at the frequencies, so any signal around here is just wasted power and cone excursion. It will also protect the woofer from any cone flapping/damage if some really low frequency is sent it's way.

For the woofer circuit you're going to want -

A shelving low pass to compensate for bafflestep. Linkwitz describes how to calculate values for the circuit.

A notch filter to kill the resonance from the L18s bell like qualities. Again Linkwitz describes how to implement one of these. But please bare in mind you absolutely need an opamp after the notch filter circuit. So in other words you have to place another buffer after the notch filter circuit, but this time it doesn't really need the C or R in his first diagram.

A 24 dB/oct Linkwitz-Riley low pass filter. This is obvious and to do it right you need to measure your system.

Place the low pass filter last in the chain, this will help to reduce any hiss that the other stages might have happened to create.

The tweeter circuit will be fairly simple. You're going to want a 24 dB/oct Linkwitz-Riley highpass filter followed by two-three delay stages. Linkwitz again describes how to calculate the delay requirement, this is only a rough calculation mind you and measurement should be used to fine tune the system. Finally the tweeter will require a variable gain stage, this should be version A and should be the last thing in the circuit, with the high pass before it and the delay stages before that.

Keep most resistor values below around 50k and scale the capacitors based on that. The resistor to ground in the notch filter may require a larger size. Using 5nF film caps should be good for the low/high pass sections and delay stages. If you want you can use trim pots for the resistors as this allows you to easily alter xover frequencies etc. In fact I recommend you use trim pots, especially on the delay stages because they usually require fine tuning to get right. Also decouple each opamp power pin to ground with a 0.1uF cap. A X7R ceramic will do fine for decoupling, to keep costs down and also to save on board space. I like using 1206 surface mount style caps for bypassing as they really help you save on space and keep the boards less cluttered.

Texas Instruments data sheets for opamps are quite useful in explaining how to best use their devices.

This may sound like a lot but once you've broken it all down, it's simply a combination of several very simple things.

I've been thinking about adding a section to the wiki on how to make PCBs because it seems like one of those things that every DIYer should be confident in doing. Being able to easily fabricate your own PCBs opens up a lot of possibilities and also gives you far more options of what you could do next!
Excellent post! I just downloaded the freeware version of Eagle 5.7

A how-to wiki on the board process would probably be appreciated by those, like me, on a learning curve. A simple mic pre-amp would probably be first on my list...something simple.

New software for evening decihering...I'm doomed I tells ya!
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Old 15th February 2010, 11:31 PM   #8
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Quote:
Originally Posted by 40 watt View Post

New software for evening decihering...I'm doomed I tells ya!
We've all been there My first PCBs were a disaster, they were just about good enough for what I wanted to use them for - so I considered them a success. Sub standard chemicals and raw PCB material were partially to blame.

Now however I can make PCBs good enough to use the smallest of surface mount components with a 100% success rate. I say 100% cause I've not had any fail, yet - except for my stupidity - where I forgot to remove the backing on the double sided tape with a double sided board. I went to turn the PCB over to expose the other side and the board just slid out... well you don't do that one twice.
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Old 15th February 2010, 11:40 PM   #9
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Quote:
The Marchand Electronics XM-1 would work nicely for this purpose
I'm sure it will be working beautifully! this is the way to go if you like building stuff ( I do ) $40+power supply+some kind of enclosure+all connectors, pots,.......+ your time!!!! ( how much is you time?)
I have been using Behringer CX 3400 fantastic value! ( it was $99 shipped) and I do not feel any need to look for "better one" it adds nothing to the sound.

Vadim
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Old 16th February 2010, 09:26 PM   #10
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You're welcome to a pair of PCBs I've no further use for,and about to bin.They're from an Electronics Australia kit built long ago. Only need bipolar power for the 4 op-amps in dual L-R configuration,tho remember Butterworth being an option. You choose, and your XO frequency using the documentation supplied. Need a tidy-up, but you'd be quickly in action. Email me if interested.
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