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Always wanted to build an active speaker but put off by the exorbitant price of commercial crossovers? Well now help is at hand. For 20pounds you can simply build the circuit kit described here and you're ready to go. All you need is a pair of stereo amps and a signal source. As an audio engineer of 35years standing I know that the only good sounding speakers are active. But going active usually requires spending big in the equipment department. Really all you need is a good filter and a spare stereo amp. As the tweeter channel only needs a few watts of power this spare amp doesn't need to be expensive either.
If you check out the net you'll find lots of active crossovers for sale. Many use esoteric technology but all are overpriced and unsuitable for experimenters. So here I will introduce a new concept for audio experimenters, the core kit. I believe it's counterproductive to try sending heavy items overseas. Especially as most can get the heavy and expensive parts locally and at a lower price. It makes sense then to design high quality kits which can be operated by a wide range of locally available power supplies. By locally I mean everywhere with a mains supply . The circuits are designed to operate from battery eliminator type plug in power supplies. Current requirement is 20mA. If plug in supplies, or the mains aren't available the circuit can be operated from batteries, a car battery is ideal.

Similarly a basic housing is provided. If the builder wants more he can make his own arrangements locally. The payoff is less expense and higher performance for the customer and, hopefully, higher sales for us. Why go active? Audiophiles know that so called passive speakers, those driven from a single power amp passive filters will never sound as good as an active speaker. Putting a passive filter in series with the speaker drivers will rob the drivers of the full damping factor of the amplifier driving it. The result, muzzy sound. Furthermore most of the energy in music occurs below 1kHz so a single amplifier can be driven into overload passing the unwanted high frequencies distortion components into the tweeter via the passive crossover. In the active system the tweeter will be driven from a separate amp so that even if the woofer amp is overloading no damage can be caused to the tweeter and the whole system will still sound sweet.
Another advantage of the active system is that the required response curves are easily generated by standard filter stages and are independent of speaker parameters. Anyone who has tried to design passive crossovers will be well aware of the difficulties, and compromises, involved.

Step 1: GETTING THE PARTS

Getting the parts. A full circuit diagram and component list for this stereo filter is available from my website http://www.macaulayaudio.co.uk

<p>Could you replace R4,R5,R6 and R7 with pots?</p>
<p>so, if I want a cutoff around 300 hz ALL those 4 resistors would be about 53Kohm? Is there any easy way to get that value? a 50K + a 3 K in series?</p><p>I've built kits, but nothing on a breadboard - how do I figure out how to lay it all out properly (and minimizing jumper wires)??</p>
<p>you can muck about with the resistor values. However in this case use the nearest value 51k. Audibly you won't hear any difference between the calculated value and nearest value. The difference, 4% is within the tolerance of the capacitors. Hope this helps.</p>
hola no entendi para que me puede servir :S
Sorry picopop, could you let me have that in English and i'll try and answer it!
Hi thanks for that.<br>Is there an equivalent opamp to the TL074 my local store has discontinued them and im having a bit of trouble locating them
The TL074 is the simplest device to work with as it contains 4 op-amps in one device. Try for a TL84 that will work as well. If you really cant get a TL0 device you could try a LM324. Most places still stock the 74's though, try Maplin or Rapid electronics they stock them.
Hi can you tell me what the value of capacitors are and what type, I cannot quite make out if its nano or micro
Sorry, I suppose the drawing is a little small. Anyhow its nf not pf
Hi there, is it possible to create a variable x-over for a subwoofer?<br><br>Thanks =)
Hi UnKnOwN_FS, Yes it's possible but would require another instructable! If you can pin down the specific frequency you require then you can use the circuit as is. For example, a 100Hz rolloff could be produced by making C2/3/4 and 5 100nf and using 16k for R4/5/6/7. (15k would do if you cant get the 16ks. Hope that helps)
I was hopping i could change the cutoff frequency with some sort of potenciometer from 300hz or so to as low as it can get.. The sub is a 12&quot; 300 watt RMS @ 4 ohm, and its now running at fullrange on a Yamaha AV receiver..
Sorry about the websitebeing down. The link should work now I've got it back up
Is there another link. The present one is not working. <br> <br>Thanks
The site http://www.macaulayaudio.co.uk does not load..

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Bio: Freelance audio designer. Into valves and hybrid gear. Dabbles in astronomy.
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