Charge Coupled Crossovers
Dramatically improve the sound of inexpensive capacitors.
Article By Jeff Poth
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It's a simple project, and there's a significant gain to be had- You can build a higher-end capacitor than you can afford by simply using quality inexpensive caps and charge coupling them. Commercial Mylar and poly caps are available very inexpensively from surplus houses like Apexjr and Madisound seems to have an endless supply of handy little 10uF yellow caps on their clearance page. Sure you need to buy twice as much, but if you shop carefully, you can come in quite a bit less expensive than even the cheapest "audio grade" cap from Solen, Erse, Clarity Caps, or whomever. So not only can you make a capacitor that will significantly outperform most models, you can do it in values that aren't necessarily available and would be extremely expensive. At the time of this writing, a single, not terribly good sounding, Solen Fastcap of 40uF is going for $16.28 at Parts Express. That's what it cost me to build a pair of superior audio capacitors with charge-coupling. So a 50% savings and better sound. Not too shabby!
There are a lot of locations for capacitors within a speaker crossover. Other locations in most systems are less appropriate as they're usually already biased with DC and the components are using them as DC blocking capacitors rather than AC filters, so in those cases they're effectively already charge-coupled. Below is a typical, simple crossover three way speaker – there are four caps in there! You can share a single supply/battery between all of them, since they're isolated by resistors.
So, that's it. I've found charge-coupling to dramatically improve the sound of inexpensive capacitors, and it's not very difficult or expensive to implement, so I can firmly recommend charge-coupling as a tweak for our people who know which end of a soldering iron is hot. Depending on the speaker and system it may require relocating crossovers outboard, but that's on a case-by-case basis. There are significant improvements in clarity, imaging, and listenability to be had, get to it kiddies!
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