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Caps in crossovers? |
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kingkwak 
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Joined: 08 October 2010 Location: sussex Status: Offline Points: 810 |
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 Topic: Caps in crossovers?Posted: 22 August 2011 at 8:35am |
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What do capacitors do in crossovers? How will it affect the sound if I replace mine with one of a different value?
I have a crossover from a turbosound txd121 with a blown capacitor and Im having trouble trying to locate a replacment. Its an ELYTONE 25uF 100V NP.
Also, what would cause it to blow.
I know a bit about what im doing, but some of the electronic side of things Im still trying to learn, so will be looking for a book on crossovers that will help, any ideas?
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To much power? NEVER.
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MessyM2k8
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Joined: 29 October 2008 Location: Norwich Status: Offline Points: 690 |
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Posted: 22 August 2011 at 9:22am |
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Pasi
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Joined: 25 April 2010 Location: Knutsford Status: Offline Points: 2732 |
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Posted: 22 August 2011 at 9:26am |
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Capacitors are 1st order (6dB per octave) high pass filters and their value together with impedance determines the corner frequency. Higher value means lower frequency if impedance stays same.
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Tony Wilkes
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Joined: 02 August 2004 Location: West Midlands Status: Offline Points: 4840 |
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Posted: 22 August 2011 at 9:48am |
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http://www.falconacoustics.co.uk/alcap-claritycap-solen-audio-capacitors/capacitors-audio-crossover-nonpolarised-electrolytic-polypropylene-polycarbonate-polythene-1200uf-3900uf/alcap-25-00uf-100v-dc-high-power-electrolytic-capacitor-nonpolarised-reversible-series.html
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www.forteaudio.eu - BMS - db-Mark Processors - Lexon (SAE)
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stevie
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Joined: 16 March 2008 Location: Dorchester Status: Offline Points: 425 |
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Posted: 22 August 2011 at 10:08am |
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If you replace it with a different value it will change the sound. It's not likely but it could also change the system impedance. How much depends on what you replace it with. Ten percent either way should be OK at a pinch.
The usual reason for a cap to blow is too much power, but it could simply be that it wore out or failed. To make sure it doesn't happen again replace it with a polypropylene cap. These are usually rated at 250 to 400V. I've never had any problems with 100V mylars personally, but I'd advise against using 100V electrolytics unless cost is an issue or it's a low power speaker. I don't know of any books that deal with passive crossovers in any depth. The Loudspeaker Cookbook is probably as good as it gets. |
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Centauri
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Joined: 29 November 2004 Location: Newcastle Aus Status: Offline Points: 1792 |
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Posted: 22 August 2011 at 12:46pm |
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I've only just replaced all the caps in a couple of old EAW crossovers which were also 100V rated - for a big amp, that voltage is not enough, and they can fail with quite spectacular results. I use 250V polypropylene caps. For 25uF, you can use a 20uF in parallel with 4.7uf, or 2x 10uF & 1x 4.7uF all in parallel to get the approximate value (24.7uF total is close enough to 25uF in practice). It does mean you will probably need to stack them to get enough room, and possibly may even require a cable tie to hold them down.
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kingkwak
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Joined: 08 October 2010 Location: sussex Status: Offline Points: 810 |
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Posted: 22 August 2011 at 1:36pm |
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Thanks for the replys so far.
Can you tell me how a higher/lower value will affect the sound? and what part does it affect? ie is it the crossover slope itself or the high pass overall?
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To much power? NEVER.
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audiomik
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Joined: 06 April 2010 Location: Bath, UK Status: Offline Points: 2962 |
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Posted: 22 August 2011 at 1:56pm |
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Different values of capacitor will affect both the slope and frequency of a passive crossover depending upon the difference in values.
As a general rule, lower values will increase the crossover 3dB point but as the ratio of the inductor to capacitor value is changed; this will also alter the slope and phase relationship. Greater values of capacitor will lower the 3dB frequency and slope accordingly. OK somewhat of an over simplification; but in general terms what to expect. However differences of 10% are often found acceptable for capacitors due to tolerances in components. Hope this answers your question Mik |
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markie
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Joined: 31 October 2005 Location: Sunny Liskeard. Status: Offline Points: 4570 |
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Posted: 22 August 2011 at 1:56pm |
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I have some Turbosound 23.3uF caps which are marked 250v but I am reliably informed (by the manufacturer) that they are 400V spec. They are almost certainly near enough to use as replacements.
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If it's got wheels or tits it's gonna cost a fortune
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stevie
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Posted: 22 August 2011 at 2:00pm |
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It depends what the function of the cap is. The manufacturer will
hopefully have spent a lot of R&D time designing the crossover and
coming up with that value. Rather than worrying about it and making your
life difficult, why don't you just replace the original with another
25uF? As Centauri says, you can easily parallel up smaller values to make the one you want.
Edited by stevie - 22 August 2011 at 2:01pm |
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audiomik
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Posted: 22 August 2011 at 2:29pm |
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For reference, Capacitors are rated either in Volts AC or DC.
Here are some comparative working voltages for Metalized Polyester Film types: 63Volts DC is 40Volts AC (equivalent to 200 watts into 8 ohms max amplifier size) 100Volts DC is 63Volts AC (equivalent to 500 watts into 8 ohms max amplifier size) 160Volts DC is 90Volts AC (equivalent to 1000 watts into 8 ohms max amplifier size) 250Volts DC is 160Volts AC (equivalent to 3200 watts into 8 ohms max amplifier size) 400Volts DC is 250Volts AC (equivalent to 7800 watts into 8 ohms max amplifier size) Now for reliability, the 'next voltage up' is best to use for any amplifier size. Also explains Markie's post with the 2 different Voltage ratings for the same component Mik |
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markie
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Posted: 22 August 2011 at 2:54pm |
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As I understood it he prints them as specified by the client but regardless makes all his caps to 400v spec.
Either way they are a lump of a cap.
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If it's got wheels or tits it's gonna cost a fortune
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