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I want to run one set of outputs from my pre-amp to my powered Velodyne sub-woofer with its variable crossover set at 80hz, and the other set of outputs using capacitors as high pass filters between my pre-amp and my main power amp. The Velodyne is set up with a L/R input from the pre-amp, and a L/R output to the power amp. I have heard that running a high pass filter into my amp will give me much cleaner sound since I am not running the full range through the subwoofer's internal crossover. Is this true? What make of capacitors should I get (I'm prepared to spend around $20 per capacitor)? What value of capacitors should I get to give me a high pass filter of 80hz?
Follow Ups:
If you already have capacitors in your amp, instead of adding new ones, simply change out the existing capacitors with ones of smaller value. This will avoid adding additional passive components in series with your midrange signal.
I high pass @ that frequency also, I made a small silver wire module that plugs into my tube amps with silver bullets. .022uf Vitamin Q at the moment. works to good. You can much higher spl also with out the distortion. I really like doing this on small fullragers in my hybrid 3 way active OB ..You might want to down load TCJ Filter Desighner..it is a really cool thing to have..it is like $12.00 or something close to it.I really like doing this with my 2-3-6 watters..
Doesn't the Velodyne have a high pass output already?
In response to awe-d-o-file, yes, it does have a variable high / low pass filter. However, what I'm trying to do is to keep all of the really important frequencies above 80hz away from the cheaper and older electronics in the Velodyne to get the best sound possible. The state of the art 0.022uF VH Audio TFTF V-Caps that I'll be installing into the inputs of my amplifier to serve as high pass filters above 80hz should give me much better sound overall, and I'll leave the Velodyne to do what it does best - pump out those low frequencies beneath 80hz. I subscribe to the less is more school, and one top grade capacitor should be much better than whatever is inside the Velodyne. A few people, including Keith Lockwood who responded to me today, seem to bear this theory out.
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......I remember reading some years back in Stereophile, I believe, of a formula to calculate for the cap value in a passive line level x-over with regards to the input impedence of the amp.Do U or anybody have the formula or remember which issue the formula was published in?
Cheers,
...F = 159155/RC, where F equals the filter point (= -3dB point) in Hertz, C = capacitance in microFarads, and R = resistance in Ohms.The cap goes in series with the signal and drives the load resistor.
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
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....if the filter calculator that is used for speaker level would accomodate line level as well.Cheers,
Thanks for your clear and concise info, Keith. My input impedance is 100K, so I'm looking at 0.02uF caps. Thanks for the tip on the V-Cap.
Try to put the capacitors as close to the power amp input as possible: even inside if you don't mind opening and modifying it.Also be sure to damp the capacitors against acoustic vibration. Cotton batting and Teflon thread-seal tape are handy materials that are also benign dielectrics for audio use.
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I checked out the reviews at VH Audio, and the bottom line is that these appear to be the best caps available unless one wants to to into three figures - the V-Cap TFTF is around $35... seems like money well spent since I've ordered them. I plan on installing them internally, and will use the cotton to isolate them from vibration as advised. Thanks again.
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Keith, what rolloff slope would this cap mod provide?Also, any thoughts on how this method compares to the inline RCA plug type HPF's available from ACI, Harrison Labs (FMODs) etc?
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