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In Reply to: RE: Input coupling caps as high-pass filter posted by KanedaK on February 02, 2017 at 11:34:26
Of course this makes sense, and is what I use, along with the acoustic roll off, in my own system as the entire high pass filter to my mid/treble amps and speakers. Be aware that any electrical filter will act in conjunction with existing speaker system response. In other words, if there is already a filter as part of the speaker system, it has a transfer function that will be affected by whatever other filters you add. You don't state what the 400hz filter's slope is, but it will be affected by the 300hz filter at the amp input.Just as a goal of speaker xovers is to set any filters outside a two octave window of flat response, so should this amp filter be designed accordingly. I wouldn't try anything higher than 100hz. You still will be removing a considerable portion of low frequency energy demand from your amp. For a 100Hz corner freq, you would need a .03uF cap into 50k ohms. Standard cap value is .033uF, which would give 96Hz corner.
And yes, the Jupiter copper foil/wax paper caps are superb for what you're doing. There might be better caps, but I have not heard them.
Peace,
Tom E
berate is 8 and benign is 9
Edits: 02/03/17Follow Ups:
Damn.
I followed your advice and bought a bunch of NOS EROMAK polycarbonate film/foil on the big ayction site.
but I misread and made a mistake: they are 0,33uF, not 0,033uF :( so stupid.
So i guess tht would give me a useless corner frequency of 9,6Hz, right?
Maybe I can cancel my purchase. Except if I can use them for something else, but the value is too small for a CD player output coupling cap, right?
By the way the passive high-pass filter at speaker level is 6B/octave.
That's happened to everyone at least once! Don't sweat it. We all waste more money than we should on this obsession. How much are they worth, a few bucks? You could keep them around for trying as bypass of other caps.
Eventually, if this configuration works properly and sounds good, you will need to spend serious money on really good copper foil caps because the entire mid/high signal will pass through them.
What is the configuration of the current passive filter? Please supply complete, specific information. Why do you want to add another filter if you're already shelving low freq's by 6db/octave below 400hz?
Peace,
Tom E
berate is 8 and benign is 9
I want to add another filter because the 400hz high-pass is after the amplifier.
The amp is fed full range and I wanna remove some low frequencies to put less stress on it.
All is well, I've just ordered some Russian PIO caps, apparently the "best" ones.
I'm curious to try them - besides filtering the lows, they will most likely sound better than the Arcotronic caps I have now.
You didn't mention the value of the PIO caps you ordered. If you use the .033uF (that's 33 nano) as I recommended, the input to your amp will be down 1/4db @ 400hz, 1/2db @ 300, 3db @ 100, 9db @ 50, 15db @ 25hz, so that is a decent reduction of low freq energy without significantly impacting existing filter slopes, although the response of the speakers will be affected somewhat in that their lowest frequencies will be reduced as well. This will probably have a greater impact on perceived clarity than reducing input to the amp. All small speakers distort when tasked with reproducing low frequencies, whereas most decent amplifiers do not.
Depending on what it is now, you might need to tweak the response of the bass xover/amp by raising the xover point (not terribly difficult), adjusting the slope (pretty complicated), or merely increasing the volume a bit (easy!) to compensate for the increased roll off of low freq's from the mids.
I doubt that Russian PIO is the best because there is no such thing (I assume that's why you used quotes), although they may be the best value. Improving on the sound of Arcotronics caps is no tall order, so you should be pleased. If you care to eventually invest more, I guarantee you would be even more pleased with copper foil.
Peace,
Tom E
berate is 8 and benign is 9
When my speakers were fully passive, they relied more on natural roloff of the various horns to create the slopes, than on the first order crossovers - mainly there to stop the robust Atlas midrange driver from frying. So I don't think whatever happens lower than 400Hz is making really much difference ( wére not talking extreme slopes here).
The reason I went active on the low pass is because I changed bass horns, and the new ones don't roll off so quick above 400Hz - I had to have a steeper slope than 6dB/oct because it sounded like crap.
But my 8 watts amp is now driving the high pass only and there's 50watts on the bass horns, and I like the added power for sure!
But yes I ordered 0,033uF as you said :)
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