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Question on RC high pass filter

 
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rickrob



Joined: 19 Oct 2011
Posts: 1083
Location: Massachusetts

PostPosted: Wed Apr 06, 2016 1:22 pm    Post subject: Question on RC high pass filter Reply with quote

I'm building a very small practice amp to take with me when I travel-- It has a 10W @8 Ohms Class AB amp circuit, based on a TDA2030.
I have a speaker on the way, and the response is 75Hz to 13Khz. I'm thinking of adding a high pass filter to limit the low frequency
to the speaker and roll off at around 70 Hz-- so I don't bottom out the speaker. That should still allow me to play standard tuning and
drop D at 73Hz. My values for the filter are 220 Ohm and 10 uF

Question is: Should I install the filter on the input or output?

If I install on the output, I think I'll need at least a 10W resistor which is physically large (49mm length).
If I install on the input, I can use a regular resistor-- but I'm concerned that putting the filter there will change the signal from the
guitar besides filtering lower frequencies.

AFAIK, the cap will tend to act more like a short circuit as the frequency increases-- Maybe it won't affect anything then?
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Vic Vega



Joined: 15 Mar 2010
Posts: 1882
Location: SW Idaho

PostPosted: Wed Apr 06, 2016 1:59 pm    Post subject: Reply with quote

I can think of two reasons to do it before: 1) he components would be smaller and probably less expensive, and 2) if you're going to amplify a signal you'd want it cleaned up first, so you're only amplifying what you want pushed through.
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tangelolemon



Joined: 26 Jan 2009
Posts: 2691
Location: Brooklyn, NY

PostPosted: Thu Apr 07, 2016 7:14 am    Post subject: Reply with quote

a more elegant way might be to spec an output transformer that rolls off at ~60 Hz or so. Shouldn't be too hard to find. Maybe a touch more expensive, but certainly simpler and better to implement.
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rickrob



Joined: 19 Oct 2011
Posts: 1083
Location: Massachusetts

PostPosted: Thu Apr 07, 2016 12:34 pm    Post subject: Reply with quote

Thanks guys-- The cabinet has limited space, so I'll try it on the input and see how it goes.
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