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Old 4th March 2012, 02:18 PM   #1
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Default Bass Preamp, Analogue Filters

I've just got the chance to sine sweep my preamp I've been designing and building, over all im relatively happy with the results. There are a few issues. There seems to be a fair bit of ripple (from the power supply?) and the bass EQ has an interesting phase response.

The bass eq isnt +/- 12dB at 100Hz as it was designed, it instead does about +/- 5dB @ 100Hz. What is interesting is that when boosted, a approx 10dB drop appears at around 200Hz and when cut, a 10dB boost at 200Hz.

Does this make sense? I've attached a plot of what I described.

Screen shot 2012-03-02 at 20.12.26.png

Any thoughts on this?
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Old 4th March 2012, 02:36 PM   #2
DF96 is offline DF96  England
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Are we supposed to guess the circuit?
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Old 4th March 2012, 04:21 PM   #3
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Why don't you test your test procedure and setup by using a commercial product?
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Old 4th March 2012, 05:57 PM   #4
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My apologies, I've attached a copy of the schematic now. The simulation kicks up the same fuss as the sine sweep, must be a problem with the design.

image3.jpg

There are 8 filters on the schematic (2 versions of the same 4 band). The bass response in question is the one 3rd down on the left.

It's part of a uni project, deadline is Friday so just looking to get rid of these last few niggles.

As far as I am aware, we don't have the ability to use a commercial product for testing Frequency Response. I was shown this one device, not sure what it was but the academics suggested just using spectrafoo instead.

Can anyone offer advice?
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