Bass Preamp, Analogue Filters

davebassics · 4th March 2012, 02:18 PM

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?

DF96 · 4th March 2012, 02:36 PM

Are we supposed to guess the circuit?

Speedskater · 4th March 2012, 04:21 PM

Why don't you test your test procedure and setup by using a commercial product?

davebassics · 4th March 2012, 05:57 PM

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?

4th March 2012, 02:18 PM	#1
davebassics diyAudio Member Join Date: Oct 2011	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?

4th March 2012, 04:21 PM	#3
Speedskater diyAudio Member Join Date: Sep 2002 Location: Lakewood, Ohio	Why don't you test your test procedure and setup by using a commercial product? __________________ Kevin

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4th March 2012, 02:36 PM	#2
DF96 diyAudio Member Join Date: May 2007	Are we supposed to guess the circuit?

4th March 2012, 05:57 PM	#4
davebassics diyAudio Member Join Date: Oct 2011	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?