Behringer - BEQ700 Bass Graphic Equalizer  [schematic]

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modman
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BEQ700_MANUAL_ENG_Rev_A.pdf
Behringer - BEQ700 Bass Graphic Equalizer manual
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BEQ700_SCHEMATICS_REV_B.pdf
Behringer - BEQ700 Bass Graphic Equalizer schematic
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NickS
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Post by NickS »

Using a simple (non-Spice) calculation:

Code: Select all

Nominal	Calculated
freq   	freq
50	     49
120	    153
400	    394
500	    533
800	    746
4.5k	   4823
10k	    10526
Of course, tolerances will affect this but it's interesting that the "120Hz" filter should be that far out when they go to the trouble to specify a 92 nF cap for the "800 Hz" (calc 746 Hz). It would be interesting to see the curves.

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Andy2No
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Post by Andy2No »

NickS wrote:Using a simple (non-Spice) calculation:

Code: Select all

Nominal	Calculated
freq   	freq
50	     49
120	    153
400	    394
500	    533
800	    746
4.5k	   4823
10k	    10526
Of course, tolerances will affect this but it's interesting that the "120Hz" filter should be that far out when they go to the trouble to specify a 92 nF cap for the "800 Hz" (calc 746 Hz). It would be interesting to see the curves.
What was your calculation method, out of interest?

Here are some curves for mine, taken with an Android app called Spectrum Analyze, via a Behringer UCA202 USB audio interface fed with a white noise sample. The green line was live; the red line is remembered peaks.

As you can see, at full cut on all the sliders, it's all over the place. The best thing you can say is that with all sliders in the centre, it's pretty level.

It's hard to see much detail at low frequencies, with this method, so I wouldn't read too much into the apparent bass response. That's not really the issue.

The file names explain the conditions they were taken under.

The first two are with the EQ sliders all the way down, with Level full up in the first one, then centred in the second.
Behringer BEQ all cut (full level) vs white noise_2017_03_05_20_36_35.jpg
Behringer BEQ all cut, level centred_2017_03_05_20_52_02.jpg
The next one has all EQ sliders full up except the last/top one, which is full down:
Behringer BEQ all full but top full down_2017_03_05_20_46_34.jpg
Then all sliders full (if I've labelled that right - maybe not) - not sure where the level was:
Behringer BEQ all full_2017_03_05_20_46_14.jpg
Then all centred:
Behringer BEQ all zero (centred)_2017_03_05_20_50_20.jpg
Doing one at a time might be more instructive, but you get the idea. The app and the audio device are both very affordable.

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Post by Andy2No »

(No edit button?)

I used the white noise sample from here:

https://soundcloud.com/onlinetonegenerator

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NickS
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Post by NickS »

NickS wrote:Using a simple (non-Spice) calculation:
Of course, tolerances will affect this but it's interesting that the "120Hz" filter should be that far out when they go to the trouble to specify a 92 nF cap for the "800 Hz" (calc 746 Hz). It would be interesting to see the curves.
OK, I note that it's not 92 nF, it's 82 nF which brings the calculated frequency to 790 Hz. Not sure where I got that from, nor the values that gave me 153 Hz; the values on the Rev B schematic there work out to 125.
Today I used the gyrator calculator at http://www.muzique.com/lab/gyrator.htm. I thought I used that last time.

Code: Select all

Nominal	Calculated
freq   	freq
50	     49
120	    153X 125
400	    394
500	    533
800	    746X 790
4.5k	   4823
10k	    10526
They could have got closer using a 2400 pF 5% SMD cap for the 4.5k gyrator.

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