Behringer - BEQ700 Bass Graphic Equalizer  [schematic]

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Behringer - BEQ700 Bass Graphic Equalizer  [schematic]

Postby modman » 25 May 2015, 15:51

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Re: Behringer - BEQ700 Bass Graphic Equalizer

Postby NickS » 31 Mar 2016, 10:54

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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Re: Behringer - BEQ700 Bass Graphic Equalizer

Postby Andy2No » 22 May 2017, 18:19

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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Re: Behringer - BEQ700 Bass Graphic Equalizer

Postby Andy2No » 22 May 2017, 18:22

(No edit button?)

I used the white noise sample from here:

https://soundcloud.com/onlinetonegenerator
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Re: Behringer - BEQ700 Bass Graphic Equalizer

Postby NickS » 08 Aug 2018, 20:47

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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