Passive Mastering EQ

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I have now carried out a range of tests on the low frequency end of the EQ using the custom inductor supplier by Sowter. Here are the results:

30Hz boost and cut:

30_Hz_Boost.jpg


30_Hz_Cut.jpg


I was initially concerned about the 30Hz boost only having a Q of 0.3 but the curve actually looks pretty good.

Here is 50Hz boost and cut:

50_Hz_Boost.jpg


50_Hz_Cut.jpg


60Hz

60_Hz_Boost.jpg


60_Hz_Cut.jpg


80Hz:

80_Hz_Boost.jpg


80_Hz_Cut.jpg


100Hz:

100_Hz_Boost.jpg


100_Hz_Cut.jpg


140Hz:

140_Hz_Boost.jpg


140_Hz_Cut.jpg


160Hz:

160_Hz_Boost.jpg


160_Hz_Cut.jpg


200Hz:

200_Hz_Boost.jpg


200_Hz_Cut.jpg


240Hz:

240_Hz_Boost.jpg


240_Hz_Cut.jpg


400Hz:

400_Hz_Boost.jpg


400_Hz_Cut.jpg


480Hz:

480_Hz_Boost.jpg


400_Hz_Cut.jpg


480Hz:

480_Hz_Boost.jpg


480_Hz_Cut.jpg


725Hz:

725_Hz_Boost.jpg


725_Hz_Cut.jpg


870Hz:

870_Hz_Boost.jpg


870_Hz_Cut.jpg


They all look good to me. I just need to find out why the actual boot/cut is not quite the expected value but this could be as simple as the load presented by the  Scarlett 2i2. Notice to cut is less affected than the boost because it is lower impedance. lastly here is a pic of the array of capacitors I used in these tests. As you can see some of them are quite big and a few cases needed three caps to get the right value:

basscaps.jpg



Cheers

Ian


 
ilfungo said:
Great!!!
which software have you used for this tests?
It is a free program called REW which stands for Room EQ Wizard.

https://www.roomeqwizard.com/

It has a lot of features for measuring rooms but it also has an excellent spectrum analyser that is great for audio measurements. Plus, it has a built in signal generator. For EQ measurements I set this to white noise and just check the spectrum to get the frequency response. It runs on Windows, Mac and Linux.

It can also measure distortion and noise. All you need is a decent audio interface to your computer. I use a Scarlett 2i2.

Cheers

Ian
 
dagoose said:
Any progress? Just curious  8)
I have just finished the PCB layout for the higher bands EQ boards. Expecting prototypes in a couple of weeks. I am about to start laying out the low frequency PCB now I know the Sowter inductor works as I expected.

Cheers

Ian
 
supersonic said:
Breadboard it? Hard to get a more simple circuit  :)

Oh, yes the breadboard has all five bands on it. I will take a pic later today and post it here.

Edit: Here is the pic showing all five bands connected (just a single frequency on each). The custom Sowter is on the far left.

Cheers

Ian
 

Attachments

  • 5bandbreadboard.jpg
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Hi Ian, a bit off topic but what ELMAs are these?

"81-124n" ?

Am I reading correct? Are they 04 series and if so, what Torque?

thanks!
w
 
Thank you Ian! Although I don't quite understand the difference between these and their 04 series (other than the vertical PCB of course)  :)
 
Ian, 
If you wanted to mount switches off board for say a stereo ganged version would flying leads of a few inches be a problem?
 
Gold said:
Ian, 
If you wanted to mount switches off board for say a stereo ganged version would flying leads of a few inches be a problem?

That should be fine. Unlike my other passive EQs, this one operates at a relatively low impedance so short runs to switches ought to be OK.

Cheers

Ian
 
very interested,  if i could fit this in a 1u id be thrilled.  with a discrete makeup gain.  focued on clean  no color.  i assume you can take on any amp you want for makeup?
 
buschfsu said:
very interested,  if i could fit this in a 1u id be thrilled.  with a discrete makeup gain.  focused on clean  no color.  i assume you can take on any amp you want for makeup?

That should be possible. You would have to remote the individual EQ boards if you wanted to squeeze two channels into a 1U. Any amp that loads it with no more than 10K will be fine for gain make up.

Cheers

Ian
 
sr1200 said:
Any plans for filters on the top and bottom?  ;D ;D

If you mean HPF and LPF then the answer is no - that ought to have been taken care of before mastering!!

But it might not be too hard to add them at the end of the chain.

Cheers

Ian
 
hello ian.

im doing a mouser order right now and made some search on ferrite cores again. i made a new rough blueprint of an inductor of 750mH and some taps.

with a PM50x39 (BIG MAMA) core and 0.35mm wire, each layer should contain 63 turns. rolling an inductor with whole layers could give us taps of:
40 or 63mH
90mH
202mH
302mH
490mH
and what ever we want in the end.

of course when its done it my something else. cores are -+3% in tolerance.
this are with center holes so they can stand some more amplitude.

still interested?

dont forget to check the size of the cores!
 
5v333 said:
hello ian.

im doing a mouser order right now and made some search on ferrite cores again. i made a new rough blueprint of an inductor of 750mH and some taps.

with a PM50x39 (BIG MAMA) core and 0.35mm wire, each layer should contain 63 turns. rolling an inductor with whole layers could give us taps of:
40 or 63mH
90mH
202mH
302mH
490mH
and what ever we want in the end.

of course when its done it my something else. cores are -+3% in tolerance.
this are with center holes so they can stand some more amplitude.

still interested?

dont forget to check the size of the cores!

Definitely interested. At the moment the Sowter I have has a smallest inductance of 50mH but 40mH would definitely be better and provide a better overlap with other bands.

Cheers

Ian
 
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