Passive Mastering EQ

[ruffrecords]

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:

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:

60Hz

80Hz:

100Hz:

140Hz:

160Hz:

200Hz:

240Hz:

400Hz:

480Hz:

480Hz:

725Hz:

870Hz:

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:

Cheers

Ian

 

[ilfungo]

Great!!!
which software have you used for this tests?

 

[ruffrecords]

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

 

[ilfungo]

Thanks!

 

[dagoose]

Any progress? Just curious  8)

 

[ruffrecords]

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]

Any progress? Just curious  8)

Breadboard it? Hard to get a more simple circuit 

 

[ruffrecords]

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

 

[alexc]

Those are some pretty sweet curves 

I think I'd like to make a pair with those!

 

[warpie]

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

 

[ruffrecords]

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

They are from ELMA's Uniselector range:

http://www.elma.com/en/products/rotary-switches/rotary-switching-products/product-pages/uni-selector-detail/

Part number US-B1-124N

Torque is 4 Ncm and they come with a right angle header so you can mount the directly to a PCB

Cheers

Ian

 

[warpie]

Thank you Ian! Although I don't quite understand the difference between these and their 04 series (other than the vertical PCB of course) 

 

[Gold]

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?

 

[ruffrecords]

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

 

[buschfsu]

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?

 

[ruffrecords]

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]

Any plans for filters on the top and bottom?  ;D ;D

 

[ruffrecords]

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

 

[5v333]

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!

 

[ruffrecords]

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