Passive Mastering EQ

[5v333]

i played around with a blueprint of an inductor that would be filled to max using a rm12 core/bobbin with an AL of 1000nH 5% tolerance and 30AWG wire. at 750mH the DCR would be around 16R.

to do a nicely wound multi tap inductor i liked the idea of having wire ends that dont end up in the middle of a layer. because when you have to drag that end over that layer to the sides, next winding will start to look a bit caotic and will get worse further on. perhaps this is not a problem for the function of the inductor.

with some ruff calculations doing the first three windings with whole layers and the last windings with stops in the middle of the layer we could get this

52mH
117mH
209mH
300mH
500mH
750mH

i would buy one or two extra sets of cores and try to find the best combinations for a matched pair of inductors.

if you cant get a source i could prob try make you two of theese.

 

[ruffrecords]

i played around with a blueprint of an inductor that would be filled to max using a rm12 core/bobbin with an AL of 1000nH 5% tolerance and 30AWG wire. at 750mH the DCR would be around 16R.

to do a nicely wound multi tap inductor i liked the idea of having wire ends that dont end up in the middle of a layer. because when you have to drag that end over that layer to the sides, next winding will start to look a bit caotic and will get worse further on. perhaps this is not a problem for the function of the inductor.

with some ruff calculations doing the first three windings with whole layers and the last windings with stops in the middle of the layer we could get this

52mH
117mH
209mH
300mH
500mH
750mH

i would buy one or two extra sets of cores and try to find the best combinations for a matched pair of inductors.

if you cant get a source i could prob try make you two of theese.

That sounds very good. I do not mind separate windings - it is not a problem to connect them on the PCB. Flying leads is also OK if there are not enough pins on the core.

I have ordered a pair from Sowter but they are mu-metal screened so expensive. It is always good to have alternatives. I would be grateful if you would make me a pair. Happy to pay you of course.

Cheers

Ian

 

[5v333]

i dont dare to ask what the price was.

ill get back to you about the inductors. gotta order some parts.

 

[ruffrecords]

i dont dare to ask what the price was.

ill get back to you about the inductors. gotta order some parts.

It is no secret. Their standard price is for the CEQI product on this page:

http://www.sowter.co.uk/cgi-bin/sh000001.pl?WD=ceqi&PN=E_A_Sowter_Ltd_EQ_INDUCTORS_6%2ehtml#a288

but as I said it does come in a mu-metal shielded can.

Cheers

Ian

 

[ChrioN]

5v333: Its easily doable, but without a center hole  it will sature way before we reach pro-levels. The one you're stating actually have one. But yeah, some tests are in order regarding levels.

Edit: Actually it seems like the core is indeed without centerhole.

 

[5v333]

hallå så chrion!

seems you are right about the core is lacking a centerhole. thanks for reminding me about it.

i honestly dont know much about the difference. but i guess i should see if theres anything more suitable out there.

 

[ChrioN]

Nästan rätt 5v333

High signal conditions, with high L, low DCR and tight tollerance. Its a tricky task.

 

[ruffrecords]

At a rough gues, I would estimate the maximum rms audio current in the inductor to be no more than 13mA.

Cheers

Ian

 

[5v333]

it seems that mouser and perhaps others have thrown out alot of cores from their selection..!

cant seem to find what im looking for...

if anybody can find me a P (22x13 or higher) or RM (10 or higher) core with an AL of 3000nH or higher with a center hole, please let me know. preferably with low tolerance and tuning screws.

 

[ruffrecords]

if anybody can find me a P (22x13 or higher) or RM (10 or higher) core with an AL of 3000nH or higher with a center hole, please let me know. preferably with low tolerance and tuning screws.

Here is what Farnell has:

http://uk.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=44&storeId=10151&categoryId=700000005705&pf=111776291

Cheers

Ian

 

[5v333]

thanks ian!

theres at least one there that could be used. but its AL and size is a bit overkill. ill have more looking around when i get the time. somethings wrong with my tube amp build for my eq and its eating my heart out.

 

[ruffrecords]

The Sowter custom inductors arrived today. I go on holiday for a week tomorrow so I will not get a chance to try them out until I return.

Cheers

Ian

 

[ChrioN]

N30 is about the worst material you can use in a high level eq.

Here is what Farnell has:

http://uk.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=44&storeId=10151&categoryId=700000005705&pf=111776291

Cheers

Ian

 

[5v333]

interesting!!

can you shed some light about differencies in core material?

i had my eyes on the big P36/22  N48 cores that farnell had from ians link.

 

[ruffrecords]

Back from holiday now so I have been looking at the low end of the EQ in more detail now that the custom Sowter inductors have arrived. The attached pic shows the possible frequencies at different Qs that are possible with the values of inductance available. Below that I have selected an ascending set that cover 30Hz to just under 1KHz tabulated with the corresponding Q, L and C values.

As you can see at 30Hz we can only achieve a Q of 0.3. I think this is fine because a Q of 0.6 would have a bandwidth of just 50Hz anyway and I am inclined to make the curves more like an enhanced shelf than a true bell shape. Now I know the kind of cap values we need I can order some and put it through its paces.

Cheers

Ian

 

[thomasdf]

Can't. Wait.
Ian, you are a genius!

 

[JCN1218]

Been following this thread for a while now. This seems like it's turning into a really awesome project. I'm very excited to see how it turns out and to hopefully get my hands on some boards when it's all finished. Keep up the great work, Ian!

 

[ruffrecords]

Thank you both for the words of encouragement. Once I get the bass end up and running the next step is to design the PCBs for each band and then I can but a complete set together.

Cheers

Ian

 

[frederickalonso]

Nice project, looks like you are almost at the finish  8)

Like the curves in your tests Ian.
What transfo's will be used in this project?

 

[ruffrecords]

Nice project, looks like you are almost at the finish  8)

Like the curves in your tests Ian.
What transfo's will be used in this project?

There is quite a way to go yet but the basic principle seems sound. I like the curves too. A q of 0.6 gives quite inteesting shapes. The other night I was trying to EQ a rather poorly recorded guitar and the usiual shelving boost/cut controls could not restore a reaslistic sound. Then I tried a mid boost/cut and for some reason I set the Q to 0.6 (probably because IO had been working on the EQ earlier in the day). I was astonished at how it brought this dull guitar back to life with just a few dBs of boost. I think I am a convert.

The EQ is passive in and out so strictly speaking it does not need input or output transformers. In the simplest form you can just drive it from a regualr balanced out, provided it can drive a 600 ohm load. The output of the EQ van be fed to a regualt 10K bridging line input. The insertion loss is only about 12dB so you can easily make up the gain  on most mixers.

At the other end of the spectrum you can make a stand alone EQ with balanced in and out and a built in gain make up amplifier to restore the loss in the EQ. The input transfoprmer would need to be a 600:600 type and it should preferably be capable of handling signal levels of up to +20dBu; probably something like the Sawter 1460.

The output transformer depends on the type of gain make up amp you use. Most DOA amps use a 1:2 ooutput transformer or something similar. basically you should use the transformer re3commended for the DOA.

if you use one of my tube desiogns like the Twin Line Amp for gain make up then that requires a 2:1 transformer. My prefered transformer here is another Sowter, the 1461. Alternatively you can use the lower cost Carnhill VTB2291 or the even cheaper Edcor XSM 2.4K/600.

Cheers

Ian