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Simple Inductor EQ schematics for DIY
Old 3 weeks ago
  #1
Simple Inductor EQ schematics for DIY

Hi Friends.
I have recently started learning the basics of electronics and have built a few simple circuits from schematics on the web and I´m seriously thinking of quitting my job This is way too much fun!

I have a big love for Inductor based Eq´s, but as soon as I start to investigate if it is something maybe I could try to build it always ends up being way to complicated, for my very very limited knowledge.

Question 1:
is there a simple way to implement inductors into, a simple EQ design consisting of only caps and resistors, lets say Baxandall for example?
Question 2:
Is there anyone that know of some less complex Inductor EQ schematics a
newbie like me could build?

I have attached an image of an old tone control design from Gibson that makes my head spin.

Question 3:
Can you call the attached schematic design for an "Inductor eq"?
In other words, is the inductor in this schematic being used/playing the
same role as in other more complicated/classic designs?

Thank you all for your time.
//Ted
Attached Thumbnails
Simple Inductor EQ schematics for DIY-gibson-varitone-1961-2862193610_64cb78d779_z.jpg  
Old 3 weeks ago
  #2
Gear Head
 
rob f's Avatar
 

Quote:
Originally Posted by Ted Krotkiewski View Post
Hi Friends.
Question 1:
is there a simple way to implement inductors into, a simple EQ design consisting of only caps and resistors, lets say Baxandall for example?

//Ted
Baxandall eq's are by nature active, so you couldn't make one with just caps resistors & inductors. The eq element is in the feedback loop of an active element.
Old 3 weeks ago
  #3
Quote:
Originally Posted by rob f View Post
Baxandall eq's are by nature active, so you couldn't make one with just caps resistors & inductors.
Right.
The bax designs I built had TL072 opamps. So I should add that to the list.

Quote:
Originally Posted by rob f View Post
The eq element is in the feedback loop of an active element
ooooh this makes my head spin so much.
Care to elaborate this for a dummie like me?

Thanks a lot!
//Ted
Old 3 weeks ago
  #4
Gear Head
 
rob f's Avatar
 

Read this. It's Peter Baxandalls original document
https://learnabout-electronics.org/D...edbackTone.pdf
Old 3 weeks ago
  #5
An intuitive explanation of filters in a negative feedback loopj
- As negative feedback increases, output drops
- A passive filter selects what frequencies to attenuate
- That filter, put in a feedback loop, decides which frequencies have less negative feedback.

Less negative feedback = more gain

For example, a lowpass filter in a feedback loop makes the amount of low freq gain less, which is equivalent to making the high frequency gain larger in comparison.

There is more to it; phase plays an important role in design. But that's a basic concept overview.
Old 1 week ago
  #6
Thanks a lot for your explanation Philbo. I am still not sure about how this works, but I am sure I´ll figure it out and end.

Below, I found a very basic schematic for a Mid Control circuit that uses an Inductor.
Since Inductors are very expensive and I can´t play around with values like I would with Caps and resistors, my question is. What area of Henries are common for mid freq´s in this case?

Are we talking 10mH - 200mH or higher around 1-5H?

Anyone know of cheap inductors that can be used for audio circuits like this that I can use for experimentation?
The only one I know of is the rather expensive Carnhill ones that can be bought through AML audio.

If I search for inductors on the web that can be used in audio circuits like this, what is it that defines it being suitable for audio? what are the markings and materials etc to look for?

Many questions in one go.
Sorry and thank you so much for your help.
I am sure others will find this interesting too.
My best.
//Ted
Attached Thumbnails
Simple Inductor EQ schematics for DIY-screen-shot-2020-05-14-3.51.00-pm.jpg  
Old 1 week ago
  #7
Lives for gear
 

inductors for eq

Quote:
Originally Posted by Ted Krotkiewski View Post
If I search for inductors on the web that can be used in audio circuits like this, what is it that defines it being suitable for audio? what are the markings and materials etc to look for?
Opamp Labs in Hollywood has or had audio grade inductors.
Mouser used to stock various values of Xicon inductors that were suitable for the UA model 508 feedback equaliser.
Quad/Eight's model 312 used what appears to be inexpensive ferrite pot core inductors (in no way a diss as that eq sounds amazing).
Attached Thumbnails
Simple Inductor EQ schematics for DIY-inductor.jpg  
Old 1 week ago
  #8
Quote:
Originally Posted by Ted Krotkiewski View Post
Thanks a lot for your explanation Philbo. I am still not sure about how this works, but I am sure I´ll figure it out and end.

Below, I found a very basic schematic for a Mid Control circuit that uses an Inductor.
Since Inductors are very expensive and I can´t play around with values like I would with Caps and resistors, my question is. What area of Henries are common for mid freq´s in this case?

Are we talking 10mH - 200mH or higher around 1-5H?

Anyone know of cheap inductors that can be used for audio circuits like this that I can use for experimentation?
The only one I know of is the rather expensive Carnhill ones that can be bought through AML audio.

If I search for inductors on the web that can be used in audio circuits like this, what is it that defines it being suitable for audio? what are the markings and materials etc to look for?

Many questions in one go.
Sorry and thank you so much for your help.
I am sure others will find this interesting too.
My best.
//Ted

It depends on the impedance of the circuit surrounding the inductor. The impedance (technically, reactance), in Ohms, of an inductor, is 2*pi* F* L. F is the frequency (Hz), and L is the inductor value (H). Your guesses are in the ballpark. For a coil to have 100 Ohms at 10 Hz it would have a value of 6.28 H.

There are a lot of specs for inductors besides value. Interwinding capacitance, core matrrial & permeability and current rating come to mind. There's a lot of complexity in analog filter design, but it's fun to play with.

I suggest starting by doing a little reading. This is a decent reference for designing passive LCR filter circuits:
https://web.stanford.edu/class/ee133...erCookbook.pdf

There are many similar 'cookbooks' that move on to filter design using opamps as well. One classic reference that is still relevant is Don Lancasters Active Filters Cookbook:
https://www.tinaja.com/ebooks/afcb.pdf

There are also an online calculator on analog.com that allow you to enter filter specs and will give you a completed schematic and parts list.
The books will give you understanding; the calculator will give you results. Both are good...
Old 1 week ago
  #9
Awesome!

Quote:
Originally Posted by Philbo King View Post
...The books will give you understanding; the calculator will give you results. Both are good...
Excellent info here Philbo!
Thanks so much for explaining and giving me te books.

I am completely lost when it comes to math and logic, (kind of skipped it at school) but, I just started to understand Ohms law. So I hope in time I will grasp how the calculating aspect of this works as well.

I am so happy that you provided the "Cookbooks" That makes it possible for me to actually try the things mentioned in there and hopefully through trial and error, understand what is written.
I am a hands on type of person.

Have a fantastic day.
//Ted
Old 1 week ago
  #10
I'm glad you found it helpful
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