Equaliser design for a total n00b - diyAudio
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Old 17th August 2012, 03:17 PM   #1
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Default Equaliser design for a total n00b

Hi all

I've been reading these forums for a while, trying to learn as much as possible about basic electronics. I have a good basic level of knowledge but there are many many gaps which will become blindingly obvious in very little time at all
I am trying to build my first circuit instead of paying 800 for the equivalent commercial product (I'm sure many projects start this way...!). I would at least like to 'have a go' first but am more than happy to concede that it may be beyond my reach as a first project.
The thing I want to build is two three band stereo equalisers that have the ability to 'kill' or cut each frequency and boost each one by approx 6dB. This is sometimes known in DJ circles as an isolator. Luckily the lovely people at RANE have made available on their website a schematic of one of their mixers that contains this kind of EQ circuit. See attached file.

The screenshot is from page 9 of the schematic pdf

http://www.rane.com/pdf/mp2016ssch.pdf

I wondered if it would be possible to take this circuit and breadboard it? As a proof of concept it looks like I'd only need five of the ICs, three 20k pots and then the capacitors and resistors. I should hopefully be able to build something for under $30 and if it turns out that it doesn't work it's not a lot of money to burn before shelling out for the commercial offering. If it does work though it'll be amazing!

I just thought I'd ask your advice to see if it's something a beginner should contemplate and whether or not you think the circuit will work in a standalone manner (i.e not being connected up to the rest of the circuitry inside the MP2016 mixer).

Thanks for any advice or suggestions!

Stuart
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Old 17th August 2012, 04:21 PM   #2
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Welcome here stubertio!

Yes it will work as a stand-allone. Remember you will need a dual 15volt power supply. I would also, for protection, put a bipolar capacitor (47uF at 60 volt) at the input and output
The ICs shown use house numbers but the LM/NE5532/5534, TL072/82 or the LM/MC1458 should work just fine
If it is for home stereo use you will find that +/- 12 to 15 dB is used
For bredboarding, check out Welcome - Fritzing
Cheers and happy diy! E
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Old 17th August 2012, 07:39 PM   #3
AndrewT is offline AndrewT  Scotland
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Read the linkwitz lab website. One of the best around for filters & eq.
He also gives circuits and PCBs that can be applied.
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Old 22nd August 2012, 10:47 PM   #4
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Thank you for your positive replies. I was fearful I was trying to run before learning how to walk.
I will have a good look on the Linkwitz site, it looks fascinating.

I have a few Qs:

1) Could you explain or give a link to the theory behind the bipolar capacitor for protection? What exactly will they protect and how?
2) When you say house numbers, do you mean numbers that are internal to RANE?
3) I am struggling to pick the necessary capacitors for the project. I have read a bit about 'audio' capacitors but am unsure if I need to go down this route? Can anyone recommend a capacitor type that should work? I was naively under the impression that so long as I used one with a sufficient voltage and capacitance rating that I'd be ok...
4) I've never built anything that has required a positive, negative and second negative supply. What's this type of power supply called and where can I read more about it? Presumably I can buy ac adapters off the shelf from the more specialist electronics stockists rather than having to build my own?

Many thanks

Stu
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Old 23rd August 2012, 12:08 AM   #5
sreten is online now sreten  United Kingdom
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Hi,

FWIW a three band active EQ really isn't that useful for stereo, compared
to passive line level tonal tweaking, especially with +/- 6dB limits to the EQ.

Also FWIW you simply can't build anything nowadays for less than the new
cost of a decent implementation or the used cost of a good implementation.

Factoring everthing in, you cannot build equipment to save money, you can
build equipment to build it the way you wan't, better know your stuff though.

If you don't know your stuff, building is a very hard learning curve.

rgds, sreten.
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Old 23rd August 2012, 09:25 AM   #6
AndrewT is offline AndrewT  Scotland
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Don't buy "audio" caps, certainly not expensive versions.

Ordinary commercial grade capacitors are good enough, particularly in the early stages and well into the later stages of design and build.

Capacitors come in many types.
Each type can do only one or two duties. You must specify the correct cap type for the duty you have. eg ceramic are great as local decoupling. and VHF interference attenuation. Electrolytic are very good at big capacitance for a small volume for power supplies.

House numbers. Rane have renamed the chips with their own unique name.
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Old 23rd August 2012, 03:24 PM   #7
pern is offline pern  Sweden
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That schematic is not the same as a commercial DJ-ISO. These use 18db or 24db filters. But if it's just a rotary kill EQ you need, then it will work.

I would add an input buffer and DC blocking caps etc. on the input and output.


For PSU you need something like this:

Click the image to open in full size.

Last edited by pern; 23rd August 2012 at 03:52 PM.
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