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Old 1st April 2011, 06:12 PM   #1
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Default Parametric EQ project

Hi,

Im currently undertaking a self led university project to explore the possibility of a portable, battery (pref 9v) powered 3 band parametric EQ to be used by a soundman on location when recording vocal interviews.

Im struggling with adapting the parametric EQ design on this webpage:

Spectrum Analyzer and Equalizer Designs

I have a prototype of the unit built and cant get all aspects of the filter to work together,

I need to know a few things;

1.) Is this design adaptable and if so would it be possible to cascade 3 of these filters.

2.) how do i handle power issues? im of the understanding that a 4.5 volt supply is required for the IC's but i have a feeling im going about this the wrong way which is the source of my issues.

3.) any tips on simulation as im currently using LTspice and having trouble simulating a pink noise test signal.

Any help or any additional pointers would be very much appreciated as i seem to be circling the same issues.

Thanks
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Old 1st April 2011, 06:27 PM   #2
Mooly is offline Mooly  United Kingdom
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All the opamps in these circuits need a split supply i.e. a plus and minus rail with centre ground. The opamp data sheets will tell you the minimum supply.
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Old 1st April 2011, 06:42 PM   #3
Boofers is offline Boofers  Canada
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Don't use a TL074, there are so many better op amps out there. You can get decent op-amps for just a few bucks.

You could use two 9V batteries for your rails to get a +9V and a -9V rail. Check your op amp datasheet for voltage rail options.
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Old 2nd April 2011, 12:38 AM   #4
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ok thanks for the tips, 2 batteries is a possibility, another noob question how do i pull a negative voltage from a second 9v cell? prefereably without the use of another IC as uni is closed for the weekend and i was hoping to get this running over the weekend
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Old 2nd April 2011, 12:50 AM   #5
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Quote:
Originally Posted by ianmgreen View Post
ok thanks for the tips, 2 batteries is a possibility, another noob question how do i pull a negative voltage from a second 9v cell? prefereably without the use of another IC as uni is closed for the weekend and i was hoping to get this running over the weekend
Think in the "inverse". Merely ground the positive (+) terminal of the 9v battery, and run the negative (-) terminal to your -9 volt rail. No need for any IC's...... this is very straightforward. When you do it, remember that all voltages are "referenced" to your ground..... Your + battery gives you +9 volts, while your - battery will give you -9 volts.

Easy one......
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Old 2nd April 2011, 08:51 AM   #6
Mooly is offline Mooly  United Kingdom
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Or to draw it,
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File Type: jpg Split Supply.jpg (9.0 KB, 216 views)
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Old 2nd April 2011, 01:22 PM   #7
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IMHO there is nothing wrong with the quality of the TL074 for your aplication or any audio aplication for that matter.

However, when you have as many as 4 or 5 or more in a circuit they may not fair well on battery power time.

You might want to consider a low power opamp version for your final product.

Below is a data sheet of your average 9v battery.

A TL074 has an average power dissipation of around 200mw and can be as high as 680mw when pushed hard enough.

jer
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Old 2nd April 2011, 02:43 PM   #8
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jer is right. The TLO7x/08x are great. I allways liked the built-in white noise generator. E
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Old 2nd April 2011, 02:54 PM   #9
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this is all great info thankyou very much, i have my dual battery supply sorted and am not bothered about power consumption at this stage as its only concept proving. im using a minirator and minilyzer to generate a pink noise test signal, i have gain control and cut/boost control but no filter shaping, i think im making a silly mistake when interperating the diagram, the "earths" on the diagram (white arrows) are where my confuson is, do i connect them to the ground (0v) from my batteries or connect it to the non hot line from my minirator?
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Old 2nd April 2011, 03:00 PM   #10
Mooly is offline Mooly  United Kingdom
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The white arrows all go to the zero point (0) in diagram in post #6 That point, the 0, is then reffered to as ground and becomes the point from which all voltage and signal measurements are referred to.
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