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Old 15th January 2004, 02:43 PM   #1
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Default Parametric Schematic

Hi again. Here is a schematic I found for a parametric eq. The design looks pretty good to me, its simple but looks very clean. Does anyone know how to calculate the values needed to change the frequency range the filter sweeps?

Thanks a lot.
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Old 23rd January 2004, 02:28 PM   #2
mskeete is offline mskeete  United Kingdom
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1
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2 * PI * sqrt ( (r10+r12) * c4 * (r11+r12) * c5)


for r12=0 I calulated 36Hz
for r12=100k I calulated 1250Hz


Where did you find this circuit
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Old 23rd January 2004, 02:29 PM   #3
mskeete is offline mskeete  United Kingdom
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forgot to say - sqrt = square root function
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Old 30th January 2004, 09:16 PM   #4
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Thanks so much, that really helps me out. I got the schematic from a website I can't seem to find anymore. It's originally from a piece of Studio gear, I'm not too sure which one. All I know it that on the website it said the design was highly regard.
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Old 10th February 2004, 05:05 AM   #5
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This might help, note the value changes for the two different range bands. It's too bad they didn't include an equation for determining the values
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Old 10th February 2004, 07:03 AM   #6
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Whops forgot to attach.
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Old 10th February 2004, 09:42 AM   #7
mskeete is offline mskeete  United Kingdom
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Same circuit, same formula
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Old 15th February 2005, 06:56 AM   #8
Slab is offline Slab  United States
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It's nice to see some people on the right track. This is a generic circuit using op-amps. Other successful parametric designs are very similar. By the time "they" get their digital circuits adjusted the CD is over. A circuit like this, properly built and adjusted to do it's job, built with 25 year old XR4136 bipolar op-amps as compared to a newer one built with the latest National j-fet op-amps, will be indiscernable to a critical listener on a good system. In other words, correct parametric equalization is one of the most important factors of a great sound system. It doesn't matter what kind of religious annointing you have bestowed upon your transistors, as long as they are operating where they are supposed to be, and constructed on a good backbone. Anyone want to have a tug of war? (Your power amp and mine, output connected to output, any way you like with any load, and any input signal you want. The first smoker is the loser.) Back to Tom Waits. Don't go into that Barn.
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Old 8th March 2005, 08:26 PM   #9
giggles is offline giggles  United States
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Default Parametric Schematic

I downloaded the schematic for the parametric EQ. I have been simulating it using Pspice. It is very nice. I am still a little unsure how it all works, and that is why I am writing.

Does anyone know the calculations for "Q" ? The present circuit values provide a very low Q, even with the pot all the way up. I would like to increase this even further. Any ideas?

What I like about the circuit is that the Q setting affects the overall output amplitude very little. This circuit offers a good independece of Gain, Frequency, and Q control.

I would really like the formula for Q if anyone knows how to derive it.

Thanks,
Joel
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Old 1st January 2006, 06:54 PM   #10
tocs100 is offline tocs100  United States
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Default Re: Parametric Schematic

Quote:
Originally posted by giggles
I downloaded the schematic for the parametric EQ. I have been simulating it using Pspice.
I would really like the formula for Q if anyone knows how to derive it.
Center Freq./(high -3dB down point minus low -3dB down point)=Q. What's Pspice?
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