Parametric Schematic

[punchpeanut]

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.

[mskeete]

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

[mskeete]

forgot to say - sqrt = square root function

[punchpeanut]

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.

[nine76chris]

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

[nine76chris]

Whops forgot to attach.

[mskeete]

Same circuit, same formula

[Slab]

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.

[giggles]

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

[tocs100]

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?