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Old 22nd May 2004, 04:08 PM   #1
Nuuk is offline Nuuk  United Kingdom
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Default Passive EQ to active EQ

I want to convert the passive EQ that I am using for my OB speakers to active.

This is the current passive arrangement.

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Can I just split this into a low pass and high pass filter using the circuits below?

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Click the image to open in full size.

Or is it more complicated than that?

Also what sets the input impedance of the above circuits and what controls the level of cut?
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Old 22nd May 2004, 04:45 PM   #2
Svante is offline Svante  Sweden
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Cascading the two lower circuits will not give the same result as the upper circuit. It will remove low and high frequencies, whereas the upper circuit attenuates a band in mid frequencies.

The simple solution is just to take the first circuit and a buffer on its output.

Why do you want to make it active?
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Old 22nd May 2004, 06:46 PM   #3
Nuuk is offline Nuuk  United Kingdom
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Quote:
Why do you want to make it active?
Mainly to do with impedance matching through the 'chain'.

My new DacKit needs to see a load of at least 10K, then Iwould like to lower mthe values in my attenuator to feed into the buffers (22K input impedance) that preceed the GC amp.

I had a feeling this wasn't as simple as I had hoped

Is there an active circuit that does do the same as the passive circuit?
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Old 22nd May 2004, 06:56 PM   #4
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If you go to the Analog Filter Wizard, you may find something there that will help
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Old 22nd May 2004, 07:19 PM   #5
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Thanks Al but I don't seem to be able to get it to do much!
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Old 22nd May 2004, 09:58 PM   #6
Svante is offline Svante  Sweden
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Quote:
Originally posted by Nuuk


Mainly to do with impedance matching through the 'chain'.

My new DacKit needs to see a load of at least 10K, then Iwould like to lower mthe values in my attenuator to feed into the buffers (22K input impedance) that preceed the GC amp.

I had a feeling this wasn't as simple as I had hoped

Is there an active circuit that does do the same as the passive circuit?

I thought a bit, and came up with this. The upper can be made to have the same response as your circuit (apart from being inverting), but the lower one seems simpler and the component values would be the same as you have now.
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Old 22nd May 2004, 10:16 PM   #7
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Thanks Svante, I'll give it a go starting with the lower circuit.
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Old 23rd May 2004, 04:28 PM   #8
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I had another think about this and wondered about including the EQ, or at least the bass 'lift' in the feedback loop of the inverted Gainclone circuit.

This would save including more opamps in the signal path. Any ideas or comments on this?
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Old 23rd May 2004, 04:39 PM   #9
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What exactly does your current PLLXO do, (asking is easier than getting my brain in gear to calculate frequencies)?

Btw, I am hoping, (that in that other project we have already discussed), to do something similar if I can get away with low order crossovers. I see no reason why it should not work, especially with the OPA chips that are designed to work exactly like opamps.
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Old 23rd May 2004, 05:22 PM   #10
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Quote:
Originally posted by Nuuk
Thanks Svante, I'll give it a go starting with the lower circuit.
I hope you realise that there should be a resistor to gnd on the first opamp, and decoupling capacitors for the power etc. You probaly knew this, but just in case...
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