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Old 27th May 2012, 04:34 PM   #1
emosms is offline emosms  Bulgaria
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Default adding opamp filter stage

Hi, I have this schematic:
Click the image to open in full size.
But I would like to add one more parametric filter for the mids, so changed it to:
Click the image to open in full size.
Did I get it right? Just simply cloning by analogy.
The part of the schematic above the PQ filter (U2.x)
- these opamps are, stage buffers, followers?
Is it ok I just clone it that way?
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Old 28th May 2012, 11:05 AM   #2
emosms is offline emosms  Bulgaria
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Reading here and there:
The way U2 opamps are connected in the second schematics - is that a 'state variable topology'?
Best Regards
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Old 28th May 2012, 02:29 PM   #3
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emosms: I do not have the time to analyze your circuit, but go to the Rane site: Rane Corporation they graciously provide full schematics and manuals of their gear. Check for the PE15 in the discontinued section. E
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Old 28th May 2012, 03:34 PM   #4
Jay is offline Jay  Indonesia
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I have no experience with this, but your circuit will have 2 band filters working on the same bandwidth. I don't know if this is common or not, but the operational problem I see is to control the real interaction, e.g. to know/predict the total boost/cut when both filters working on very close frequencies. At least, the more filter you added, I expect a sharper Q (i.e. to have a higher fixed maximum Q by increasing resistors in series with the pot for adjusting Q).

I only comment by logic. Not really know the common practice.
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Old 28th May 2012, 04:49 PM   #5
macboy is offline macboy  Canada
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I would recommend not trying to save a single opamp in the top half. Just build two of the complete circuit and cascade them (input to output). In the end you will have an even number of opamp sections so a whole number of dual opamps will be used.
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Old 28th May 2012, 10:48 PM   #6
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by macboy View Post
I would recommend not trying to save a single opamp in the top half. Just build two of the complete circuit and cascade them (input to output). In the end you will have an even number of opamp sections so a whole number of dual opamps will be used.
Yes, that would also automatically prevent the signal from being inverted.
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Old 29th May 2012, 10:52 PM   #7
emosms is offline emosms  Bulgaria
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the frequency range of the two parametric sections I will adjust later on.
f.ex. they might overlap for one octave, now the range is 4 or more.
---
Saving one opamp is cause there are 3 more outside this schematic and then I would have 12 in 6 dil's.
One for the input, one for simple low/high filter, and one for the output. Input is preamp, output is maybe impendance issue, not sure there are too many already..
---
Thx for the Rane corporation LInk !!
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still confused about the circuit's design, cannot recognize the topologies and 'what does what' completely.
If someone can point me what the parametric section is (topology to read about).
---
Also, the upper part, where the parametric sections are connected - some followers or whatever.. is that part of the filter or smth else
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