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Old 14th January 2012, 02:20 PM   #1
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Cool Frequency cut out switches. Graphic EQ.

Hi All

just a quick question, on the following schematic, If I were to add switches to the input of each of the 3 frequecy responses after the resistor and before the Pots, would this act as a Kill switch for each selected level (Bass, mid + Treble) ??

Would I need to add any other circuits??

thanks

Chris
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Old 14th January 2012, 03:44 PM   #2
DF96 is offline DF96  England
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No. That appears to be a 3-way version of the Baxandall active tone control. It can't cut out any frequency range, but just boost or reduce.
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Old 14th January 2012, 04:44 PM   #3
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Quote:
Originally Posted by DF96 View Post
No. That appears to be a 3-way version of the Baxandall active tone control. It can't cut out any frequency range, but just boost or reduce.
I interpreted it as disabling the control function of the pot, not changing the audio response. I don't think it would work that way but it wouldn't hurt to try.

G
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Old 15th January 2012, 11:09 PM   #4
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Where do bad seeds come from?

R1, 2 should not go to ground, but to the junction of R3/C2 and than to the junction of pin 5 of the IC. Than the 1uF after pin1 of the IC can be eliminated. And all of that is not optimal.

To go back to your query: A swithc after the pot should be sufficient. E
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Old 16th January 2012, 11:23 AM   #5
DF96 is offline DF96  England
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R1 should still go to ground, but you are right about R2 - it should go to the reference point for the second opamp.

A switch 'after' the pot (presumably after the wiper) would not cut a band, but merely render it uncontrollable so it would pick up the tails of whatever was set by the adjacent bands. For the top (bass) pot there is the complication that this also provides DC bias so the switch would need to be bypassed by a high value resistor. Arrangements would have to be made to avoid switching clicks.

Much better to start with a circuit designed to allow cutting each band independently.
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Old 16th January 2012, 05:59 PM   #6
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Smile Schematic update,,,,

Hi Mickey / DF69

ok,, being as I know v.little about this and in learning phase... I have adjusted the schematic correspondingly with your advice.

Is this correct now.??

many thanks

Chris
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Old 16th January 2012, 06:30 PM   #7
DF96 is offline DF96  England
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No. You have no bias supply for the first opamp. Also, the CR across the + and - inputs for the second opamp should not be there. Why don't you use normal symbols - the colour coding is confusing.

As I said, I suggest you find an existing circuit which does what you want. You need to learn more before trying to design your own.
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Old 16th January 2012, 09:44 PM   #8
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lol... funny thing is, this was an existing design,,, I didnt have a CAD program so had to use Excel for the time being however,
I now have a CAD design program, hopefully this will assist,, I will try to upload as soon as Ive implemented the design..
as for the Bias (??) I thought the LM358 only had on VCC and Ground, hense this is shown on the 2nd (1B) opamp.

really appreciate your patience..

Chris
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Old 16th January 2012, 10:09 PM   #9
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The bias for both op-amps appears to come from the two 10K resistors on the right hand side. They form a voltage divider giving Vcc/2 at their junction.
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Old 17th January 2012, 11:52 AM   #10
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Do you want to cut each frequency range or defeat each tone control?
For defeating the mid and treble controls, you could just disconnect (that is, insert a switch in series) the pots center lead. For the bass, try shorting (that is, connecting a switch between leads 1 and 3) the pot (this may affect the other bands, I dunno).

Emerson Prado
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