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Old 30th March 2006, 02:39 PM   #1
DD_Davo is offline DD_Davo  United Kingdom
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Default preamp active filters

Hi, ive a working mic preamp however im wanting to alter the tone of the output by adjusting trebel and bass. I understand the principal behind the common 741 active trebel and bass circuits such as shown here http://www.antonine-education.co.uk/...ve_filters.htm

However is it possible to combine a trebel boost and bass boost filter on one output and swap the resistor value in each for a log potentiometer to vary the amount of trebel and bass, in essence to form a basic tone control?

If so, linking the circuity in parallel should work?

Thanks for any help
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Old 30th March 2006, 02:55 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

search on active baxandall tone controls.

/sreten.
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Old 30th March 2006, 03:29 PM   #3
DD_Davo is offline DD_Davo  United Kingdom
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hi thanks, the active versions look rather ideal, but for now im wanting something much simpler. Basically i want to link a high pass and low pass simple active filters and add relplace a resistor with a pot to allow me to alter the bass and trebel individually.

This should be possible?

Thanks
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Old 30th March 2006, 04:09 PM   #4
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You can sort of do it, but I stress that you heed sreten's advice as it's the only way you are going to get the result you want. The Baxandall tone control is no more complicated than an active filter and recombination circuit.
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Old 31st March 2006, 02:03 AM   #5
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Default Re: preamp active filters

Quote:
Originally posted by DD_Davo
Hi, ive a working mic preamp however im wanting to alter the tone of the output by adjusting trebel and bass. I understand the principal behind the common 741 active trebel and bass circuits such as shown here http://www.antonine-education.co.uk/...ve_filters.htm

However is it possible to combine a trebel boost and bass boost filter on one output and swap the resistor value in each for a log potentiometer to vary the amount of trebel and bass, in essence to form a basic tone control?
Yes, but why would you want to?

Quote:
Originally posted by DD_Davo
If so, linking the circuity in parallel should work?
You'd need another op-amp to make a linear adder, otherwise, you might run into a race situation where the output transistors of the op-amps try to short out the DC rails. Not a good thing.

Why not use This instead? Straight from an elementary text on op-amps: uses but one op-amp (do replace the suggested op-amp with a really good one) provides both bass and treble cut/boost, and is a helluvalot simpler and easier to implement.
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Old 31st March 2006, 06:08 AM   #6
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Thanks basically the Baxandall system.
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Old 31st March 2006, 07:10 AM   #7
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Try this link,

http://www.theworld.com/~cmoore/AN12.pdf



K a n w a r
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Old 5th April 2006, 10:19 AM   #8
DD_Davo is offline DD_Davo  United Kingdom
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right thanks everybody im testing out all the varying options. One question though, take a standard bass boost active filter using a 741, 2.2K, 2.2M, 10K and 47Nf capacitor. It works fine, in that it boosts the bass frequencys a little however something is not quite right as powering the opamp makes no difference, therefore it seems to be working passively. Im using 9V pp3 batteries but i should have thought them to work fine?

Thanks
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Old 5th April 2006, 03:03 PM   #9
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If you post up the schematic you are using or even just link to it, that will help us diagnose the problem. Sounds like your breadboarding could be wrong though.
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Old 5th April 2006, 04:38 PM   #10
DD_Davo is offline DD_Davo  United Kingdom
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well the bass boost, and trebel boost filters both work to an extent but passively not actively with the opamp. Here is the link to the site where I got the schematics from and ive attached the bass boost schematic.

Thanks
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