Simple tone control?

I'd like to add a simple op amp-based tone control circuit to my preamp for desktop speakers & sub that I'm modifying from stock.
This is the simplest I found:
<http://www.simplecircuitdiagram.com/2010/02/03/single-op-amp-tone-control/
(I have +/- supplies so I will be eliminating all coupling caps and changing Vcc/2 to ground.)
What are the positives and negatives to this design?
Better circuit (yet simple)?
Thanks.
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This circuit, "mechanically" lifted from the tube era into op-amp implementation, has a flaw: If the treble control is set to maximum, then its gain is not limited at +20dB at 10...20kHz, but keeps rising as far as the gain-bandwidth product of the op-amp allows. Input impedance goes down accordingly. It might result in Hf oscillations in the whole audio chain, even to burning the speakers out if say you leave input unconnected and close to the speaker cable.
To fix the (potential) problem: - insert 470R in series with the input 4.7uF capacitor or insert 470R between the wiper of the treble control and the inverting input of the op-amp; - throw a 47pF cap from the op-amp output to the op-amp inverting input.
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A general question:
Should pots used in the audio tone filter circuits be audio (log) taper? Or does this apply only to volume pots?
Thanks.
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Linear
d
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On 21.11.11 5:53 , DaveC wrote:

This is the classic Baxandall tone control. There is plenty of material if Googling for 'baxandall'.
--

Tauno Voipio


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"Tauno Voipio"

** It's not actually.
Seems like a ballsed up version with missing resistors that will be become unstable at full treble.

** And like most stuff on hobby web sites it is bunkum.
The "Baxandall" tone control design was published in Wireless World in 952 - it used valves. The network is different to the one in the link above and produces variable turnover at both the high and low ends of the range.
http://www.novotone.be/_site/projets/Projet25/Baxandall%20WW.pdf
... Phil
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Thanks! It really helps to know what it's called... ;-)
This page:
<http://sound.westhost.com/dwopa2.htm
says: " This circuit must be driven from a low impedance, so connecting it after the volume control (for example) is a no-no. Ideally, the output of an opamp will be the source, thus ensuring the required low impedance. " The input to this circuit will be the output of a computer's sound card. I don't know if it's an opamp driving the output or not.
What do you suggest to insure driving by low impedance? Add a buffer opamp (gain of 1) at the input of this circuit?
Thanks.
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The sound card output will be fine for driving this.
d
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DaveC wrote:

<http://www.simplecircuitdiagram.com/2010/02/03/single-op-amp-tone-control/
It looks bog-standard to me. Go ahead and use it and use your mind to go on to greater things! :-)
Cheers! Rich
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It would really help to explain what you mean by that. 6" drivers in wood cabs plus a 12" sub? Or 2.5" pc speakers plus a 4" sub? Very different animals.

As said, the odds are the freq response wont match what you want. A 5 band graphic equaliser would be better, and is pretty aesy to make.

If you wanted simplest, the circuit can be far simpler if you use the existing amp's nfb path to simply insert treble & bass boost controls.
Bass boost: Pot and C in parallel in the nfb path, Treble boost: Pot and C in series from nfb path to ground, after a resistor.
NT
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< http://www.harmankardon.com/EN - US/Products/Pages/ProductDetails.aspx?PID=SOUNDSTICKS3AM>
The video is pure marketing.
I don't have these speakers, but I do have the original SoundSticks I which are USB input devices (no analog input). I've converted them to analog input.
Looking for an op-amp-based filter circuit. Anybody have a favorite you can link to? Or put up an ASCII or Spice diagram?
Thanks.
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nothing there

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NT wrote...

Nothing here either.
I think the HK site redirects if it doesn't think you are in the US.
UK version here http://uk.harmankardon.com/harman-kardon-product-detail-uk/soundsticks - iii.html
Recommended by the News Of the World:-)
--
Ken O'Meara
http://www.btinternet.com/~unsteadyken /
  Click to see the full signature.
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On 11/21/2011 11:47 PM, UnsteadyKen wrote:

You're links are broken/segmented. <http://www.harmankardon.com/EN-US/Products/Pages/ProductDetails.aspx?PID=SOUNDSTICKS3AM Does work...
"Praised for its stunning design, the harman kardon SoundSticks II speakers and subwoofer system became a milestone in harman kardon history when it became part of the permanent collection at New York Citys Museum of Modern Art (MoMA). Improving on its famous siblings pop-culture appeal, the SoundSticks III system is all that and much more. As a three-piece, 2.1-channel multimedia sound system, SoundSticks III brings a new level of excitement to music, games and movies to your home with its exceptional sound clarity, enhanced color scheme and bare minimum of wiring. Beyond its eye-catching appeal, SoundSticks III continues to be incredibly capable with 40 watts of dazzling amplification, a down-firing powered subwoofer, eight full-range transducers and compatibility with all sorts of multimedia devices. As the sublime sequel to a prized performer, SoundSticks III is performance art at its finest."
Only $169
Jeff-1.0
--
"Everything from Crackers to Coffins"

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"Jeffrey Angus"

<http://www.harmankardon.com/EN-US/Products/Pages/ProductDetails.aspx?PID=SOUNDSTICKS3AM
** Not from outside the USA it don't.
And the UK one is the same.
How boring of them.
... Phil
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On 11/22/2011 12:07 AM, Phil Allison wrote:

Well that sucks, what's the point of that?
Jeff-1.0
--
"Everything from Crackers to Coffins"

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wrote:

Just need a proxy within the USA - always useful to have one available for every major country.
d
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http://www.harmankardon.com/EN - US/Products/Pages/ProductDetails.aspx?PID=SOUNDSTICKS3AM

Yes there is. Maybe you have to copy & paste the URL, but it is valid.
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"DaveC"
http://www.harmankardon.com/EN-US/Products/Pages/ProductDetails.aspx?PID=SOUNDSTICKS3AM

** The link leads to a home page and nothing else.
... Phil
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If you just want to change the tone (lower), not adjustable, put a capacitor across the volume control. Start with a disc a little smaller than a dime and work up and down from there.
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