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Simple tone control?

Discussion in 'Electrical Engineering' started by DaveC, Nov 21, 2011.

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  1. DaveC

    DaveC Guest

    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:


    (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)?

  2. DaveC

    DaveC Guest

    If you just want to change the tone (lower), not adjustable, put a
    I want adjustment of at least 2 bands. Not a 10-band equalizer, though... ;-)

  3. This looks a lot like the kind of tone controls mass-market
    consumer-electronics equipment has been using for the past 60 years.

    I don't know /exactly/ what your plans are, but the 1kHz corner frequency is
    about the worst possible if you're trying to correct errors in the speakers
    you're designing.

    Unless you want a "tone control" that produces shrill treble and boomy bass,
    you need to move the treble corner up, and the bass down.

    Furthermore, it would make sense to design the speakers first, and see what
    sort of correction they need. There are plenty of inexpensive drivers with
    relatively flat response (if you believe the spec sheets). Neither they nor
    most recordings will need much in the way of correction, so the best tone
    control would be one that supplies small amounts of boost and cut at the
    frequency extremes.

    Unless you're looking for lots of boom and sizzle.

    There are plenty of op-amps with a wider voltage range -- the 5534 and
    TL-074 come to mind, but these are rather old designs. I'm sure someone will
    be able to recommend something newer.
  4. DaveC

    DaveC Guest

    It would really help to explain what you mean by that. 6" drivers in

    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?

  5. DaveC

    DaveC Guest
    Yes there is. Maybe you have to copy & paste the URL, but it is valid.
  6. Phil Allison

    Phil Allison Guest

  7. You're links are broken/segmented.
    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
    City’s Museum of Modern Art (MoMA). Improving on its famous sibling’s
    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

  8. Phil Allison

    Phil Allison Guest

  9. Well that sucks, what's the point of that?

  10. Don Pearce

    Don Pearce Guest

    Just need a proxy within the USA - always useful to have one available
    for every major country.

  11. Rich Grise

    Rich Grise Guest

  12. DaveC

    DaveC Guest

    Is *that* why many boomboxes and home stereos(cheap ones) have a tone
    These pots on the circuit references aren't on a common shaft.

    In other words, you can have muffled *and* tinny/hissy! ;-)

  13. Tauno Voipio

    Tauno Voipio Guest

    This is the classic Baxandall tone control.
    There is plenty of material if Googling for
  14. DaveC

    DaveC Guest

    This is the classic Baxandall tone control.
    Thanks! It really helps to know what it's called... ;-)

    This page:


    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?

  15. Don Pearce

    Don Pearce Guest

    The sound card output will be fine for driving this.

  16. Phil Allison

    Phil Allison Guest

    "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. WW.pdf

    .... Phil
  17. DaveC

    DaveC Guest

    A general question:

    Should pots used in the audio tone filter circuits be audio (log) taper? Or
    does this apply only to volume pots?

  18. Don Pearce

    Don Pearce Guest


  19. 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
    - throw a 47pF cap from the op-amp output to the op-amp inverting input.
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