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is it worth it to replace caps in old equalizer??

Discussion in 'Electronic Repair' started by Derwin, Mar 24, 2007.

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  1. Derwin

    Derwin Guest

    Hello, I have an old 70s-era 5-band equalizer made by Realistic (radio shack),
    which I like to use in my guitar effects chain, and I opened it up the other
    day just to see what it looked like inside, and I noticed that there are two
    large electrolytic capacitors. They look fine, and the unit sounds OK, but
    given that it is probably at least 30 years old now, and may have sat around
    for many years not being used before I got my hands on it, could I expect
    improved performance if I were to replace those two big electrolytics with new
    ones?

    Thanks for any advice!
     
  2. Arfa Daily

    Arfa Daily Guest

    Probably not. If it sounds OK with no signs of hum, then it's likely that
    the caps are still working up to spec. If you have access to an ESR meter,
    you could check them, or if not a meter, you could look at the ripple across
    them with a scope. I'm a great advocate of " if it ain't broke, don't fix it
    " - a philosophy that has served me well for 35 years in the business.
    Shotgun replacement of components, or replacing just for the " might be "
    hell of it, often results in problems that weren't there in the first place,
    in my experience. If they are really easy to get at, and you can get
    replacements with similar or better specs, and are determined to put your
    stamp on it, as it were, then go ahead and replace them. It won't do any
    harm.

    Arfa
     
  3. No.
     
  4. It's not uncommon for electrolytic caps to last 40 years or longer. I have
    KLH table radios that are 45 years old, and still work with their original
    electrolytics.

    Electrolytic caps are odd -- they aren't anywhere nearly as unreliable as
    you'd expect them to be.
     
  5. Guest

    No. If youre considering doing jobs that dont need doing it may be
    time to reevaluate ones life.


    NT
     
  6. Jack

    Jack Guest

    Don't replace them till they need it. The old high voltage ones can
    last a long time, but if you've got a few spare minutes, some spare
    dollars, do it by all means.
    Dont worry about re evaluating your life. Life is full of cynics. You
    do right, its wrong you do wrong its still right etc . Its how you
    feel its your life......
    PS Fixing things that dont need fixing is not good, only if youre
    there. Priority says fix things that you need that need fixing, or as
    a preventative.
    Most likely you'll drop the equipment of a truck first...or similar.
    Lifes like that....
     
  7. PeterD

    PeterD Guest

    If it ain't broke, don't fix it...

    Especially if it is Realistic!
     
  8. Scott Dorsey

    Scott Dorsey Guest

    Probably not, since all the electrolytic coupling caps in there are bad too.
    And even if you do, you're stuck with 1970s Radio-Shack grade op-amp design.
    --scott
     
  9. Guest

    I am an expert on audio, certain areas, and this is one of them.

    I totally agree with those who say if it ain't broke don't fix it,
    but, some things are built broke.

    To get the best quality integrated audio, which is the type of signal
    for which this EQ was designed, they chose the wrong frequncies.

    Now replacing the power supply filters is probably useless because of
    the low current drain of the unit, there is simply almost no ripple
    current to "wear out" the capacitor. However there are other things
    one can do.

    I have modified a couple of these, but then that was for integrated
    program material, if you use it on a guitar you might want to go a
    different direction. I don't remember the component values, but once
    you understand how it works you can do things, many things.

    A buddy of mine had his speakers in the corners, which made them very
    boomy. They have bass, but it is shitty.

    At the wiper of the 60Hz control there is a cap, a coil and a
    resistor. What I did was to take and change that control to about 35Hz
    and made it shelving, that is to extend the control's range all the
    way down, instead of that peaked response it originally had. I did
    this by taking the resistor value down to less than ½ the original and
    installing a capacitor about ten times the capacity of the original.

    The 250Hz control was lowered to about 100Hz by cutting the resistor's
    value in about ½ and installing a capacitor about three times the
    original value.

    The 1 Khz control was left alone. The 3.5 Khz control had it's range
    extended slightly downward by increasing the value of it's capacitor.

    Finally the 10 Khz control was modified to be shelving, and it's range
    shifted upward. This brings out the timbre, rather than the tinny
    treble. This was accomplished by actually lowering the capacitor value
    as well as the resistor value, and shunting the coil with a low value
    resistor, about ¼ the resistance of the new resistance value in the
    tuned circuit for that band.

    Actually if you know how to futz with it, you could have a nice setup.
    run the channels in tandem but change some of the frequencies. Lower
    the low ones on the left and raise the high ones on the right. And if
    you tandem the channels you also can use a Y adapter to pick off the
    signal for another amp, between stages.

    Tell you what, if you get a chance to play a guitar on two amps at
    once, enjoy. Set one clean and one fuzzed out. With a little adjusting
    and practice you can make it sound like you are playing two guitars.

    JURB
     
  10. Eeyore

    Eeyore Guest

    As suggested elsewhere, the PSU caps seem to be ok. You might want to consider
    replalcing any electrolytics in the signal path though.

    Graham
     
  11. Eeyore

    Eeyore Guest

    *After* replacing the caps !

    Yes.

    Graham
     
  12. Guest

    If youre going to muck with it then start with a 10 band or more,
    pointless to play with something as very limited as a 5 band.

    If you wanted to adapt it for guitar use only, I'd make each side
    different freqs and you can feed the signal thru both sides to get a
    10 bander. And refrequency the 1kHz slider, which is the least useful
    of them all.

    But... its not worth bothering, might have been 25 yrs ago.


    NT
     
  13. James Sweet

    James Sweet Guest


    If it sounds fine I wouldn't worry about it. On the other hand caps are
    cheap and replacement is easy.
     
  14. Mogens V.

    Mogens V. Guest

    Plus many/most inexpensive EQ's arent phase liniar anyways...
    Mostly useless for high quality audio. Besides, problems with a hifi
    setup is better addressed actually fixing those problems at the source,
    not trying to EQ them out.
     
  15. Mogens V.

    Mogens V. Guest

    And as Scott mentioned, it's based on quite old opamps.
    Not worth the efforts, not even if tone is under par. Then better go get
    a better one. Unless the OP prefers that killer vintage tone.
     
  16. Derwin

    Derwin Guest

     
  17. Plus many/most inexpensive EQ's arent phase liniar anyways...
    Linear, not liniar.

    This has been discussed ad-nauseum. If you are correcting for errors (as
    opposed to introducing them), you don't want constant group delay. You want
    the phase shift the equalizer introduces, because it offsets the phase shift
    of the error.
     
  18. Derwin

    Derwin Guest

    Great ideas, thanks for the response, Zzactly!
     
  19. Derwin

    Derwin Guest

    I appreciate your response as well, but the cirumstances are that I have some
    free time while I wait for some parts to arrive before I can get back to
    recording, and for the past few weeks I've been doing a lot of soldering.
    Since I've got all the tools laid out from the previous work, and can't get
    back to recording, I figured I'd open up anything I have around that is
    essentially worthless but still potentially useful (in my opinion) and see if I
    could do any worthwhile modifications (I was hoping I'd be able to replace an
    op amp in the equalizer, but there aren't any in it). However it does seem
    like my rudimentary self-learned knowledge of electronics has already caused me
    to do some useless things, such as replacing the op amps in an Alesis
    Microlimiter with ones with lower noise specs, hoping to get a lower noise
    floor, which did not happen because I didn't understand the circuit well enough
    to realize that swapping op amps wouldn't result in a quieter unit.
     
  20. Derwin

    Derwin Guest

    But unfortunately it appears I won't be able to try them. The plastic ends on
    the sliders don't come off the sliders, they're either glued on or were
    manufactured that way, so it is impossible to take off the front panel to get
    behind it where the circuit board is. Oh well.
     
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