Graphic eq sounds different in the loop vs inline

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maximumpower
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2013/03/29 21:45:13 (permalink)

Graphic eq sounds different in the loop vs inline

I have a two channel DOD graphic EQ. I have had it for a very long time. I have been using it with my PA system but more recently put it in the series effects loop of my guitar amp.

Tonight I was experimenting with running one channel inline between my guitar and input of the amp. When I do this, it kills the high end. When I say high end, I mean the relatively low high end of a clean guitar. As if I was turning down the tone knob on the guitar. I thought something must be wrong with it. However, when I put it in the series effects loop of my amp, I don't get the same high end cut. It sounds normal (I.E. transparent when set flat).

Is this an issue with impedance and line levels?

Thanks

Win 10 (64 bit), i7-2600k 3.4GHz , 8 GB RAM, SATA III (500GB SSD - System, 2TB WD Black - Data), Sonar Platinum x64, m-audio Profire 610

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    The Maillard Reaction
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    Re:Graphic eq sounds different in the loop vs inline 2013/03/29 22:22:19 (permalink)


    You may be experiencing a classic impedance mismatch and the high end attenuation that can occur when an output is loaded down by to low an input value.

    The DOD graphic EQ's input impedance may be so low that it loads down the guitar pickups and causes the high end attenuation.

    Do you by chance have a spec on that EQ?

    A guitar amp usually has a input impedance of 1 megaohms or maybe 1.5 megaohms.

    The pickups have an output of 5k or maybe 10k.

    If the DOD has a input impedance of 600 ohms you've probably already guessed the issue correctly.

    If the DOD has a 10k ohm input impedance... it's probably also the case that you have figured out the reason.

    It's rare that people get to actually experience and hear a impedance mismatch. It's certainly possible that this is what you are hearing, but without more information it is just a guess.

    I'd say that this might be a great learning experience about how impedance bridges actually work.

    In general, higher input impedance allows for higher frequency response.

    I don't mean to seem pendantic, but there are so few opportunities to recognize and learn why and where impedance values really matter... that I got excited at the prospect that this may be one of those instances.

    Crazy like that. :-)

    best regards,
    mike



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    maximumpower
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    Re:Graphic eq sounds different in the loop vs inline 2013/03/29 22:48:17 (permalink)
    :-)

    I do not have the specs. It is an old (inexpensive graphic EQ). I think I got it used, many years ago.

    It sure sounds like an impedance issue. I could buffer it with some pedals (if I still had them). But no biggie.

    Thanks!

    Win 10 (64 bit), i7-2600k 3.4GHz , 8 GB RAM, SATA III (500GB SSD - System, 2TB WD Black - Data), Sonar Platinum x64, m-audio Profire 610

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    bitflipper
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    Re:Graphic eq sounds different in the loop vs inline 2013/03/30 20:59:29 (permalink)
    I think Mike hit the nail on the proverbial head. Especially if the equalizer is passive. You could test that theory by placing an active device between the guitar and EQ, such as a distortion pedal, which will act as an impedance matching stage.


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