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Hammond AO-29 Frequency Response

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  • enor
    replied
    Nice work! I love it when science confirms what my ears tell me...

    Leave a comment:


  • Wes
    replied
    Signal generator or tonewheel generator input?

    Very awesome graphs, btw!

    Leave a comment:


  • stefanv
    replied
    Here is the end-to-end frequency response with the pedal at the lowest volume,

    Click image for larger version

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    and here is the difference in frequency response between the two:

    Click image for larger version

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    You can see that reducing the volume with the pedal changes the tone, de-emphasizing the mid-range.

    All plots are normalized to a peak of 0dB. These are not absolute levels.

    Leave a comment:


  • stefanv
    started a topic Hammond AO-29 Frequency Response

    Hammond AO-29 Frequency Response

    I'm in the midst of a ground-up rebuild of a Hammond AO-29-13 amplifier, as used in a 1962 M-100 series. I actually bought a second AO-29 amplifier, and am using the chassis, most of the tube sockets, and the percussion transformers from that, taking only the power and output transformers from my original AO-29 once I'm ready.

    As part of the rebuild, I'm doing extensive before and after measurements of the performance of the amplifier, so that (a) I can see the rebuilt one is working right, and (b) see if anything changed. I thought I'd share some of my findings here.

    First, here is the end-to-end frequency response of the stock amplifier (electrolytics are new), with the pedal at full volume, and the Volume Soft switch up (i.e. volume not soft):

    Click image for larger version

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    You can clearly see the 6dB/octave roll-off at 3.5kHz, beginning gradually at about 2kHz, that Hammond designed in to minimize key click.

    More to follow in later posts ...
    Last edited by stefanv; 05-12-2016, 05:56 PM.
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