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Thread: Having trouble with my Vibrato and line box on the a100

  1. #21
    ff Fortissimo Sweet Pete's Avatar
    Join Date
    Oct 2014
    Vancouver BC

    The resistor inside the vibrato switch(R44?) should read 12K on an A100. Higher resistance = less vibrato mixed into the non vibrato signal.
    My B2 had no obvious tone changes on the vibrato dial just like you.I swapped the 22K(which read 33) for a fresh 12K and BINGO......
    many thanks again to George Benton.
    Also made the 'balance' resistor in the AO10 fresh!AO28 has it too.
    He also had me remove thumps in the vib manual switches with fresh caps!

    Break out some early Jimmy Smith ( 1957)
    Then listen to the chorus 'C3' on the early sixties stuff. Hear the difference?
    Englewood Cliffs,Rudy Van Gelder. RCA 77 and Neumann U47 mics.
    Hammond changed the R44 chorus resistor to 12K in 1959 when the A100 was introduced.

    All Blues,The Cat and many many more.The Sermon....

    Hope this helps.
    Happy Spring!
    A100/147 B2/147 A102/222 M102/145 M111/145 L133/770 1937 Northern Hammond(third one built) BCV/122 NordStage2 EX88 Yamaha MOX6,Neo Ventilator
    Radial J type DI's ,Mogami Starquad wiring ,various Yorkville Powered Speakers,Allen+HeathMixWiz3,Behringer X32,SWR Pro220 bass amp,Fender ProReverb

  2. #22
    ff Fortissimo enor's Avatar
    Join Date
    Jan 2013
    Vargön, Sweden

    Quote Originally Posted by PGR View Post
    I am assuming that the introduction of the v's is the triggering of the vibrato scanner into the mix? If this is not correct straighten me up please.
    The vibrato delay line has multiple taps, each phase delayed a bit in relation to the previous one. The effect is that each tap provides a "snapshot of the tone taken at a different time", so to speak. Then, the scanner uses these delayed "snapshots" and sort of fades them in and out, sequentially.

    The result is sort of what you hear when a police car passes by on the highway - the Doppler effect makes the pitch of the siren go down as the car pulls away (and up as it approaches, but this effect is more subtle). As the scanner runs up and down the delay line the perceived audio goes up and down in pitch - a vibrato.

    In other words - the delay line in itself doesn't vibrate the tone; the delay line and the scanner together make up that action and provide vibrato (the V settings). The C settings (chorus) is a mix of straight and vibrating audio.

    If you have very little difference between settings, two things could be the cause:

    1. A short in the scanner or switch assembly. This would make all of the settings more of a pulsating tremulant than a vibrato
    2. Bad caps in the delay line. This would make the vibrato diffuse and "muddy".

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