Hammond H-Series Modifications

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H-Series organs are pretty underestimated nowadays. Once designed as top-of-the-line concert organs, they never matched the acknowledge of Hammonds like B3, A-100 , M3 or M-100. Nevertheless, they have a distinctive sound -- accomplished by eleven drawbars on upper manual with 14 harmonics (sub-sub-third only on percussion).

But, as being real concert organs: a H-100 simply doesn't sound like a A-100. If you want them to do so, you have to sacrify some of their superfluous features, but you get a real nice organ with some work. Imagine having 13 harmonics on your A-100, a factory string bass, reverb, percussion 2nd and 3rd, but also up to 6th! 


My HX-100 with Leslie 760 from Hammond Germany, Hamburg - fully modified and with a piano laquer finish

What's the issue?

It was done by omitting the "manual tapering" (getting a proper tonal balance through different resistor values in the manual wiring) and, instead of that, just low-pass-filtering the signal in the recovery and preamplifier stages. As a result, the organ sounded dull and mellow -- like my HX-100 before. BTW: A HX-100 is a H-100 in a X-66 like body, made by Hammond Germany in the very late 60s (see picture above).

Additionally, a multi-triggered percussion was introduced: Percussion was triggered on every key pressed, not only on the first one when playing legato. You may turn legato triggering on or off on your H-100, but the percussion preset voices are pretty bad.

What to do?

Be patient, I will announce that in the near future. Things to come:

  • Straighten frequency response by modifying recovery amps
  • Generator recalibration
  • Direct Leslie speaker output from the built-in 3-channel tube amp. The transistor amp of the 770 Leslie pictured above was dumped.
  • Usable percussion and preset voices
  • Additionally a circuit similar to the Ibanez tube screamer to get a real nice distortion
  • MIDI output for upper and lower manual, working with a dirt-cheap 8031 and single-sided PCBs only

First download the full H-100 schematics (1,5 MBytes, parts to be modified marked green) for an overview and the H-100 percussion section schematics. If you have a H-100 with transistorized percussion/pedal gate amps, you need the H-100 percussion addendum also.

I suggest buying a complete service manual if you don't have it already, especially if your organ has other defects. Mr Spitzer from Hammondstore Germany offers nicely made PDF service manuals for most Hammonds. Or invite me for a modding session (not cheap, either),

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