Hohner Bass 1/2/3 -1974     Weight = 10 Lbs. ? Number manufactured = ? MSR = $?

User Manual: Hohner Europe's page
Reset Proceedures: N/A
Operating System code:
MIDI or other control protocol:
Software related Links:
Patches or knob settings:
Circuit Overview: below
Scematics/Service Manual: Hohner Europe's page
Common Service Issues/Tips: below
Parts Sources: Keys knobs semiconductors misc
Uncommon chips/modules used:
General Info Links: Matrixsynth

Circuit Overview:
      Very simple transistor organ with envelope and three voicing options. Really crude. They have a resistance ladder keyboard and tune pot in series in the feedback loop of an inverter chip with a capacitor to ground on the front end so that it just charges and discharges to create the oscillations as threshold is crossed on the Schmidt Trigger inverter. (ST's have hysteresis so that when the signal crosses threshold going up, the threshold shifts down so that there is time before the capacitor can discharge enough to flip the output again.) Trimmer R5 offers a fine tuning amount. Which is strange since you would think the fine tune would be on the panel and the coarse tune inside?? Oh well... Then 4024 dual JK Flip Flop chip divides down for lower footages. These footages are then proportioned into a couple of mixes who envelope character can be adjusted independently by trimmers R2 and R3. The volume/timbre is affected by R1 and R4 respectively.

Service Tips:
      Seems like we mostly had bad connections, dirthy switches etc. R2 and R3 can get so hot it smokes when set too close to the end of travel! (And blow out the 78L05 voltage regulator since it draws about 400mA or so when this condition is initiated. WHY they didn't put a limit resistor there I don't know! )

Ask if you need a specific part. I don't have original knobs but can come up with something close probably. No keys.
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