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Hammond X-66 Manual

Vibrato driver preamp
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X-66
Hammond
   
Renovating the
Vibrato Driver Preamp
by Dan.Vigin
Hammond® and Leslie® are registered trademarks of Suzuki Musical Instrument Manufacturing Co. Ltd.
Binche / Belgium
Dec.2010
X66 Vibrato Driver Preamp
Dec.2010
dan.vigin
Page 1

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  • Page 1 X-66 Hammond     Renovating the Vibrato Driver Preamp by Dan.Vigin Hammond® and Leslie® are registered trademarks of Suzuki Musical Instrument Manufacturing Co. Ltd. Binche / Belgium Dec.2010 X66 Vibrato Driver Preamp Dec.2010 dan.vigin Page 1...

  • Page 2: Table Of Contents

    TABLE OF CONTENTS Forewords & Purpose of this project P. 3 General Description P. 4 Original Vibrato Driver Preamp circuit X-66 Headroom concept P. 6 New VDP circuit P. 8 Transistor MJE340 P. 9 Emitter resistor P. 10 Schematic Diagram of new VDP P.

  • Page 3: Forewords & Purpose Of This Project

    The first reaction is to find and replace this faulty component by a new one. Unfortunately, this driver transistor labelled 21221 in the Hammond parts list is the equivalent of RCA 39699. This transistor was produced in the early 60's and is in the line with the first generation of Si NPN transistors launched at that time by RCA, about 50 years ago !.

  • Page 4: General Description

    General Description. Original Vibrato Driver Preamp circuit. The board AO-32297-1 is located at the back side of the scanner block, under the Upper keyboard. Personnaly, I don't like at all the way this board has been engineered. This is the kind of board commonly used to create prototypes in lab's but not for production units.
  • Page 5 There is no so much to tell about the circuitry. Basic 'Common Emitter' configuration is used with a partial decoupling in the emitter resistors. Refer to original schematic diagram hereunder. Fig 5-7 (partial) of X-66 Service Manual. X66 Vibrato Driver Preamp Dec.2010 dan.vigin...

  • Page 6: X-66 Headroom Concept

    We can notice on the diagram that those preamp's are fed by a voltage of +250 Vdc which is totally unusual for a conventional audio preamp. In the X-66 console, this voltage is even more, +265 Vdc were measured ! When looking on the original schematic diagram Fig 5-7, we can see that the incoming voltage at the Treble Vibrato Drive Preamp (Drawbars) is only 0.05 Vpp (Pt.
  • Page 7 VDP are almost pure sine waves or harmonics components of them. The X-66 designers of this VDP do have certainly other good technical reasons which remain unclear to me up to now. X66 Vibrato Driver Preamp Dec.2010...

  • Page 8: New Vdp Circuit

    New VDP circuit. Since very few information as far as the specifications of this VDP board are available in the X-66 Service Manual, the original board AO-32297-1 board was dismounted and put on the workbench for test. As stated earlier, only one channel was defective (noisy), so the two others were workable for measurements.

  • Page 9: Transistor Mje340

    The overall new schematic diagram can be found on the next page. This new schematic diagram is almost identical to the original one. Beside the replacement of the old RCA transistor by MJE340, only the collector resistor has been changed from 10K/5W into 12K/5W to slightly decrease the collector current and reduce to a certain extend the power dissipation that is not negligeable due to high B+ voltage involved.

  • Page 10: Emitter Resistor

    33 Ω Ω Ω Ω Emitter resistors. In addition to that, if one wants to keep an equivalent output level at each section of the VDP board, it is also important to carefully select the foot emitter resistor of 33 Ω. Higher value of this 33Ω...

  • Page 11: Schematic Diagram Of New Vdp

    X66 Vibrato Driver Preamp Dec.2010 dan.vigin Page 11...

  • Page 12: Output Levels

    7.2 Vpp as on the original board. It's a matter of choice. There is no indication whatsoever in the X-66 Service Manual as far as the effective load composed by the vibrato phase line circuits. When analysing the structure of those circuits, it seemed to me that this load should fall in the range of 12 K.

  • Page 13: Pcb Layouts

    PCB Layouts Components side Copper side X66 Vibrato Driver Preamp Dec.2010 dan.vigin Page 13...

  • Page 14: Datasheet Mje340

    DATASHEET MJE340. X66 Vibrato Driver Preamp Dec.2010 dan.vigin Page 14...
  • Page 15 X66 Vibrato Driver Preamp Dec.2010 dan.vigin Page 15...
  • Page 16 X66 Vibrato Driver Preamp Dec.2010 dan.vigin Page 16...

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