RTZ 4840393 User manual

RTZ Professional Audio, LLC
Alpharetta, GA USA
Web: http://www.rtzaudio.com
Email: [e-mail]
COPYRIGHT © 2022, RTZ PROFESSIONAL AUDIO, LLC
RTZ® IS A REGISTERED TRADEMARK OF RTZ PROFESSIONAL AUDIO, LLC DOC-REV-A03
3/5/2022
MOTOR DRIVE AMPLIFIER
4840393
AMPEX UPGRADE ELECTRONICS
Owner’s Manual

Motor Drive Amplifier
4840393
RTZ Professional Audio, LLC 2
1. INTRODUCTION
Thank you for purchasing your new RTZ motor
drive amplifier for Ampex MM-1200 studio
recorders! All cards are hand built and
individually tested prior to shipping. Before
installing the card, please read this document
thoroughly and retain it for future reference.
Additional copies of this manual are available
upon request or may be downloaded from our
website at http://www.rtzaudio.com.
All items are carefully packed to endure the
rigors of shipping and handling. However,
please inspect all contents and packaging
immediately upon receipt. Please report any
problems to us immediately. In the event of
damage, retain all shipping and packaging
materials for shipper damage claims inspection.
2. DESCRIPTION
The RTZ MDA (motor drive amplifier) replaces
the original Ampex MDA for the MM-1200 and is
designed for use in machines with three TO-3
motor driver output transistors on the MDA
heatsink chassis. The RTZ MDA is optimized to
work with the DTC-1200 digital transport
controller, but can also be used with the
standard Ampex transport controller as well.
The RTZ MDA includes torque offset adjustment
trimmers that allow fine adjustment of the torque
balance between reel motors. Balanced torque
offset is critical for use with the DTC-1200
controller.
The RTZ MDA torque offset is calibrated by
using the DTC-1200’s zero torque adjustment
diagnostic feature. The offset trimmers are
adjusted until the motor just begins to develop
torque at a known reference DAC level. The
motor drive torque signal can be observed with
an oscilloscope connected to test points on the
MDA board as well.
3. WARNING! - ELECTRICAL HAZARDS
ARE PRESENT IN THE MDA AREA!
THE MDA CIRCUIT AND ASSOCIATED
COMPONENTS CONTAIN RECTIFIED AC
MAINS VOLTAGE. HIGH VOLTAGE DC IS
PRESENT ON THE MDA CARD AND
EXTREME CAUTION SHOULD BE USED ANY
TIME MEASUREMENTS OR ADJUSTMENTS
ARE BEING MADE. WHEN INSTALLING OR
WORKING WITH THE MDA OR IT’S
ASSOCIATED COMPONENTS, USE A
QUALIFIED SERVICE TECHNICIAN. ALWAYS
USE EXTREME CAUTION ANY TIME YOU
ARE WORKING WITH THE MDA CARD!
NEVER DIRECTLY TOUCH THE MDA CARD
OR ANY OF IT’S PCB COMPONENTS WHILE
THE BOARD IS INSTALLED IN THE
MACHINE. ALWAYS ASSUME THAT THE
MDA BOARD AND ANY OF IT’S
COMPONENTS CONTAIN LIVE VOLTAGES
PRESENT WHILE INSTALLED IN THE
MACHINE!
USE EXTREME CAUTION IF THE MDA CARD
IS INSTALLED IN THE MACHINE ON AN
EXTENDER CARD! MAKE ABSOLUTELY
SURE THAT NO BODY
PARTS, TOOLS, TEST
CLIPS, WIRES OR OTHER
OBJECTS COME INTO
CONTACT WITH THE MDA
BOARD OR ANY OF IT’S
COMPONENTS AT ANY
TIME!
A MOMENTARY SHORT TO THE CARD CAN
CAUSE SPECTACULAR ARC-AND-SPARK
ACTIVITIES AS WELL AS THE VERY REAL
POSSIBILITY OF DAMAGING THE MDA
CARD AND THE REST OF THE MACHINE!!!
DO NOT HOT SWAP THIS CARD! ALWAYS
REMOVE POWER BEFORE INSERTING OR
REMOVING THE MDA CARD FROM THE
MACHINE!!!
DISCLAIMER
THE USER ASSUMES ALL RISK BY
INSTALLING OR USING THIS MDA
CARD. RTZ PROFESSIONAL AUDIO,
LLC ASSUMES NO LIABILITY OR
RESPONSIBILITY FROM USING THIS
CARD. THE MDA CARD IS SOLD AS IS
WITHOUT WARRANTY AND WITHOUT
ANY MECHANTABILITY OR FITNESS
FOR ANY PARTICULAR PURPOSE.

Motor Drive Amplifier
4840393
RTZ Professional Audio, LLC 3
4. CONFIGURATION JUMPER
Jumper JP1 must be correctly strapped before
the MDA is installed in machine! The MDA card
ships strapped for use with the DTC-1200 or
default non-tension kit equipped machines. You
must change the jumper setting if you plan to
use this MDA card with a legacy Ampex tension
equipped machine.
If the Ampex tension kit is used, jumper JP1
must be set to positions 2 & 3. Otherwise, set
this jumper to the position 1 & 2 for use with the
DTC-1200 controller or legacy Ampex
controllers.
Table 1 - Jumper Configuration
JP1
Jumper Configuration
1 & 2
This jumper position must be
strapped if the MDA is used with
the DTC-1200 controller or the
stock Ampex controller card on
machines not equipped with the
legacy Ampex tension kit.
2 & 3
This jumper position must be
strapped if the MDA will be used
with the legacy Ampex tension kit
equipped machines only.
Refer to Figure 1 to select the appropriate
configuration required for your machine. Unless
you plan to use the original Ampex tension kit,
it’s best solder this in position 1 & 2 to avoid any
potential issues that might arise from use of a
removable jumper.
Figure 1 - Jumper Strapping
5. PROTECTIVE FUSES
The RTZ MDA card uses fuses to protect the
MDA card in the event a TO-3 output power
transistor fails/shorts, a power surge occurs or
an over-current situation occurs that exceeds
the time delay fuse limit. A large TVS spike
protection diode is connected with the fuse such
that the fuse will blow in the event of an over
voltage or over current condition.
Check the TO-3 output transistors carefully
should your MDA card ever blow a fuse.
Replace the fuse with the same 500mA SLO-
BLO type specified. Always replace the fuse with
same type shown in Figure 2 below or with an
equivalent replacement fuse type.
Figure 2 –Fuse Replacement
Manufacturer:
Bussmann / Eaton
Part Number:
BK/S506-500-R
Fuse Type:
Time Delay/Slow Blow
Current Rating:
500 mA
Fuse Size:
5 mm x 20 mm
AC Rating:
250 VAC
ALWAYS REPLACE THE FUSE WITH THE
SAME TYPE FUSE OF THE SAME RATING
IN THE EVENT A FUSE EVER BLOWS.
ALWAYS CHECK THE LARGE TO-3
TRANSISTORS ON THE MAIN MD
HEATSINK CAGE IN THE EVENT A MDA
FUSE EVER BLOWS. TYPICALLY, A
BLOWN MDA FUSE INDICATES A
SHORTED TO-3 OUTPUT TRANSISTOR
ON THE MDA HEATSINK.

Motor Drive Amplifier
4840393
RTZ Professional Audio, LLC 4
6. OFFSET TRIMMER ADJUSTMENT
FOR USE WITH DTC-1200 DIGITAL
TRANSPORT CONTROLLER
Trimmers R3 and R4 are 10-turn precision
trimmers that allow adjusting the input reference
voltage to the op-amp motor drive servo loop.
These trimmers allow adjusting the starting point
at which the motors first begin to develop torque
and begin to spin. This alignment procedure is
best done with the DTC-1200 diagnostic MDA
DAC zero alignment procedure available in the
DTC TTY configuration console.
Open the DTC-1200 serial TTY configuration
console window, select the diagnostic menu and
then select option #5 “MDA DAC zero adjust”to
output the DAC reference values. Make sure no
tape is loaded on the machine before running
this diagnostic procedure as the reel motors will
spin.
Advance the DAC output level to 75 at the
prompt and adjust each trimmer until the motor
just begins to develop torque and spins as
slowly as possible. Adjust each motor to spin
closely to the same speed. Do not adjust the
trimmers to either end stop extreme. In general,
you should not need to adjust the trimmer in
either direction more that 2-3 turns. This
calibrates DAC level 75 as the starting torque
point for the constant tension servo loop.
7. OFFSET TRIMMER ADJUSTMENT
FOR USE WITH LEGACY AMPEX
CONTROLLER
The RTZ MDA card works with the original
Ampex controller and is optimized to work with
the RTZ DTC-1200 Digital Transport Controller
card. It includes offset adjust trimmers to allow
adjustment of the starting torque point for each
reel motor.
The MDA error inputs are 5mA current loop
interfaces. The offset trimmers allow adjusting
the point at which the motor first begins to
develop torque for a given input current. The
motor should drive full torque at 1mA or less,
and no torque at 5mA current present at the
error input.
Remove the MDA card from the machine and
adjust multi-turn trimmers R3 and R4 both to the
mid-scale position (approximately 5-turns). You
can measure the trimmer resistance (across the
wiper and an end stop pad on the PCB) with a
DVM. Adjust the trimmer for 1.1K ohm center
scale with the MDA card removed from the
machine.
The RTZ MDA offset adjust trimmers can be
calibrated by removing the transport controller
card and connecting a couple 4.8K resistors to
the MDA take-up and supply “error input” pins to
ground. Connect a resistor lead to MDA edge
connector pin 8 or J and the other lead to
ground. Connect another resistor to pin 10 or L
and ground. Note you can also access the MDA
error inputs via TP2 & TP3 on the RTZ MDA
card.
The 4.8K shunt resistors provide 5mA current to
the MDA error input to signal no torque from the
motor. At 1mA and lower, the motor should run
at full torque. The Ampex transport control card
extender is another easy way to gain direct
access the MDA current loop error input signals.
Once you have the shunt resistors connected,
fire up the machine and observe the reels for
any motion. If no motion, adjust the
corresponding offset trimmer counter clockwise
up to 1-3 turns and motion should start. Adjust
just until till no motion is present. If the motor is
already running, adjust clockwise 1-3 turns till it
stops. Generally, the offset trimmer should have
around 1.1k resistance (or nearby).
Do not turn the trimmer to end stop extremes. If
unsure, kill the power, remove the MDA card
and measure across the trimmer center and end
stop and adjust for around 1.1k if necessary.
Basically, we want to apply 5mA current loop
load to the MDA inputs, and then adjust till
motion just stops fully. No further adjustment
should be required on the MDA unless major
components or the line voltage change. This
completes the MDA balance and input level
calibration procedure. Go back and align the
Ampex controller overall gain and readjust all
the tension settings as usual.

Motor Drive Amplifier
4840393
RTZ Professional Audio, LLC 5
8. PCB COMPONENT LEGEND

Motor Drive Amplifier
4840393
RTZ Professional Audio, LLC 6