Thorens TD125 Mk 2 with Grace 707 tonearm.
Text from owner:
1) Motor controller board
- replaced all resistors with 1% metal film resistors.
- replaced op-amp ICs and driver transistors.
- replaced / modify power supply section for better load regulation.
- replaced corroded wire and connectors.
- speed 16 modified to speed 33, when set to this position, speed calibration are done
with fixed resistors in series, no trimmer (variable resistor). The other two speeds done
with potentiometers (variable resistors).
** Fine turn the motor driver board for a smooth, undistorted and balance sine wave output
to the synchronous motor (with digital frequency meter / multimeter , dual channels
2) Tone Arm (Grace 707)
- Replaced Tone Arm cable with van den Hul MC502 Hybrid cable.
- Replaced RCA plugs with Audioquest RCA.
From my experience, to get the best out of the TD 125 & TD 126, the first attempt is to correct
the motor driver board as the electronics are aging ( over 25 years ). The sine wave output from
the motor driver are distorted, positive half and negative half are not balance, this can be verify with
a dual channels oscilloscope.
Unlike TD 150 & TD 160 which the motor is driven direct from AC main in series with a voltage
divider resistor, speed based on the main frequency (50 / 60 Hz sine wave), speeds are not
Thoren TD125 MkII speed control is based on an op-amp Wien Bridge frequency oscillator, it
have the advantage of speed accuracy + heavy, quiet and stable plinth, excellent isolation from
external vibration and flexible with various type of tone arm.