DC Motor Shunt Reg

[Salas]

A friend with a Pink Triangle TT and Origin Live DC motor + OL PSU was experiencing frequent RPM slowdown drift after playing some LPs. He had to trim his PSU all the time. He asked me to devise some PSU for him. I did. He actually made it, and he reports excellent stability over long time plus top sonics. Speaks about strong gains in image size, sweetness, pitch stability and authority. He is raving so much that I thought I better show it here for anyone interested. Don't ask me more, he lives far away on an island and I can't confirm his experience first hand.
He actually used a LM317 regulated 12V DC 1.5A input to my shunt reg as I asked him to do, and leaves the reg on almost at all times, since he gets added sound benefits after an hour or so. He actually watched the voltage stability and compared it to the OL PSU. The new reg is measurably superior for voltage stability he says, both by itself through time, and after playing LPs, as well as when spinning 220g vinyl and watching the voltage when the motor actually consumes.
Anyway, here it is. Try it out if you fancy. Its not a thoroughly checked out application by me. So I show it with caution. The pre regulation is part of the recommended circuit. You may use a well stabilized 12V DC 2A wall wart or brick PSU even. If there is noise in such a device (you can check with oscilloscope), better make a typical LM317 reg with 12V output and put it in a remote box along with mains trafo and rectification away from the TT. The shunt reg's Mosfet and Darlington need a 1C/W sink.

[Salas]

P.S. When someone trims for 33RPM and 45RPM using a stroboscope, he can use 2 trimmers and with a switch, employ one or the other, for instant RPM flip.

[Salas]

This time a shunt reg for the little Maxon was made. Used with an LM317 pre reg and monitored for 15 days. Does not move a hair of Vout or rpm on a modified Walker CJ55. That assortment needs 4.85V for 33rpm on the stroboscope. Its run at 300mA CCS for a Maxon like the one Origin live used to name DC100 (Maxon order no: 110191) its an A-Max 26mm. This reg will do for anything needing over 4V DC or a bit lower. Less it can't due to the Mosfet Vgs limit. Chuffed for sonics and tempo. The whole combo is a success. What an upgrade from AC motor!

P.S. You have to trim RPM with an actual vinyl disc on the platter as the cart is reading with your preferred tracking downforce.

[Salas]

We have tried MJE350 in the parallel Mosfet's place later on and it worked fine for less than 4V by the way. So the application's scope widens to more pulley, belt, diam. sets.