Thorens TD-125 Mk II power supply

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TD125 Power supply

I visited Norbert Bayer's web site and had a look at the Verdier reg, but could not found a reg suitable for Thorens. The Verdier regulator is for DC motors only.

The TD125 has a low voltage synchronous AC motor, which is fed by a sinus generator (switchable and tunable oscillator plus power output). The oscillator and power output work with unregulated DC. At the moment I do not remember whether 12V or 15V.

There are two means to beef up your TD125. First, you could use a larger unregulated power supply by an outboard power transformer, big and fast rectifiers, and big electrolytic caps.

Second, you could use just a regulated DC source (like your standard laboratory DC voltage power supply) and feed the DC directly to the circuit, behind the original rectifying section. Just connect the DC supply to the existing electrolytic cap. You have to disable the original AC supply coming to the board then, but you need the old small power transformer for the strobe light, still. But then, you could install a modern quartz controlled strobe light, instead.

Be careful not to mix plus and ground, or you might see some fireworks. :att'n:

BTW, being at the power supply board, just replace the old electrolytic cap with a modern one. The old caps are likely going to fail after long years of usage.

BTW, the second method is used by Phonosophie in their P3 record players, which are based on the Thorens TD2001/3001 models.

best regards,
If you look at the schematic in the manual, the power amp is the Wein bridge oscillator. You would have to disconnect the positive feedback network and you would need to replace the light bulb in the negative feedback loop with a resistor to use it as an amp.
You could also build Dhaen's oscilator shown in Raka's thread and feed its output directly to the power amp section of the Thorens own psu, bypassing its wien-bridge oscilator.
You can't do that, the 125 uses a quadrature oscillator. That means in this case two sine waves, shifted by 90°. The Thorens motor (MKII) needs between 3.5 - 6V, not more. Go lightning up yourself :dead: (no offence meant)

You can't do that, the 125 uses a quadrature oscillator. That means in this case two sine waves, shifted by 90°. The Thorens motor (MKII) needs between 3.5 - 6V, not more.

Thank you for your technical contribution to this thread. Unfortunately, it's useless because it is wrong. First, the Thorens MkII PSU does not use a quadrature oscillator. Secondly, and referring to the Thorens MkII PSU schematic, the output of the push-pull pair on the right connects to the opamp on the left through an RC network (C8/R7). This network provides the 90 degree phase shift. So you only need one sine wave signal, because the psu itself provides the phase-shift plus power amplification. Therefore, if you do what was suggested by Ray, and feed the output of Dhaen's circuit to the opamp on the right, it will work. You still have to check about signal levels, see how you're going to power the digital board from the Thorens rails, and so on...
But my point is that conceptually it can be done, and that it makes sense to explore this route. On one side you have the Thorens PSU with the power stage done, but with an oscillator that leaves room for improvement, and on the other you have Dhaen's circuit which provides a very stable sine wave, but lacks the power boost to drive the motor. And note that once you remove the wien oscillator circuitry from around the opamp on the right, you free a set of terminals on the speed selecting switch, which could then be wired back to the digital board to select the frequency (as it is drawn, the digital circuit does not provide room for this, but it can be done), making the final circuit work exactly the same way as the original.

Go lightning up yourself (no offence meant)

Maybe not. But for someone with such an apparent lack of understanding of basic electronics, you sure do sound quite arrogant. And you probably meant "enlighten".

the way you describe it now, it may work. But, as you said, you can't simply bridge the wien-bridge ocscillaor, unless you take the phase shift arrangement into account. This, and the lower voltage, have not been mentioned before. And so it had to be mentioned, because dhaens psu is not a drop in.
Sorry for the crashed joke, it was referring to the inherent light bulb of the oscillator.

Edit: I was referring to a wrong schematic. You are right that dhaens actual schematic of a sine wave generator does not imply high voltage.
(the word PSU did, at last for me)
A difficulty with the TD125 is that the motor supply is at 40Hz for 33.3rpm and pro rata for the other speeds. Unfortunately its not exactly 40Hz but around 38Hz. Ideally one would like to use a crystal controlled psu to improve the relatively poor frequency stability of the wein bridge oscillator that comes with the turntable. Most off the shelf crystal controlled tt psus give 50 or 60Hz outputs for 33.3rpm and often appropriate frequencies for 45rpm as well. These psus are rarely continuously adjustable in frequency and even more rarely does the adjustment go down to 38Hz. As far as I can see the best solution is to precision turn a new metal pulley to replace the stock plastic one, so that a 50Hz input to the motor will rotate the platter at precisely 33.3rpm. The small increase in speed shouldn't lead to a perceptible increase in motor noise.
If you decide to experiment with motor pulleys make sure that you get, or make, an appropriate pulling tool. The pulley is an extremely tight push fit onto the motor spindle and attempting to pull it off directly is almost certain to damage the motor.
I have never understood why Thorens use 16 pole synchrous motors on their record decks ( even today ), surely the more widely available 24 pole types will have less cogging and lead to improved wow and flutter performance? It should be easy enough to replace the stock Thorens motor with a 24 pole type, turn an appropriate pulley, and use a crystal controlled power supply?
Hello, I have used a TD125 mk2 and a mark one for a number of years and have seen this subject raised on quite a few ocasions! I replaced the motor and psu with the Origin Live kit. This includes the outboard psu( get the large one!) with speed change and speed trim on the regulator case. The motor comes with a fixed pulley and does not use a slipping clutch arangement.
I think that this is the next upgrade to the 125, apart from the plinth, damping the hub, top plate and intermedeate plate. remaking the pu arm board etc etc. I can recomend the Mark Baker kit as I haver used a few of them an different t/ts In comparison to a Mitchell Gyro this t/t inc. a motor kit is really quite inexpensive.
Easy and cheap: record two sinewaves in quadrature to an mp3 and play back on an ipod through a Sonic impact "T amp". You can play with the actual phase relationship until you find the optimal point (89 degrees on the motor I have to hand). I call it the vinylpod, it costs $30 if you already have an ipod or other MP3 player. You'll be amazed at how well this works.

Expensive but perfect: buy a high end HP two channel waveform synthesiser with internal precision reference (eg HP3326A + option 001) and put the output through a small stereo amp of your choice. You did say cost no object.
psu for TD125

I too have tried the diy route for t/t psu's but for absolute reliabilty I chose , eventually, to buy a new motor and psu from Origin Live. I chose the Advanced kit. I have had no problems with this unit and have been using it for over two years now........... I think the build quality of the Advanced system is the equal of the riginal TD125 and should present no problems to any TD 125 Owner.
My thorens 125

My thorens was running well. I bought a Lux PD 121 with Grace arm and put that in my main system. Now the Thorens is in the second system but the motor refuses to turn. It seems to vibrate back and forth quickly. Is this the power supply issues discussed in this thread? Did I insult the Thorens with the Lux and this is its way to get back at me? Patrick
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