Technics 1200MK3 Power Conversion

I was recently visiting some family in Japan and bought two beat up two Technics 1200Mk3 for a very small sum of money, roughly $500 for the pair. As a reference point, a single unit domestically seems to go for $700-$900.

Of course, they were built to run on Japan’s 100V mains power and didn’t have a voltage switch so would require some modification or a step-down transformer to operate. Curiously, I found out that western Japan runs at  60Hz and the east at 50Hz, pretty weird for a country that is thin north to south. Anyway, the step-down transformer lacked elegance so I ruled it out. I had also been reading about the benefits of external transformers with the Technics units and eventually decided to just remove the whole transformer are associated power supply components and build up a new completely external power supply.

After ripping out the superfluous components and soldering in a 4 pin CB radio connector for power things looked like this (Note my ziptie strain relief, not ideal…)

DSCF4246

DSCF4248

Alright, that left the construction of the power supply itself. The technics unit wants +21V with about 500mA supply capability, which isn’t a difficult thing to do. I will note that that I always overbuild my power supplies by a factor of 2, and generally put as much capacitance as possible in there. During backcuing with all lights on the turntable will consume much more power than just 500mAh so overdoing it a little is a particularly good idea. There are many strong opinions on the internet about this modification – probably because there are quite a few companies offering overpriced and over engineered supplies that they are eager to sell. The truth is, a basic LM317 supply works fine with an 18V transformer. This means the regulator is dropping 4 Volts or so. I had all the bits lying around and put one together pretty quickly. Now, I’m sure that the fancier supplies work even better than mine, but even an LM317 is an improvement on the original (which was a classic piece of ‘bare bones’ engineering) and shouldn’t be dismissed as an upgrade. I’ll restate that I’m not trying to redefine the SL-1200 as an ‘audiofool/audiophile’ deck with this modification, I’m just trying to get a cheap set of 1200’s.

Eventually however, curiosity got the better of me and I decided to make something a little more involved. I was in the midst of modifying an old Power One power supply to generate +/-18V and so was reading quite a bit about the old but truly classic LM723 chip, mostly on this website:

I decided to build something up using the LM723 with a BD139 pass transistor. Also worked great and I decided to keep that design since it was done. I jammed the ratsnest into a small enclosure which would up looking like this:
DSCF4249.JPG
I don’t have any photos of the internals and to be honest I can’t really be bothered taking it all apart again.
So forgetting that I had to do all this to operate the turntables on my native 240V power, lets hypothetically ask was it worth it? Well I can’t really say, I didn’t use them before pulling them apart and the last time I owned a Technics 1200 was quite a few years ago. I can say that they work very well and things are sounding good at home.
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2 thoughts on “Technics 1200MK3 Power Conversion

  1. Hi Mate,
    nice little blog you got here, you look very passionate audio and electronic engineering.
    What has caught my interest is your simple aproach to builting an external power supply for your 100v jap 1200. Are you making these available for sale ? if so, i would be interested.

    cheers,
    Jason

    Like

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