Technics SP-10 Mk 2 Power Supply
1-2020
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Intro
Intro
I've built a couple power supplies for the Technics SP-10 mk2 turntables, and I recently came across some appropriate panel meters, so this webpage describes the construction of an SP-10 power supply with a bit more eye candy in the form of three voltmeters (that really only give an indication that all is well with the power supply). The following paragraph, describing the power supply, is an updated version from my pretty comprehensive 2015 SP-10 rebuild (webpage here):
The stock power supply provides 5VDC and 32.5VDC for the logic and motor, along with 140VDC for the strobe lamp. Since I had replaced the existing strobe lamp with LEDs (mostly for reliability), I only needed the 5 and 32.5V supplies. I designed a supply based on LM317 regulators, with some of the enhancements from the datasheet schematics, mostly based on Gary Gallo's design published in The Audio Amateur magazine, issue 4/90, p.47. The LM317HVT regulators were suggested for this application by Dave Cawley here, see post 82. Note that the Technics power supply holds off the 32.5V supply until after the 5V supply is up and running. I believe they only need to come on simultaneously for the unit to work. The capacitor in the adjustment leg of the LM317 determines charge-up time, so in my supply, I used a larger 47uf cap in the 32.5V supply (for a slow ramp-up) than in the 5V supply, where I used a 10uf cap (for a fast ramp-up). This has worked just fine for my SP-10s.
Schematic
Schematic
Below is my schematic for the power supply, with parts values and pinouts of the XLR connector (note the INSIDE view, as you wire it up) and the LM317 regulator IC.
The Component Parts
The Component Parts
As usual, this project started with a chassis from Par-metal.com. I ordered a custom size for this project of their Series 12 all-aluminum chassis. I use these chassis almost exclusively lately: they always fit together well and have pressed in metal inserts for the screws holding it together.
This chassis is 10.5" wide by 9" deep by 3" tall.
The faceplate was designed using Frontpanelexpress.com, and is shown here with the paper copy printed before ordering to confirm dimensions and fit. Their Front Panel Designer software (for Windows or OSX) allows me to design virtually any panel I need, and included either printed or engraved (which I use) labels.
The faceplate is slightly larger than the chassis: 11" wide by 3.5" tall.
The front and rear panels marked for drilling & cutting. I always wait for the front panel to arrive before starting the front sub-panel to ensure all the switches, LEDs, meters, etc. line up correctly. In this case, I drilled two of the 1/8" holes (which will eventually hold the meters in place) and attached the faceplate to the sub-panel with two screws, then proceeded with all the other drilling to ensure good alignment.
This shows the faceplate with the front sub-panel and rear panel after drilling and cutting. I cut the meter holes with a jigsaw, so they're pretty rough, but won't show at all in the finished unit. Only you and I will ever see them.
The rear panel at the back only needs holes for the IEC connector, fuse, and XLR connector to supply the SP-10.
The 6" ruler below gives you an idea of size.
The chassis ready for assembly.
I found some appropriate PCBs on ebay that fit all the regulator parts nicely, one for the 5V supply and one for the 32.5V supply.
This shows the two PCBs from the AC input side, 5V PCB on the left and 32.5V supply on the right. The main input smoothing cap is toward the camera with the MUR860 rectifier diodes to the left on each PCB.
This shows the output side of the regulators, with the LM317 and its heatsink as well as the voltage-setting resistors and output cap.
The 3 meters for this unit. These are all NOS vintage Simpson 2.5" units. The 150VAC meter (on the left) is a model 1257, and the 10VDC (center) and 50VDC (right) meters are model 1227.
Test fitting all the components before assembly & wiring.
Transformers are from Antekinc.com, also recommended.
Completed Power Supply
Completed Power Supply
After assembly, it actually looks neater without all the long transformer leads. Note the 5V supply has the transformer secondaries wired in parallel, but the 32.5V supply has two 15V supplies wired in series, as shown above on the schematic.
Another shot of the interior from the rear showing the inside of the front panel and the meter connections.
Note the AC volt meter (on the right here) has 120VAC on its terminals (like the power switch, IEC connector, etc.), so they're covered in adhesive heat shrink to prevent anyone from accidentally touching then while servicing the unit.
The completed unit, buttoned up, powered up and showing the correct voltages.
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