Cosmetics and Physical Construction         views:

Some SP10 owners like to, or want to, dispense with the black cast alloy 'bathtub' that shields & protects the underside of the SP10. I'm keeping mine: I believe it adds helpful electromagnetic screening, and gives the top chasis added rigidity.

After acquring the real SP10 chassis from Shaun O. in Cape Town, I needed to restart my PCB layouts to make the boards fit inside the bathtub, and match the SP10 chassis' mounting holes. I changed my mind concerning the power supply: there is no space to fit a full power supply inside the bathtub, so I'm going with the original design concept of an outboard power box. As described previously, the power supply consists of a transformer and circuitry for five regulated DC outputs: +15V, -15V, +7.5V, -7.5V, and +5V TTL logic. All linear regulators - general switching regulators are too noisy for use here, and making them sufficiently quiet is just too much work & expense.

The power supply generates more heat than the other circuitry, so it is better off, if less convenient, in a separate enclosure where it will not heat up the platter.

The inboard circuitry consists of a 3-phase drive system (=power amplifier) and a PLL controller (2 printed circuit boards). The user interface (7-segment LED display and keypad) will be external, since I do not want to cut into the top chassis. The original 3 pushbuttons - start, 33, 45 & 78 - and speed LEDs will be retained.

Here is a photo of some mockup pc boards, cut from cardboard, to show how they will fit into the chassis.

Originaly, the SP10 came with a wired-in umbilical cord to connect it to its power supply box. I'm using a 25-pin "D"-connector to bring power into the chassis, and provide serial data in/out for control purposes. (N.B. European DIYers - the D connector hex-standoffs are NON-METRIC. Don't try to use a 3mm thread here!)

The power supply box can be any convenient or aesthetically pleasing instrument case or housing. I've had a broken 'Dantech' generic power supply in my junk box for years: its transformer is still good though and its housing will make a neat PSU for the SP10. A completely new circuit board is required (9"x4") The PCB layout is shown below (as yet un-built).

Sharp-eyed readers will notice the 'psu-on' line on the I/O connector. This allows remote on/off switching of the PSU from the SP10 pushbutton pad - or any other exotic control method that comes to mind (IR?!).

Note that this power supply is NOT a drop-in replacement for the original SP10 with its factory electronics. It doesn't have the appropriate grounding system - although it could be modified to be compatible with the original if someone required a replacement PSU for original SP10 electronics.

The three-phase power amplifier, exciter oscillator and phase envelope detectors, plus PWM and phase sequence reversal switching PCB layout is shown below, (as yet un-built).

These boards have been specifically laid out (manually routed, no autorouting!) with a view to DIY contruction & manufacture: single sided, wide traces, wide component spacing, no surface mount components, no traces between IC pins except in 'emergencies'.

The board size is limited (the left edge of the circuit board is blank) so it will fit on less than one-half of an A4 sheet of 'Press-&-Peel' toner transfer film in portrait aspect.

The heatsink for the power amp stage can be any convenient aluminium panel or strip that is physically compatible with the chosen case or plinth. I selected a 50mmx50mm "L" extrusion since I had it left over from another project. 28cm (11 inch) lengthwise just fits in the SP10 bathtub. The L165s will not dissipate a great deal of heat, probably less than 5 watts under normal running, but my philosopy is that with any heatsink, bigger means cooler and hence better, so "L" angle is better than a flat strip. This allows good thermal headroom for coping with 'problem' situations, such as a stalled motor.
A crescent portion in the centre will have to be cut away to accommodate the curve of the motor casing.

A second length of 20mm "L" extrusion - bolted to the heatsink - forms a mounting flange for the circuit board, and mounting surface for the three L165V semiconductors' TO-220 cases.

The PC board I made using Press-'n'-Peel Blue laser printer film. I prefer phenolic board because it's easier to work than fibreglass.
The pins that mate with the MJX-12A motor connector are harvested from a 25-pin male "D" connector: these are soldered directly into the circuit board.
Various section of the circuit are tested as the board is populated.

January 3^rd 2010:

Below, the essentials of the drive system are complete. The PWM block and direction control blocks are still not installed (two DIP sockets centre-left). The white flylead is a temporary link to make up for a ground commoning that exists in the custom power supply, but not in the test-bench power supply. The tiny Veroboard on pink & blue flyleads is for temporary DC balancing since the DC balancing part of the circuit board is not yet populated (DIP socket extreme left). Correct DC balancing will allow the elimination of the three small blue electrolytic capacitors, which are there to protect the motor from DC latchup during testing/prototyping. The power op-amps are on temporary individual heatsinks.

The circuit in operation! Since the PWM and direction-control chips asre not yet installed, the rotation is CCW, and speed is uncontrolled. However, getting the motor to rotate is an important step.

MOVIE - 1.2MB