Bill and Will's Synth
MOTM 900 & 950 Construction

The first module we built was a MOTM 900 power module.  We did this because it's one of the simplest (Paul Schrieber rated it as a "1" by  on his scale of 1-5 difficulty) and because we'd need power to test the other modules as we build them.

Early on, our plans were smaller - our synth plan just a little more than a Synthi-A's worth of modules and so, for power, we only planned on one 900 (+/- 15V) and also a 950 because the 510 Wave-Warper and 650 Midi-CV converter we ordered would require the +5V power of the 950; and because we needed more 15V supply as well (+/- 15V, +5V).

As our plans evolved, and our system grew to nearly the functional equivalent of a Synthi-100 and to be housed in four separate cabinets, we needed a lot more power.  But here, in the interest of completeness,  we're going to just cover the 900 and 950... we'll cover the larger power distribution system on a different page - "Our Medium-Sized Synth Power Distribution" Page.

Table of Contents

This page has become really long, so here's a table of contents that we hope will make it easier to traverse:

Background - presents an explanation and Paul Schrieber's initial description of the Module with a couple photos from Larry Hendrey

Parts - presents a Bill of Materials and notes about it

Construction -

Set up / Testing

Use notes

Background

Each MOTM900 and MOTM950 has a 3-unit panel that beautifully supports the power supply stuff - the plug & fuse unit, the switch, a Power-One power supply gadget, and the power-supply distribution board.

Here's what Paul says about the 900:

"The MOTM-900 is a 3U wide, low-noise linear supply that accepts AC line inputs from 100 to 240VAC 50/60Hz (jumper selected) and outputs +-15VDC at 800ma. The easy-to-change fuseholder accepts standard 5mm x 20mm fuses. Instead of noisy 3-terminal regulators, the MOTM-900 uses a 723-based design, using a pre-assembled and tested Power-One supply. This makes assembly of the kit fast and almost fool-proof.

"Each MOTM module uses a 4-pin connector called an MTA-156. These are "industry standard" connectors that have been in use for over 20 years. The MOTM-900 contains a special pc board that has 12 individual MTA male connectors. A 4-conductor, 18ga wire harness (part number PWR-20, included with each kit) connects the module to the MOTM-900. In this manner, a "star" power distribution scheme is used for lowest noise and avoiding ground loops.

"Specifications for the supply include:

  • LINE REGULATION: +-0.05% for a +-10% AC input change (very likely!)
  • LOAD REGULATION: +-0.05% for a 50% load change (highly unlikely!)
  • RIPPLE: 5mv pk-pk MAX. <1mv pk-pk typical

"Since the average MOTM module draws 20ma from each supply, at 65% rated capacity (to keep the heat down) the MOTM-900 can power over 20 modules. An additional power distribution board can be purchased (see the catalog) to supply over 12 modules.

"In the past, "homebuilt" synthesizers with 3-terminal regulators have suffered from noise, hum, and crosstalk. The MOTM-900 design and power distribution system eliminates these problems, and will provide years of trouble-free service.

Paul doesn't have a schpiel about the 950 on his site.

Here's our rap:

Each MOTM900 and MOTM950 has a 3-unit panel that beautifully supports the power supply stuff - the plug & fuse unit, the switch, a Power-One power supply gadget, and the power-supply distribution board.

The 900 has an HAA15-0.8-AG dual Power-One (click here for ,pdf spec sheet) that provides .8 Amps (800 milliAmps) of +/-15Volts DC.  Each 950 has an HTAA-16W-AG triple Power-One (Click here for .pdf spec sheet) that provides .4 Amps (400mA) of +/- 15V DC and also 2 Amps (2000 mA) of +5V DC.

The 900 power distribution board has twelve .156 MTA four-pin headers. The 950 has .156 six-pin headers and .156 MTA four-pin headers.

And here are diagrams of how the components go together:

 

Construction

 

Set up / Testing

Use Notes

 

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The fine Print:
Use this site at your own risk.
We are self-proclaimed idiots and any use of this site and any materials presented herein should be taken with a grain of Kosher salt. If the info is useful - more's the better.  Bill and Will

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