Bill and Will's Synth
Our Medium Size Synth
Power Distribution

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 a 900 (+/- 15V) and also a 950 because the 510 Wave-Warper and 650 Midi-CV converter we ordered would require the +5V 575 ma power of the 950; and because we needed more 15V supply as well (+/- 15V, +5V).

But 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 figured we'd need more power.

Exactly how much power?

Well - that's an interesting question.  Our ultimate design includes modules we won't be building for a while and that we don't even show yet in our synth design on our main synth page:

Supply

We ordered four power supplies from Paul - two each of the 900s and 950s - so we'd have four panels - one each for our cabinets with plug, fuse, and switch.  But instead of mounting the power supply units and power distribution boards on the panels, we'll mount them separately in the cabinets. 

Each 900 has an HAA15-0.8-AG dual Power-One (click here for .pdf spec sheet). Each 950 has an HTAA-16W-AG Power-One  (Click here for .pdf spec sheet).  We'll put one HAA15-0.8-AG and one HTAA-16W-AG in each top cabinet (that's where the +5V is needed).  In each of the bottom cabinets, we'll put an HBB15-1.5-AG; 1.5 amps of +/- 15V.

Indicators

We want to have LEDs to indicate when the power is on - green for each +15V "rail," red for each -15V "rail," blue for each +5 "rail."

We didn't know exactly how to go about it, so we asked Dave Brown. He wrote us back:

"LEDs on all three supplies is a good idea. I always make sure that there are modules on every power supply that have LEDs. The brightness of the LED will tell you that the voltage is reasonable, but not accurate. For example, if for some reason the +15 was only at +12, the LED brightness would probably be indistinguishable.

"...Sometimes a power supply will "crowbar" meaning the inrush current was sufficiently high that it goes into current limit. LEDs will tell you that they all came up.

"Figure out how much current you want to drive the LEDs with for a reasonable brightness. If they are all the same, then make each of the currents be the same. LED brightness varies with color and efficiency so I run my blue LEDs on much less current. Also, the voltage drop varies with color.

"Assume a standard red LED with 2.0 volt drop. 3 - 5 mA would be enough current.

"For the +15 volts supplies: (15-2.0)/5 mA = 2600 ohms. Use probably the next higher value, so 2K7. Use this for both the + and - 15 volts supplies. For the -15 volt supply, just turn the diode around. Connect the cathode to -15 and the anode to ground.

"For +5 volts, you want the current to be the same. Use the same formula to find that resistor. Using 2K7, (15-2.0)/2K7 = 4.8 mA. (5-2.0)/4.8 mA = 625R. Use a 620 ohm resistor.

"You could probably get away with higher resistance values. It depends on the brightness you want."

But we're total idiots so we asked Dave to show us exactly how to do it.  We mentioned that we were going to use a blue LED for the +5V indicator.  He reminded that these are a little brighter that the green and red.  He provided us with this little diagram - thank goodness - easy as cake.  (Thanks Dave!)

Distribution

Here's the distribution plan for the top cabinets:

Here's the distribution plan for the bottom cabinets:

Special Power for DFA875 Oscilloscope Module

We're going to include the DFA875 Oscilloscope Module in the bottom-Right cabinet and rather than building a special power supply PCB to convert the +/-15V to the 6V required for the scope, we're going to use a little wall-wart transformer. So we'll include a power outlet box in the cabinet and increase the fuse accordingly.

Power cables illustrated...

The above synth layout (four cases - each two rows high and 18U wide) can be accomplished with a couple power cable layouts.

One uses all standard 20" MOTM power cables, but with two distribution points. This may have advantages, given power distribution considerations:

Another layout is with mostly 20" power cables (red), but some custom  24" cables (or 30" cables) (green) and centrally located distribution. 

Set up / Testing

Use Notes