Bill and Will's Synth
Cat Girl Synth - CGS63 "Power Delay" Construction

October 2009 -

In anticipation acquiring of our Synth cases, we decided we'd better build a power delay for each one just to be on the safe side.  We asked Dave Brown about it and he recommended these from Cat Girl Synth.

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 Thomas White's list of the Module's features

Parts - presents a Bill of Materials and notes about it

Modifications - minor modification to the mounting screw holes

Construction Phase 1 - Resistors, Capacitors, IC Sockets, Power Plugs, MTA headers

Construction Phase 2 - Trimmer, Relay

Set up / Testing

Background

This is how Ken Stone desribes it:

"The Power Supply Delay is a support module of sorts. Due to rather heavy usage of bypass capacitors in the synth and diy scene (a good thing) some shortcomings of commercial power supplies have come to light. The most frequent is the failure of one or both power rails to come up at power-on, caused by the initial demand of all the bypass capacitors. The power supplies sense this as an overload and shut down.

"If modules were brought on-line in groups instead of all at once, the power-up surges would be limited to what the power supply can handle. Of course, once a group of modules has started, its current demands are less, allowing ample capacity for the supply to start another group of modules.

"The Power Supply Delay does exactly that. After a predetermined time, it closes a set of relay contacts, powering the modules connected to it.

"There is another advantage to doing this as well. The power supply has started and settled before modules are connected to it, giving them a cleaner power-on, and thus a cleaner reset signal for those modules that use a power supply based reset.

"The delay is adjustable, so as more modules are added, extra Power Supply Delays can be added, adjusted to different times to keep the start-up load distributed.

"It is better of course to have all Power Supply Delay boards powered directly from the power supply in a "star" configuration than to run them connected in series.

A little on how it works:

The schematic for the Power Supply Delay

"The circuit can be considered to be three parts, the delay, the +/- 15 volt system, and the +5 volt system.

"When power is applied, the voltage across the 1uF capacitor slowly rises. When this voltage passes the reference voltage set by the trim pot, the output of the voltage comparator to which they are attached swings positive, turning on the buffer transistor and the relay(s). This in turn routes power from the inputs to the outputs.

Parts

Will and I used Ken Stone's BOM to develop our own.

Modifications

The CGS63 PCBs each have four mounting holes the right size for a size 4 screw. We want to use size 6 screws (like on the Syth Tech power boards), so we drilled the holes out bigger. We didn't actually figure this out until after we'd built the Power Delays. No biggie, we just carefully enlarged them after the fact. But you might want to consider this up front.

Construction Phase 1

All the stuff in Phase 1 gets soldered using "Organic" Solder.  At every break in the action, we wash the board off to get rid of the flux.

Jumpers and Resistors

Capacitors, Semiconductors, IC Jack

IC sockets, Diode, Power Stuff

This is how we put in the power headers -

first the source header

we solder just one pin

then adjust  the header, making sure it's in all the way

then we set the supply headers in place

we used a piece of cardboard to hold the headers in while we flipped it over

like this

again, we soldered just one pin per header

then we adjusted them as required

then we soldered the rest of the pins

all done

Construction Phase 2

All the stuff in Phase 2 gets soldered using "No Clean" Solder.

Trimmer & Relay

RCO Resistor

The RCO resistor needs to be determined with the Relay in the circuit. Ken Writes:

"If you are using only +/- 15 volts in your synthesizer, and using relays with 12 volt coils a little measurement and calculation is required. Once the relay (or relays) is/are in circuit, measure the resistance across the coil(s). RCO needs to be one fifth of this resistance in order for the relays receive the correct voltage."

The Relay we used has a rating of 720 ohms across the coil... but we measured it like Ken instructs:

In this photo, the coil is reading about 700 ohms - but when we re-calibrated the meter, it read a little higher - approximately 720.  And all the relays read the same so we're betting it's a good reading.

720 / 5 = 144

The nearest value of 1% resistor is 143 ohms.  So we'll order some up from Mouser and finish construction when we get them.

Done

Set up / Testing

Use Notes