Ray Wilson authored this content while he was actively running MFOS as the founder and resident genius.
We retain the content because it reflects a valuable point of view representing that time and place.

Article by Ray Wilson

PC Board Parts Layout Illustrations

IMPORTANT INFORMATION ABOUT TEMPCO INSTALLATION

Metal film 2K Ohm 1/4W +/-2% T.C. +3300 PPM temperature compensators are recommended for R15, R67 and R109. They are not mandatory but will provide improved VCO stability relative to temperature change. The drawing at left shows the relative areas of the PC board where these resistors are located. Do not install tempcos AND resistors or the oscillator scaling will be one half of what it should be or 1/2 octave per volt. Hand matched discrete NPN transistors (2N3904 or equivalent) can be used in place of the SSM2210 matched pairs. The transistors should be in thermal contact with each other and with the tempco. The pads where the tempco replacing R15 is installed are highlighted in red rectangles. Install the socket and SSM2210 first then install the tempco in thermal contact with the SSM2210. DO NOT install R15 if using the tempco. If a tempco is not used then install R15 normally (where the legend is) since putting a regular resistor in contact with the expo transistors will have no effect. The pads where the tempco replacing R67 is installed are highlighted in red rectangles. Install the socket and SSM2210 first then install the tempco in thermal contact with the SSM2210. DO NOT install R67 if using the tempco. If a tempco is not used then install R67 normally (where the legend is) since putting a regular resistor in contact with the expo transistors will have no effect. The pads where the tempco replacing R109 is installed are highlighted in red rectangles. Install the socket and SSM2210 first then install the tempco in thermal contact with the SSM2210. DO NOT install R109 if using the tempco. If a tempco is not used then install R109 normally (where the legend is) since putting a regular resistor in contact with the expo transistors will have no effect.

Using Two Discrete Transistors Instead Of SSM2210

Just to reiterate you can use 2 non-matched transistors just to get the oscillators going but you need matched transistors in order for the ULTIMATE's VCOs to track 1V/octave accurately. When using two discrete NPN transistors (matched or unmatched) in place of the SSM2210 you just insert them onto the PC board in the holes where the SSM2210 chips would have gone. As you can see from the diagram below the SSM2210 chip contains two NPN transistors. One is connected to pins 1 (collector), 2 (base) and 3 (emitter) and the other is connected to pins 6 (emitter), 7 (base), and 8 (collector). Pins 4 and 5 are not connected (N.C.). Thus if you use discrete transistors instead (2N3904 or 2N2222) just insert them into the holes where the SSM2210 IC would have been mounted. One of the transistors will go into the holes for SSM2210 pins 1 (collector), 2 (base) and 3 (emitter) and the other will go into the holes for SSM2210 pins 8 (collector), 7 (base) and 6 (emitter). Nothing goes into the holes for pins 4 and 5. Simply do the same thing for each SSM2210 you replace with discrete transistors. NOTE! You can insert the pins of the two discrete transistors into the appropriate pins of the 8 pin socket that fits in the space for the SSM2210 instead of soldering them if it is a high quality socket with machined pins. While the less expensive sockets work adequately with ICs (though I always use machined sockets) I would not trust the connection with transistor pins and would solder them directly into to the board rather than use the sockets. Attach an aluminum spring clip heat sink to each lead as you solder it when using matched discrete transistors to avoid changing their characteristics with overheating.

PC Board Module Map

This view shows the locations of the various modules on the PC board. While doing some troubleshooting recently I found out first hand that this is a handy thing to have.

PC Board Part Designators View   Larger Image

PC Board Part Values View   Larger Image

Notice that you do not install resistors: R118, R76, or R21 shown in the designator view above. These designators are simply not used. This view is VERY HANDY while populating the PC board. The PDF can be printed and used for a bench reference. The large size image can be printed in pieces by dividing it in your paint program and perhaps printing the board as four separate quadrants.

PC Board Silk Screen View For Reference

PC Board Top Copper View For Reference

PC Board Bottom Copper View For Reference