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Need +15 volts from schematic

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10/10/1999 6:41 AM
Aron	Need +15 volts from schematic On the memory man schematic: http://www.fortunecity.com/tinpan/humperdinck/223/memory.gif Can anyone tell me how to get +15 volts from this schematic? I only see negative voltages. I guess alternately, is there a way to reverse the polarity? Thanks, Aron

10/11/1999 2:36 AM

Something to notice - the 4047, a CMOS logic part with VDD at pin 14 and VSS at pin 7 - is being run with VDD at GND, and VSS at some negative voltage (didn't notice if -15 or what). For some reason, they're running this circuit 'upside down'.

I also failed to find where B1, B2, etc go. Is there another page or some stuff missing?

Flipping the circuit over to run from a 'positive' supply shouldn't be too tough. The IC pins at GND go to +15, the pins at -15 go to gnd. The opamp and transistor biasing will have to be re-thought.

Any particular reason for your concern?

10/11/1999 3:19 AM
Aron	I gave up. I understand how it works now. I just wanted to "splice in" a JFET buffer instead of using the existing buffer. I fixed my problem by replacing the JRC4558D chip with a good TL072. Fixed! Thanks, Aron

10/11/1999 9:34 AM

The circuit uses a negative voltage supply because the delay chip is a p-channel device. The power supply connections and biasing for the opamps and the cmos chips are then modified to use ground/V- for V+/ground respectively. Think of it in relative terms - on the opamps, pin 8 is more positive than pin 4. That is true of the either of the power connections gr/v- or v+/gr and the opamp would be biased to 1/2 the supply voltage: -7.5v (neg. supply) or +7.5 (pos. supply). Confused yet?

regards, Jack

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