# How wire to VREF & VCC on a breadboard & how to draw them in LTSPice?



## disthymia (Aug 27, 2019)

I'm currently learning how to read schematics and set-up a breadboard but while trying to study the Mach 1 Overdrive (Greer Lightspeed) schematic, I got stuck on the VREF & VCC connections.

I started off by studying this video ( youtu.be/yWZmX79_gcU ), but he only mentions positive and negative (ground).

Does VREF just mean connecting back to positive?


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## phi1 (Aug 27, 2019)

Looking at the Mach1 schematic:

The + and - connections are from the power jack or battery.  Assuming a 9V supply, VCC is almost 9V (there is a small voltage drop across the 1N5817).  The VREF is roughly 4.1V after the 4.7k/5.6k voltage divider.

Pretty much all circuits with op amps will have a VREF near 4.5V to bias the input of the op amp.

On your breadboard just set it up according to the schematic.  You could omit the diode if you want (it's just there for polarity protection in case you wire up the power backwards.  Not mentioned on the schematic is Op Amp pin 8 to VCC and Op Amp pin 4 to GND.  This is assumed for all op amp circuits.  (These pin numbers are the same for all dual op amps, but different for single op amps like TL071).


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## Chuck D. Bones (Aug 28, 2019)

In LTSpice, Vcc, Vref and any other voltage source is represented by the VOLTAGE component.  After you place it on the schematic, you can set the attributes such as DC voltage, AC voltage (for AC sweep) or a waveform of your choosing (for transient simulation).  You can make Vref the same way the actual circuit does with two resistors and a capacitor.

I strongly advise you to keep the 1N5817 protection diode.  It's 200mV drop is trivial and it will not only protect you against wiring errors, it also protects against accidentally hooking up an AC or positive center pin power supply.


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