I'm trying to build these 2 pedals:

  1. http://byocelectronics.com/lilgrayodschematic.pdf
  2. http://byocelectronics.com/lilcompschematic.pdf

enter image description here enter image description here

both circuits have these parts separated from the "main" circuit.

When I find symbols such as "+9v", "Vr", "VrefA", "V+" and the likes, does it mean I have to connect the component from the "main" circuit to these kind of "outs" that are pointing upwards on those separated parts? Like this?

enter image description here

What am I missing here?

  • \$\begingroup\$ Yes. this is the common way to show voltage supplies. Since they are used all over the place they're typically not connected with lines and rather reference with symbols like what you see. \$\endgroup\$
    – MadHatter
    Sep 7, 2020 at 4:25
  • \$\begingroup\$ So the +9v on the power supply should be connected to the dc input, right? and the other +9v on the circuit could be connected to the common 9v line I set in my breadboard? \$\endgroup\$
    – JMz
    Sep 7, 2020 at 4:41
  • \$\begingroup\$ @JMz yes. In short, you connect all the identical-named connections together: All +9V connections go to the common +9V input on your breadboard, all Vr connections go the positive terminal of C5, all ground connections (upside-down triangles with no names) go to the common ground (the negative terminal of the 9VDC input) of the breadboard, etc. \$\endgroup\$ Sep 7, 2020 at 5:12
  • 1
    \$\begingroup\$ draw lines connecting all of the ground points together ... see how cluttered and unclear the schematic diagram becomes \$\endgroup\$
    – jsotola
    Sep 7, 2020 at 6:34

1 Answer 1


Yes exactly. Those symbols dont represent actual components they are just a "bus" symbol. All it means is every symbol that matches needs an electrical connection between them. It also implies what voltage those lines should be at constantly when powered on. Usually a voltage regulator will be somewhere in the schematic if its a complete schematic.

In the Li'l Gray OD schematic +9V is the external 9 volt power source. V+ is just wired up to the power source through 100 ohm resistor so its effectively also 9 volts. Not really sure why they did that, its generally bad practice. Vr probably stands for "voltage reference" and basically is just sitting at around 4.5 volts. Vr is basically used to bias the opamp in the schematic which is typical for an Opamp.

  • \$\begingroup\$ this being a guitar pedal, I suspect there won't be a voltage regulator and the input is supposed to be +9v only (battery or wall-wart) \$\endgroup\$
    – RJR
    Sep 7, 2020 at 7:19
  • \$\begingroup\$ @RJR That could be, but in that case having a V+ is a bit confusing.. perhaps its battery driven but the batteries are double A and the 9V is from a Dc-DC converter... that would make some sense as 9 volt batteries are rarely used due to being very inefficient. \$\endgroup\$ Sep 7, 2020 at 7:24
  • \$\begingroup\$ @JeffreyPhillipsFreeman - have a look at the schematics, they use an external "9V" supply. :) In the Gray, V+ connects to +9V through a 100R resistor. In the Comp, they appear to have missed the connection from +9V to +V, but just connect. For this sort of application, 9V is nominal, not precise. \$\endgroup\$
    – awjlogan
    Sep 7, 2020 at 8:29
  • 1
    \$\begingroup\$ Ahh I see, thanks I'll update my answer. \$\endgroup\$ Sep 7, 2020 at 8:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.