Hi just having some issues understanding what's happening with my opamp circuit. enter image description here

Vin is a Sine wave at 1kHz and VG is 4.5V.

From what I understand this circuit should boost the signal I provide it with my guitar. Simulated the circuit on LTSpice which provided the expected output at Out. But when I built the circuit, and supplied it with an input signal from my guitar and output into a guitar amp, it was significantly more quiet than what the guitar would sound going straight into the amp. What would be the reason for the signal being so quiet and what would I further need to read up on to understand what is going on with the opamp circuit.

EDIT: For the built circuit I used an NJM4560D opamp.


1 Answer 1


Guitar pickups have a high output impedance. The should be connected to a load with a high input impedance - typically 100 kΩ to 1 MΩ. Your pre-amplifier has a 1 kΩ input impedance so there is a large voltage drop across the internal coil impedance.

Try increasing R1 and R2 by a factor of 100 and see what happens. Let us know.

  • \$\begingroup\$ oh amazing thank you it worked really well! It's still a little bit more quiet than the plain guitar signal but I'm going to guess that the values are either still too low for the resistors or the filtering on the opamp isn't great but thank you so much for your help! \$\endgroup\$
    – Koobz866
    Commented Jul 19, 2018 at 6:44
  • \$\begingroup\$ Good work. Remember that your ear's response to volume is logarithmic so a gain of 2 won't sound like an awful lot. \$\endgroup\$
    – Transistor
    Commented Jul 19, 2018 at 12:19

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