I made an op amp buffer using a TL071 for my guitar but it is very noisy. buffer schematic

The circuit is a simple follower. Originally I had no feedback resistor but I added it later in case it decreased the noise but it didn't make a difference. The noise is not a hum, it's like white noise. It's audible only with distortion but it's pretty loud when it's audible. Even if I ground the non-inverting input (together with the input signal as I've soldered it) it doesn't change. I'm using two 9v batteries for power supply which pass through the 3-way pickup selector which I'm using to cut power to the two supply rails. The guitar is a Cort X-1. The output goes directly to the jack. The input is directly from the bridge pickup.

EDIT: I added 2 ceramic 100nF capacitors to the op amp supply rails. It didn't help much. Also actually when I connect it to my amplifier (while my amp is on) and then either turn off the buffer or disconnect the cable the noise seems to almost go away but it comes back when I close my amplifier (Marshall MG15CF) and turn it on again. That happens with and without the capacitors. buffer schematic 2

  • \$\begingroup\$ Could be oscillations (above audio range). Do you have both + and - DC bypassed to ground very close to the op-amp with short-lead capacitors? \$\endgroup\$
    – glen_geek
    Jun 23 '19 at 13:44
  • 1
    \$\begingroup\$ Shows us physical photos of your circuit. \$\endgroup\$
    – DKNguyen
    Jun 23 '19 at 15:43
  • \$\begingroup\$ Do the pickups share the same ground? \$\endgroup\$ Jun 23 '19 at 16:04
  • \$\begingroup\$ @ScottSeidman Yes \$\endgroup\$ Jun 23 '19 at 16:49
  • \$\begingroup\$ Why do you need the buffer? Why isn't the guitar pickup connected directly to the amplifier's input? Is it because you are using a low impedance dynamic mic input instead of a high impedance line input? \$\endgroup\$
    – Audioguru
    Jun 23 '19 at 22:10

You should try adding a .1 blocking cap on the input and also connecting a 1M resistor to Ground and another 1M resistor to the 9v rail, after that cap, on the plus input. The resistors will set a bias point for the opamp and the input cap will block DC from interfering with your pickups. You can omit the 220r and add a big cap on the output of the opamp. Something like a 4.7 if or 10uf will work.


The opamp in that configuration has very high Zin, and will accept any Efield and Hfield interference induced on the pickup cable. Is the cable a coax? Insert 10Kohm and 0.01uF between output of coax and the opamp; this is 1,600 cycle-per-second lowpass, and will greatly reduce EMI and RFI. Ensure the shield of the coax is tied to the common-VDD node ( the common GND of the two bypass caps) with very short (1/4")wire.


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