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I've been attempting to make a very basic guitar/condenser microphone amplifier for a long time, and I think I'm getting close (this is the first time I'm reaching out for help on the matter). I'm running into a problem with a TL071 Op Amp: the output is noisy. I have a single-sided supply. In a basic non-inverting configuration, with a guitar connected, my output range is somewhere between +/- 1 volts, which isn't enough to drive an output stage (not pictured). IN+ and IN- are from the guitar's mono jack.


The output I get from the scope in this configuration, when plucking the high E string rather hard, is something like this. Note that the increments are set to 1 volt, and this is not sufficient for me to drive an output stage. However, distortion is minimal.

Basic Setup

First setup output from scope


I tried an alternate configuration. This produced a decent voltage with a much gentler pluck on the high E string, but as seen, way too much distortion. Note that the increments are set to 5 volts. My reasoning behind adding R3 was that I needed a "floating ground" of sorts, but clearly this backfired terrifically.

Second Setup

Second Setup output from scope

A couple of notes:

  1. I have tried connecting IN- to ground instead of the inverting input, but in that configuration, I get no output at all.
  2. I have tried putting a capacitor in lieu of R3, since I suspected the incoming voltage on IN- through R3 would cause IN+ to have a higher voltage as well (as it would go through the pickups). That also did not work. The most I got was a couple of pops when I put my wrist on the strings.
  3. I have tried adjusting the resistors to have a lower gain. This only lowered the output voltage, but did not affect the distortion.

Can someone please explain to me where I went wrong, and how I might be able to rectify this so I can get (1) a decent output voltage and (2) minimal distortion?

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    \$\begingroup\$ The guitar input to op-amp is not connected correctly. And the next problem is that your design does not work on single supply. Have you done any research on the subject, like googled how other people made a single supply op-amp? \$\endgroup\$
    – Justme
    Oct 24, 2021 at 20:18
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    \$\begingroup\$ What does a condenser microphone and a guitar pickup have in common? Pretty much nothing, so far as I know. The guitar pickup uses variable reluctance and the condenser microphone uses variable capacitance. I would imagine the need for two different 1st stage pre-amps here. In your case, is there already a pre-amp for each? \$\endgroup\$
    – jonk
    Oct 24, 2021 at 20:20
  • \$\begingroup\$ I was under the impression both used an inductor with a magnet, which produces alternating current. This is why I stated it that way. I have searched Google up and down and I couldn't seem to find anything that didn't have a ton of extra components. \$\endgroup\$
    – Aaron R.
    Oct 25, 2021 at 17:27
  • \$\begingroup\$ A transducer (this is anything that converts between some physics parameter and some electrical parameter -- usually where some physicist uses materials that have a pronounced effect that can be used for this purpose) requires care. You don't just slap a circuit onto a transducer and expect any reasonable performance. So, each transducer uses a carefully crafted electronic circuit, called a "pre-" amplifier stage, in order to nurse the transducer so that the useful qualitiies of the electrical signal are maximized, with minimum noise. Then you can slap circuits around. But only after. \$\endgroup\$
    – jonk
    Oct 27, 2021 at 8:06
  • \$\begingroup\$ The pre-amplifier you'd want for a guitar pickup is NOT the same pre-amplifier you'd want for a condenser microphone. Now, it is possible that the guitar pickup includes a built-in pre-amplifier. The condenser microphone may also have a pre-amplifier built in, as well. For example, electret microphones come naked, while some come with FETs as a simple pre-stage, and some more come with entire ICs as their pre-amplifier stage. And each need to be considered separately from the other, despite the fact that all of them are "electret microphones." \$\endgroup\$
    – jonk
    Oct 27, 2021 at 8:09

1 Answer 1

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Do it like this then turn down the volume to avoid clipping. guitar preamp

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  • \$\begingroup\$ Also add an output capacitor to block DC. \$\endgroup\$
    – tobalt
    Apr 27, 2023 at 4:02
  • \$\begingroup\$ Thank you for this. I tried it but still no dice. I tried first with the TL071. I've had a lot of trouble with TL0xx op amps in the past so I tried it with an LM324 as well. Neither circuit showed any sign of a correlated output given my guitar's input on a scope or using a piezo speaker. \$\endgroup\$
    – Aaron R.
    Jul 3, 2023 at 3:06
  • \$\begingroup\$ The TL071 preamp I showed has a gain of 11 times then if you strum loud the output will have clipping distortion. Increase the resistance of R2 to reduce the gain. \$\endgroup\$
    – Audioguru
    Jul 4, 2023 at 0:12

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