Rolling Off the Volume: Why the Extra Hiss and Tone Suck?

by Jerry Catanescu, February 2024
updated March 2026

Have you noticed your guitar gets noisier (more hiss) when you roll the volume down, compared to full up or fully off? This is especially obvious with high-gain amps or pedals. 

Here's what's going on.

Any electrical resistance produces thermal (Johnson) noise. It's caused by the random motion of the electrons in the material, and  appears as a small noise voltage across the resistor. The higher the resistance, the more noise.

A guitar pickup has a DC resistance somewhere between 5kΩ and 20kΩ (let's say 10kΩ on average). A common value for a passive guitar volume pot is 500kΩ. This resistance is chosen to be much higher than the pickup's to avoid loading it excessively, which would cause it to sound dark and lifeless. Higher pot resistance causes increased thermal noise though, except at or near the pot extremes:

- When the pot is 100% up, it looks like a 500kΩ resistor directly in parallel with a 10kΩ pickup. Their combined resistance is lower than 10kΩ (about 9.8kΩ), so the pot's high resistance doesn't actually degrade the fairly small amount of hiss produced by the pickup's 10kΩ.

- When the pot is all the way down, its wiper is shorted to ground (zero Ω). A short circuit makes no thermal noise, so this is your guitar at its quietest. Any remaining hiss comes entirely from the amp or pedals.

But what happens when you roll off the volume? You can think of the pot as two resistors wired in series. The top resistor comes from the pickup(s) and goes to the wiper, and the bottom one goes from wiper to ground. Let's say the volume is at 50%. We have the pickup's own resistance, say 10kΩ, in series with the top half of the pot (250kΩ), for a total of 260kΩ. On the bottom side, there's 250kΩ from wiper to ground. The top 260kΩ appears in parallel with the bottom 250kΩ, for an equivalent 127kΩ between the pot's wiper and ground. This is what the guitar amp sees at this point: a 127kΩ source resistance. This will generate quite a bit more hiss than the 10kΩ of the pickup alone (with the pot at max). 

The same mechanism is also the cause of "tone suck" (loss of treble) with a long guitar cable. Our 127kΩ source resistance forms a low pass RC filter with the cable's capacitance, which can easily be on the order of 1000pF (1nF) or more. 127kΩ with a 1nF capacitor to ground creates an RC low pass filter with a corner frequency of 1.25kHz. Pretty dark, eh?

So, how can we fix this? Easy. We get rid of the 500kΩ pot and use an active buffer (such as this) directly after the pickups, followed by a low value volume pot that will not cause significant hiss (or tone suck due to a long cable) when part of the way down.

This is what active guitar electronics do, in a nutshell. Less noise/hiss when backing off the post-buffer, low value volume pot, and consistent tone at all volume settings, thanks to the low output impedance that's not significantly affected by the cable capacitance.

Of course, the active buffer itself should have low self noise, so it doesn't add significant hiss to the unavoidable pickup noise. Ideally, you'll want the buffer to produce no more noise than a single 5kΩ resistor, which is a typical resistance of a single coil pickup. A 5kΩ resistor has a voltage noise density of about 9nV/rtHz. I won't explain this unit of measure here, but it's the same unit used to specify op amp voltage noise density, so we can go through an op amp's datasheet to see how if it's quiet enough for the job.

To give an example, a common TL072 op amp has a voltage noise density of 18nV/rtHz. This is the same as a 20kΩ resistor, so it's not the best choice for a guitar input buffer if you want the lowest noise. TL062, a low power op amp often found in onboard guitar preamps, is quite a bit worse!

Check out the noise simulation below, it's quite revealing. Note the very different vertical axis scales used in the two graphs.