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Generally you want to avoid noise early on in the gain chain just because it gets amplified later on. Headroom is entirely relative, you just need to design you

Generally you want to avoid noise early on in the gain chain just because it gets amplified later on. Headroom is entirely relative, you just need to design your gain stages such that the power amp isn't railing when you turn your guitar up halfway.

grandalf 12y ago
I see. Intersting. How do you think about the desirable distortion characteristics vs bad "noise"? Is there an industry standard definition for guitar amps? Seems like the bad noise in the case we're discussing would be what the tube circuit generated when it was not being intentionally driven to distortion... is that a correct interpretation?
- hamiltonkibbe 12y ago
  Noise would be thermal noise generated in circuit components, or mains hum, anything that is there when you aren't playing any notes. I wasn't spraking exclusively about guitar amps, all this applies to analog electronics in general.
- kazinator 12y ago
  Noise is anything that is still present when you take away the desired input signal, excluding deliberate time-based effects like reverbs and delays. Frequency components that are not in the original signal, but are only present when the signal is there are usually distortion. (Why "usually": radio-frequency interference is noise. In audio, you may not notice RF when there is no signal. But when signal is present, it may mix with RF in a nonlinear way, causing additional distortion products attributable to the RF. I.e. the RF noise is "descends" into the signal's frequency range via intermodulation.)
kazinator 12y ago
Note that your two points are contradictory: - avoid noise early on in the change - turn your guitar up halfway If you want to avoid noise early in the gain chain, do not rob your guitar of signal by attenuating the output of the pickups with the guitar's volume. Now though that is done, by some players (and works for them), it isn't a way to get headroom or minimize noise. You get the least amount of noise by keeping the volume of the guitar at maximum, and switching tones later in the chain. A clean pre-amp channel has much better noise characteristics than a dirty channel, and rolled down guitar volume control.
- hamiltonkibbe 12y ago
  The point I was making about turning the guitar up halfway was that you need to design amplifier gain stages so that there is not so much gain that the amplifier hits the rails with a reasonable input signal. E.g. If your preamp stage has a voltage gain of 100 and your expected input signal is 1v p-p but you only have +/-20v rails for the power amp stage, you objectively don't have enough headroom.

grandalf 12y ago

I see. Intersting. How do you think about the desirable distortion characteristics vs bad "noise"? Is there an industry standard definition for guitar amps? Seems like the bad noise in the case we're discussing would be what the tube circuit generated when it was not being intentionally driven to distortion... is that a correct interpretation?

hamiltonkibbe 12y ago
Noise would be thermal noise generated in circuit components, or mains hum, anything that is there when you aren't playing any notes. I wasn't spraking exclusively about guitar amps, all this applies to analog electronics in general.
kazinator 12y ago
Noise is anything that is still present when you take away the desired input signal, excluding deliberate time-based effects like reverbs and delays. Frequency components that are not in the original signal, but are only present when the signal is there are usually distortion. (Why "usually": radio-frequency interference is noise. In audio, you may not notice RF when there is no signal. But when signal is present, it may mix with RF in a nonlinear way, causing additional distortion products attributable to the RF. I.e. the RF noise is "descends" into the signal's frequency range via intermodulation.)

kazinator 12y ago

Note that your two points are contradictory: - avoid noise early on in the change - turn your guitar up halfway If you want to avoid noise early in the gain chain, do not rob your guitar of signal by attenuating the output of the pickups with the guitar's volume. Now though that is done, by some players (and works for them), it isn't a way to get headroom or minimize noise. You get the least amount of noise by keeping the volume of the guitar at maximum, and switching tones later in the chain. A clean pre-amp channel has much better noise characteristics than a dirty channel, and rolled down guitar volume control.

hamiltonkibbe 12y ago
The point I was making about turning the guitar up halfway was that you need to design amplifier gain stages so that there is not so much gain that the amplifier hits the rails with a reasonable input signal. E.g. If your preamp stage has a voltage gain of 100 and your expected input signal is 1v p-p but you only have +/-20v rails for the power amp stage, you objectively don't have enough headroom.