5 ms·

Not necessarily bad, but something that breaks up easily at low signal levels limits your headroom which leads to more noise later on

kazinator 12y ago
That is nonsense. Headroom is inversely proportional to how much distortion you are getting, no matter where in the signal chain. A metal tone has very little headroom. You can't add headroom to it without gating tricks: measuring the level of the pre-distorted signal, and using that to control the volume of the distorted signal. Headroom is bad anyway. The electric guitar has way too much dynamic range to be useful. For clean guitar, your best friend is compression, so that you don't disappear in the mix against other instruments when you articulate some passage of notes softly.
- grandalf 12y ago
  Why couldn't you just introduce attenuation after each stage to preserve headroom in the next stage (assuming you had sufficient dynamic range)?
  - kazinator 12y ago
    Of course, that's how it's done. Thus distortion is just an effect and not amplification. You can put a gain of thousands. The resulting may be swinging close to rail-to-rail (relative to the distortion effect's power supply). This is too much for the next thing in the chain, so it is turned down. No brainer.
- hamiltonkibbe 12y ago
  To clarify what I meant about headroom, I was specifically talking about headroom before the circuit starts to clip/break up/etc. e.g. If you have a diode clipping OD/Distortion circuit made out of some diodes with a Vf of 5mV as opposed to the 700mV of a normal diode, you would need to have a smaller input signal for an equivalent amount of distortion. That smaller signal has a lower SNR given some constant noise floor from thermal noise etc, and the SNR can only stay the same or get worse after you start amplifying it.
  - kazinator 12y ago
    That is well and good, but pointless. People use such a circuit to get a heavier distortion with the same input signal, not to get light distortion with a smaller signal. Let's put it this way: if you have high gain metal distortion circuit gained up to a 5mV clipping threshold, and then you roll down your guitar volume knob to play the blues, you're kinda using it wrong.
    - hamiltonkibbe 12y ago
      It's pointless in the case that you mention, where you're going for a hard clipped metal distortion tone. I was envisioning more of an overdrive sort of application where hitting the rails is NOT the desired effect. The 5mV hard clipper was an extreme example, but you could conceivably use it for soft overdrive/compression with a small enough input signal which was what I had in mind.
      - kazinator 12y ago
        If hitting the rails is not desired, then don't configure the effect to have so much gain. The point still stands that you can get the distortion effect, at the desired amount, at various places in the signal chain. The problem you're talking about is about using too weak a signal and then using make-up gain. That can also happen anywhere in the chain. I can reproduce the problem without distortion at all, using a clean signal chain. Repro 1: turn down the guitar volume to simulate an extremely weak pickup. Then turn up the input gain to compensate. Result: noticeable increase in noise. Repro 2: turn down pre-amp volume, and crank up power amplifier volume to compensate. Result: noticeable increase in noise. Gains/levels have to be evenly distributed in the chain. Sure, you will lose headroom if your intent is to have some soft distortion from the back-end of the amplifier, but you put a heavier distortion earlier in the signal chain. The heavy distortion masks the later one; it evens out the level so the headroom from the back is not available. There is a fix for that: you can punch that distortion in and out with your foot as needed.
  - grandalf 12y ago
    are SNR issues like that and the headroom an issue for a guitar amp? I mean why couldn't the solid state part be designed conservatively with extra headroom? Or do the desirable distortion products make that difficult even with a conservative design in later stages?

kazinator 12y ago

That is nonsense. Headroom is inversely proportional to how much distortion you are getting, no matter where in the signal chain. A metal tone has very little headroom. You can't add headroom to it without gating tricks: measuring the level of the pre-distorted signal, and using that to control the volume of the distorted signal. Headroom is bad anyway. The electric guitar has way too much dynamic range to be useful. For clean guitar, your best friend is compression, so that you don't disappear in the mix against other instruments when you articulate some passage of notes softly.

grandalf 12y ago
Why couldn't you just introduce attenuation after each stage to preserve headroom in the next stage (assuming you had sufficient dynamic range)?
- kazinator 12y ago
  Of course, that's how it's done. Thus distortion is just an effect and not amplification. You can put a gain of thousands. The resulting may be swinging close to rail-to-rail (relative to the distortion effect's power supply). This is too much for the next thing in the chain, so it is turned down. No brainer.
hamiltonkibbe 12y ago
To clarify what I meant about headroom, I was specifically talking about headroom before the circuit starts to clip/break up/etc. e.g. If you have a diode clipping OD/Distortion circuit made out of some diodes with a Vf of 5mV as opposed to the 700mV of a normal diode, you would need to have a smaller input signal for an equivalent amount of distortion. That smaller signal has a lower SNR given some constant noise floor from thermal noise etc, and the SNR can only stay the same or get worse after you start amplifying it.
- kazinator 12y ago
  That is well and good, but pointless. People use such a circuit to get a heavier distortion with the same input signal, not to get light distortion with a smaller signal. Let's put it this way: if you have high gain metal distortion circuit gained up to a 5mV clipping threshold, and then you roll down your guitar volume knob to play the blues, you're kinda using it wrong.
  - hamiltonkibbe 12y ago
    It's pointless in the case that you mention, where you're going for a hard clipped metal distortion tone. I was envisioning more of an overdrive sort of application where hitting the rails is NOT the desired effect. The 5mV hard clipper was an extreme example, but you could conceivably use it for soft overdrive/compression with a small enough input signal which was what I had in mind.
    - kazinator 12y ago
      If hitting the rails is not desired, then don't configure the effect to have so much gain. The point still stands that you can get the distortion effect, at the desired amount, at various places in the signal chain. The problem you're talking about is about using too weak a signal and then using make-up gain. That can also happen anywhere in the chain. I can reproduce the problem without distortion at all, using a clean signal chain. Repro 1: turn down the guitar volume to simulate an extremely weak pickup. Then turn up the input gain to compensate. Result: noticeable increase in noise. Repro 2: turn down pre-amp volume, and crank up power amplifier volume to compensate. Result: noticeable increase in noise. Gains/levels have to be evenly distributed in the chain. Sure, you will lose headroom if your intent is to have some soft distortion from the back-end of the amplifier, but you put a heavier distortion earlier in the signal chain. The heavy distortion masks the later one; it evens out the level so the headroom from the back is not available. There is a fix for that: you can punch that distortion in and out with your foot as needed.
- grandalf 12y ago
  are SNR issues like that and the headroom an issue for a guitar amp? I mean why couldn't the solid state part be designed conservatively with extra headroom? Or do the desirable distortion products make that difficult even with a conservative design in later stages?