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I have a yamaha THR5 which models a low-gain preamp('CRUNCH') and a hi-gain preamp('BRIT-HI').

For some reason Brit-Hi works just fine, but Crunch doesn't sound any different from clean(except louder). My wiring diagram is a standard one from SD(HSS): https://www.seymourduncan.com/wiring-diagrams?meta_params=guitar-options,3-pickups,neck-s,middle-s,bridge-h,1-volume,1-tone

Does this behavior imply my guitar's output is too low to get any effects from the low-gain preamps? Or is there some other issues?

  • Maybe you're not running the amplifier louder enough for breakup to occur? – jazzboy Oct 31 '17 at 10:48
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    Usually "low gain" means little to no distortion, and "hi gain" means a medium amount to a lot of distortion. Seems like the amp is working as intended. – Todd Wilcox Oct 31 '17 at 11:28
  • IIRC, one of the ways to cause distortion is to have your "input volume" higher than your "output volume" - so a low-gain preamp might not be creating a higher input volume, where the high-gain preamp is creating the higher input volume. Don't know if this helps with your question, but I thought it might be interesting. – theGleep Oct 31 '17 at 14:09
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The THR tries (supposedly) to model all-tube amps. In such an amp, distortion is produced at (at least) two different spots: in the preamp and in the power stage.

  • Preamp overdrive is mostly used for long-sustain lead sounds. This requires very high gain in the first stage, but not necessarily very high volume.
  • Poweramp overdrive is an inevitable side-effect of making an amp loud - basically, of reaching its power limits. This is a more dynamic distortion, good for rhythm parts.

The “crunch” model of the amp probably focuses on the power stage, i.e. the preamp doesn't have so much gain that it really distorts by itself, it merely makes the signal really loud so it can then overdrive the power stage. But that will only actually happen if you also turn the volume way up, since the volume control sits between preamp and power stage.

With real tube amps, in particular full stacks, this is often a bit of a problem: the amps only sound good if played brutally loud, i.e. so loud that nobody else in the band can hear anything. With the THR5, don't know... but apparently that has gain, volume and additionally master controls. For a crunchy sound you'll want to turn gain medium to high, volume pretty high, and only the master down again if necessary.

Note that it's a hallmark of a tube amp to give you a good warm overdrive without sounding very obviously distorted. This is unlike analogue transistor amps, which tend to sound pretty nasty already in crunch setting.

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I don't have enough info to answer this question comprehensively but here is my experience.

Gain is something tha can be seen as a type of volume or distortion maker but it isn't. Gain is the effect that makes and instrument more sensitive to minor things. Gain increases sensitivity, not distortion or loudness. The reason why people may think that distortion of sound is due to gain is the fact that a lot of guitar amps can't take the sensitivity of the gain and this produces distortion, or the guitar amp is designed to give out a more distorted sound when sensitivity in increased. Note pre amps are those things that are made to amplify your guitar before the speaker or amp. They are initially made for those low output instruments to amplify the sound. This is why the CRUNCH amp is simply louder. If the effects on the CRUNCH preamp don't work for your guitar I would say the preamp is the problem, not the guitar. If you are wanting a higher output from your guitar then I would say that you have to put an onboard preamp on it or change the pickups to a higher output type.

In a low gain situation (CRUNCH), rubbing the pick against a guitar string should cause little or no sound. This is why low gain is usually used in a situation where a clean strumming or picking sound is needed. It can also be used to make notes clearer.

In a high gain situation (BRIT-HIGH), you should clearly be able to hear a pick rubbing against the strings. The guitar has just been made more sensitive. This is useful in situations such as pinch harmonics where the sound of the harmonic is very low and the sensitivity needs to be increased, to hear that harmonic. Volume can sometimes increase the sound of a pinch harmonic but it also increases the sound of the pick rubbing on the string making the pinch harmonic sound sloppy.

In my experience I would say that there is nothing wrong with your guitar. Just a misunderstanding. If the crunch preamp effects don't work for your guitar then the preamp is probably broken. Give both of the preamps a test with different guitars and see what happens, this may give you more information on the problem.

Good luck. :)

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