More headroom on amp ?

charleshaupt

Hi all ,does the increase of level on an amp mean more or less headroom ? Have heard various opinions on this topic ,just asking thanks

GuitarDoge

I'm not sure exactly what you're asking, but I'll try to explain everything.

Increasing the power increases the level/volume. At some point however the amp cannot cleanly amplify a signal anymore and it becomes clipped, giving us overdrive/distortion that we all know and love.

Amps rated at a higher wattage rating can amplify cleanly to a higher level ie have more headroom. This maximum headroom is determined in the design and cannot be altered.

Most modern valve guitar amps have at least 2 main controls, gain and level/volume.

Gain means voltage to the pre-amp section. This section is usually designed to clip the signal, meaning as soon as gain increases the signal clips more and more giving overdrive.

The volume knob controls the voltage to the power amp section. The power amp is usually designed to increase the loudness as much as possible without distorting the sound. There will however be a point at which even the power amp starts distorting, and this will be your maximum clean headroom.

Please correct me on anything I may have wrong.

psyx

Swapping out preamp tubes like replacing a 12ax7 with a 12ay7 will increase headroom and also biasing the amp a little cooler will increase headroom. Some amps can be modded to change the preamp structure, altering headroom.
Different types of power amp tubes also break up at different amplitudes.

ezietsman

psyx wrote: Swapping out preamp tubes like replacing a 12ax7 with a 12ay7 will increase headroom and also biasing the amp a little cooler will increase headroom. Some amps can be modded to change the preamp structure, altering headroom.
Different types of power amp tubes also break up at different amplitudes.

I don't believe swapping the preamp tube changes headroom. If you exchange a 12ax7 with a 12ay7 (lower gain) all that happens is that the power section sees a smaller input signal, dropping the volume. You then need to turn the volume knob a bit further to get back to the same volume.

Only way to get more headroom is to somehow make the amp louder, i.e. install a more efficient speaker, or tweak the amp so that each amp section can handle a higher input signal without distortion. This is done by increasing the rail voltage over the tubes (can only go SO far before you fry them) or using a different set of tubes and altering the bias accordingly i.e. you can (only just) run a 5E3 with 6L6 valves instead of the standard 6V6 (This is what Neil Young did with his 5E3).

Best bet -> change the speaker to a louder one or get a different amp. My 5E3 is not stupendously loud, because of the speaker (I think it has 93dB efficiency) so it breaks up readily at reasonable volumes, but not so much when I play it through my 100dB Marshall Cab.

psyx

ez wrote: Best bet -> change the speaker to a louder one or get a different amp. My 5E3 is not stupendously loud, because of the speaker (I think it has 93dB efficiency) so it breaks up readily at reasonable volumes, but not so much when I play it through my 100dB Marshall Cab.

But thats related to speaker breakup, isn't it? And higher speaker efficiency means that the speaker does more or less with the power it receives...

AlanRatcliffe

Strictly speaking, headroom is the amount of gain before distortion. But that's more of an audio engineering/hi-fi definition. It gets a lot more complicated with guitar amps because we have multiple stages of gain and we purposely clip certain stages and then apply more clean gain stages to boost the level of the clipped signal. And don't get me started on compression effects - that's a whole other ball 'o wax...

And yeah, a more efficient speaker will let you get higher volumes for everything, so it effectively increases your headroom. Very few speakers add much distortion of their own until you really push them and most designs seem to avoid stressing the speaker.

Headroom limits apply to every amplification stage in a system, so it usually defined by the lowest headroom of any stage. You can be distorting the heck out of a pedal while your amp is just ticking over. Modern master volume amps can get high levels of distortion in the preamp at a range of volumes.

I've learned that for most guitar players "more headroom" means one of two things - more clean volume or more gain range/lower gain. With the former, more efficient speakers can work - as long as you don't mind your dirt going up a step too. For the latter, substituting lower gain preamp valves often does the trick as it keeps the amp at it's maximum rated output but provides more graduation between clean and dirt and often works better for those who like using their volume controls (remember a lot of modern high gain amps, there is soo much gain that the guitar's volume acts more like an on/off switch than a volume/ gain control).