Hey guys, just one question - does the power rating of an amp only refers to its power section/stage, or this includes preamp section?
Wattage rating of amps...
- Thread starter nervirasme
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Trevoire520
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sprack
Thread Killer
Also the wattage rating is what the tubes are pulling just idling. Fully cranked, pushing air its much higher.
PaoloJM
Member
Wattage on a guitar amp refers to the clean musical output power available from the power amp. It's got nothing to do with the power the valves are pulling at idle, but it's frequently the same value.
TheWinterSnow
Den Mørke Natt
The rating on the amp is that when the tubes are biased to class A. For most AB amps the idle will be around 60-84 watts total at idle. When the tubes begin to conduct the total current among them does not change because the current is shifted to the push and pull side of the transformer. So when they are cranked yes, the power dissipated on a pair of tubes will increase, but the overall power in all 4 (or 2) power tubes will be the same.
But something else happens as well when an audio signal is being sent to the power section. When the amp is in idle, there is no current going to the speaker even though there is idle current in the tubes. When a signal is applied an AC output is seen on the secondary winding of the transformer and therefor on the speaker. The speaker is also dissipating power separate to what the tubes are dissipating, but the power is relative to the coefficient of current (the AC voltage on the secondary) in the primary side of the transformer (the idle current). There was a discussion about this not too long ago and we agreed that at saturation or when the amp is fully cranked, most 120 watt amps dissipate around 300 watts in the power section alone.
A simplified math problem to view the total power of a power section when it is being played is something like (Idle Current x Vp) + (Vac(rms)/R(load) x Vac), or the idle current plus the total power at the load, where the power of the load is the output AC voltage and the load to give you current, and the current and output AC voltage to give you the load power.
So as you crank up your amp, you are increasing the power at the load, not the tubes.
sprack
Thread Killer
TheWinterSnow
Den Mørke Natt
Mater volumes hold a lot of myth to them. All the master volume pot is, is an extra pot right after the channel pots and right before the power section that controls the amount of current going to the power section. Its only purpose is to allow the user to dial in the channel volumes to each other the way they want and if they want more or less volume, just turn up the master volume, saving you from turning more than one knob and screwing up the channel volume relationship. Its just a global volume (attenuator) on top of the channel volume (attenuators), just to give you more control of the volume levels of your amp.
The power section only cares about the strength of the signal, so it doesn't make a difference in tone or operation to have a master volume other than adding extra self noise from the pot.
Yeah the concept of a master volume seems to boggle peoples minds. All my friends that are guitar players seem to think that cranking the MV pot, but putting the channel volumes low, is essentially pushing the power amp to it's full potential while keeping volumes low. It's tough to get them to understand what the MV actually is. As winter snow has said, it's just another leveling pot after the tonestack to help balance channel volumes.
Post PI masters are slightly different, but you rarely see those in the amps we use anyway.
Post PI masters are slightly different, but you rarely see those in the amps we use anyway.
sprack
Thread Killer
I should have phrased it better. I was trying to ask that since on a non MV amp as you turn up the Output you're turning up the gain to both the pre stage as well as the power at the same time. I would guess that a higher gained signal from the pre into power (being driven) would mean more dissipation on the power tubes. Otherwise, if I understand you the only thing that will change load on the power tubes would be a hotter bias?
I'm still new to this. Thanks for being gentle.
I'm still new to this. Thanks for being gentle.
