# amp volume



## vadsy (Dec 2, 2010)

Can anyone chime in on what are the major factors that determine how loud a tube amp is? I know that low watt amps are still usually loud and a 100 watt is really only a few decibels louder than a 50 watt, or at least I think I read that somewhere here. I just want to know if it's the size of transformers or efficient speakers or cab size, etc.
Thanks


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## doriangrey (Mar 29, 2011)

I'm curious to hear what some of the more technically knowledgeable folks here have to say - but my two cents would be that speakers have as much to do with it as the wattage of the amp. A 25 watt amp through a 4 x 12 is probably gonna be just as loud as a 100 watt head through a 1 x 12. It's also interesting how my 100 watt head going through a 4 x 12 gets loud quickly up between 1 and 4 but past 4 the volume difference isn't as great but the clean headroom and breakup obviously changes...I don't think this question has a simple answer...looking forward to what others have to say - I'm gonna research it too cuz Im also curious about the technical aspects of your question...


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## Jim DaddyO (Mar 20, 2009)

I may be a bit out on this, but as I understand it, to double the volume (in dB) you need 10x the wattage. Therefore, all things being equal, a 10 watt amp is 1/2 as loud as a 100 watt amp.


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## dtsaudio (Apr 15, 2009)

> all things being equal, a 10 watt amp is 1/2 as loud as a 100 watt amp


That is correct. 
A doubling of power whether it's 5 watts to 10, or 50 to 100 is only a 3db difference in volume. 3db is about the minimum change in volume the human ear can hear. It is a logarithmic relationship, not linear (for those into math).
The biggest single contributors to volume is the speaker efficiency, (It doesn't matter whether it's a single speaker, or multi-speaker set up) and distance from the sound source. There's a ton of math on this I won't go into. 



> A 25 watt amp through a 4 x 12 is probably gonna be just as loud as a 100 watt head through a 1 x 12


See above - It depends on the efficiency of the speakers used to a great extent.
What will happen is, that up to a point, both amps run into the same speaker will be capable of the same volume levels. At least until the 25 watt amp runs out of power. The 25 watt will distort much sooner than the 100 watt and the 100 watt will be able to get louder cleaner. This is known as headroom. Very important if you want clean undistorted sound, like coming from the PA or monitors



> interesting how my 100 watt head going through a 4 x 12 gets loud quickly up between 1 and 4 but past 4 the volume difference isn't as great but the clean headroom and breakup obviously changes...


Two things going here. One is the characteristics of the volume control. The other is characteristics of how the ear perceives the sound.


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## loudtubeamps (Feb 2, 2012)

Yeah. It's a whole bunch of things for sure.
How the pre-amp is designed(voicing and gain),number of gain stages etc.
How the phase inverter is designed.
Big factor is how much high voltage (B+) do the output tubes see.
Output tansformer,choke vs resistor, B+ filtering,and of course size (surface area) and efficiency rating of speaker(s) and enclosure type.
And on and on...........


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## loudtubeamps (Feb 2, 2012)

doriangrey said:


> I'm curious to hear what some of the more technically knowledgeable folks here have to say - but my two cents would be that speakers have as much to do with it as the wattage of the amp. A 25 watt amp through a 4 x 12 is probably gonna be just as loud as a 100 watt head through a 1 x 12. It's also interesting how my 100 watt head going through a 4 x 12 gets loud quickly up between 1 and 4 but past 4 the volume difference isn't as great but the clean headroom and breakup obviously changes...I don't think this question has a simple answer...looking forward to what others have to say - I'm gonna research it too cuz Im also curious about the technical aspects of your question...


"Not necessarily" or to rephrase, a different approach.
If you take a 100 watt +- 4 valve output amp and plug it into a 10" x 100 watt speaker, you can take the amp up to it's full ouput potential but take the same amp and chuck it into a 4 x 12" cab and stand back.Suface area of 4 x12" vs surface area of a single 10"....no contest.


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## dtsaudio (Apr 15, 2009)

> How the pre-amp is designed(voicing and gain)


That is related to apparent volume - a treble control turned up on an amp will sound louder. The number of gain stages has nothing to do with volume, just how quickly it gets to that volume via the volume control. An amp with a gain of 30 is as capable of playing as loudly as an amp with a gain of 50. The higher gain amp will just get there with less volume control rotation. All other things being equal of course.



> Big factor is how much high voltage (B+) do the output tubes see.
> Output tansformer,choke vs resistor, B+ filtering


Nothing to do with volume. Everything to do with power.


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## dtsaudio (Apr 15, 2009)

> If you take a 100 watt +- 4 valve output amp and plug it into a 10" x 100 watt speaker, you can take the amp up to it's full ouput potential but take the same amp and chuck it into a 4 x 12" cab and stand back.Suface area of 4 x12" vs surface area of a single 10"....no contest.​


You're basically correct. The 4 x 12 can move a lot more air than a single 10. However, if all the speakers have the same efficiency rating (including the 10"), singly they would all appear to have the same volume. However every time you add a speaker to the mix you increase sound pressure by 3db. So the 4x12 would be theoretically about 12db more efficient than the single 10. That doesn't take into account cabinet design, impedance, power handling capacity and a whole slew of other parameters. 

As an aside, 2 8" have the same area as a single 10, 2 X10 = 12", 2x12= 15" (approximatly)


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## loudtubeamps (Feb 2, 2012)

dtsaudio said:


> That is related to apparent volume - a treble control turned up on an amp will sound louder. The number of gain stages has nothing to do with volume, just how quickly it gets to that volume via the volume control. An amp with a gain of 30 is as capable of playing as loudly as an amp with a gain of 50. The higher gain amp will just get there with less volume control rotation. All other things being equal of course.
> 
> 
> 
> Nothing to do with volume. Everything to do with power.


Some interesting stuff here. FWIWEL34 - Wikipedia, the free encyclopedia
A quote from the link:
"In common with all 'E' prefix tubes, using the Mullard-Philips tube designation, the EL34 has a heater voltage of 6.3V. According to the data sheets found in old vacuum tube reference manuals, a pair of EL34s with 800V plate voltage can produce 90 watts output in Class AB1 in push-pull configuration. However, this configuration is rarely found. One application of this type was in "Australian Sound" public address amplifiers commonly used in government schools in Australia in the 1950s, using four EL34s for ~200 watts. More commonly found is a pair of EL34s running Class AB1 in push-pull around 375-450V plate voltage and producing 50 watts output (if fixed bias is used), while a quad of EL34s running Class AB1 in push-pull typically run anywhere from 425-500V plate voltage and produces 100 watts output. This configuration is typically found in guitar amplifiers, especially Marshalls and is quite hard on the valves."

As well, Hiwatt was known for high plate voltages(700+) on the output section to produce the STA 200 and 400 series of amps.
http://i1132.photobucket.com/albums/m570/loudtubeamps/DSC03800.jpg
Cheers, d


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## dtsaudio (Apr 15, 2009)

I've seen one of those Hiwatt's with a 700 volt plate. I thought my meter was wrong when I first measured it. Most modern EL34's won't take anywhere near 700V anymore. They're just not made for it. Interesting, though this 1960's (I'm guessing) still had the original Mullard EL34's in it, and they were testing fine. Modern tubes would have died within months. It was one powerful amp.


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## Wild Bill (May 3, 2006)

6550's will take a higher plate voltage no problem. They aren't quite as sensitive as EL34's so will need more to overdrive them.

The size of the transformers has nothing to do with MAKING power! Power is drawn, not pushed. If we have tubes run with high enough plate voltages and grid drive they will try to deliver more power. If the tubes are only capable of delivering 25 watts then they will just try too hard and burn themselves out. Likewise, transformers must be big enough to handle the power being asked from them. If the tubes demand too much power the transformer will just try to deliver, getting hotter and hotter in the process. If the power draw exceeds the transformer rating then we have a meltdown situation.

The same with an output transformer. A trannie rated to handle 25 watts will burn up if asked to deliver 50 watts of output power. A 50 watt output trannie in a 25 watt amp will run 25 watts. It will just run cold and never likely burn out.

Also, if you check those data sheets again I think you will find that the 800 volt rating was given for a pair of EL-34s running class B, which has the tubes conducting no more than half of each cycle and thus having more cool down time. Class B is rarely used for audio since it requires very complicated and expensive transformers to negate the extra distortion.

What's more, you may see 800 volt as a maximum rating - which is NOT the same as an operating suggestion! At that voltage the current must be kept much lower to not exceed the Plate Dissipation Rating.

Wild Bill/Busen Amps


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