Question for experienced amp try-er out-ers

Soap · 12-07-2006, 10:31 PM

Is there some constant one could multiply by to compare tube wattage and solid state wattage for a volume comparison?

Example: How loud is a 15 watt tube amp as compared to a 50 watt solid state?

or: 1 tube watt = 2.5 solid state watts (just an example, not accurate)

Help me out here.

**thesteve** · 12-07-2006, 10:41 PM

No accurate comparison: too many mitigating factors.

People will tell you that it's about 3 SS watts per tube watt, but I honestly don't buy it. I do know that in my experience 15W tube is ALOT louder than 15W SS, but I think that a large reason for that is because most, if not all 15W SS amps are cheap beginner amps, and 15W tube amps, while often designed as an entryway into the tube amp universe, are built with professionals in mind.

I've yet to see any solid scientific reasoning behind the volume difference.

I read this article once. It was written by Stewart Ward, amp designer for Award-Session, which is a manufacturer of high-end British SS amps. http://award-session.com/pdfs/GEAR_TALK_1.pdf

Major Tom · 12-08-2006, 02:12 PM

Keep in mind - the overall volume of an amp is more about the speaker configuration (# of speakers, closed vs. open back) and their efficiency than anything. 12" guitar speakers range from around maybe 94db for 1 watt of input, to 103db @1 watt. That difference alone is 9 db, which is the equivalent of going from a 15 watt amp to 120 watts!! (the formula is that each 3db gain takes double the wattage, so 15x2=30, 30x2-60, 60x2=120)). Now smaller speakers like 8" are going to be even less efficient than 12", so their range will be lower. Of course there are mitigating circumstances, like the fact that speakers are going to reach a saturation point, for example, a 50 watt tube amp with a single 12" - its probably maxing out the speaker's acoustic output with 10 - 20 watts, the rest is mostly wasted... One example - I have a Peavey Bravo, tube amp @ about 15 - 20 watts (Peavey exaggerates its output to 25 watts), the same power tube config as Blues Jr.s and many others rated at 15 watts. I mounted one in a 2x12" cabinet that has speakers on the high end of efficiency, probably 100db @ 1 watt. Anyway, that thing is LOUD. If you were to plug in to it and start playing, you might think I had a Twin hidden inside.

Yes, and its got plenty of clean headroom too.

IMO, the difference between "solid state watts" and "tube watts" is probably due to the way mfr's rate the wattage of tube amps vs. solid state, and the fact that so many solid state amps are the small practice variety that have small speakers (like 8") that put out much less sound per watt of input. Even the ones with 12" speakers - SS amps tend to be low end (yes, I know there are exceptions), and therefore, their speakers will also tend to be low end. AFAIK, tube amps are generally rated at a clean output, when you drive them into distortion, they are putting out significantly more than their rated power. A SS amp with the tube-mimicing distortion circuitry in the preamp is a different animal - in heavy distortion, the SS ain't gonna put out more than its rated power (unless its under-rated). As an example, a 50 watt SS vs. 50 watt tube with a heavy distortion tone - the tube amp is maybe putting out 80 watts, the SS = 50 max.

Bottom line, don't worry so much about amp watts, its really not that significant of a specification without factoring in the speaker config. Its like horsepower in vehicles, the hp rating doesn't mean much without the context - what its mounted in. A 200 hp in a small coupe = fast car. 200 hp in a delivery truck = slow. I really don't think you can find any type of formula or ratio of watts and SPL, tube or SS.

**thesteve** · 12-08-2006, 02:32 PM

if sounds like you and Stewart Ward might be friends Tom

One of the things he talks about is how much the tone of the Sessionette 75 amps changed when it was used by Mick Ralphs from Bad Company, because Mick ran it through two Marshall 4x12 stacks with Greebacks. the amp was the same, but changing the speakers so drastically radically altered the tone.

Major Tom · 12-08-2006, 03:04 PM

Quote:

Originally Posted by thesteve

if sounds like you and Stewart Ward might be friends Tom

One of the things he talks about is how much the tone of the Sessionette 75 amps changed when it was used by Mick Ralphs from Bad Company, because Mick ran it through two Marshall 4x12 stacks with Greebacks. the amp was the same, but changing the speakers so drastically radically altered the tone.

Yes, I absolutely agree. The efficiency is a whole subject by itself - how much SPL's you get for a given amount of wattage. Speakers do vary a bunch in tonality also, and then the configuration (1x12, 2x12, 4x12, etc. ) and closed vs. open back has a big impact too. One example - my faithful Peavey Bravo again... I have a couple old Peavey Sheffield guitar speakers, they were supposed to be voiced like Celestions, mounted in a closed back 2x12. When I hooked up the Bravo to that, it took on a very Marshally tone; in its present combo config, its Vox-like. I believe that amps need to be matched up to the right speakers and configuration to get the desired tone. I hooked it up once to the speakers in my HR DeVille 4x10 - it sounded more like the HR than it sounded like a Bravo, if you know what I mean...

Soap · 12-10-2006, 10:11 PM

Cool. So, example, a Vox AC30 with 1x12 would be considerably louder than my 50 watt valvetronix 1x12?

**thesteve** · 12-11-2006, 01:07 AM

Quote:

Originally Posted by SoapbarII

Cool. So, example, a Vox AC30 with 1x12 would be considerably louder than my 50 watt valvetronix 1x12?

hard to say. One of the things I noticed with my AD50vt was that each one of the models seemed to have a different output level. this made volume balancing very fun.

Major Tom · 12-11-2006, 06:21 AM

Quote:

Originally Posted by SoapbarII

Cool. So, example, a Vox AC30 with 1x12 would be considerably louder than my 50 watt valvetronix 1x12?

Probably not - a single 12" speaker is only capable of putting out a certain amount of SPL. IMO, 15 or 20 watts or thereabouts will pretty much max out a single 12, at least most 12's used for guitar amps. I would guess that a 50 watt Valvetronix would pretty much max out the single 12, as would the AC30. When you reach the point of maxing out the speaker, anything over that is just going to produce more speaker distortion, and not increase in volume... A little may be ok, and speakers hitting their saturation point may be part of the mojo of cranked amp tone, but too much can sound pretty flatulent, and muddy.

Col. Ghillie · 12-11-2006, 08:28 AM

But a vox-ac30 will still be plenty loud enough for basically any application.