Home (amp tone and effects placement)

5-watt tube amps are still as loud as a trumpet! 50 mW is needed for 1/8 the volume of 50 W

The sound of a blaring 5-watt amp is at least as loud as a trumpet!

>I'll just take a Fender Champ and cheap guitar cable.

Those who hope a 5 watt tube amp will enable them to play at 2am in their apartment, the fact is, you will still have to use a power attenuator or speaker isolation cabinet, if you want cranked power tube tone at low room noise levels. Shout really loud -- that's how loud 5 watts is.

For most people, 5 watts is completely unacceptable at home, except perhaps during the middle of the day. The lxh2 ultra-low power tube amp is only about 20 mW. Thus the Champ is 5 / .002 = 2,500 times louder than the desired level, which is headphone level.

Relative to the standard amp power of 50 watts:

50 mW - thousandfold decrease in power (1/8 as loud) 3 orders of magnitude 0.5 W - hundredfold decrease in power (1/4 as loud) 2 orders of magnitude 5 W - tenfold decrease in power (1/2 as loud) 1 order of magnitude 15 W - threefold decrease in power (about 2/3 as loud) 50 W - unity 100 W - twofold increase in power (maybe 25% louder) 500 W - tenfold increase in power (twice as loud)

1/8 the volume of a 50 watt amp sounds like the level I want to hear. Everyone can agree, 1/8 the volume would be nice. But let's look at the amazing decrease of power that will give this result. A 1/8 decrease in volume amounts to 3 orders of magnitude of power, yielding just 50 mW -- a *thousandfold decrease* in power. *Three* orders of magnitude! A 50 watt amp is *a thousand times too powerful*.

X% louder = 2^log10(P2/P1) * 100%

40 watts is 94% as loud as 50 watts.
30 watts is 86% as loud as 50 watts.
25 watts is 81% as loud as 50 watts.
22 watts is 78% as loud as 50 watts.
20 watts is 76% as loud as 50 watts.
18 watts is 74% as loud as 50 watts.
15 watts is 70% as loud as 50 watts.
12 watts is 65% as loud as 50 watts.
10 watts is 62% as loud as 50 watts.
9 watts is 60% as loud as 50 watts.
8 watts is 56% as loud as 50 watts.
7 watts is 55% as loud as 50 watts.
6 watts is 53% as loud as 50 watts.
5 watts is 50% as loud as 50 watts.
4 watts is 47% as loud as 50 watts.
3 watts is 43% as loud as 50 watts.
2 watts is 38% as loud as 50 watts.
1 watt is 31% as loud as 50 watts.
3/4 watt is 28% as loud as 50 watts.
1/2 watt is 25% as loud as 50 watts.
1/4 watt is 20% as loud as 50 watts.
1/10 watt is 15% as loud as 50 watts.
50mW is 13% as loud as 50 watts
20mW is 10% as loud as 50 watts.
10mW is 8% as loud as 50 watts.
5mW is 6% as loud as 50 watts.
1mW is 4% as loud as 50 watts.
0.5mW is 3% as loud as 50 watts.
0.1mW is 2% as loud as 50 watts.
50uW is 1.6% as loud as 50 watts.
10uW is 1% as loud as 50 watts.

The formula and this usage of it is from knowledgeable, respected math/guitar people in this newsgroup thread: Calculating the power/volume relation for amp wattage?

There are only two tube power amps I've heard of that get down to the 10 mW level: the LXH2 project and the Studio amp by London Power. I have heard a cranked 5 watt tube amp but not driving a serious speaker cabinet. The 5 or 6 watt Fender Champ is far too loud for my needs, and so is the 5 watt Crate VC508. The Studio is particularly interesting as far as pointing the way for designers of truly low-power tube amps, because it can be adjusted instantly to any value from 0 to 10 watts, and was tested in the milliwatt range, while of course keeping the output transformer and speaker system constant. The enables easy testing of the above calculations about perceived volume vs. wattage. This amp is supposed to produce the same classic amp-breakup tone whether at 10mW or the wide-open 10 watts, so a brief test with this amp should be able to settle whether or not cranked-amp tone must necessarily involve driving speakers hard and pushing air hard. Let us hope that top-notch tone can be achieved at 10mW, as the LXH2 and Studio claim, and give it a try, in more designs.

I have been in correspondence with product designers at various companies. One designer replied that he is designing a 7 watt tube amp. I commended him but encouraged him to consider even further reductions of power, even if the industry is not consciously ready for it though it's what people really need and unconsciously want. Like the H&K Crunch Master, a 1/2 watt tube amp would be essentially a perfect solution for what people need, but too far ahead of its time. Here is a summary of his message, and my reply to him.

Hey Monk,

Just wanted to let you know that we have been working on a low power all tube DI amp for a while. It will be about 7 watts output, 2 channels, and the same basic feature set as our rackmount preamp. If you are interested in reviewing a preproduction sample unit, let me know.

I'm in agreement with many of your ideas as represented on your site regarding the efficacy of low powered amplification for recording purposes. I actually built a low powered tube amp specifically for a recording project I was doing at my home studio to get a full cranked Marshall type tone at a sound level that would be reasonable.

Best of luck with your projects, and stay in touch.

Regards, Bob, Design Engineer _______________________________________________

Thanks for the response. It's good to know that designers are working on very low-power tube amps. You might also consider a 1-watt or 3-watt version, or some sort of power-starving capability. I haven't seen the power-starving circuits, but I get the *impression* that it's not very hard; I'd like to study some products such as the Studio 0-10 watt rackmount tube amp by London Power. I will probably build the 1-watt Moonlight amp soon (when that new project at the AX84 site is ready), or the 3-watt AX84 amp. It's taking the amp industry a while to get down to *truly* low, apartment-level volumes. The industry has a certain sluggishnish due to settling for halfway there -- for example, for ten years people thought that a preamp tube for a gain stage would sound like a tube power amp, and for five years, 15 watts was considered to be "low power, appropriate for apartments". I seriously consider 15 watts to be high power -- I have read many times, in user reviews of 15 watt amps, "when driving a serious cabinet, 15 tube watts are plenty loud enough for knocking down the walls." It's usually said as though that's a good thing -- but for apartment studios and quiet jamming, of course it's *bad* that 15 watts is so loud. So, we need to reduce power by orders of magnitude: from 50 watts not merely down to 15 watts, but rather, to 5 watts. 15 and 50 watts are in the same ballpark. To get truly quiet, for (as Kevin O'Connor of London Power states) 3 A.M. in an apartment, we need another order of magnitude reduction: from 5 watts down to 1/2 watt... and another: from that 500 milliwatts, down to 50 milliwatts. Much of the testing of the Studio amp by London Power was done in the *milliwatt* range, which implies less than 1/2 watt. There is a huge audience for this -- larger, I think, than the audience for a 7 watt amp.

When you built a low-power tube amp, such as a 7 watt amp, for a home recording studio project, I don't see how you could accurately monitor what the mic was hearing, given that 7 saturating tube watts would be far louder than the level in your nearby monitor speakers or headphones. Only during playback would you be able to meaningfully hear what the mic and post-amp processing sounded like. This assumes that you have essentially no isolated control room, for separation between the monitor speakers and the guitar speaker cabinet.

The industry continues in self-contradiction: thinking in terms of the irrelevant measure, "I want lots of watts for my buck," while out of the other side of their mouth they wish for great tone without bothering anyone. I am trying to fully express what the industry is only starting to consciously realize: tone comes before volume, tone comes before special effects, tone comes before everything. Another meme that is ready to be discarded is the "practice amp" idea -- and even the "studio amp" label. A low power amp is simply a quiet amp -- how one uses it is arbritrary, and can be any application: practicing scales, pro studio recording, playing an arena via sending a mic signal to the PA. Playing a tiny club is about the only thing that a 1/2 watt tube power amp is poorly suited for, unless used in a more complicated way such as: low-watt power amp -> speaker -> mic -> bigger amp with full-range speakers or low-watt power amp -> load -> bigger amp with guitar speakers

If I review a 7-watt tube power amp, I will probably still have to use my speaker isolation cabinet, and even then I worry about sound leakage (bass booming that leaks through my *double* layer, insulated, iso cab). Even though my jamming space is in the basement, of a house, my lease states *no musical instruments* -- so my landlord must not know that I even *have* a guitar or amp. It has to be a stealth solution. The *majority* of rock guitarists are in the same boat. Despite their shortsighted wish to get lots of watts for their dollar, most guitarists, most of the time at home, have a great unmet wish and need for a stealth-level tube power amp, something that can be disguised as just a home stereo played at very moderate levels. "Oh, that wasn't a live electric guitar, that was just some music on the stereo." Discussing this product concept and implementation with designer Kevin O'Connor and user Scott Hunt, I think the London Power - Studio tube amp has achieved this ideal, without using any post-power-tube attenuation (which tends to sound fizzy) or cabinet simulation filter (which tends to sound flat). Scott Hunt's interesting review is on my Studio page. They both assert that speaker distortion and pushing air hard are *not* required for authoritative cranked-tube-amp tone. That's why I'm interested in building (or buying) a 1-watt tube amp, or even much lower wattage.

There's one point that warrants repeating: the home-studio jammer does not necessarily want to hear the guitar speaker directly -- just like in a recording studio, the recording engineer does not want to hear the instruments directly. That's why there is a heavily insulated control room -- to *avoid* hearing the guitar speaker. What matters, for the studio, is hearing the processed mic signal, *only*. The home studio does not have the advantage of an isolated control room, so the guitar speaker needs to be *far* quieter than the level used in a recording studio. I see, we really need to add a qualifier before "studio amp". 6 watts, or even 15 watts, is indeed a good level for a studio -- as long as it's a pro recording studio. But *home* studios... that's very different; take everything down yet *another* order of magnitude. A 5 watt amp is good for a pro studio, a 1/2 watt amp is what's really needed for a home studio. Specifically, I want this chain at home, which is the pro recording studio processing chain:

EQ-based effects preamp EQ tube power amp guitar speaker (not heard directly) mic compression EQ time-based effects monitors (*this* is what I want to hear)

With no control-room isolation, the guitar speaker needs to be vanishingly quiet. 7 watts is a nice level for monitoring *directly*, but that's not where I want to monitor, as the recording engineer in my nonexistent control room.

I applaud this move from 15 watts down to 7 watts (the level of a trumpet) and look forward to telling people about your very low power amp, once it's announced. I look forward to further power reductions as well. Perhaps you could consider a future design that is as great a reduction from 7 watts as 7 watts is from 50 watts. I think that the audience would be there to buy it, *if* there is clearer thinking in the industry, about the needs and potential for top-notch, stealth home recording and jamming. My ultimate main vision seems to be heading toward this: a laptop computer with software fx modules onscreen, looping out to a miniature tube power amp, guitar speaker cabinet, and mic, then more processing onscreen, and finally, headphones -- and no one can hear the guitar speaker, because it's only at 1/2 watt. There are other packaging combinations, but that one really captures the spirit the best, turning the guitar rig into a sheer abstraction, except retaining, in miniature, quiet form, an actual cranked tube power amp and speaker, halfway along the processing chain. You have every reason to consider reducing the power by yet another order of magnitude -- it's what home jammers want, even if they are confused about what they want and think that more power is better even as they complain about needing quieter amps. Basically, the *purchasers* of the gear are just as slow as the designers, reviewers, and the rest of the industry, in realizing that a 1/2 watt tube power amp is what they really need and should want.

-- Michael


What do you think about this view? Is a 7 watt tube amp what guitarists now *think* they want but it's actually far too loud? Is what guitarists *really* want, but don't know it, a 1/2 watt tube power amp? How many years will it take for power to be commonly reduced from the current standard for "low power" of 15 watts or recently, 7 watts and 5 watts, down to *truly* low levels below the 3 watts (Clark Lil Bit, Signature 284, AX84 project) such as 1 watt such as the Moonlight amp, 1/2 watt, or 20 mW such as the LXH2 EL84 amp or the power-starving Studio amp by London Power?

Should I be satisfied with a 7 watt amp, even though I'm constantly worried about neighbors, roommates, or landlord hearing me, when I should be relaxed and creative? And though I'm unable to monitor my processed mic signal because the guitar speaker is ten times louder than my headphones or monitor speakers?



Added 12/2002:


>A 65-watt solid-state amp (Princeton) vs. a 22-watt tube amp (Deluxe Reverb).
> Does having a tube amp somehow make up for the low wattage to give equal loudness?
> Jeff


Yes or no, depending on whether the manufacturer publishes wattage at low (1%) or high (10%) distortion.  Below I demonstrate some specific %distortion/wattage combinations and calculations.


The expression "tube amps have gradual onset of distortion" implies the following.  For a tube amp, there is a large increase in output wattage required to make a given tube amp climb from 1% to 10% distortion.  In contrast, only a small increase in output wattage is needed to make a given solid-state amp climb from 1% to 10% distortion.


Assuming that guitar amps are rated at 1% distortion, and that tube power amps have gradual onset of distortion, it immediately follows that a tube amp rated as 15 watts at 1% distortion can get louder -- measurably and audibly louder -- than a solid-state amp that is rated as 15 watts at 1% distortion.  People agree that "it depends on % distortion", so to follow through on this idea and spell out the ramifications, consider specific hypothetical numbers: *multiple* distortion % ratings paired with wattage rating.


To say that "tube power amps have gradual onset of distortion", which everyone agrees with, is immediately to say or imply that a tube amp and solid-state amp will have different wattage at a high % distortion though they have the same wattage at a low % distortion.


Assume a 15-watt tube amp and solid-state amp with the same advertised wattage, where the wattage is based on 1% distortion.


Tube amp at 1% distortion: 15 watts
Solid-state amp at 1% distortion: 15 watts


Tube amp at 10% distortion: 25 watts
Solid-state amp at 10% distortion: 18 watts


It takes the tube amp longer, as you increase its output, to reach 10% distortion.  The solid-state amp quickly moves from 1% to 10% distortion, after you increase its output only a little.


Going the other way, if a manufacturer advertises the wattage produced at high, 10% distortion, the principle "tube power amps have gradual onset of distortion" implies that that manufacturer's tube amp will have less wattage, when measured at 1% distortion, than that manufacturer's solid-state amp.


Manufacturer B, who publishes wattage at 10% distortion:


Tube amp at 10% distortion: 15 watts
Solid-state amp at 10% distortion: 15 watts


Tube amp at 1% distortion: 8 watts
Solid-state amp at 1% distortion: 12 watts


These figures are hypothetical and it would be helpful to see bench numbers comparing actual amps' wattage at different distortion percentages, of a solid-state amp and tube amp of whatever advertised wattage, to confirm whether tube amps have "more gradual onset of distortion" in the sense described here.


In general, when holding % distortion and speaker efficiency constant, a 22-watt amp is 72% as loud as a 65-watt amp


http://www.amptone.com/g112.htm -- I coordinated the math problem at alt.guitar.amps to determine this formula:
X% louder = 2^log10(P2/P1) * 100%


Plugging in 65 and 22 watts, and *assuming* the same % distortion and same amp type (the same "rate of onset of increased distortion") and same speaker efficiency, a 22-watt amp is 72% as loud as a 65 watt amp, as follows.


Warming up the calculator with a reality check, a 5 watt amp should be half as loud as a 50 watt amp; the 50 watt amp should be twice as loud as the 5 watt amp:
2^log10(5/50) * 100% = 2^log10(0.1) * 100% = 2^-1 * 100% = 0.5 * 100 = 50%
2^log10(50/5) * 100% = 2^log10(10) * 100% = 2^1 * 100% = 200%


Now considering 22 versus 65 watts (assuming % distortion and speaker efficiency are same):
2^log10(22/65) * 100% = 72% as loud
2^log10(65/22) * 100% = 139% as loud


-- Michael Hoffman

Amptone.com ultra gear-search page

Home (amp tone and effects placement)