Your chance to combat ignorance. Here. Now.

First let me say that I am lazy. I would much rather post here and glean wisdom from several people I believe know what they are talking about then find a book or website. Besides it helps post counts.

Second, there may be no practical application for the answers although I am noticing a few things about playing bass through a guitar amp that I don't like as much as I used to. Bottom line (insert rimshot here, please), there may be a new amp in my future but no guarantees I will actually use my new found knowledge.

Several people have stated several times that tube amps are louder. Being the anal sort who measures things, this initially bothers me.

I assume that, regardless of design, the sound level from identically rated amps, operating at the rating spec, into the same speaker load would be identical. If that's not true then please explain.

Otherwise, the reason people say tubes are louder is that amps are rated at a distortion level and tube amps have a pleasing and usable sound at higher distortion levels. So if the amp is rated at 1% total harmonic distortion (THD) but is usable at 5% then by definition it will be louder than the rating (20W RMS @ 1% THD into 8 ohms) might suggest.

So if I am not totally mistaken...

If my goal is to reproduce the input exactly then THD will be driving my decisions and the perceived volume should not be different between tubes and solid state. Correct?

Is there a rule of thumb to compare amps rated at different THDs? Obviously the usable distortion level for a tube amp is a subjective matter, but is the output at the sweet spot approximately 1.5x the rated output? 2x? 10x?

Is there an amp spec that gives you an idea of how much headroom there is?

Anything else I should have asked to understand the assertion that tube amps are louder?

Thanks.

Can't give you any kind of scientific answer, but I do know that first of all, power ratings for amps are all over the place, and often not very eh..."correct".

And tube amps are definitely more dynamic, so they "feel" louder for sure.

Hi Frono; let me see if I can increase my post count ... sorry ... I mean offer something useful by getting some help from the Wikis ... particularly in separating THD from garden variety amp distortion.

Sayeth the wikis: Total Harmonic Distortion (THD) is not a drug similar to THC but, instead: "When a signal passes through a non-linear device, additional content is added at the harmonics of the original frequencies. THD is a measurement of the extent of that distortion." Since there is just about no such thing as a perfectly linear device - one whose waveform output is identical to the input - THD is a measure of the added harmonic 'trash' that the signal has acquired ... and not distortion in the sense you are discussing it here. Lower THD statistics means that the device; tuner, CD player, amp, or speaker is contributing the least amount of tone gunk. I think you already understand this.

Clipping is the flattening of the top of the waveform because the "The extra signal which is beyond the capability of the amplifier is simply cut off, resulting in a sine wave becoming a distorted square wave type waveform. Many electric guitar players intentionally overdrive their guitar amplifiers to cause clipping in order to get a desired sound (see guitar distortion). Guitar Distortion says "...Distortion can be produced by many components of an instrument's signal path, including effects pedals, the pre-amplifier, power amplifier, speakers, or more recently, digital amplifier modelling devices and software. Many players use a combination of these to obtain their "signature" tone."

Power ratings are usually done at maximum power before distortion/clipping ... wattage is volts times amps. So, if we were in the LTG Sound Lab and had one of Walter's amps there, we'd inject a signal ... him playing would be fine ... and we'd have the amp output tied to a scope. When the signal clipped, we'd measure the voltage and the current, calculate watts, and then we'd have lunch. Headroom is the available range of increase in power from idle to highest volume before distortion/clipping and, as far as I know, there's no metric for it.

Yes; tubes amps at or beyond distortion produce more pleasing tone than transistor amps. Your math problem doesn't work because of some confusion between THD and garden-variety amp distortion. Finally on the subject of apparent volume differential; I think two amps - one tube and one transistor - with the same rated output power and the same speaker, if metered at the same distance, would measure about the same sound pressure .... but I think the tube amp would seem louder because of the differences between each's audio characteristics. John

Not being anything more than a half-assed guitar player with waaaayyy too many good sounding amps, I would suggest that you audition some amps at GC, like Wednesday, 2pm(when the wankers are still sleeping) and see what you like. There are quite a few bassplayers that prefer transistors.



Boy, I hate even typing that. :evil:

capnjuan said:

Your math problem doesn't work because of some confusion between THD and garden-variety amp distortion.

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I think you nailed it for me. Thanks. I had this idea that you could pick an output level, look at the "difference" between input and output, "measure" that and call the result THD. Thus running an amp to the point where it is clipping (or beyond) just increases measured THD. What I think I was missing is that somewhere in the Big Book of Rules for Testing Amps it says that you never, ever make a measurement for power rating purposes at a level where the amp is clipping. That rule invalidates my logic and thinking. The basic idea - tube amps are louder - still comes down to how much (unmeasured) distortion is acceptable.

Thanks!

PostCount++

Default said:

There are quite a few bassplayers that prefer transistors.

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What did the bass player get on his IQ test?
Drool.

Default said:

Boy, I hate even typing that. :evil:

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I've only owned solid state amps. In my advanced age, the weight of the amp and speaker (as well as the ability to fit in a compact car with room for a passenger) seem to be the driving factors for me in amp choice. Still, I find that the tone controls on the Princeton Reverb, that we pretend is Mrs. Fro's but always gets used by me as an alternative to 75+ lbs. of bass equipment, to be lacking when used for bass and I keep wondering about one of the many under 50lb combos out there.

Hi Frono; I see your point; it's THD however the distortion is caused. Re/ your amp musings, so much depends on how much clean (or dirty) volume you want (codewords power and headroom) and the desired tone. Any chance you'd consider head/cab instead of a combo? I guess I was thinking of the Guild Thunderbass amps... like one of these:



This one was designed for either bass or guitar; master volume so you can cook the preamp tubes and throttle the volume back ... has an effects loop too. Don't know what a cab with a 15" speaker would cost (or weigh) ... but the total volume ... space consumed ... would be similar to a combo ... yes; would mean an extra trip to the car and back. J

capnjuan said:

Don't know what a cab with a 15" speaker would cost (or weigh) ...

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Peavy solid state head putting out about 200 watts is 35 lbs.
Peavy 2x15 cabinet is 110 lbs.
Woodson 1x15 is about 45 lbs.

It's kind of sad that I know these numbers, isn't it?

fronobulax said:

capnjuan said:

Don't know what a cab with a 15" speaker would cost (or weigh) ...

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... 35 lbs ... 110 lbs ... 45 lbs. It's kind of sad that I know these numbers, isn't it?

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Well ... now that you mention it, they do seem like the mile markers on a well-worn path ... maybe it's what happens after the nose has been pressed up against the glass for a while ...

Frono,
Ever since Walter Woods broke ground with his insanely tiny 1000w+ monsters manufacturers have been making tiny bass heads. There are a lot of choices nowadays. I'm interested in the Carvin BX500 which seems a steal at $399 new. 500W at 5.8lbs :shock: a tube preamp. There are huge threads on TalkBass about'em. There are lots of raves about the MarkBass Little Mark series too which also have a tube preamp. The MarkBass Mini CMD combo and its similar predecessors are really small and sound surprisingly good for a 29 lb package. It also comes in a 15" speaker version at 40lb. if you're feeling frisky. Best of both worlds with solid state and tubes. I think both the Carvin and MarkBass can also switch to SS preamp if you need more punch. The older versions of the MarkBass combo are more affordable, which is the route I'd take.

If you've got deeper pockets, unlike mine which always seem to have holes, I'm sure you know about the pricier small head alternatives, i.e., Mesa Walkabout, Genz Benz, or Acoustic Image, et al. If you want a compact speaker cab DIY project, Electro Voice has a buncha Thiele cab designs to download that are spec'd for their speakers.

In my perfect world, I'd have time to build a little Thiele 12" cab and grab a Carvin BX500, which would suit my needs perfectly.

fronobulax said:

If my goal is to reproduce the input exactly then THD will be driving my decisions and the perceived volume should not be different between tubes and solid state.

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The meaning of THD has been covered, but the other thing I would say to this, is that not all "distortion" sounds like what most people think of when they hear that word. The sound that you hear when you run a magnetic guitar pickup directly into a squeaky clean signal chain, is not at all a classic guitar tone. It does not sound like the great "clean" guitar sounds you hear on records. The only well known player who is known for that sort of signal chain is guitarist/producer Nile Rodgers, best known as a member of the disco band Chic and as the producer of the David Bowie album "Let's Dance" among others; his clean rhythm guitar chord work is done that way. He uses a strat or superstrat and the result is very bright and has almost no mids or bottom and no ambience; this works well for a rhythmic part in a dense mix, but it sucks for anything else.

Tube amps are "useable" at least for some styles up to over 100% THD ! A heavily crunching tube amp will do that. I'm not sure at what point you would say a guitar amp gets into what is unmistakeably a distorted sound, but I'm sure it's more than 5% THD. I run my Bassman rig pretty clean, but I can definitely hear prominent lower harmonics in the output that are much more present than in the input, all the time (which is a big part of why I only use tube amps). Harmonics added by a distorting amplifier tend to blend in with the harmonics that are already present in a guitar sound as they are in the sound from any acoustic source, and your amp will add harmonics to the harmonics of the source signal. The point being, harmonics in general are not something to avoid in principle and indeed are impossible to avoid for any guitarist.

fronobulax said:

Anything else I should have asked to understand the assertion that tube amps are louder?

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Another thing that comes to mind is that tube amps naturally compress. This reduces the dynamic range of the output compared to the input, but makes the overall average level higher, so they also seem louder for that reason. Some amps do this a lot more than others, particularly push-pull amp designs that use lower voltage tube rectifiers.

As far as bass rigs go, I've been happy with my Bergantino AE112 cabinet, which uses a neo driver and thin walled design to come in at about 36 pounds. It's rated for 300 or 400 watts or so and sounds nice. If I'm playing bass I usually use an old Vox AC50 head, sometimes a blackface Bassman head, or for bigger gigs an old Triumph 100 watt head from England. Those are kind of exotic heads other than the Bassman, but if you're playing bass a lot, you'd love the light weight of the single 12. I've heard that there are some great single 10 cabs too.

Thanks, teleharmonium. Useful insights.

I am a mathematician by education and have done a fair amount of digital signal processing professionally. Thus I tend to break up problems into small single function modules. One such module would be a component that amplified the input, period, which helps explain my focus on distortion as if it were the single parameter of interest.

My practical experience is rooted when the audiophile craze took off and so I still tend to believe that "separate" components chained together properly are "better" than integrated systems, even though that is not the case in the marketplace 30 years later. Old habits and prejudices die hard.

I'll also note the emerging market where you have amps for acoustic instruments. The sales pitch is that what goes in, comes out, only louder. The presumption is that the user has a pickup or mic that captures the desired acoustic sound accurately and so the primary function is just to make it louder.

Looks to me if I actually spring for a new bass amp, I'll have to thread a request for suggestions here.

Thanks, again.

did not read every post yet, but...

jp said:

...Carvin BX500....

...In my perfect world, I'd have time to build a little Thiele 12" cab and grab a Carvin BX500, which would suit my needs perfectly...

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jp,

+1 for the carvin, but the the thiele cabinets were designed for guitar and don't suit to bass as good as you hope.

there are also great lightweight cabinets on the marked. I'd recommend a lite 2x12" cabinet or as I use at the moment: 4x8" + 1x15" cabinets which work great if the bass and amp deliver proper mids.
and, if you put the 4x8" on the ground it is also great for small events. (mine weighs with regular speakers about 32 pds). mine got about 500 watts rms.

the rumour about markbass is: love it or hate it and the only good markbass with tubes seems to be the full-tube-head.
neither of them I would buy.

I would prefer an eden hybrid, ebs fafner, the mentioned carvin or the old one I have: swr 350 bass II, maybe aguilar, but I couldn't play one yet.
if fulltube then probably the mesa carbine 6/9. ampeg always sounds only like ampeg - not that I don't like it, but reduced.
the weber mywatt head is also praised a lot.

edit:
if I would not have to carry or pay the bass rig, I would also choose a full tube head. but the hybrid amps usually are cheaper, more reliable and because of the preamp tube also add a lot of the wanted harmonics which is always a good compromise.
if you want a real clean basstone more high-fidelity-wise then solid state amps are the way to go, i. e. glockenklang from germany is the high end stuff here.

krysh said:

jp,

+1 for the carvin, but the the thiele cabinets were designed for guitar and don't suit to bass as good as you hope.

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Thanks krysh. I didn't know that. I've only tried a small closed back guitar cab, and it pounded out a lot of bottom end. I perhaps mistakenly recalled someone on TalkBass raving about an EV Theile 1-15 cab that was really effective.

There are monster threads on TB about the BX500. They've had a lot of problems at the debut, but supposedly the kinks have been worked out. It seems a like great deal for the money.

I need a light setup too because I don't want to haul my '67 Ampeg B-18X all over the place. I played through an older Ashdown EVO 300 hybrid head that I really liked. A hybrid is much more versatile to get warm tone and still have some solid state punch.

the 15" thiele have been created for bass in pa systems if I remember right.
the 12" mainly for guitar.
a 15" thiele might work well, but it will also be heavy.
markbass makes this new "new york 604". sounds awesome if you put it directly on the floor and I bet if you combine it with a 1x15" and the carvin....
also phil jones cabinets like this one seem to be very interesting:
http://www.philjonespuresound.com/PJWeb11_NCab6B.aspx
the amps seem to lack a bit punch though.