Double Bass anyone else using low watt all tube heads?

[atmasphere]

You have pointed to a very often cited characteristic of tube sound. That is, the "warmth." Many on the hi-fi end of things have mentioned this as well. That "warmth" can be traced directly to the typical broad peak in the lower midrange that comes about as a result of the interaction between the output transformer and the speaker. It's the primary frequency response anomaly that I posted about earlier. In fact, it was the lack of that "warmth" which, in the early days of solid-state amps led many to reject them. Of course, one can mimic that response with solid-state circuits and that's exactly what Carver did in his demo.

Not meaning to start anything here but I've been doing amps for a long time too- over 40 years. There is a simple reason why tubes get audible preference, and its not a frequency response error. It has to do with a lack of a certain type of distortion, namely the 5th, 7th and 9th harmonics, which the human ear happens to use to determine the loudness of a sound.

In fact our ears are so sensitive to these harmonics that 100ths of a percent are audible. General Electric proved this back in the mid-60s and its easy to prove with very simple test equipment.

Transistors inherently make more of these harmonics than tubes do. So they sound harsher/less warmth to the human ear. On top of that tube circuits are generally simpler, and in that first watt of power where all the detail lies, well that's the place that transistors tend to not have as much resolution.

Carver's experiments were fun but crude. The fact of the matter is you can take one of his amps and in a double blind test easily pick it out against a top-performing tube amp, and this has nothing to do with overdrive.

For string bass I would expect that you really don't want to overdrive the amp anyway, so transistors seem to have the weight advantage, but I have built tube amps that don't weigh whole lot more by leaving out the output transformer. That's one of the ways you can get the slew rate up, distortion down and really open up the bandwidth (most of the amps I have built are full power to 2 Hz, I limit them to that frequency to make the power supplies easier to build).

IOW while I regard many of your arguments as valid, they are in fact generalizations and do not apply to all tube amps. However the distortion thing I mentioned earlier (often caused by to much negative feedback) is a major hangup for transistors. There are zero-feedback transistor amps that are some of the best I've heard. What I am pointing out here is that its all about distortion **caused by the use of feedback** (which seems counter-intuitive). Tubes simply are a very easy way to design a successful amp that uses little or no feedback and thus will sound better. It is very easy to demonstrate.

 

[Ric Vice]

...... There is a simple reason why tubes get audible preference, and its not a frequency response error. It has to do with a lack of a certain type of distortion, namely the 5th, 7th and 9th harmonics, which the human ear happens to use to determine the loudness of a sound.

Atmasphere

Since I'm not a engineer or amp designer I can only compare amplifiers using my "musician's ears". What they tell me is that a Walter Woods MI-400-8 amp that uses FET's does sound very much akin to my Ampeg B-15 N(Model C) is much lighter at 9 lbs. and more powerful, at 400 watts. Walter's amplifiers have a very tube like quality, much like the Aguliar all tube heads did.

Ric

 

[drurb]

Not meaning to start anything here but I've been doing amps for a long time too- over 40 years. There is a simple reason why tubes get audible preference, and its not a frequency response error. It has to do with a lack of a certain type of distortion, namely the 5th, 7th and 9th harmonics, which the human ear happens to use to determine the loudness of a sound.

Well, I've been publishing psychoacoustic research for three decades. I'll not go over my credentials here. If you're interested, you can PM me. What you're saying simply is not true in general about loudness or specifically with regard to harmonics-- UNLESS you are including intentional distortion as part of the amplification that's desired. I covered that in post #10 in this thread.

If you are not referring to intentionally overdriving the circuit to produce an even-order "euphonic" distortion profile, then your argument ignores at least two very important details so far as amplifiers go. The first is that some tube designs actually do produce odd-order distortion (it depends on the circuit design and topology). The second is that, with modern solid state amplifiers, even the odd-order distortion can be vanishingly small. If it is not audible, then the particulars of its profile don't matter. There is an entire literature on the audibility of various types of distortion including harmonic, IM, and TIM.

In fact our ears are so sensitive to these harmonics that 100ths of a percent are audible. General Electric proved this back in the mid-60s and its easy to prove with very simple test equipment.

That's exactly the type of literature to which I was referring except that much has occurred since the mid-60's within the Journal of the AES and Journal of the Acoustical Society of America. It is on the basis of that research that you can see that, absent overdriving the circuit, the distortion produced by modern solid-state circuits is essentially inaudible.

Transistors inherently make more of these harmonics than tubes do. So they sound harsher/less warmth to the human ear. On top of that tube circuits are generally simpler, and in that first watt of power where all the detail lies, well that's the place that transistors tend to not have as much resolution.

These are oversimplifications that, taken together, lead to false conclusions. If it's below audibility, the fact that one circuit produces more of a type of distortion than another is irrelevant. It is not true that "all of the detail lies" in the first watt of power. Furthermore, the anomalies, such as "notch" or "crossover" distortion that plagued early transistor circuits were resolved decades ago. That doesn't, however, prevent this argument from being repeated over and over.

Carver's experiments were fun but crude. The fact of the matter is you can take one of his amps and in a double blind test easily pick it out against a top-performing tube amp, and this has nothing to do with overdrive.

I'd like to see those data. My contention is that if you control for overall level effects and implement the transfer characteristic of the tube amp via solid-state circuitry-- especially with the power of modern technology-- you'll not have a chance.

For string bass I would expect that you really don't want to overdrive the amp anyway, so transistors seem to have the weight advantage, but I have built tube amps that don't weigh whole lot more by leaving out the output transformer. That's one of the ways you can get the slew rate up, distortion down and really open up the bandwidth (most of the amps I have built are full power to 2 Hz, I limit them to that frequency to make the power supplies easier to build).

In the end, though, no sonic advantage accrues and you have a product that costs far more.

IOW while I regard many of your arguments as valid, they are in fact generalizations and do not apply to all tube amps. However the distortion thing I mentioned earlier (often caused by to much negative feedback) is a major hangup for transistors. There are zero-feedback transistor amps that are some of the best I've heard. What I am pointing out here is that its all about distortion **caused by the use of feedback** (which seems counter-intuitive). Tubes simply are a very easy way to design a successful amp that uses little or no feedback and thus will sound better. It is very easy to demonstrate.

Actually, it is you who has overgeneralized with regard to solid-state amps amps I've described. I, for one, have never argued that a tube amp cannot be built that is every bit as good as a modern solid-state amp, whether for musical instrument amplification or sound reproduction. The point is that, after it's done, you have a circuit that is more expensive to build, more costly for the consumer, consumes more power, is generally heavier, is less reliable, and offers no real sonic advantage that could not be incorporated into a solid-state design.

By the way, I have no conflict of interest here in terms of offering any of these products commercially or being involved in their sale.

 

[drurb]

Atmasphere

Since I'm not a engineer or amp designer I can only compare amplifiers using my "musician's ears". What they tell me is that a Walter Woods MI-400-8 amp that uses FET's does sound very much akin to my Ampeg B-15 N(Model C) is much lighter at 9 lbs. and more powerful, at 400 watts. Walter's amplifiers have a very tube like quality, much like the Aguliar all tube heads did.

Ric

Precisely what one would expect from FETs. Walter was no fool in designing that. Your example reinforces my points.

 

[atmasphere]

That "warmth" can be traced directly to the typical broad peak in the lower midrange that comes about as a result of the interaction between the output transformer and the speaker.

Actually, if you want to have a credible argument, this particular comment should be avoided. It is about as false and ridiculous as it gets in any of these tube/transistor debates, which we have seen rage on the 'net for the last 20 years (I was on the newsgroups before the web existed). Even the most seasoned transistor guys will not make a comment this absurd. If this were really true, you could just add a tone control to a transistor design and presto!- sounds just like tubes.

In fact, tube 'colorations' mostly exist out of lower ordered harmonics. OTOH transistor 'colorations' mostly come from higher-ordered odd harmonics. In the case of tubes, the lower orders are often 1-2% at full power. In the case of transistors, the higer orders might only be 0.005% at full power- yet they are easily audible due to the way our ears work.

As I mentioned earlier, 100ths of a percent enhancement of the odd-ordered harmonics is audible. In the home audio world, audiophiles use 'bright', 'hard', harsh', 'brittle', etc. to refer to such distortion- despite being so low as to be nearly unmeasurable. Again, this human perceptual rule is very easy to prove with simple test equipment. Just compare the apparent difference in volume between a sine wave and a square wave and you will see what I mean. A square wave has to be about -20db compared to the sine to sound about the same level.

Simply put, we use odd-ordered harmonics to detect volume.

While it is true that some tube amps do make higher, odd-ordered harmonics (5th and above) it is not true to say that all tube amps do. That is a function of design. If the amplifier is all-triode and fully differential, the main distortion component will be the 3rd only. Generally speaking, tubes will make lower orders if not being over-driven, and transistors will make higher, odd orders if not being overdriven. There are exceptions to this on both sides.

One of the reasons transistors do this is due to a non-linear capacitance in the junction of the device that is magnified with increased current. This is why it is difficult to design a zero feedback transistor amplifier; why so many of them use feedback to 'linearize' the design.

Tubes OTOH have interelectrode capacitances that are not affected by the current through the device; its not much of a variable other than bandwidth.

While I totally concede that transistor power is cheaper and usually lighter, the advantage stops there, IME. Tube amps can have the same bandwidth (or nearly so- amps that I have built go full power from 1Hz to 200KHz) and similar distortion specs, depending on design. To get similar THD, you have to employ feedback, and that messes up the sound of any amplifier by enhancing those pesky odd harmonics I mentioned earlier. In essence what we are talking about here is human perceptual rules and the way our electronics can be made to violate them or obey them. Feedback is a fundamental violation.

 

[drurb]

Actually, if you want to have a credible argument, this particular comment should be avoided. It is about as false and ridiculous as it gets in any of these tube/transistor debates, which we have seen rage on the 'net for the last 20 years (I was on the newsgroups before the web existed). Even the most seasoned transistor guys will not make a comment this absurd. If this were really true, you could just add a tone control to a transistor design and presto!- sounds just like tubes.

Asserting that it's "absurd" is hardly a credible counterargument. That fact remains that much of what people identify as "warmth" in conventional tube amplifiers is exactly what I said it is, your assertions to the contrary notwithstanding. Most "transistor guys," seasoned or not, know very little about hearing.

In fact, tube 'colorations' mostly exist out of lower ordered harmonics. OTOH transistor 'colorations' mostly come from higher-ordered odd harmonics. In the case of tubes, the lower orders are often 1-2% at full power. In the case of transistors, the higer orders might only be 0.005% at full power- yet they are easily audible due to the way our ears work.

You seem quite unfamiliar with the literature and the science of how our ears work.

As I mentioned earlier, 100ths of a percent enhancement of the odd-ordered harmonics is audible. In the home audio world, audiophiles use 'bright', 'hard', harsh', 'brittle', etc. to refer to such distortion- despite being so low as to be nearly unmeasurable. Again, this human perceptual rule is very easy to prove with simple test equipment. Just compare the apparent difference in volume between a sine wave and a square wave and you will see what I mean. A square wave has to be about -20db compared to the sine to sound about the same level.

Simply put, we use odd-ordered harmonics to detect volume.

There's so much wrong with this, it's difficult to know where to begin. The mistake you make is a common one and ignores the distinctions of what CAN be detected under laboratory conditions (where I have spent my professional life) and what people DO detect in uncontrolled conditions, and finally how any of that impacts actual preference.

While it is true that some tube amps do make higher, odd-ordered harmonics (5th and above) it is not true to say that all tube amps do. That is a function of design. If the amplifier is all-triode and fully differential, the main distortion component will be the 3rd only. Generally speaking, tubes will make lower orders if not being over-driven, and transistors will make higher, odd orders if not being overdriven. There are exceptions to this on both sides.

I never made any claims about "all" tube amplifiers. Quite the opposite, I was the one pointing out that your generalizations about distortion profiles were incorrect.

One of the reasons transistors do this is due to a non-linear capacitance in the junction of the device that is magnified with increased current. This is why it is difficult to design a zero feedback transistor amplifier; why so many of them use feedback to 'linearize' the design.

Tubes OTOH have interelectrode capacitances that are not affected by the current through the device; its not much of a variable other than bandwidth.

While I totally concede that transistor power is cheaper and usually lighter, the advantage stops there, IME. Tube amps can have the same bandwidth (or nearly so- amps that I have built go full power from 1Hz to 200KHz) and similar distortion specs, depending on design. To get similar THD, you have to employ feedback, and that messes up the sound of any amplifier by enhancing those pesky odd harmonics I mentioned earlier. In essence what we are talking about here is human perceptual rules and the way our electronics can be made to violate them or obey them. Feedback is a fundamental violation.

Oh, this is an old song that's about 35 years behind the times. Feedback, judiciously and properly applied does not always degrade the sound. As for the possibility of building really fine tube amplifiers, I was the one who pointed out that that surely can be done. My claim is that there is no real advantage in adopting that technology over modern solid-state designs.

I guess, though, as one who offers 500 watts/channel for a mere $147,000, I don't expect that you'd say anything different.

 

[Gearhead43]

I would just like to make a small point by saying:

Blah blah blah, fa fa fa, fooey fooey, as it were, and tutty tut tooey, and futhermore, sniff sniff, snark snarky foo foo.

 

[atmasphere]

I would just like to make a small point by saying:

Blah blah blah, fa fa fa, fooey fooey, as it were, and tutty tut tooey, and futhermore, sniff sniff, snark snarky foo foo.

I'm sure drurb and I agree on this one

 

[Jazzdogg]

That was an intriguing detour! I feel as though the vehicle in which we TBers have been riding was suddenly hijacked and taken across rutted roads, pot holes, and railroad tracks at high speed; my fellow passengers and I had our beverages spilled and our fillings jarred loose while the two co-hijackers argued about how many angels can dance on the head of a pin.

Now, what was the original subject of this thread?

 

[pasta4lnch]

^^ here's my low watt tube head. . . (studio only)

Invalid Link Removed

 

[fdeck]

Precisely what one would expect from FETs. Walter was no fool in designing that. Your example reinforces my points.

Walter Woods used a circuit topology called source feedback, which I also happen to be interested in. I designed a "complete" preamp using source feedback gain stages, schematic shown below. So far I have only built one prototype.

If I am correct about the chronology, Woods would have been familiar with op amp design techniques, but disappointed by the audio performance of op amps available at the time. Thus the source feedback circuit would have made sense for his designs.

Note my boo-teek point to point wiring.

 

[drurb]

I'm sure drurb and I agree on this one

We do!

 

[meRTKendrew]

if someone prefers the tone they get from their low wattage all tube amp, who cares about the technical lack of benefits?!



-RTK

 

[drurb]

if someone prefers the tone they get from their low wattage all tube amp, who cares about the technical lack of benefits?!



-RTK

You raise a very valid and important point. If someone enjoys his/her tube amp, that's great. I enjoy mine very much! On that dimension, to each his own. You can't argue with personal preferences. The issue that often sparks discussion concerns technical advantages/disadvantages.

 

[fdeck]

if someone prefers the tone they get from their low wattage all tube amp, who cares about the technical lack of benefits?!

That's certainly a good point. My lame excuse for digging into the technical details is simply that, aside from playing bass, I also happen to be afflicted with an obsession for knowing how things work.

 

[atmasphere]

There is also the issue that this thread is *about* low watt tube amps... but dig into the hows and whys- that's where the demons lie in wait.

 

[JtheJazzMan]

I also happen to be afflicted with an obsession for knowing how things work.

With you there. Damn I need to hit the textbooks on how amps work

In my experience though in listening in detail to the tone of my various bass pickups, the above arguments are largely overshadowed by the quality of the pickup signal. Its hard to find pickups that have good clarity with high amplitude vibrations from the bass. If you have a good quality recording input box and a quality set of headphones, its a whole different world of resolution than what you usually hear from your amps.

Hell, everything is completely irrelevant if you dont put in practice time