THD claims of audio signal generators

AP offers their oscillator only with their test set whgich starts at about $7000-8000 new. A good used 200CD or its relatives is $25-50 in working shape. Also, although the AP's gen is cleaner, it won't put the level into the loads the HP will. And the HP will survive hobbyist and student oopses for decades. With the AP you can kill it by walking over a dry enough carpet and grabbing a test lead! I was a witness to that one (it was the analyzer rather than the gen side that died-AP fixed it gratis, but it was JUST back from cal.)

Your debating petard has hoist you as usual. My claim was based on the idea that when listening to classical music at normal room volumes through a speaker of particular efficiency, (where I don't know what efficiency that is the author-it might have been PWK or an employee thereof), the average power might be two to five watts, with peak overloads that a 20-watt tube amplifier would render listenably clipped whereas to be similarly undistracting (to say nothing of not killing tweeters) a 250 watt (output) solid state amplifier would be needed. A Class B amplifier is of roughly 50 percent efficiency and so I figured

500 watts power consumption. A 20 watt Class AB tube amplifier might at most pull fifty watts, depending on its Class A power point and heater draw. Therefore, as anyone can see, the solid state amplifier has better power efficiency, but, the tube amp at 50 watts pulls less power than the SS amp at 500 (at full output) or even 80 (I speculated its quiescent draw.) to do what to the human listener is "the same job". My numbers may be a little off but anyone but you would get the concept.

That ought to be self-evident.

>

"Richard Crowley" bravely wrote to "All" (05 Jan 06 10:52:44) --- on the heady topic of "Re: THD claims of audio signal generators"

RC> From: "Richard Crowley" RC> Xref: core-easynews rec.audio.tech:186148 RC> sci.electronics.design:537334 sci.electronics.repair:354106

RC> dpierce wrote... > Arny Krueger wrote: >> AFAIK, *everything* in the JAES is peer-reviewed. >

RC> Yes, that was my experience. I published an engineering RC> report in JAES (from a presentation at the LA convention) RC> and it was not peer-reviewed. It was on a digital subject RC> in the mid-70s, so maybe they couldn't find anyone to RC> review it? :-)

Transistor amplifiers in the mid 70's were pieces of crap. They had no idea what they were doing with respect to TIM and other time domain anomalies. Often transistor amplifiers of that vintage would oscillate ultrasonically and infrasonically when overloaded and it caused really odd sonic artifacts that nobody realized or understood back then.

It really was a matter that transistor amps were basically unpredictable when they clipped and tube amps generally behaved nicely. This erratic behaviour was probably due to the comparatively radical amounts of negative feedback used in transistor amps. Back then, it was like comparing apples and oranges.

Fast forward the discussion 30 years into the future to today... The real discussion should be if they both sound different under linear operation? Musically I hear a difference but most might not.

A*s*i*m*o*v

... A stereo system is the altar to the god of music.

What? No explanation? Just no?

It was a tongue-in-cheek response to Arny's comments. That was what the ":-)" thingie was all about. However, I think it is rather pointless to compare two circuits that are as completely different as a direct-coupled, transformerless transistor power amp and a typical iron-laden tube amp. I would expect a direct-coupled, transformerless tube amp to sound much more like a transistor amp, if such a design is even practical.

Are you saying that just because most modern CD's have peak levels very close to Dfs, you *always* listen to them at the exact same peak SPL, day or night? Or do you actually use the volume control like most people, based on your knowledge of recorded levels and the system gain structure that you have already ascertained?

I simply refuse to believe that more than a handful of people do actually "set and forget" the volume control, even with CD.

MrT.

Agreed! (assuming a rather broad definition for "little" :-)

MrT.

No, but I know where to set the volume control (-6dB, to be precise) to *ensure* no clipping.

Yes.

Me, too! :-)

--

Stewart Pinkerton | Music is Art - Audio is Engineering

In article , Karl Uppiano wrote: [....]

I've heard one and it sounded very good, if that's what you mean.

It isn't.

--
--
kensmith@rahul.net   forging knowledge

Do what? First of all, there will be many conditions where the 20 watt amplifier will be well into gross clipping while the 250 watt amp is loafing along. Next, even assuming 50% final stage efficiency, which is a stretch for most tube implementations, there's no way in hell the tube amp will draw merely 50 watts at full output.

Let's assume 6BQ5s - they'll deliver 17 watts wound out, but that's in the ball park and we want to use the lowest-dissipation tube for this examination: each tube's filament eats 6.3 volts at 0.76 amps, so a pair takes 1.5 amps at 6.3 volts. That's another 10 watts there, plus another

10 or so for the driver and input stage heaters, not to mention 20 more watts for all the quiescent currents. Things are starting to heat up, which is pretty obvious to anyone who's spent much time with tube amps. At this point we're talking close to 40 watts quiescent for this 20 watt tube amp, so it's about 80 watts maxed out. Now let's look at a 250 watt transistor amp: the rails will be at +- 50 volts (full power @ 4 ohms), so comparing apples to apples and setting quiescent dissipation at 40 watts (less a third for the drivers et al) means you get a output stage bias of 250 milliamperes. Not huge, but not bad either.

On the other hand, even assuming Hamm's paper is still relevant 32 years after publishing and several generations of amplifier designs since, and comparing amplifiers which he claims would have more-or-less equal resistance to overload, 60 watt tube amps have a quiescent dissipation around 70 to 90 watts: that would bias the SS output stage at 0.7 ampere. Note this is enough to maintain class-A operation into several watts. The extra dissipation all goes into the output stage, as opposed to warming up an armada of tube heaters; one could argue that a transistor amplifier dissipating as much heat as a tube amp half its size uses that heat more efficiently!

In any event, the core of the argument here is not so much the thermal efficiency of various amplifiers (which is a hell of a way to defend tubes), but how they _sound_, and I can come up with any number of scenarios for which a 20 watt amp, no matter how liquid its midrange*, will be Not Enough.

• which I suspect is a function not of transfer characteristics but more of non-zero output impedance changing frequency response when driving a loudspeaker.

Francois.

Whether any tubed hifi amp design is practical is open for debate, but only if the tubie wants to lose the debate.

In fact a goodly number of transformerless tubed audio amps have been built and sold

Here are some schematics:

"(null)"

** Just for the record:

The final stage efficiency of a *class B* amp is NOT a number but a curve on a graph.

The *maximum* efficiency, with sine wave drive and a resistive load, is

78.5 % and occurs at full output swing ( rail to rail).

At 1/2 power, efficiency falls to 55%.

At 1/10th power it is 24 %.

At 1/100th power it is only 8% !

So, a 100 watt class B amp dissipates over 12 watts when delivering only 1 watt to the load ( aside form any idle dissipation due to the bias setting).

OTOH:

A class A amplifier has a maximum efficiency of 50% at full power.

So, a 100 watt class A amp will dissipate 100 watts when delivering 100 watts.

At 1/100th power, efficiency falls to a mere 0.5% !!

It will dissipate 199 watts when delivering 1 watt !!!!

......... Phil

I was working as a repair tech in a stereo store back then and one day someone brought in one of those Marantz $1000 receivers with the little Oscope in the corner for the FM tuner. We plugged it in and all the techs working there stopped and commented that it was a damn good sounding receiver.

Funny thing is, you really can hear a difference sometimes.

You'll know it when you hear it.

Watch which petard you have in your own back pocket, Mr. Ludwig, a'fore you make such comments.

You made absolutely NO such claim, Mr. Ludwig. You're claim was VERY simple, unambiguous and wrong:

"Subjectively tube amps of a given specification often (not always) sound better than solid state amps of better spec. Russ Hamm proved it in 1973 with his paper which appeared in JAES and it has not been contradicted."

Hamm's article makes NO such claim, it deals SPECIFICALLY with operation under conditions of sever clipping when THD amounts are on the order of 30%.

Absolute nonsense. Hamm's article makes no such statement. You have not provided a single shred of evidence to support such a claim.

Further, NO one here ever made such a claim, save you. The statement was VERY simpe: ANY solid state amplifier with substantially more power than 20 watts is going to sound MUCH better than ANY 20 watt tube amplifier when both are being asked to deliver more than 20 watts.

That means a 50 watt SS amplifier will do better at 35 watts than a 20 watt tube amplifier trying to do 35 watts,.

So what? What on earth does class B operation have to do with it, since almost NO audio amplifier since that time ran class B. There is but one or two such examples, and all are LONG off the market.

Further, what on earth does power consumption and efficiency have to do with it?

Just like a class AB solid state amplifier, which comprises MOST of the solid state amplifiers on the market. The only difference is the SS amplfiier doesn't have to provide power for filaments..

This is utter and completely irrelevant claptrap, Mr. Ludwig. We're not talking about efficiency, we're simply dealing with the fact that ANY higher power amplifier will sound better than any LOWER power power amplifier when trying to produce more power than the lower power amplifier is capable. It has nothing to do with bias class, it has nothing to do with amplfiier efficiency.

Your numbers are WAY off and completely irrelevant.

The concept that is clear is that you made a specific claim which was wrong:

"Subjectively tube amps of a given specification often (not always) sound better than solid state amps of better spec. Russ Hamm proved it in 1973 with his paper which appeared in JAES and it has not been contradicted."

and now you're making further claims which have only solidified the fact that you were wrong to begin with.

What is evident is either your inability or dogged refusal to deal with the fundamental tecnnical errors behind your assertions, not to mention the fact that your cited an article which utterly fails to support your, ahem, "thesis."

I have it, actually. It's in a book published by Newnes, isn't it?

I may have given the wrong HP part number. (Didn't I say 204C? I think that's right.) It's transistorized and does not contain a light bulb.

The name of the article is:

"Max Wien, Mr. Hewlett and a Rainy Sunday Afternoon", included in the book "Analog Circuit Design: Art, Science and Personalities" . See Amazon, etc.

I wholly agree. However what happens when both are asked to deliver

2000 watts? But only for a very miniscule time, and average putting out, say, 500 mW? Given sufficient crest factor of the material and sufficiently efficient speakers that is actually a possible (if very extreme case) scenario. It's the case McIntosh, the purveyors of specmanship themselves, made, and very well, with the advent of their first high power solid state amplifier. It is they who IMO have hoist themselves by their own petard!

Actually very little, juice is cheap.

Yes, that filament power is a deal-breaker. How many watts do four

6L6s and six 12AT7s pull?

To the extent you never clip your amp, that is true. Hamm et al dealt not at all with reasons for hobbyists (not studio owners) in 2006 (not

1973) to build their own tube boxes, like the satisfaction of the job and the appearance of the glowing tubes (which has gotten more than one audiophile laid more tha once, I'd wager...)

A 36dB transient ? You are joking yes ?

Graham

Any recording medium saturates at a reasonable, but not extreme, level above average program level, CDs run out of bits, vinyl runs out of groove width, mag tape saturates, even live FM is deviation limited.

John