Do audio differences exist between capacitors? - Page 4

Quote:

Originally Posted by Steve Eddy 

 

"Dynamic headroom" as you're using it here is just a meaningless term to make an inadequate power supply seem like some sort of a virtue.

 

A tube amp that can output 50 watt peaks during transients is no different than a solid state amp that can output 50 watt peaks during transients except that the tube amp with the looser supply will start crapping out sooner at continuous levels.

 

se

Well, no, not exactly.  Not quite a meaningless term, it's an actual measured parameter.

Many amplifiers can produce very steady-state maximum power vs short-duration peak power.  In fact, it's part of the THX Ultra 2 spec., and required.  Older, and many current solid state amps have stiffly regulated supplies.  When the output swing hits the supply rail (minus transistor drop, if any), that's it, it clips.  However, it's possible to provide that same steady-state clipping level yet with proper power supply design allow for as much as 3dB of headroom above that level, but for very short durations.  Tube amp power supply designs tended to be softer, high voltage, low current designs, which often were just plain unregulated.  Large value filter caps at high voltages were hard to make years ago, so they went smaller, just enough to keep ripple down.  That meant you you couldn't sustain the same power level continuously as you could for short peaks where the supply had a chance to completely recover and charge the filter cap fully.  When the move was made to solid state, we no longer needed high voltage power supplies, and so large filter caps were now possible, which resulted in stiff power supplies at lower voltages.  The max was the max, no matter how long the peak lasted.  Now, if the supply was high enough and the output devices up to the task, you just ended up with a biggie sized amp with plenty of headroom above normal listening levels.  But if you didn't want a product that cost a lot, you'd want to stay around 100 to 140 watts per channel.  To keep cost down, you wouldn't want the biggest high-current power transformer, runs cost up.  So you could get higher power on a short peak basis using a smaller transformer at higher voltage, save some money, and still deliver high peak power.  

The first amp made that used this design, and a couple of other interesting power supply tweaks, was the Apt-Holman Apt 1.  Holman wrote an AES paper about it which covered the concept quite well, "New Factors in Power Amplifier Design", presented at the 1980 AES Convention, and published that year also.  Paragraph 1. "Load Matching and Dynamic Headroom" begins the discussion.  The concept has been adopted by many manufacturers today, and as I said, is required to meet THX Ultra 2 specs.

The point is, even though typical tube amps didn't have the steady-state output power capability of their solid-state cousins, they did manage high enough peak power, where a solid state amp of the same continuously rated power would clip at the same peak level.  It was an accidental design point in tube amps, and so was the lack of it in SS amps, until the value of dynamic headroom was better understood, which didn't happen until 1980.  SS amps of the 1970s would have zero dynamic headroom. 

Quote:

Originally Posted by bigshot 

....Yes.

NOOOOOOOOOOOOOOOOOOOOOO! Rick Wakeman. AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAH!

I have to say, on the subject of old and new gear, although bigshot paints things very black and white, he's pretty much right. Mechanical build quality tended to be less 'value engineered' in days gone by, and there are exceptions to every rule, but audio equipment is pretty good now. Look at the Sansa Clip. Most heads would have sold their souls for SQ like that in the '70s, to say nothing of the miniaturization, and for U$35. Instead we had vinyl LPs that always deteriorated no matter how much care you took, or how much you spent on a turntable. Parties were hell, between trying to get laid and trying to keep some idiot from falling on the stereo. Unless, of course, it was somebody else's party, and I was the idiot falling on the turntable.

w

Quote:

Originally Posted by jaddie 

The point is, even though typical tube amps didn't have the steady-state output power capability of their solid-state cousins, they did manage high enough peak power, where a solid state amp of the same continuously rated power would clip at the same peak level.

Ok. So what?

Let's say you have a solid state amp whose continuous power is the same as the tube amp's peak power. How is the solid state amplifier somehow a worse amplifier than the tube amplifier? Similarly, if we take that same amplifier, significantly reduce its power supply capacitance so that it's continuous power rating is the same as that of the tube amp, how is that somehow a better solid state amplifier?

And how does dynamic headroom inform the consumer in any meaningful way? Let's say the tube amp will do 100 watts peak and 50 watts continuous giving it a dynamic headroom spec of 3dB. And we also have the same solid state amp as mentioned above and let's assume it's power supply is stiff enough that for all intents and purposes, it has a dynamic headroom of 0dB. So now the consumer's going to look at the spec sheets and go "Oooh, this amp has a dynamic headroom of 3dB and the other one has a dynamic headroom of 0dB. I've heard dynamic headroom is important so I'll buy the one with 3dB of dynamic headroom." But there would be no practical difference between the two amplifiers.

I'm sorry, but I just don't see any meaningful value of dynamic headroom outside of marketing, much like "PMPO." And if you don't think engineers didn't know anything about dynamic power until 1980, you're sorely mistaken.

So what? By the 1970's, watts were cheap. So you buy your 100 watt continuous solid state amp instead of the 50 watt continuous, 3dB dynamic headroom tube amp.

se

Quote:

Originally Posted by Steve Eddy 

Ok. So what?

 

Let's say you have a solid state amp whose continuous power is the same as the tube amp's peak power. How is the solid state amplifier somehow a worse amplifier than the tube amplifier?

 

If both have the same continuous power capability (lets talk measured, not rated), but one amp has 3dB of dynamic headroom, that means that amp can produce an undistorted peak at twice the continuous output power.  So if the continuous power is 100W, it can produce an undistorted peak at 200W.  Without that dynamic headroom, both amps clip at 100W.  

So which would you rather have, a 100W amp all the time, or a 100W amp that can do 200W  during peaks, and only costs a little more?  Or a 200W continuous amp that costs a lot more?  Considering how little time we spend listening to 200W peaks, the 100W amp with dynamic headroom would be the best deal.  Perhaps not a big deal with two channels, but if you have 5 or 7, the cost savings adds up.

The Holman paper introduced the concept to the industry in quantified terms.  Certainly some engineers knew about it, but it wasn't a design constraint in consumer amps until well after 1980.  It wasn't a required feature anywhere in any design until THX specs were written for home systems in the early 1990s. The chances of a vintage SS amp having any dynamic headroom before 1980 are very very small.  

PMPO was a deliberate attempt to publish inflated power figures for marketing, which is why the FTC outlawed it.  Dynamic headroom goes the other way as far as the consumer is concerned.  Rather than elevate the power spec for any amp, it defines a difference in performance that delineates different amps from each other.  Alone it may not be the deal breaker, but more knowledge is better, isn't it?

If you don't value the design, don't buy it.  I'm not marketing anything, so I really don't care.  The discussion hinged around the differences between todays mid-range amps and vintage amps.  Be it ever so small, dynamic headroom is one difference, there are others.  I would define a difference as one that could be heard.  You can, in fact, hear the difference in raising the clipping threshold 3dB.  

By the way, the prices for power amps in the 1970s was just over $1/watt.  Scale that by today's inflation, where do you end up?  WAY more than $1/watt.  A THX Ultra 2 AVR at $1200, 7 channels of power amp, 140/WPC, dynamic headroom, ends up where in price? A bit over $1/watt.  But that's today's $$. So you tell me if watts were cheap in the 1970s.

Let's talk real world here.

Onkyo TX-NR3009. THX Ultra2 Plus certified. $1,499 at Crutchfield.

Continuous (FTC) power is rated at 140 watts into 8 ohms. Only two channels driven.

Dynamic power is rated at 160 watts into 8 ohms. Only one channel driven.

Dynamic headroom? A whopping 0.58dB.

Show me an AVR with 3dB of dynamic headroom.

I don't know what you mean by "design constraint."

And keep in mind that Holman had a direct financial interest in selling the concept.

Nonsense.

Almost no power amplifiers out there use regulated power supplies (at least not for the output stage). And every power amp that doesn't use a regulated power supply will have some amount of dynamic headroom. Including those made in the 1970's.

Dynamic headroom is just the ratio of undistorted power that can be achieved for a very short period of time (200ms I believe it is in the IHF standard) versus how much undistorted power can be achieved continuously. With an unregulated power supply, the latter will always be a bit lower than the former. How big a difference that is will depend on how much you've decided to skimp on your power supply.

In fact it was various gimmicks just like "dynamic headroom" that manufacturers were resorting to back in the late 60's and early 70's that caused the FTC to finally step in and establish some standards with regard to power ratings. Manufacturer A might rate their power as the continuous power into 8 ohms. Manufacturer B, who's trying to compete with Manufacturer A would rate their power based on the peak power into 8 ohms (without making any mention of that qualification) so it would appear more impressive to the consumer. Manufacturer C, who's trying to compete with Manufacturer A and Manufacturer B would come along and rate their power based on the peak power into 2 ohms (again without making any mention of that qualification).

PMPO was typically used for multimedia systems which weren't covered by the FTC regulations. Also, the FTC doesn't require that you use their method EXCLUSIVELY. It just has to be included (and I believe at the top of the list). After that manufacturers can add whatever they want.

I don't see that dynamic headroom is fundamentally any different than PMPO.

Look, I can design an amplifier that will deliver a peak power of say 200 watts and a continuous power very close to that. That would give a rather low figure for dynamic headroom. Then I can take that same amp, and start whacking down the power supply such that it can still maintain that same peak figure of 200 watts, but the continuous power gets lower and lower, the result being that the dynamic headroom figure goes higher and higher. I can take it down so that continuous power is only 20 watts. That would give a dynamic headroom figure of a whopping 10dB! Wouldn't that be impressive!

But of course at just 20 watts continuous, you're going to start running into clipping in order to achieve adequate SPL with the more inefficient loudspeakers out there.

So how exactly does dynamic headroom provide the consumer with any meaningful figure of merit?

As I said previously, even the amplifiers in the 70's had dynamic headroom. It's just that after the FTC stepped in, manufacturers largely stopped using gimmicks like that in their spec sheets and simply gave the FTC figures.

And as I asked previously, show me a real world example of an amp with 3dB of dynamic headroom.

A couple of issues here.

Fist, show me a $1,200 THX Ultra2 AVR that will deliver 140 watts continuous from all 7 channels simultaneously.

Second, that $1,200 AVR is being made in China by workers who are probably being paid less per day than the Japanese workers in the 70's were making per hour, and that's NOT adjusting for inflation.

And for what it's worth, $1 in 1975 is equivalent to about $4 in today's dollars.

Anyway, I'm sorry, but I simply don't see dynamic headroom as being any sort of discovery or technological advancement, rather I see it as little more than a marketing device.

se

I can think of 2 1970's vintage tube amplifiers with at least 3db of headroom.

And both have serious high power power supplies (although neither are regulated)

Mcintosh MI-200  monoblock rated at 200 watts RMS, typically 500 watt peaks.

( i have a pair, too bad the output tubes are impossible to find) DHT amps, very sweet.

Mcintosh MI-300.  monoblock rated at 300 watts RMS, typically 1kw peaks.

(i have a pair of these too, too bad i'm now so old and feeble i can't lift the things)

The SAE amplifiers back in the 1970's also had at least 3db of headroom. Probably more.

until they overheated.

Originally Posted by Steve Eddy 

 

Let's talk real world here.

 

Onkyo TX-NR3009. THX Ultra2 Plus certified. $1,499 at Crutchfield.

 

Continuous (FTC) power is rated at 140 watts into 8 ohms. Only two channels driven.

 

Dynamic power is rated at 160 watts into 8 ohms. Only one channel driven.

 

Dynamic headroom? A whopping 0.58dB.

 

Show me an AVR with 3dB of dynamic headroom.

 

The 3dB figure I used was an example because it's an easy number to get heads around.  There's nothing wrong with the Onkyo specs, except their dynamic headroom doesn't illustrate my point.  

 

One of the things I appreciate about this back and forth is it gives me a chance to reaffirm what I think to be true.  And guess what?  Sometimes, the truth isn't what I think.  I have a copy of the "original" THX specs on file, sorry I can't share it.  I can assure you, they did call out for more than a fraction of a dB of dynamic headroom.  And there have been AVRs that had some pretty whopping headroom (an NAD model comes to mind, though out of production).  Several things have happened over the past few years.  First is THX ain't quite what it used to be.  There have been staffing changes, ownership changes, etc., and yes, certification spec changes.  Where do you think Select and Select 2 came from?  They're trying to be a business, and they don't have a product, except to charge to certify things.  When interest in that slacks (wasn't there a wobble in the economy recently?) they have to do something.  From what I can see, the specs may have been just a bit too hard to hit, so they apparently adjusted a few things.  THX doesn't publish specs, so we have to discern from the result.  The results are, almost all main-stream AVR manufacturers except for Onkyo/Integra and Pioneer have dropped THX certification completely.  I would guess that has the THX folk a bit worried. What I see for specs on AVRs from Onkyo/Integra and Pioneer don't seem to meet with the original figures, but they got certified.  That indicates a requirement change.

 

So, I stand corrected, and I can't show you any current production AVR with any significant dynamic headroom.

 

Quote:

Originally Posted by Steve Eddy 

 

I don't know what you mean by "design constraint."

 

And keep in mind that Holman had a direct financial interest in selling the concept.

 

Active regulators, no. But large current capacity transformers and huge filter capacitors are a basic form of regulation.  Thats electronics 101, man.  I'm sure you know that.  Those big parts cost big money, and sometimes big money isn't the target. 

Sorry, again I screwed up.  You are correct about PMPO, I was thinking of the old "IHF Music Power figure" of the 1960s and pre 1974 when the FTC did their first go-round to fix that mess.  Guess the brain's not as good as I hoped.  PMPO and DH are similar, the differences are sort of academic, having mostly to do with how you measure.

But, if you read the last FTC re-hash of audio amplifier power specs, you'll probably be as disappointed as I.  What a mess.  Arguing on both sides, in all directions, and one of the arguments the FTC listened to was that publishing complete specs that included power bandwidth and THD vs frequency was "too expensive" a burden for manufacturers!  Huh.  Really.  And, as you confirmed, the specs just aren't there today either.  What the FTC has done is caved to the manufacturers wishes, and consumers take the hit with less meaningful specs.  That wasn't the goal when Holman introduced DH.  His product that he introduced associated with that paper was one of the highest performance per dollar amps ever made.  That's not taking advantage of the consumer, that's giving him high value.  It was that same motive that moved Holman to write the original Home THX specs, and yes they included significant DH.  By that time, he gained nothing from the specs themselves.  One thing is for certain, THX specs were unpopular with manufacturers!  And they're the ones paying to have them on the box.  The intent was higher quality for the consumer, not sure if the numbers would show they succeeded. Probably not.

That, of course, was a ridiculous example.  I preferred your "real world" approach earlier in the post.

It is my belief, which you are free to disagree with, that the attempt to quantify dynamic headroom measurements gave both consumers and designers tools with which to evaluate a performance aspect that could have impact in the real world.  Prior to that time, there were amps with it and without it, but you really couldn't tell from the specs.  Sadly, I see that in today's world things reverted, at least specs wise.

PAs with 3dB of DH: I already cited the Apt-Holman Apt 1 power amp.  The MX series by QSC (all had between 2 and 3dB, but I admit, not your usual consumer gear, and QSC no longer specs DH), NAD 2700 THX receiver (I had to look that one up, it goes back a few years, but sported 4.3dB of dynamic headroom at 8 ohms)

A couple of issues here.

 

Fist, show me a $1,200 THX Ultra2 AVR that will deliver 140 watts continuous from all 7 channels simultaneously.

There aren't any, and doesn't need to be.  The demands of multi-channel audio never, and I do mean NEVER, require full power from all 7 channels simultaneously.  Typical power distribution is 70% center, 15% L and R, and all the rest shared in all the surrounds.  The sub is out of the picture, being self powered.  High levels of L and R may coincide with high levels in C, but statistically not at the same instant.  I'll agree if you say it's a cheat, and I'll agree that I'd like to have full power in all 7 available, but in practice, nobody will need it or use it, and we sure don't want to pay for it.  If we do, we can always use 4 2 channel power amps.

 

 

Quote:

Originally Posted by Steve Eddy 

Second, that $1,200 AVR is being made in China by workers who are probably being paid less per day than the Japanese workers in the 70's were making per hour, and that's NOT adjusting for inflation.

I agree that seems very wrong.  And you'd think quality would suffer.  Some manufactures retain high quality from China by paying for and demanding it, but that doesn't change the situation much.  The point is, however, irrelevant when talking about the quality of amps.  Underpaid Chinese labor isn't the problem, greedy consumers and manufacturers are.  We may not get 1/4" thick milled brushed aluminum front panels any more, but they don't contribute to performance as much as all those DSPs.  Performance is there, you just can't park your car on the thing today.

 

Quote:

Originally Posted by Steve Eddy 

And for what it's worth, $1 in 1975 is equivalent to about $4 in today's dollars.

If anything, that further underscores my point about the cost per what.  Way cheaper today than 40 years ago.  Want to build a discrete transistor DSP?  How about a vacuum tube DSP?  Me neither. 

 

Quote:

Originally Posted by Steve Eddy 

Anyway, I'm sorry, but I simply don't see dynamic headroom as being any sort of discovery or technological advancement, rather I see it as little more than a marketing device.

 

I see your point, Steve.  DH might have started out as a noble cause.  It might have benefitted consumers had there been continued effort to sustain high DH in product.  There were amps with deliberately higher DH designed purposefully.  I concede that today's gear seems to have reverted.  

 

All that said, and we've probably said too much, dynamic headroom was only one of several aspects I cited that may have contributed to better amp designs in newer amps.  Perhaps the cost per watt is the only one worth discussing, perhaps not.  But I remain in my position that though build quality in older gear may be impressive, there are plenty of newer more advanced designs that are better in many aspects.  

 

One thing a new amp can't provide is the sense of nostalgia and comfort that comes from looking at a piece of vintage gear while you listen to it.  That alone will make it sound good.

Ok.

Ok. But why? Why is a 200 watt amp with a fraction of a dB of dynamic headroom necessarily worse than a 100 watt amp with say 3dB of dynamic headroom? I mean because throughout this entire discussion you've been implying that amps with very little dynamic headroom are somehow bad, and that good amps should have a good amount of dynamic headroom. In other words, what exactly is bad, from a performance point of view, about an amplifier with just a fraction of a dB of dynamic headroom?

Sure. I'm just pointing out that because of the financial interest, some of those "developments" can be nothing but sizzle and no steak.

Ok. But I thought the THX standards were about performance criteria, not about how manufacturers can save a few bucks by skimping on the power supply. And besides, manufacturers were skimping on power supplies even in a lot of those solid state amps back in the 70's.

It would certainly cost a lot less than THX certification.

What do you mean he gained nothing from the specs themselves? He was working for Lucasfilm at the time.

Of course it was a ridiculous example. That was intentional.

If next to no dynamic headroom is "bad," and say 3dB of dynamic headroom is "good," then why isn't much more dynamic headroom even better still? At what point exactly does more dynamic headroom transition from being "good" to being "bad"?

Fine. But I still don't see dynamic headroom as being any particularly meaningful figure of merit. I mean really all it's saying is "We skimped a bit on the power supply so you can only get 100 watts continuous, but that's ok because you can still get 200 watt peaks for 20 milliseconds."

Yes, but let me remind you that THIS is what I was replying to:

You can only get that "a bit over $1/watt" if you multiply 140 watts by seven. But as you say, you're not going to get 140 watts per channel simultaneously from all seven channels in that $1,200 AVR, so in order to make a more apples to apples comparison, you can't derive the cost per watt by dividing $1,200 by 980 watts and your cost per watt's going to have to be rather more than "a bit over $1/watt."

Sure, silicon's cheap and has largely followed Moore's Law. But we're talking about the power amplifier side of things.

But high dynamic headroom amplifiers have been with us all along. High dynamic headroom basically just translates to "loose power supply." Those Japanese receivers in the 70's weren't using 2 kVA power transformers and 100,000+ uF of reservoir capacitance.

Sure. But can you even demonstrate that there's even any actual audible difference between a decent Japanese receiver from 1975 and any modern amplifier you care to name?

se

Quote:

Originally Posted by Steve Eddy 

 

Ok.

 

 

Ok. But why? Why is a 200 watt amp with a fraction of a dB of dynamic headroom necessarily worse than a 100 watt amp with say 3dB of dynamic headroom? I mean because throughout this entire discussion you've been implying that amps with very little dynamic headroom are somehow bad, and that good amps should have a good amount of dynamic headroom. In other words, what exactly is bad, from a performance point of view, about an amplifier with just a fraction of a dB of dynamic headroom?

 

I think I intended the comparison was to be between a 100W amp with no DH and a 100w amp with DH, OR the cost of a 100w amp with DH vs that of a 200w amp.  I do recognize the difference is small.  I also recognize that comparing costs is almost impossible because the two devices are completely different.

 

Quote:

Originally Posted by Steve Eddy 

 

What do you mean he gained nothing from the specs themselves? He was working for Lucasfilm at the time.

When you work for a company and invent something, THEY own the patents, THEY own the rights.  The most you can hope for is a raise, but THX was never Lucasfilm's cash cow. The entire goal of THX was to improve exhibition.  The fact that something could be licensed was not even considered until much later.  It's not like they were Dolby and licensed Dolby B to every cassette manufacturer.

 

Quote:

Originally Posted by Steve Eddy 

 

Fine. But I still don't see dynamic headroom as being any particularly meaningful figure of merit. I mean really all it's saying is "We skimped a bit on the power supply so you can only get 100 watts continuous, but that's ok because you can still get 200 watt peaks for 20 milliseconds."

I agree that you don't see DH as being any particularly meaningful figure of merit.

Quote:

Originally Posted by Steve Eddy 

Sure. But can you even demonstrate that there's even any actual audible difference between a decent Japanese receiver from 1975 and any modern amplifier you care to name?

 

se

 

Now we're into the area of pointless debate.  There were some horrible receivers back then, I had to repair many of them. Sansui comes to mind, they had a particular line of receivers that became high power oscillators.  They would sound bad by comparison to anything made today.  But what's the point?  We can argue specific models, or design trends in general, when it comes to this topic, the back/forth is now probably just a p---ing contest.  

My position is this: mid-line new stuff beats mid-line old stuff, and some high end old-stuff.  High-end new stuff beats some high-end old stuff.  There are a lot of technical reasons, we've picked dynamic headroom to death, but that's not the only reason.  Anyone his free to ignore the entire DH discussion, and even if I throw it out, it doesn't change my position.