HCC, Harman-Kardon and Amplifier Weight

[Brian JB]

Denon

Admin - This thread picks up from the AVR-5805 thread which got a bit off-topic.

 

[anjali3417]

Hi DVV,

Re - 31 May 2005/#76

Thx for the history & input re HCC and Harman-Kardon. Appreciate it.

On the basis of what you have experienced w HK, do you believe that their new engine aka AVR7300 is a good machine and that HK have overcome their apparant quality problems w prior engines in the AVR line. AMP failure come to mind along w a host of intermittent problems like involuntary mode switching, memory loss etc etc.

Media Reviewers do not tell the full story, but tend to talk about the 'sizzle' at hand and have no recollection of prior issues w a piece of equipment in earlier prod lines.

I have asked the same to HK and the reply is standard - 'we always strive for quality products'. Yet I know for a fact that they have had many component failures in earlier AVR lines due to 'heat related' component malfunctions. It makes sense when engines generate use 1000+ watts of power , on a continuous USE basis say 10-12 hours per day per week, that this power goes somewhere, and the heat generated has to be dissipated. Hence the new huge heat sinks.

However:

No one answers the questions directly, or address the core issue - when expensive electronics [HK AVR] are outsourced to places like China - then what kind of MTBF can we expect from components used in these engines aka capacitors, relays etc.

Why wd not the Chinese component suppliers & even HK themselves: knowingly design in a component life of 2-3 years so that as HK product lines evolve in these 2-3 years the previous engines are naturally out of mfg warranty and fail and have to be replaced by the customer? or repaired by the customer at high cost.

Which company that you know off designs to last? My 20 year old Pioneer stereo receiver, Technics Quartz turntable, Dual tape deck, AR speakers still work fine. Where has this kind of longevity and quality gone?

I used to believe that HK Denon etc were quality brands because of features and quality of machine life - ie performance and longevity. The returns for HK in its AVR line are abysmal and retail stores try not to sell it.

Is this an unfair knock on HK? Is Denon better in the longevity reliability scale?


If you have insights please share them. BTW - is there a tech name w credibility re HK that you recommend I contact.

Thank You/Anjali3417

 

[Dan Banquer]

Denon/HK

"No one answers the questions directly, or address the core issue - when expensive electronics [HK AVR] are outsourced to places like China - then what kind of MTBF can we expect from components used in these engines aka capacitors, relays etc. "
An excellent question.
From the limited experience I have with dealing with Chinese made units I can tell you that they prefer to use their own parts that they have on hand or made there instead of using parts from elsewhere. The quality as I have observed so far is essentially a crapshoot. The real hard part about reviewing is that we may not be able to tell in the first 6 months or so of use, so I think these forums are a great way to inform people of problems with certain models. If enough people find the same problem then we have a definte trend and pressure can be brought to bear if necessary.
I have had the same thing happen to me years ago with my first CD player, after two trips to the repair shop, for mechanical and premature laser diode failure I decided not to buy from that manufacturer ever again, and I haven't.
To all of you I still recommend the extended warranty that some retailers offer. It's the only way I know to get the kind of protection that appears to be required in certain instances.
Hope this helps;
d.b.

 

[DVV]

Hi DVV,

Re - 31 May 2005/#76

Thx for the history & input re HCC and Harman-Kardon. Appreciate it.

On the basis of what you have experienced w HK, do you believe that their new engine aka AVR7300 is a good machine and that HK have overcome their apparant quality problems w prior engines in the AVR line. AMP failure come to mind along w a host of intermittent problems like involuntary mode switching, memory loss etc etc.

I'm afraid I cannot answer that question. I have neither heard nor seen, much less looked under the hood of the new H/K series receivers; in other words, I know practically nothing about them.

What I can do is draw a line between three points of H/K that I do know of. The oldest in the bunch, 6550, integrated amp (2x50/70W into 8/4 ohms) was made in Japan, with above average quality components (e.g. ELNA 15.000 uF caps, etc). That one was made in November 1993.

The next one, H/K 680, their top of the integrated amp line offering, made in March 1999, uses a true dual mono configuration, with lavish execution (e.g. using a full bridge rectifier for each suuply line, so there's 4 of them rathe than the usual 2, 2x8,200 high quality ELNA caps per channel, best FET switching I have ever seen in my life, etc) was still made in Japan - but that was the ONLY model in the series made in Japan, the rest were made in Korea, and not nearly as well.

The last was a stereo reciever about three years ago - that was a pale shade of white in comparison, totally run-of-the-mill products, with parts I have never even heard of. And it sounded like it, rather nondescrepit. I'd never buy it, and consequently, I'd never recommend it to anybody.

That's where my monitoring of H/K's efforts stops.

Media Reviewers do not tell the full story, but tend to talk about the 'sizzle' at hand and have no recollection of prior issues w a piece of equipment in earlier prod lines.

I have asked the same to HK and the reply is standard - 'we always strive for quality products'. Yet I know for a fact that they have had many component failures in earlier AVR lines due to 'heat related' component malfunctions. It makes sense when engines generate use 1000+ watts of power , on a continuous USE basis say 10-12 hours per day per week, that this power goes somewhere, and the heat generated has to be dissipated. Hence the new huge heat sinks.

Agreed on the heat sink issue. Sorry to hear they had so many failures, I tended to think of them as a good cut above the pack.

However:

No one answers the questions directly, or address the core issue - when expensive electronics [HK AVR] are outsourced to places like China - then what kind of MTBF can we expect from components used in these engines aka capacitors, relays etc.

Why wd not the Chinese component suppliers & even HK themselves: knowingly design in a component life of 2-3 years so that as HK product lines evolve in these 2-3 years the previous engines are naturally out of mfg warranty and fail and have to be replaced by the customer? or repaired by the customer at high cost.

Well, Dan Banquer answered this above, and all I can say is that I completely agree with him. Perhaps we are both two old farts who believe in some totally outdated things, like good sound, quality build, longevity, low service requirements, but believe me, we can't help it. I know what quality is, and I can't look anybody in the eye and claim quality for anything I am not absolutely certain of. Definitely not one of the new whizz kid generation.

Your question touches on the problems of mass production. H/K has, after so many years, succumbed to modern day trends, it seems, and has not only moved its manufacturing to China, but also its component sourcing. Use low quality components and all you can possibly end up with is a poor reliability product.

Which company that you know off designs to last? My 20 year old Pioneer stereo receiver, Technics Quartz turntable, Dual tape deck, AR speakers still work fine. Where has this kind of longevity and quality gone?

It's gone to incredible top manager staff paycheques, to fancy advertising, to graft, you name it.

I know EXACTLY what you mean. My own Dual TT, Phlips open reel tape deck, a monster of 60 lbs, purchased in 1981, still works pefectly with only a change of the belt (since the capstan is belt driven via a 7 lbs flywheel).

I used to believe that HK Denon etc were quality brands because of features and quality of machine life - ie performance and longevity. The returns for HK in its AVR line are abysmal and retail stores try not to sell it.

Is this an unfair knock on HK? Is Denon better in the longevity reliability scale?

If you have insights please share them. BTW - is there a tech name w credibility re HK that you recommend I contact.

Thank You/Anjali3417

I am now somewhat embarassed, because if I were to answer your quality issue question truthfully, I'd have to advertise people on this forum. In my defence, these are the people I know about, but certainly not the only people still pursuing audio and build excellence.

Of the people you are likely to have heard of at all, the only person I would vouch for is James Bongiorno, a giant in each and every sense, except physical. He beat cancer twice, he was designer and chief designer for companies such as Dynaco, SAE, GAS, Sumo and now his favorite pet project, the Ampzilla amp. Peek at it at http://www.ampzilla2000.com .That man is God, and the rest of us designing amps can only hope to be his little angels - very little angels. His build quality is like his sound - out of this world.

To put it in a nutshell, for quality of sound and build you need to look at:

1. The high end gang, where build quality is usually excellent, but the quality of sound rarely matches the price tag, and

2. the outskirts of the audio world, the little guys, who are still trying to be better than the rest, at prices lower than anything you'd have to pay for something similar from established brand names. Their problem is that most people SAY they want quality sound, but are most unwilling to buy from little guys, believing their say $1K price is unfair, or whatever. Yet, in many cases, you'd find that their $1K price translates to literally $5K from a famous name, but the $5K famous name price tag does not include the sound quality of the little guy.

In that respect, Europeans are far ahead of Americans, they are much more flexible.

Lastly, the general public cannot escape its part of the blame for this sad situation. Just look at current trends - if your front plate is not at least 10 mm thick, you are not going to be selling much. Professional RAL standards require 3 mm, but the consumer market demands 10 mm? What are people into these days, selling and reselling aluminium? And believe me, a 10 mm thick front plate is far from being cheap no matter how many you buy.

Current push for more and more options, more and more processing power inside receivers, auto setups, etc, etc, etc, results in more and more money being spent on beads and trinkets and less and less money on the sound and build quality.

How much build quality do you want when a 7 channel receiver costs like $300, or $400? And it has to have all the latest fads.

You get the point, I'm sure, so I better stop ranting now, I'm beginning to froth.

Cheers,
DVV

 

[Buckeyefan 1]

DVV,

You've lost me with the whole front plate "weight" issue. If they are made from aluminum, how can they actually affect weight to a point to disguise quality? You're probably talking a lb here or there. Heck, most Denons use plastic front plates. When you compare a 61 lb HK7300 to a 20lb Denon 1705, you get the idea the power supply is the issue, not the front plate.

 

[DVV]

DVV,

You've lost me with the whole front plate "weight" issue. If they are made from aluminum, how can they actually affect weight to a point to disguise quality? You're probably talking a lb here or there. Heck, most Denons use plastic front plates. When you compare a 61 lb HK7300 to a 20lb Denon 1705, you get the idea the power supply is the issue, not the front plate.

Well, if your fascia is made of 10 mm thick aluminium, rather than the usual 1-1.5 mm as on mass made products, it will surely weigh in far more, won't it? Now, if the thin, pressed sheet metal, as used in the mass manufacture industry products, is also substituted by 5 mm thick aluminium, your net empty case mass will increase from say 4-5 lbs to something like 22-25 lbs.

Anyone lifting a unit can't help noticing the difference, can they? It strongly suggests build quality, but in actual fact, it does NOTHING for the sound. Well, not exactly nothing, in view of aliminum's desirable electrical properties, but very little.

On the other hand, it costs more, MUCH more, and we, the customers, are expected to pay the price. So, you end up paying hundreds of dollars for what is effectively just a lot of useless aluminium. And this can be a very expensive sport; a local high end manufacturer pays something like $500 for his bare case alone, so when using the typical manufacturer/end user price multiplier of just 3.5:1, the end used is paying almost $2 grand for the case alone. On a product with a price tag of $5.4K. And that end price would have been $1.2K less if he had used professional standard aluminium thickness of 3 mm. But he wouldn't have sold much, of that I'm sure, because of the sound per pund logic prevailing these days, where if it ain't heavy, it ain't high end.

Cheers,
DVV

 

[MacManNM]

Well, if your fascia is made of 10 mm thick aluminium, rather than the usual 1-1.5 mm as on mass made products, it will surely weigh in far more, won't it? Now, if the thin, pressed sheet metal, as used in the mass manufacture industry products, is also substituted by 5 mm thick aluminium, your net empty case mass will increase from say 4-5 lbs to something like 22-25 lbs.

Anyone lifting a unit can't help noticing the difference, can they? It strongly suggests build quality, but in actual fact, it does NOTHING for the sound. Well, not exactly nothing, in view of aliminum's desirable electrical properties, but very little.

On the other hand, it costs more, MUCH more, and we, the customers, are expected to pay the price. So, you end up paying hundreds of dollars for what is effectively just a lot of useless aluminium. And this can be a very expensive sport; a local high end manufacturer pays something like $500 for his bare case alone, so when using the typical manufacturer/end user price multiplier of just 3.5:1, the end used is paying almost $2 grand for the case alone. On a product with a price tag of $5.4K. And that end price would have been $1.2K less if he had used professional standard aluminium thickness of 3 mm. But he wouldn't have sold much, of that I'm sure, because of the sound per pund logic prevailing these days, where if it ain't heavy, it ain't high end.

Cheers,
DVV

Aluminum to steel, are you saying that the EM shielding properties are that different?

Lets go back to the 70's when amps were amps and sheep were scared.

 

[Buckeyefan 1]

DVV,

Some other items in a previous post I'm confused about.
You mentioned:

Now, here's the grand trick - please note that in this approach, it makes no difference whatsoever what the load impedance is! So, if the manufacturers were forced by active standards to declare their power supply capabilities in joules, they would not be able to hide under different load impedance/voltage output schemes as they do today.

But, then you say that 1 joule is for easy loads and 2 is for evil loads - which you imply that 1 is for 4 or 8 ohm loads and 2 is for 2 ohm loads. You then go on to calculate that your amp would have 64.2 joules x 10 watts/joule = 642 watts for easy loads and 321 for evil loads. So to me, you are contradicting yourself in that it DOES make a difference what the load impedance is as you get more power as the impedance lowers.

Also, you says that 321 watts is "rather good" for a 100w/8 ohm load. I think its below average. Any "good" amp that is rated at 100w/8 ohm, will also put out 200w/4 ohm or 400w/2 ohm. So when you say that translates into 450+ watts, to me, that is an extremely efficient amp, not just efficient speakers.

Just trying to understand your reasoning here.

 

[anjali3417]

Hi Dan & DVV

Thx for the replies from yesterday.

Anjali3417

 

[DVV]

Aluminum to steel, are you saying that the EM shielding properties are that different?

Lets go back to the 70's when amps were amps and sheep were scared.

Yes. let's! For one thing, the cases in those days were made with decent metalwork, not flimsy things they use for cases these days. However, while sturdier, the cases of yesteryear were, or so I feel, made well within reason and good practices.

I am not saying that they were THAT different, but I am saying they were somewhat better. Whether that "somewhat" is good enough to justify all aluminium construction is open to debate; my personal position is that yes, they are better by just that much. Which is why I use them so.

Cheers,
DVV

 

[DVV]

DVV,

Some other items in a previous post I'm confused about.
You mentioned:

Now, here's the grand trick - please note that in this approach, it makes no difference whatsoever what the load impedance is! So, if the manufacturers were forced by active standards to declare their power supply capabilities in joules, they would not be able to hide under different load impedance/voltage output schemes as they do today.

But, then you say that 1 joule is for easy loads and 2 is for evil loads - which you imply that 1 is for 4 or 8 ohm loads and 2 is for 2 ohm loads. You then go on to calculate that your amp would have 64.2 joules x 10 watts/joule = 642 watts for easy loads and 321 for evil loads. So to me, you are contradicting yourself in that it DOES make a difference what the load impedance is as you get more power as the impedance lowers.

Also, you says that 321 watts is "rather good" for a 100w/8 ohm load. I think its below average. Any "good" amp that is rated at 100w/8 ohm, will also put out 200w/4 ohm or 400w/2 ohm. So when you say that translates into 450+ watts, to me, that is an extremely efficient amp, not just efficient speakers.

Just trying to understand your reasoning here.

Here's the trick - to combine 2 ohm loads with inductance and capacitance, so as to cause the amp to be forced to drive a 2 ohm load with at least a -45 degree phase shift. To the best of my knowledge, NOBODY I have ever come across does that in testing. A -45 degree phase shift, which would qualify as a really evil load, means the amp is seeing effectively 1.4 ohms as a load. This is, in electrical terms, very near a short circuit.

Next, I refer, and I see not too clearly (sorry for that) which is probably why you asked the question, to steady state operation, not pulse. This by deauflt eliminates at least 99% of all amps out there, because most would simply choke and trigger some protection, while the remaining few might operate but would still start to heat up at such a rate that their overheat protection will surely trigger rather fast.

To be sure, some, mostly exalted models CAN pull this trick; Krell comes to mind, as does Levinson (which I positively KNOW can do this, because I tried it on a Levinson some years ago, don't remember the model designation, and it just went and ddid it, no fuss).

I beg to disagree with you that "any "good" 100 WPC amp can do that; please list three if you will, and with any luck, I can try one out. My experienece of 35 years tells me quite the opposite - VERY few actually can in anything like steady-state, meaning for any period longer than 2 seconds or so.

However, in short term bursts, as required by typical standards (e.g. IEC standard = 20 msec, or just 0,02 seconds), quite a few will indeed deliver prodigious power bursts. Which are realistically meaningless for anything but producing good advertised results.

Lastly, energy ratings are that irrespective of what the load is like; a bit like horsepower ratings on cars, you have so many brake horsepower no matter if the road is downhill or uphill, your powers is the same. This is why I think it would be a good idea to make them declare the value. You eliminate many variables used to hide behind these days.

Cheers,
DVV

 

[avliner]

Hk / Denon / Yamaha

Hi there,

I'm posting this thread in order to have your comments, as there are some comments of real interest regarding to the quality of products made.

As a matter of fact, I've been a DENON enthusiast for so many years and I am still. My actual receiver is the AVR-2803, which I'm very proud of.

I'm also considering the possibility to upgrade it in the future, for:

a) DENON AVR - 3805
b) YAMMIE RX- V2500
c) HK 7300 (after reading some coments on this forum threads).


I personally believe that products MADE IN JAPAN are far better than MADE IN CHINA. I got the example of my gear (Made in Japan). I got a friend that recently bought an AVR - 2105 (Made in China) and the sound is by far worse than the older 2803 (we compared the 2 on my system and my friend was the first one to admit that). Really don't know why, much to my surprise!

After reading the Audioholics reviews (from Denon 3805 & Yammie RX-V2500), I've realised that the Denon wins for a very tight margin, in terms of overall performance. In other hand, the Yammie wins with a good margin, if we consider that it's THX badged, more wattage, the set-up mike is included and the price is better. At a glance, the Yammie wins easily, but I have the feeling that people likes & buys the Denon most.

My opinion as a consumer: it does worth to pay more for real Japanese stuff.
I've never had Yammies before, but as far as I know it's a damn good brand.
I admit that I'm very attracted by the RX-V2500

By the way: I've seen some "heating" issues ragarding the Yammies.
Never heard the same on Denon...

Last but not least and after reading one of the above threads, I'm wondering whether it's worthy to move for a HK 7300, considering that at the price level they are offering now is a real steal. In principle the HK is - by far - the best bet between the three (flagship against mid-high level).


Your comments will be appreciated.
Avliner.

 

[MacManNM]

Hi there,

I'm posting this thread in order to have your comments, as there are some comments of real interest regarding to the quality of products made.

As a matter of fact, I've been a DENON enthusiast for so many years and I am still. My actual receiver is the AVR-2803, which I'm very proud of.

I'm also considering the possibility to upgrade it in the future, for:

a) DENON AVR - 3805
b) YAMMIE RX- V2500
c) HK 7300 (after reading some coments on this forum threads).


I personally believe that products MADE IN JAPAN are far better than MADE IN CHINA. I got the example of my gear (Made in Japan). I got a friend that recently bought an AVR - 2105 (Made in China) and the sound is by far worse than the older 2803 (we compared the 2 on my system and my friend was the first one to admit that). Really don't know why, much to my surprise!

After reading the Audioholics reviews (from Denon 3805 & Yammie RX-V2500), I've realised that the Denon wins for a very tight margin, in terms of overall performance. In other hand, the Yammie wins with a good margin, if we consider that it's THX badged, more wattage, the set-up mike is included and the price is better. At a glance, the Yammie wins easily, but I have the feeling that people likes & buys the Denon most.

My opinion as a consumer: it does worth to pay more for real Japanese stuff.
I've never had Yammies before, but as far as I know it's a damn good brand.
I admit that I'm very attracted by the RX-V2500

By the way: I've seen some "heating" issues ragarding the Yammies.
Never heard the same on Denon...

Last but not least and after reading one of the above threads, I'm wondering whether it's worthy to move for a HK 7300, considering that at the price level they are offering now is a real steal. In principle the HK is - by far - the best bet between the three (flagship against mid-high level).


Your comments will be appreciated.
Avliner.

Pretty sad when we start comparing jap and china products. What ever happened to "Buy American"

 

[avliner]

Point of vie question

Pretty sad when we start comparing jap and china products. What ever happened to "Buy American"

thanks for your reply, but IMHO,the " Buy American" does not apply in this case at all, otherwise we'll have to dive deep inside into several other fields.
We must, however, admit that japs are far better than the chinese, right?

Question is, in my point of view, is the HK 7300 as reliable as we believe?

The idea of this forum is to help users to get the best they can and that's why we're exchanging mails back and forth. This is the right place to make up your mind in terms of AV gears and that's why we place our questions here.

If I can choose between a MC INTOSH, a DENON / YAMMIE, etc., be sure I'll take the MC INTOSH at once.

Question still remains, though, which one to choose from:
DENON 3805 / YAMMIE 2500 / HK 7300??

Regards.
Avliner

 

[DVV]

Pretty sad when we start comparing jap and china products. What ever happened to "Buy American"

It died with the demise of companies few have even heard about these days.

John, do you remember the once big, BIG, names like Fisher, H.H. Scott, Craig, and yes, Marantz, when it was still run by the late and great Saul Marantz? Who remembers AR, KLH, Infinity and JBL of those days? Who remembers the kind of value-for-money speakers Jensen used to make in those days? Where have companies like Dynaco, SAE, GAS, Sumo and the likes of them gone?

All with the Great Big Note in the sky now.

For what it's worth, it's not only American, and it's not only audio. A small parallel here - whatever happened to cars which were FUN to drive? The rawhide, blood spitting bulldog machines of yesteryear companies, like Austin-Healey, like Triumph TR3, TR4 and Spitfire, like the Jaguar E Type? Where is Carol Shelby's Cobra? What we have in their place today is far removed from the credo of those days, it's now all electronics, soft ride, easy suspension, and the difference between them and Hyundai is decreasing every day. The only one left is TVR, and, to be fair, a few models here and there, notably the immortal Ford GT just revived. Plus the Lotus Elise and its derivatives, and UK's Noble looks promising.

Exactly the same could be said of European companies. Where is Studer/ReVox gone? Studer is now owned by Harman International (as are Infinity, JBL, Revel, Madrigal Labs, Mark Levinson, AKG, dBX and a slew of others), ReVox is a separate company now all but dead. Dual is gone for good. Nordmende is dead. Elac has changed beyond recognition. And so forth.

The times they are a-changin', but not always for the better.

So, either sit back and lament, or do what I am doing, build your own audio, and build your own car. And have your way with them.

Cheers,
DVV

 

[DVV]

thanks for your reply, but IMHO,the " Buy American" does not apply in this case at all, otherwise we'll have to dive deep inside into several other fields. We must, however, admit that japs are far better than the chinese, right?

I would agree with that. The Japanese have a much lomger tradition, and they manufacture superior parts, so it stands to reason their products should by all rights be better and last longer.

Question is, in my point of view, is the HK 7300 as reliable as we believe?

That's impossible to answer unless one has had that product long enough for it to show up any possible faults.

The idea of this forum is to help users to get the best they can and that's why we're exchanging mails back and forth. This is the right place to make up your mind in terms of AV gears and that's why we place our questions here.

If I can choose between a MC INTOSH, a DENON / YAMMIE, etc., be sure I'll take the MC INTOSH at once.

Question still remains, though, which one to choose from:
DENON 3805 / YAMMIE 2500 / HK 7300??

Regards.
Avliner

I would go for the Denon. In my view, it's a better balanced voicing than the H/K. The H/K has an outstanding bass quality, drive and energy, but will fall somewhat short in the high range.

The Denon on the other hand is perhaps a bit more cvilized, but is in my view better balanced on overall voicing, and a little more relaxed. Also, judging from a quick look over the schematics, it is very competently designed, those people knew what they were on about.

Cheers,
DVV

 

[PENG]

DVV,

Any "good" amp that is rated at 100w/8 ohm, will also put out 200w/4 ohm or 400w/2 ohm.

From electrical theory stand point, I can't see how that can be true. Even if you ignore any losses/voltage drops on the electronic side, the P/S transformer alone will guarantee an amplifier cannot double down. No transformer has a voltage regulation of 100%. They are all subject to voltage drop under load. For a given input signal, surely if the load impedance is halved, the current will theorectically double, provided the voltage remains the same. The fact is, the voltage cannot remain the same because there is always a voltage drop that is proportional to the load current.

The best 100W into 8 ohms amplifier may be capable of giving close to, but not quite 200W into 4 ohms. You may be able to name a few that can do it, but I would be willing to bet that they do so by simply understating their output into 8 ohms figure. I have an Adcom and a Bryston power amplifer. I know there are not the best amps by any means, but I do think they are generally considered as "good" amps. Neither one can come close to doubling the power when presented with a 4 ohm load.

 

[MDS]

The best 100W into 8 ohms amplifier may be capable of giving close to, but not quite 200W into 4 ohms. You may be able to name a few that can do it, but I would be willing to bet that they do so by simply understating their output into 8 ohms figure.

That's exactly how they do it. No amplifier can achieve the theoretical ideal of 'doubling down'.

 

[DVV]

I don't see why it's such a big deal doubling your power into lower loads?

It seems everyone expects a lof of voltage sag. While this is the most common reason for failing to double the power, and weak output stages, this is by no means quite as it appears to be here.

Voltages sag significantly only on poorly done power supplies. Assuming you have porportioned your power supply well, the actual voltage sag will be very small, 1V or so from 8 to 4 ohms. This has been so even in realtively simple DIY projects, published in popular magazines, such as Elektor. They had a mid-sized amp, designed by Tom Giffard, published in 1990 or so, which uses three pairs of complementary output devices (BD 711/712, 90W, 100V, 15A, price per unit less than $2), 40,000uF capacitance per channel and 200VA toroids (one per channel), to achive 50/100/170W into 8/4/2 ohms. Having built this several times, and having measured it, I can attest to the fact that it really does so.

There's no big secret to it. You need capable output stages, where your key problem is not power dissipation as such (unless you grossly undersized), but heat. Move from 50W/8 ohms to 100W/4 ohms and things start to cook. Feeding that amp, you need a transformer rated well above what you plan to actually use and some solid filter capacitance. Just how much you can work out easily, look at what the filter cap's manufacturer says is its maximum current, work out the current you will be needing, and then simply add as many caps as required.

For example, say you want 50/100/200W into 8/4/2 ohms; for 200W/2 ohms, you will be shipping out 14.2 amps peak. If your filter cap delivers say 5 amps, you'll need three per supply line. You can get away with two, but at high power levels, the quality of the voltage fed to the amp will deteriorate quite a bit. If 200W/2 ohms is your top power, you will need a 300 VA toroid to back that up without quality degradation.

But the heat sinks you will require for 200W/2 ohms ... they are, well, kinda BIG! That's assuming you want steady state 200W/2 ohms; if you are happy with the amps capability to do that, but not longer than say 1 minute because of overhating, then you can stop at calculating the heat sink requirements for 4 ohms steady state.

After all, to the best of my knowledge, nobody listens to a sine wave at full power into 2 ohms. Also, you can never let any amp work with real music signal at full blast, else you'd be into clipping awful fast. Heat sinks for class AB amps (say 99% of all amps out there) are always worked out on basis of average power dissipation, only the real high end, where price is no object, uses more to far more.

And all of the above applies to non-regulated power supplies; if they are regulated, the rules of the game change. You can use lower supply rail voltages because you have extremely stiff power supplies with practically zero sag, and the price you pay is in much lower transient power outputs. It's all a game of trade-off.

So why isn't it the norm, rather then being an exception? Simple - it costs money and case real estate. Too much of both for a run-of-the-mill products. How many nominally 50/100W into 8/4 ohms amps you know which use large heat sinks, with 300VA toroids for each channel, and with three pairs of output devices (which could be two, if you use more powerful devices)?

Cheers,
DVV

 

[DVV]

From electrical theory stand point, I can't see how that can be true. Even if you ignore any losses/voltage drops on the electronic side, the P/S transformer alone will guarantee an amplifier cannot double down. No transformer has a voltage regulation of 100%. They are all subject to voltage drop under load. For a given input signal, surely if the load impedance is halved, the current will theorectically double, provided the voltage remains the same. The fact is, the voltage cannot remain the same because there is always a voltage drop that is proportional to the load current.

The voltage drop is NOT proportional to load current, excpet on such poorly made units as I have never seen in my 35 years in audio.

There is a voltage drop, to be sure, but on decently done stuff, it will be less than 1 V.

For a nominally 100/200W into 8/4 ohms amp, I use a 500VA toroid; you think it will sag at 200W/4 ohms? Well, it won't - try it and see. Each power supply line is fed by a separate full wave bridge rectifier (a good US high end practice!), two per channel, each feeding 3x10,000uF capacitors (60,000 per channel). Sag? What sag? My typical sag is below 0.5V.

The best 100W into 8 ohms amplifier may be capable of giving close to, but not quite 200W into 4 ohms. You may be able to name a few that can do it, but I would be willing to bet that they do so by simply understating their output into 8 ohms figure. I have an Adcom and a Bryston power amplifer. I know there are not the best amps by any means, but I do think they are generally considered as "good" amps. Neither one can come close to doubling the power when presented with a 4 ohm load.

Any self-respecting amp manufacturer will say 100/200W into 8/4 ohms. When measuring under specified conditions, you will very likely find it delivers say 110W into 8 ohms and say 205W into 4 ohms. Nobody in their right mind will forget to include some tolerance because you can't escape small variations in production no matter what you do. They would want to be sure you get what you paid for, although I must say this practice of old is not quite so popular these days.

As for Bryston, my experience with them is not very extensive, but the three units I did get onto my lad bench did, all of them, very happily double their output into 4 ohms. And one of them is now 15-16 years old, never had its caps changed! Bryston is about the worst possible example you could have given for sagging, but about the best you could come up with ideal doubling. Bryston, Krell, Levinson, Kensonic Accuphase - these people do it routinely without batting an eyelid.

Since the amps were not mine, I didn't try for 2 ohms, and am still regretting it.

Cheers,
DVV