Yamaha Power consumption clarification help

[DVV]

Are you clueless or do you just like to show that you have some engineering knowledge? 20 volts into 8 ohms is 50 watts. Period. Loss inherent to internal devices is irrelevant.

Are we timing our audio equipment now? Joules= Watts X Seconds.

Watts in the case of audio is RMS; a 50-watt amp has an infinite amount of Joules output?


So we rate the amp at 1 KHz?

50 Watts sounds much better than 50 mJ

Please re-read your own post - you explicitly said "20V on the rails".

I reacted to the "on the rails" comment. That would be PEAK voltage anyway, so 20V on the rails would in fact be 14.14 V RMS, which is 24.99 watts into 8 ohms.

If you want 20V RMS, which indeed does correspond to 50W/8 ohms, you need 28,3V Peak. Add losses across transistors, and you'll come to about 35V on the rails.

Perhaps you might try reading your own posts before reacting to others, which is a sort of shoot first, ask questions later approach. Not very conductive for a cozy discussion.

Cheers,
DVV

 

[MacManNM]

Please re-read your own post - you explicitly said "20V on the rails".

I reacted to the "on the rails" comment. That would be PEAK voltage anyway, so 20V on the rails would in fact be 14.14 V RMS, which is 24.99 watts into 8 ohms.

If you want 20V RMS, which indeed does correspond to 50W/8 ohms, you need 28,3V Peak. Add losses across transistors, and you'll come to about 35V on the rails.

Perhaps you might try reading your own posts before reacting to others, which is a sort of shoot first, ask questions later approach. Not very conductive for a cozy discussion.

Cheers,
DVV

Then I would have said P-P Volts. One would assume RMS.

 

[DVV]

Then I would have said P-P Volts. One would assume RMS.

John,

We could now argue no end on assuming whatever. Let me simply state that I try not to assume much, although like other people, sometimes I simply have to assume something as a starting point.

Anyway, let's just say we had a slight misunderstanding in our initial concepts. As I am quite new here, and as I am here because this forum had been warmly recommended to me by friends tried and true, it will take some time for me to get the hang of this particular forum. So let's chalk this up to my lack of experience on this forum and move on.

In reference to my previous mention of joules, I have thought before and still do that it would be very handy if one of the published specs the manufacturers would be obliged to provide is the energy rating of their power supplies, as expressed in joules per channel capacity. This would help remove many a doubt in consumers' minds, but would inevitably show up quite a few foul plays.

By "foul play" I refer to a practice much in evidence today, which is to use rather small power transformers, but with elevated supply rails. The manufacturer wants great 8 ohm power ratings, but is not even about to try for load tolerance, and is quite happy to "protect" his output stages by inordinate supply rail sagging.

I hope we can agree that while this is not an out-and-out lie, it is misleading for the average consumer, who still believes a reasonably priced amp or receiver should be able to drive his 4 ohm speakers. With this approach and fairly meagre filter capacitors, the actual available energy to each channel will be, shall we say, modest. Also, the sagging effect will start to limit the available power once the capacitors are seriously discharged, so while the unit will be drawing its nominal power from the wall socket, the associated losses will be such that the ACTUAL power available for the speakers will be out of reasonable proportion with the power drawn from the wall.

Hence my comment in a previous post that the power drawn is merely an indication, not an outright statement which could be extrapolated reliably into real world power figures.

Hence my comment regarding joules.

But these are simply my views, no more, and are quite open to debate.

Cheers,
DVV

 

[MacManNM]

John,

We could now argue no end on assuming whatever. Let me simply state that I try not to assume much, although like other people, sometimes I simply have to assume something as a starting point.

Anyway, let's just say we had a slight misunderstanding in our initial concepts. As I am quite new here, and as I am here because this forum had been warmly recommended to me by friends tried and true, it will take some time for me to get the hang of this particular forum. So let's chalk this up to my lack of experience on this forum and move on.

In reference to my previous mention of joules, I have thought before and still do that it would be very handy if one of the published specs the manufacturers would be obliged to provide is the energy rating of their power supplies, as expressed in joules per channel capacity. This would help remove many a doubt in consumers' minds, but would inevitably show up quite a few foul plays.

By "foul play" I refer to a practice much in evidence today, which is to use rather small power transformers, but with elevated supply rails. The manufacturer wants great 8 ohm power ratings, but is not even about to try for load tolerance, and is quite happy to "protect" his output stages by inordinate supply rail sagging.

I hope we can agree that while this is not an out-and-out lie, it is misleading for the average consumer, who still believes a reasonably priced amp or receiver should be able to drive his 4 ohm speakers. With this approach and fairly meagre filter capacitors, the actual available energy to each channel will be, shall we say, modest. Also, the sagging effect will start to limit the available power once the capacitors are seriously discharged, so while the unit will be drawing its nominal power from the wall socket, the associated losses will be such that the ACTUAL power available for the speakers will be out of reasonable proportion with the power drawn from the wall.

Hence my comment in a previous post that the power drawn is merely an indication, not an outright statement which could be extrapolated reliably into real world power figures.

Hence my comment regarding joules.

But these are simply my views, no more, and are quite open to debate.

Cheers,
DVV

Good post. Well put, and I agree with you.
I'll take it a step further, and say that thouse lyin' cheatn' bastards are out to screw every last one of us.

JK, I'm not a big fan of many of those products, because, like you, I actually understand the physics behind the sound. All specs are not created equal. I prefer to measure and compare, it's the only way to get an accurate grasp on what is out there.

 

[Buckeyefan 1]

MacManm and DVV,

We certainly can use guys like you to help a lot of the newbie's with receiver and amp purchases. A lot of guys are running to BB and CC buying up the lower end garbage, thinking they are getting the same power and output as their higher end counterparts. If more of the members understand the physics of power supplies and output, they can make informed decisions on their purchases. Simply waiting two months and saving an extra $250 towards a few model lines up could really make a difference in the end product. It's not good enough for me to tell guys to "pick up the product" to see what it weighs. They need to know why one unit weighs 15lbs and one weighs 61lbs. They also need to understand why "10 additional watts" doesn't mean much if they are comparing apples to oranges. Thanks for the posts. Hopefully you'll chime in when someone asks "what do you think about the KLH 100 watt receiver for $85."

 

[MacManNM]

MacManm and DVV,

We certainly can use guys like you to help a lot of the newbie's with receiver and amp purchases. A lot of guys are running to BB and CC buying up the lower end garbage, thinking they are getting the same power and output as their higher end counterparts. If more of the members understand the physics of power supplies and output, they can make informed decisions on their purchases. Simply waiting two months and saving an extra $250 towards a few model lines up could really make a difference in the end product. It's not good enough for me to tell guys to "pick up the product" to see what it weighs. They need to know why one unit weighs 15lbs and one weighs 61lbs. They also need to understand why "10 additional watts" doesn't mean much if they are comparing apples to oranges. Thanks for the posts. Hopefully you'll chime in when someone asks "what do you think about the KLH 100 watt receiver for $85."

One word:
Stellar
Incredible
Unbelievable......................................... GARBAGE

 

[DVV]

MacManm and DVV,

We certainly can use guys like you to help a lot of the newbie's with receiver and amp purchases. A lot of guys are running to BB and CC buying up the lower end garbage, thinking they are getting the same power and output as their higher end counterparts. If more of the members understand the physics of power supplies and output, they can make informed decisions on their purchases. Simply waiting two months and saving an extra $250 towards a few model lines up could really make a difference in the end product. It's not good enough for me to tell guys to "pick up the product" to see what it weighs. They need to know why one unit weighs 15lbs and one weighs 61lbs. They also need to understand why "10 additional watts" doesn't mean much if they are comparing apples to oranges. Thanks for the posts. Hopefully you'll chime in when someone asks "what do you think about the KLH 100 watt receiver for $85."

Unfortunately, audio in general, and high end in particular, is today more than ever bought by the pound, not the sound.

Just look at those idiotically thick front plates - professionals are happy with RAL standards, which stipulate front plate thickness of 3 mm, yet these days you're not going to sell much if your front plate is less than 10 mm thick, and they go up to 25 mm. End result - you add mass, it 'weighs" better in your hands when you pick it up, it looks sexier, and of course, the percentage of the price for the case increases. Who benefits? The aluminium industry, of course.

Then look at thick case sides - if you were to take everything out, leaving just the plates (and excluding the heat sinks, they are actually being useful), I think you'd find that the cases make up for anything from 30 to 60 % of the total mass.

The power supplies themselves vary greatly. Using class E or C core transformers is a great way to put on weight, totorids are less appealing in terms of weight but are sexier to make photos of and still add nicely to the mass, while switching power supplies are a no-no for many reasons, one of which is low, low mass. Though I must add, for fairness' sake, more and more companies are moving towards switching power supplies for pratical reasons, such as their capability to deal with input voltages in the range from 115 to 230 VAC (e.g. my own Denon DVD-3910).

Lastly, look at those volume control and selector switches - each must weigh about a pound on their own these days, at least in high end.

So, mass effectively tells you very little, and most of it is related to dead weight price. The price you have to pay.

The problem is that we are dealing with what was once a solid truth which has been distorted to beyond reason. Electrically speaking, aluminium is a much better case material then typical pressed steel because of its much lower tendency to pass on eddy currents; these are small, but numerous spurios currents occurring wherever electricity passes, we can't kill them dead, but we can reduce them significantly. But for this purpose, 3 mm thick front and back plates, and 2 mm thich other plates are quite enough, you don't really need more; so you see, there is some truth, but it has been blown out of any proportion.

Few will tell you "we use x uF of capacitance per channel", which would be an indicator of power supply quality; fewer still will elaborate on what their amp for example is capable of doing with loads lower than ideal laboratory resistors. No wonder - they KNOW they are not doing much.

Unfortunately, modern receivers are the prime victims of this philosophy. Manufacturers are ever more pushed for higher performance, better DSPs, more digital in/out lines, they face sliding standards with little sure footing, so money is spent elsewhere. In most, power stages are simply slapped together to be as cheap as possible. This is a pity, because everything they may have done before will be sunk by poor output stages.

In conclusion, more then ever, must listen before buying is a rule one is forced to use unless one likes to gamble with his own money. Weight tells you little or nothing about the product these days.

Cheers,
DVV

 

[DVV]

Just in case we got carried away and turned too technical on most people with all this energy and joule talk, my apologies and I'll try to explain briefly.

For an amplifier to be capable of dealing with low and/or difficult loads, it has to have sufficiently large energy reserves from which to draw what it needs for hard transients. This energy is afforded by its power supply as a whole, but can actually be calculated using a very simple formula, which is NOT scientific, but is nevertheless precise enough to be honestly meaningful. It states:

(V+ x V+) 1/2 C = joules

where V+ is the plus supply line in volts peak and C is capacitance in Farads.

Rather than bore everybody to tears with lengthy explanations, let's use a simple example.

Say we have a power amp with supply lines of +/-55V, and say the filter capacitors are 2x10,000 uF. In the above formula, we are effectively dealing with just the positive side, so our V for the formula is 55V and our 1/2 C is just one capacitor, i.e. 10,000 uF. So we have:

(55 x 55) 0.01 F = 30.25 j

If this is for the whole amp, then this energy should be divided by the number of channels to obtain the relevant per channel figure. Say it's a stereo amp, then we have (30.25 : 2) 15.12 joules per channel.

Here's the last fact you need to know to complete the cycle. It is generally accepted that per each 10 watts of output power, one needs 1-2 joules of energy, where 1 joule is enough for very easy to drive loads, and 2 joules will be required for really evil loads.

Hence, each channel will be capable of dissipating 151.2 watts at best, to 75.6 watts at worst. You'd be surprised how little these approximations deviate from actual real life situations!

Now, here's the grand trick - please note that in this appraoch, 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 impredance/voltage output schemes as they do today.

Because of this, and because I believe a good preacher should do as he preaches, all my designs are clearly defined in terms of energy rating. So far, these were units made for friends only, i.e. on a non-commercial basis, but after all these years, I am thinking about actually selling them. Anyway, regarding the above example, my current stage supplies (which are split from voltage gain stage supplies) run at +/-51V under full load on. There are two 10,000uF caps in parallel for each supply line followed by a 4,700uF cap (i.e. 49,400uF per channel) worst case, and when calculated, this means I have energy reserves of ((51 x 51) 0.0247)) 64.2 joules per channel. So, even under worst case conditions, which are an evil 2 ohm load, the amp will still be able to dissipate 321 watt, which is rather good for a nominally 100W/8 ohms per channel amp. However, for typical modern speakers, this translates into something more like 450+ watts in peaks into 2 ohms (however, because of the rail value of +/-51V, peaks into 8 ohms are limited to approximately 145 watts), where the problem shifts to the speakers - can they take it?

All these are in fact age-old practices, which have been around for over 50 years. They are becoming rare because they cost money, and because they are strictly under the hood, so you can't impress the customer with shiny lights and sexy displays in the local audio shop. Also, to be honest, making a 7 channel receiver using this approach would make it the most bulky receiver on the planet.

But if you want quality, well, ....

Cheers,
DVV

 

[soniceuphoria]

Here is a link that I found a while back. It is an interview of Bob Carver, and it goes into some great detail about power supplies (mainly his tracking downconverting power supply) and it is definatly some interesting reading. Happy Listening.


http://www.audio-ideas.com/interview/carver.html

 

[Buckeyefan 1]

Here is a link that I found a while back. It is an interview of Bob Carver, and it goes into some great detail about power supplies (mainly his tracking downconverting power supply) and it is definatly some interesting reading. Happy Listening.


http://www.audio-ideas.com/interview/carver.html

Old article, but interesting. I've demo'd the 11x11x11 sunfire sub, and it didn't impress me at all. The woofers move like they are having seizures, but the spl output was pathetic compared to larger subs. The amazing thing about the sub was it never bottomed out. It had more excursion than a washing machine on the rinse cycle loaded to one side.

I was impressed with his statement about amplifiers here.
GB: How audible are the differences between solid-state amplifiers?

BC: What I'm going to say will fly in the face of what most people believe. I believe that you can take two solid-state amplifiers, and provided neither one is overloaded in any fashion, they'll sound identical. That's a big if. Amplifiers are overloaded in three basic ways. They're overloaded in amplitude; they've overloaded in current; they're overloaded in speed. It's very easy to do this if you don't have a big juicy amplifier. Obviously a little Radio Shack amplifier is not going to be able to touch a big Jeff Rowland or a Mark Levinson or a Sunfire amplifier. Provided the amplifier has flat frequency response and sufficiently low distortion, both of which are trivial these days, and provided there are no interface problems, the differences will always be the subtle differences associated with overload, either momentarily, like slew-rate limiting or clipping, or just running out of drive current.

 

[soniceuphoria]

As I stated I found the article a good while back and had bookmarked it and the previous discussion reminded me of it.
I have also demoed the signature sub and I think that for its size it is impressive but when put up aginst bigger subs it falls short. Bob Carver himself stated that the 2,700 watt claim is not the actual power and that the sub was getting more arround a couple of hundred watts in all actuality. My focus was more on the power supply part of the article. Happy Listening.
Greg