I see claims that 60 wpc kt88 amps can have "peaks" of up to 120 watts. I thought that the max power is dependent upon the B+ voltage, biasing, transformer load, etc. If there is such a thing as "peak power", what determines how much of a peak the amp puts out?
-Don
-Don
Well, the datasheet tells you the transfer characteristics, and the circuitry (topology used, chosen operating points, power supply, load and transformer winding ratio, etc.) and associated parameters thereof will determine how much power it can give.
Yes, there is such a thing as "peak power" and it is rarely that which you see claimed on advertising copy.
Hi
here two examples of test to check the rms power and peak power
http://www.diyaudio.com/forums/tubes-valves/309166-fab-four-4-x-kt150-monoblock.html
http://www.diyaudio.com/forums/tubes-valves/308607-p-p-el34-kt120.html
The main reason is related to a load that the tubes see; it can be a "mid-way" between distortion and efficency.
In my case I choose a single secondary of 5 ohm; the primary load is the result of different tests and seems to be right. The ratio is 27:1 for single p-p; 19:1 for double p-p
The diagram of THD vs frequency is the better test to have a right idea.
Second is the Joule that you have on power supply.
Third the tube you use; on pp with EL34 and KT120 the difference is the capability to have much anode current.
In every O.T. at low and high freq. the L is decreasing for two different reasons.
In this case if you have a tube that can deliver more current you can get power in rms and peak.
If you change the El34 with 6CA7 you will get better performances.
This as general consideration
The reason is that a same idle current the KT120 has a lower Rp; if you look at diagram of THD vs freq. of KT120 with two different bias current you can see that at 90 mA of bias the distortion is lower than 55 mA; the bias point is changed between the two current but the Rp of 120 is lower and this is a plus.
Walter
here two examples of test to check the rms power and peak power
http://www.diyaudio.com/forums/tubes-valves/309166-fab-four-4-x-kt150-monoblock.html
http://www.diyaudio.com/forums/tubes-valves/308607-p-p-el34-kt120.html
The main reason is related to a load that the tubes see; it can be a "mid-way" between distortion and efficency.
In my case I choose a single secondary of 5 ohm; the primary load is the result of different tests and seems to be right. The ratio is 27:1 for single p-p; 19:1 for double p-p
The diagram of THD vs frequency is the better test to have a right idea.
Second is the Joule that you have on power supply.
Third the tube you use; on pp with EL34 and KT120 the difference is the capability to have much anode current.
In every O.T. at low and high freq. the L is decreasing for two different reasons.
In this case if you have a tube that can deliver more current you can get power in rms and peak.
If you change the El34 with 6CA7 you will get better performances.
This as general consideration
The reason is that a same idle current the KT120 has a lower Rp; if you look at diagram of THD vs freq. of KT120 with two different bias current you can see that at 90 mA of bias the distortion is lower than 55 mA; the bias point is changed between the two current but the Rp of 120 is lower and this is a plus.
Walter
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Marketing is great!
1. Is this the one you meant?
Some amplifiers can produce larger peak powers for a brief time, until the power supply sags. But I may not want to listen to the amp if the power supply is sagging, but even if I do, I would not rate the amplifier in this way. What if the music transient lasts longer than the brief time of the amplifier's capability?
2. Or is this the one you meant?
The true Power of a sine wave = ((rms voltage)squared)/Rload
The peak voltage of a sine wave is Root(2) times the rms voltage of the sine wave.
Root(2) = 1.414
1.414 times rms voltage = peak voltage.
The Peak power of a sine wave = ((Peak voltage)squared)/Rload
Hopefully an amplifier can produce its rated rms power all day long.
And hopefully it can do so without misshaping the sine wave (so the rms and peak
voltages have a constant ratio (1:1.414)
A sine wave of 21.91Vrms into 8 Ohms is 60 Watts.
A sine wave of 21.91 Vrms times 1.414 = 30.98 Volts peak.
30.98V peak into 8 Ohms is 120 Watts peak power.
Peak power just looks good to marketing, and to the customer.
1. Is this the one you meant?
Some amplifiers can produce larger peak powers for a brief time, until the power supply sags. But I may not want to listen to the amp if the power supply is sagging, but even if I do, I would not rate the amplifier in this way. What if the music transient lasts longer than the brief time of the amplifier's capability?
2. Or is this the one you meant?
The true Power of a sine wave = ((rms voltage)squared)/Rload
The peak voltage of a sine wave is Root(2) times the rms voltage of the sine wave.
Root(2) = 1.414
1.414 times rms voltage = peak voltage.
The Peak power of a sine wave = ((Peak voltage)squared)/Rload
Hopefully an amplifier can produce its rated rms power all day long.
And hopefully it can do so without misshaping the sine wave (so the rms and peak
voltages have a constant ratio (1:1.414)
A sine wave of 21.91Vrms into 8 Ohms is 60 Watts.
A sine wave of 21.91 Vrms times 1.414 = 30.98 Volts peak.
30.98V peak into 8 Ohms is 120 Watts peak power.
Peak power just looks good to marketing, and to the customer.
Yes, 'peak power' has several meanings. All of them are useful in the right contexts, which includes knowing which one is appropriate for each context.
Not exactly!.
to understand the rms power and "dynamic" power are necessary the instruments not only numbers.
Of course the marketing works mainly with the numbers.
Under the lab test is it possible to understand the real rms power and the "dynamic" power also related to the load.
Walter
to understand the rms power and "dynamic" power are necessary the instruments not only numbers.
Of course the marketing works mainly with the numbers.
Under the lab test is it possible to understand the real rms power and the "dynamic" power also related to the load.
Walter
In engineering there is no such thing as rms power. It was invented for consumer protection, I think - presumably by someone who was not an engineer. When people say rms power they usually mean average power.
I my opinion no.
The rms power is the power with continuos signal in input
When you read with the standard voltmeter what you read?
Rms or somenthing other?
( of course I mean when the load is resistive)
Walter
The rms power is the power with continuos signal in input
When you read with the standard voltmeter what you read?
Rms or somenthing other?
( of course I mean when the load is resistive)
Walter
Your opinion is wrong. The power value calculated from RMS volts (or RMS current) for a sine wave is average power. If you know how to integrate a sine wave you can prove this to yourself. As I said, there is no such thing as RMS power - if we are talking engineering rather than sales.
Stating 'average power' when a user wants to know the maximum power an amp can produce is asking for trouble and misunderstandings.
Stating something like 'maximum average power' doesn't help either.
I can only image that users (sorry, I'm an IT engineer, not an electrical one) would want to know the maximum, undistorted power that an amp can put out.
True, you'd need to integrate the waveform to get the 'true' power produced with that speciffic waveform, but would that mean to express the maximum power in a figure depending on the musical style? More maximum power playing heavily compressed dance vs lower maximum power playing delicate acoustical or chamber music.
Nah, let's stick to the two extremes: max sine power and max quare wave power?
And drop the confusing 'average'...
Stating something like 'maximum average power' doesn't help either.
I can only image that users (sorry, I'm an IT engineer, not an electrical one) would want to know the maximum, undistorted power that an amp can put out.
True, you'd need to integrate the waveform to get the 'true' power produced with that speciffic waveform, but would that mean to express the maximum power in a figure depending on the musical style? More maximum power playing heavily compressed dance vs lower maximum power playing delicate acoustical or chamber music.
Nah, let's stick to the two extremes: max sine power and max quare wave power?
And drop the confusing 'average'...
In the 1974 FTC wrote the standard about power on amplifiers.
And I think those people were a technician. And is it possible to read the mean rules
In the lab at Audio magazine review we follow the intl indication about the rules.
We can speak in deep about sine wave of course but measuring the voltage on a resistive load with a appropriate instrument when an amps is driven with a sino signal give us the right information.
In addition, as happen in our lab, we have additional test to check more in deep the capability of the amp to delivery current to the load.
And not only static.
Walter
And I think those people were a technician. And is it possible to read the mean rules
In the lab at Audio magazine review we follow the intl indication about the rules.
We can speak in deep about sine wave of course but measuring the voltage on a resistive load with a appropriate instrument when an amps is driven with a sino signal give us the right information.
In addition, as happen in our lab, we have additional test to check more in deep the capability of the amp to delivery current to the load.
And not only static.
Walter
The term ' average' only confuses those who don't understand it. If we have to drop terms because people who don't understand them don't understand then we are left in the situation that people who don't understand still don't understand, while those who could understand are denied that opportunity because we can't use the words they would understand.Parafeed813 said:
Just to clarify: the power you get from RMS voltage or current measurements is average power (for a sine wave). The peak power of a sine wave is twice the average. The minimum power of a sine wave is zero (at the zero crossing). When people say "power" when they are talking about AC they almost always actually mean 'average power' even if they don't know that this is what they mean. You need to specifiy 'average' because the instantaneous power of a sine wave is varying at twice the frequency of the sine wave. You usually average over a complete cycle.
Most amplifiers are voltage limited, although have some other limit. In any case, when feeding a constant resistive load the net effect is that there is a peak voltage the amp can supply. If you calculate the corresponding power then you get peak power. If the signal is a sine wave then the average power is half the peak power. If the signal is a square wave then the average is equal to the peak power.
The peak voltage the amp can supply may vary depending on what the amp has just been doing. Sometimes it does, sometimes it does not. On short transients some amps can deliver more; on long continuous signals some amps can deliver less. Hence there is another meaning for peak power: the highest average power the amp can deliver for a short period. It is unfortunate that there are two quite different meanings for 'peak power'. It is unsurprising that this confuses some people. Marketing may sometimes combine the two by taking the highest peak power the amp can deliver for a short period - this is sometimes measured in 'Chinese watts' which are somewhat smaller than everybody else's watts. So a 50W amp (i.e. 50W continuous average power under sine wave drive) can become a 100W amp (i.e. 100W peak continuous power under sine wave drive) and then if it can give a bit more on short term peaks it becomes a 150W amp which is nearly 200W which can be expressed as 300W in Chinese.
There are also PMPO power, that is about 150 times normal condition power. A 1KW PMPO amplifier perhaps has a 5-10 W speaker.
(Push-pull) tube amplifiers with output transformer behave differently than push-pull transistor amplifiers. The voltage swing on their anode is not restricted by the supply voltage. Transistor amplifiers have a hard limit (literally) defined by the supply voltage.
The voltage swing of a PP valve amplifier is fairly tightly constrained by the supply rail voltage because the anode is unlikely to go below ground and so the other anode is unlikely to exceed twice the rail voltage. It is not quite as hard a limit as a solid-state amp, but it is still a limit.
You mean the anode of the cut off tube can't go more negative than the cathode? Coupling the two halves of the OT may force this condition - or not?
I didn't say it can't go negative, I said it is unlikely to go negative. Certainly the valve drawing current cannot pull it negative, and unless there is significant distortion the valve switching off is unlikely to push its anode up beyond twice the supply rail.
The general rule is that the anode swing of a PP valve is limited to the range between a bit above zero and a bit below twice the rail voltage. This is not a hard limit (unlike SS) but it is a limit and certainly limits the power output. I am puzzled why you suggest the contrary.
The general rule is that the anode swing of a PP valve is limited to the range between a bit above zero and a bit below twice the rail voltage. This is not a hard limit (unlike SS) but it is a limit and certainly limits the power output. I am puzzled why you suggest the contrary.
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In a tube p-p the limit on swing on output stage is the Vdc .
The difference can be the Rp of tubes you are using and the bias.
If you use p.e. a KT120 it has a lower Rp respect to KT88 for the same current.
This give you a better swing on output ( and a better THD)
The two tubes are considered swappable and this is true.
Walter
The difference can be the Rp of tubes you are using and the bias.
If you use p.e. a KT120 it has a lower Rp respect to KT88 for the same current.
This give you a better swing on output ( and a better THD)
The two tubes are considered swappable and this is true.
Walter
"Peak" sounds good, as does "Class A." Guitar people get to also sift thru the difference between gain and "gain." Almost every guitar amp that markets itself as “Class A” is not. "Headroom" is often mis-used too. Marketing people like to use such terms even when they are technically inappropriate or even a pure lie. I worked for an audio DJ equipment company ~25 years ago and I read an ad they were preparing on their new power amps. I was very impressed with their apparent quality and power, especially since the company was not a high-end one. The marketing guy told me it was complete BS. Since then I notice that many ads for audio stuff contain significant crappola.
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