Amplifier output question

[wilbucd]

I know someone here will know this. If the volume knob is set at for instance ten o'clock.......will the amp put out the same power regardless of the media being played? If I have to turn up a cassette to say twelve o'clock to get the same volume that I get with a compressed cd at ten o'clock is it really using more power to equal the volume of a cd or is the compressed cd using more power at ten o'clock.

Or.......what is the relation to the volume knob position, the clipping indication lights on the amp and the media signal source?

I am using a 200wpc amp with Khorns which everyone here knows are rated at 100 w max continuous (400 w peak). With other stereo systems I have always turned up the volume just to where the distortion starts and then back it off a little. I have yet to hear the Khorns distort.....not that I am trying to find the point where they do but I would like to know how loud they can be played without damaging them. Is it safe to assume that as long as the 200wpc amp isn't clipping then then they are ok?

[russ69]

The amp will be clipping long before you will hear it distort. You must be using the khorns for a PA system? I suggest you play them at a comfortable level and save the paint stripping volumes for live concerts. Your ears will thank you.

Thanx, Russ

[WMcD]

Let me explain.

Generally there is a chain of devices.

1) The level on the media is, of course, what it is. You can get an idea of this on CD's using Windows Media Player set to "bars". It is not calibrated but you can observe whether a recording has good or poor dynamics. If compressed, the bars are always bumping up high.

2) The player has some amplifier within it. Generally when the media is at its max, the output is about 1 or 2 volts. This is fed to your amp.

3) I'll assume we're talking about an integrated amp with a "pre-amp" and power amp. Generally there is an input amp which may give quite a bit of voltage gain, up to 10 x or higher.

4) Then that feeds the volume control. This will actually reduce the signal voltage being fed to it. This means there can be a very great attenuation of the signal at full CCW or none at full CW.

5) Then there is the power amp, final section of the amp which provides some additional voltage gain, and has the ability to drive a speaker. The later means it can produce current.

6) There can be meters or clipping indicators. These are not really in the chain but they can indicate when the power amplifier has been fed with so much voltage that it can't produce any more output voltage. Better said, the output voltage has maxed out probably because the amp's power supply voltage has been reached..

= = = =

As you can imagine from this explanation of the chain, The levels all along the line will vary but one spot in the chain does not look backwards or forwards to monitor. (Technically there can be some negative feedback loops but that is not what you're asking about.)

In the integrated amp, the volume control will reduce the overall gain. So at some point of rotation, you will find that there is 1 volt input from the CD player (or other source) at peaks and the output to the speaker is also 1 volt at peaks. Actually 1 volt into K-Horns even on peaks is fairly loud.

But note that the "amp", at that setting of the volume contol, is, in a way, providing no voltage gain (but it does provide the necessary current). The internal amps are producing gain but the volume control is knocking it down, according to a twist of the knob.

= = = =

I believe that in the past you've turned up the input to lesser speakers until you hear the speaker distort at a certain acoustic output. Now you've found that K-Horns don't distort at a similar output level and you've gone to higher acoustic outputs.

But be careful,. The drivers in the K-Horns still have about the same tolerance for electrical input as those in other speakers. Even though the specs say it can take 100 watts "continuous" the tweeter will only take 5 watts continuous and the mid about 30 watts continuous. In the latter cases I'm using a pure sine wave as continuous. It is my experience that you can drive a "100 watt" woofer to mechanical destruction with 20 watts if you hit it as resonance for several seconds.

Best,

Gil

[Guest " "]

It depends on a lot of things.

The example I will use is that as you turn the volume clock wise, my amp counts down using negative numbers.

lets say my 130 watt amp, at -18 db, is putting out 1.8 watts. so will say that that happens at the 9 o clock position using cd X.

I change the cd to tuner Y, and it sounds lower than than cd x, I turn the volumenob clock wise another 1 clicks and it sounds the same.

1 more click would put me at - 16.5 db, which is also 1.8 watts.

I put cd X back on, and it sound too loud. I roll back the volume to -18 db and it sounds ok.

Whats happens is the sound level of the source is processed thru the amps gain circuts in a linear way. Different sources could have different drive levels, and therefore effects the final output of the amp.

[WMcD]

I did a bit of reading on the JBL site. This may clarify the issue of "continuous" power ratings.

JBL (and perhaps the industry) is defining "continuous" power as 3 dB above pink noise. That is spectrum of power. But pink noise rolls off at 3 dB per octave. This means that the tweeter is receiving a lot less power than the woofer at 100 watts "continuous." This accounts for why a tweeter which will burn out at 5 watts of a sine wave.

This pink noise is considered to be a good representation of the power distribution in music. There is a bit more to definitions of pink noise and, of course, whether "music" is compressed or otherwise.

The pink noise addresses an issue of whether we have equal power at each frequency point (white noise) or equal power per octave.

In a woofer freq range we have a octave going from, say 40 Hz to 80 Hz. Call that 40 frequency points. The next octave up we have 80 to 160 Hz, or 80 frequency points.

In a tweeter we have an octave going from, say, 4000 Hz to 8000 Hz. 4000 frequency points. And next octave is 8000 to 16,000 Hz, or 8000 frequency points. (I've picked these to make the math easy.)

You can see that an octave (eight whole notes) is definded as a doubling of frequency. (Our muscial scale has specific freqs defined based on A=440 Hz.) But in any case, for every octave band we also have a doubling of frequency points within it.

Suppose we want equal power in each octave. It means we must cut power in half (-3 dB) for every octave going up. Pink noise has that characteristic. Actually 1/F, so it is not a step at each octave division, it is a continuous roll-off.

Let's see:

For ballpark figures we have 100 watts at 40 Hz. 50 watts at 80 Hz. 25 watts at 160 Hz, 12.5 watts at 320 Hz. At about 10,000 Hz we're at about 0.4 watts. We see that a system rated at 100 watts "continuous" is eventually putting very little power into the tweeter! We can double those watt numbers for the 3 dB above pink noise definition.

On the other hand, when an amp can put out 100 watts, that includes 10,000 Hz.

I suppose the above is confusing. My read is that a manufacturer's lab can test a speaker with 100 actual watts of pink noise measured at 40 Hz. The tweeter is getting 0.4 watts because of the pink noise definition, and survives easly. Then the lab can say, "This speaker system is good for 100 watts "continuous" " - - - even if the tweeter will fry at 5 watts of what I'll call actual power based on a sine wave.

WMcD

[artto]

If the volume knob is set at for instance ten o'clock.......will the amp put out the same power regardless of the media being played?

Or.......what is the relation to the volume knob position, the clipping indication lights on the amp and the media signal source?

The fast and simple answer is No.

The "volume" control is NOT really a "power output" control (relative to the amplifier's rated power) (as most people think). It is simply a gain control.

Example: At half way up, one volt in = two volts out. At all the way up, one volt in = four volts out. At half way up, 2 volts in = four volts out. At all the way up two volts in = four volts out.

And it actually controls (attenuates) the input signal to the amplifier, not the output directly. Its a realtive kind of thing.

In the above scenario if your amplifier output clips at 3 volts, then two volts in will overdrive the amplifier into clipping.

The "volume control" does NOT for instance mean that if you have a 100 watt amplifier, that turning it up "half way" will yield "half of 100 watts ~ = 50 watts. You can overdrive/clip the output even at volume level "one" with enough input (provided the amplifier's input stage will tolerate/not overload with that much input)

[wilbucd]

Thanks guys. These are the answers I was looking for.

[twistedcrankcammer]

Let me answer your question very simply. I am using Nakamichi PA-7 amplifiers on K-Horns, and they are rated at 200 watts per channel.

It is distortion, not power that blows speakers PERIOD!!!

If you go to where the clipping L.E.D.s are barely flickering and back off to just where they never light, you should be fine.

About a week ago I took one of my Nakamichis over to a friends house who is using a pair of old Soundcraftsman Pro 2 channel amps for two of his K-Horns and two of his LaScalas. These two amplifiers drive four channels at 385 Watts each!! We hooked my Nakamichi to the left channel and one of his to the right channel. At 12 oclock his clip lights began to flutter, at 3 oclock his LEDs were almost continuosly on and mine barely began to flutter ocassionaly, at a hair past 3 oclock, he blew a woofer from the distortion from his amp. He stated; "I think your amp sounds better, but it's Nakamichi after all, but I think my amp has more balls". I am sure he was putting at least 275 to 300 watts through that speaker before he knocked out that woofer, my seperate power meter only reads to 200 watts RMS. I will further state that same guy has blown several woofers with his Adcom amp that is only 135 Watts per channel. It is all about clean power and distortion.

Roger

[Don Richard]

It is distortion, not power that blows speakers PERIOD!!!

When one clips a power amp the top of the waveform flattens to the extent that one turns a sine wave into nearly a square wave. The crest factor (peak to average ratio) decreases from 1.4 for sine to 1 for square during significant clipping. This causes the average power to increase, overheating the voice coil until the windings delaminate or burn open. Simple harmonic or IM distortion in the percentage range won't burn voice coils, unless the amp is operating in excess of the speakers rated power at that moment.

[twistedcrankcammer]

It is distortion, not power that blows speakers PERIOD!!!

When one clips a power amp the top of the waveform flattens to the extent that one turns a sine wave into nearly a square wave. The crest factor (peak to average ratio) decreases from 1.4 for sine to 1 for square during significant clipping. This causes the average power to increase, overheating the voice coil until the windings delaminate or burn open. Simple harmonic or IM distortion in the percentage range won't burn voice coils, unless the amp is operating in excess of the speakers rated power at that moment.

Don,

I am just saying that I have pumped alot more than 100 watts through my K-Horns, and stayed away from clippping the speakers, and have never had a problem. Oh I have blown fuses, and I used to rattle the high frequency bannanna plugs out all the time, before I changed over to spade connecters. It doesn't matter that his amp is rated at 200 watts RMS if he keeps it out of clipping the speakers it shouldn't be a problem, and with the larger capactors, it should sond better at lower volumes as well when compared too an equivelant 100 watt rms amp. Most only push it like that when trying to show off the capabilities of their system (like myself), my buddy does it because he has mental issues and if he gets the sound loud enough he can stop his mind from racing.[:S]

Roger

[Islander]

Most only push it like that when trying to show off the capabilities of their system (like myself), my buddy does it because he has mental issues and if he gets the sound loud enough he can stop his mind from racing.

Maybe he should try headphones. Or get his medication levels adjusted. Just some thoughts.