Does Pink noise follow the V x V/R method?

[llwhtt]

I think your confusion comes from the way you figured out the 315 Watts. You took the 630 Watts and divided by two. That does not make sense, why would you divide by two? Each channel is capable of swinging 71 VRMS, but we all decided that was probably open circuit and therefore meaningless as far as loaded output is concerned. Since 8 Ohms is listed as the highest Ohms load the amp will produce the highest voltage into that load. Like I said in my earlier post it only takes a hair over 58VRMS to produce 425 Watts. 58 squared divided by 8 equals 420. I see nothing wrong with the specs you posted though the power supply runs out of steam into the lower Ohm loads. The specs prove that out but is typical of unregulated supplies. The old Mark Levinson ML2 would double its power every time the load was halved basically until the circuit breakers would trip, 25 Watts into 8 Ohms, 50 into 4, 100 into 2, 200 into 1, etc. That power supply was regulated. I remember a magazine test in which they used an ML2 as an arc welder!!!!!

Craig

[AndrewT]

Power=peak voltage * Peak voltage / Rload / 2 when the signal is a sinewave.
When the 71V is mistaken for Vpk then it would have been normal to divide by 2.

The open circuit clipping voltage is not meaningless.
It gives an indication of the quiescent supply rail voltage and thus a good indication of how far the supply rails sag when delivering power to a resistive load.
In this case that piece of 71V information confirms that this amplifier has a seriously undersized PSU for 8r0+8r0. Don't bother trying to drive 4r0.

[OMNIFEX]

Originally posted by llwhtt
I think your confusion comes from the way you figured out the 315 Watts. You took the 630 Watts and divided by two. That does not make sense, why would you divide by two?

Craig

Because it does not say per channel.

Crest states each channel on their Peak & RMS Voltage Swings on their old Professional & CA Series Spec Sheets.


Here is my confusion. How can a Peavey CS 800X offering Maximum RMS Voltage Swing of 73 V capable of 2-ohm loads continuous is only rated 240 watts per channel in an 8-ohm load whereas, the Peavey CS 2000 offering a Maximum RMS Voltage Swing of 71 V delivers 425 watts per channel in an 8-ohm load, but cannot handle 2 ohms on a long-term basis?

That is almost a 3 dB difference in an 8-ohm load in favour of the CS 2000.

Are the ratings on the Peavey CS 800X that conservative?

I have even taken it upon myself to examine the Crest CA 6 amplifier, which offers identical Maximum RMS Voltage Swings as the Peavey CS 800X (73 volts) yet offers 350 – 400 watts per channel in an 8-ohm load. It is still lower than the Peavey CS 2000’s published specs, yet offers the same Maximum RMS Voltage Swings as the Peavey CS 800X.

Can someone share his or her thoughts on the matter?


Cheers!

[OMNIFEX]

I just wanted to thank all who replied.

For as you can see, my confusion lies in the Peavey CS 800X (CS 800) offering a Maximum RMS Voltage Swing Of 73 V (81 on the CS 800 four-rack version) and delivering the least amount of wattage (240 Watts) in an 8-ohm load stated in Peavey specs than their higher models.


Cheers!

[llwhtt]

It does say per channel, 2 x 8 Ohms, both channels driven, that means two channels @ 425 Watts each. Now I think the confusion is voltage swing vs Watts. Just because an amp can swing the volts doesn't mean it can supply the current at the same time. It takes both voltage and current to make the power, Watts. Look at most early Japanese stereos, 8 Ohms is fine but don't even think about 4 Ohms. Why? No current capability, be it power supply, output stage or both. Now that I know we're talking Peavey ( I did Peavey warranty for years), worked on many of the old CS800s, the weight of the unit explains a lot. I'll bet the 800 almost doubles it power as the Ohms are halved, the 2000 doesn't come close. The 2000's power supply and output stage would have to do 1700 Watts into 2 Ohms. The 800 has a huge power transformer where as the 2000 is not so huge, that equates to current capability. Just pulled up both schematics but Peavey doesn't show the power supply of the 2000 so can't comment on the power supply.
The fact that the 800 is an "old school" type amp and the 2000 is a "modern technology" amp might explain some of the differences also.

Craig

[llwhtt]

Just thought of something else, do you realize that as the load goes up (less Ohms) the voltage swing goes down. 8 Ohms more volts, less current and 2 Ohms less volts, more current. NO amp can swing the same volts into any load, UNLESS the power supply is regulated. Neither Peavey has a regulated power supply. Neither amp can swing 70 volts into any load.

Craig

[llwhtt]

Did some research as to the difference between the 800 and the 2000. Like I said before the 800 is an old school type amp and runs on + and - 75VDC rails and therefore the low 8 Ohm output, but can sustain the voltages longer as the Ohms go down. The 2000 runs on low(60VDC?) or high(120VDC?) + and - rails depending on level and load. The voltages weren't listed, but with the 60volt capacitors listed they can't be more than 60VDC and 120VDC, probably much less. So that explains the output differences. The 800 is stuck with single rails and acts just like a typical amp with a simple brute force power supply. The 2000 has a semi-sophisticated power supply that can react according to signal level and load. Now everything is clear as mud, right?

Craig

[AndrewT]

Originally posted by llwhtt
NO amp can swing the same volts into any load, UNLESS the power supply is regulated.

even a theoretically perfect regulated supply would not allow an amplifier to swing the same maximum voltage into all loads within it's specification capability.
A good unregulated supply feeding a good amplifier can drop less than 0.4dBV changing the load from 8r0 to 4r0. A good regulated supply may improve this to a drop of 0.2dBV.

Can I pose the question: is the complication of designing that good regulated supply and ensuring that the good amplifier is stable when fed from it, worth the extra 0.2dBV when the load resistance is halved?
And having designed that good regulated supply, can it meet the peak current demands of reactive speaker loads? a 100W amp feeding 40Vpk to it's load needs to supply 5APk into 8r0, 10Apk into 4r0 and around 28Apk into a 4ohm speaker.

[OMNIFEX]

llwhtt, you have gone far beyond what I was expecting. Thank you very much. I now see why the comparisons amongst the two are so different.

I own eight CS 800 amplifiers and, one CS 900 amplifier that is used for my smaller sound system and always wondered why two (Out of 8) CS 800 amplifiers in bridged mono mode for bass duty performed so brutal (That’s in a good way) when they were only rated 240 watts per channel in an 8-ohm stereo mode. I’ve even ran an older Non-DDT version in 2-ohms per channel stereo mode and, it refuse to get any hotter than Luke-warm.

I am well aware of the output increase in bridging. However, it never dawned on me how much the power supply plaid a role in their performance.

Most of the blokes always say they are “built like tanks”, but never explained why they have drawn to such a conclusion. And I have spent countless hours searching Google for anything relating to Peavey CS 800 trying to find the answer. With all my amplifiers (Crown, Crest, Peavey, QSC) classed as old fashion traditional designs, I assumed the new Peavey’s followed the same performance from a longevity (13+ hour Rave events, 4-ohm Bridged Mono, 3 decibels away from 0 dB, with no issues whatsoever) standpoint as their older versions.

However, when the specifications were showing higher wattage but stating 2-ohm short-term performance in addition to lower voltage rails, I was wondering how could it be possible.


AndrewT,

Your input has not gone unnoticed Mate!


Thank you for sharing your thoughts as well. The wattage based on impedance from a voltage standpoint explanation was excellent.


Cheers!