Hi.
I am having difficulty achieving the correct sum when comparing amplifier published wattage versus maximum RMS voltage swings on a particular model. The numbers do not match although having both figures displayed on the specification sheet.
Possibly my math is incorrect?
How can you achieve 425 watts in an 8-ohm load per channel, with 0.05% Total Harmonic Distortion, both channels driven using 1 kHz from a Maximum RMS Voltage of 71?
My calculations arrive to 315 watts per channel in an 8-ohm load.
Would pink noise measurements play a factor why the numbers do not correspond?
Cheers!
I am having difficulty achieving the correct sum when comparing amplifier published wattage versus maximum RMS voltage swings on a particular model. The numbers do not match although having both figures displayed on the specification sheet.
Possibly my math is incorrect?
How can you achieve 425 watts in an 8-ohm load per channel, with 0.05% Total Harmonic Distortion, both channels driven using 1 kHz from a Maximum RMS Voltage of 71?
My calculations arrive to 315 watts per channel in an 8-ohm load.
Would pink noise measurements play a factor why the numbers do not correspond?
Cheers!
I am attaching a photo of the specification sheet.
Cheers!
An externally hosted image should be here but it was not working when we last tested it.
Cheers!
OMNIFEX said:Hi.
I am having difficulty achieving the correct sum when comparing amplifier published wattage versus maximum RMS voltage swings on a particular model. The numbers do not match although having both figures displayed on the specification sheet.
Possibly my math is incorrect?
How can you achieve 425 watts in an 8-ohm load per channel, with 0.05% Total Harmonic Distortion, both channels driven using 1 kHz from a Maximum RMS Voltage of 71?
My calculations arrive to 315 watts per channel in an 8-ohm load.
Would pink noise measurements play a factor why the numbers do not correspond?
Your calculation is correct, 315W RMS power.
It wouldn't be the first time when manufacturers are defining their own "watt", or they are flat misleading. Here, they don't say anything about the output power being RMS so God knows what they are talking about.
How did u get 315W per channel?
If it *really* can produce 71V RMS on each channel, that would be
(71*71)/8 = 630W PER CHANNEL.
But in real life, due to the internal impedance of the power supplies etc, it will not achieve a full 71V swing with both channels driven into a load. So taking into account some voltage drop, it may be able to put out the claimed 425W per Ch.
If it *really* can produce 71V RMS on each channel, that would be
(71*71)/8 = 630W PER CHANNEL.
But in real life, due to the internal impedance of the power supplies etc, it will not achieve a full 71V swing with both channels driven into a load. So taking into account some voltage drop, it may be able to put out the claimed 425W per Ch.
I think they are telling the truth, But they don't specify the duty cycle of the test signals.
look at the peak output voltage required for each of those (assumed sinewave) power figures and compare them to a maximum output sinewave of 71Vac (~=100Vpk) into what is probably an open circuit load.
425W 8r0 82.5Vpk
500W 8r0 89.4Vpk
700W 4r0 74.8Vpk
825W 4r0 81.2Vpk
1000W 2r0 63.2Vpk
1325W 2r0 72.8Vpk.
It appears that these claimed output voltages are all consistent with an amp running ~+-105Vdc on the PSU.
It also appears that the PSU is severely undersized for a 2ohm capable amplifier due to the 3dB drop in output voltage from the 8ohm single channel output figure.
Even the 4ohm power output is compromised by an undersized PSU. It drops >1.5dB when a drop of -0.4 to -0.8dB is easily achievable.
Based on the data provided I suspect this is a robust 425+425W into 8ohm amplifier that will perform poorly into 4ohm loads. Forget about trying to use it on 2ohm speakers.
If the data provided by the manufacturer is accurate and clearly specified, one can decipher a lot about the way it may perform into real loads.
Let's go a bit further. Look at the single channel power figures.
500W 8r0 and 825W 4r0.
The 40hm power has dropped by -0.84dB. This indicates that the PSU is struggling to supply a single channel 4ohm load.
I suspect that if the amp were run in single channel mode the extra voltage on the output stage may destroy the transistors. It would be my guess that to keep reliability in this amplifier they have deliberately underrated the PSU to ensure the resultant voltage sag on the supply allows the output and driver devices to stay within their limited SOAR capability. Don't beef up the PSU and don't run it in single channel mode into 4ohm loads until you have properly investigated the output capability of the devices used.
As I said earlier it is probably a good 8ohm amplifier.
look at the peak output voltage required for each of those (assumed sinewave) power figures and compare them to a maximum output sinewave of 71Vac (~=100Vpk) into what is probably an open circuit load.
425W 8r0 82.5Vpk
500W 8r0 89.4Vpk
700W 4r0 74.8Vpk
825W 4r0 81.2Vpk
1000W 2r0 63.2Vpk
1325W 2r0 72.8Vpk.
It appears that these claimed output voltages are all consistent with an amp running ~+-105Vdc on the PSU.
It also appears that the PSU is severely undersized for a 2ohm capable amplifier due to the 3dB drop in output voltage from the 8ohm single channel output figure.
Even the 4ohm power output is compromised by an undersized PSU. It drops >1.5dB when a drop of -0.4 to -0.8dB is easily achievable.
Based on the data provided I suspect this is a robust 425+425W into 8ohm amplifier that will perform poorly into 4ohm loads. Forget about trying to use it on 2ohm speakers.
If the data provided by the manufacturer is accurate and clearly specified, one can decipher a lot about the way it may perform into real loads.
Let's go a bit further. Look at the single channel power figures.
500W 8r0 and 825W 4r0.
The 40hm power has dropped by -0.84dB. This indicates that the PSU is struggling to supply a single channel 4ohm load.
I suspect that if the amp were run in single channel mode the extra voltage on the output stage may destroy the transistors. It would be my guess that to keep reliability in this amplifier they have deliberately underrated the PSU to ensure the resultant voltage sag on the supply allows the output and driver devices to stay within their limited SOAR capability. Don't beef up the PSU and don't run it in single channel mode into 4ohm loads until you have properly investigated the output capability of the devices used.
As I said earlier it is probably a good 8ohm amplifier.
Cheers Mates!
It does not say 71 V RMS on each channel it says 71 V RMS.
I arrived to the same sum as well however, divided it into two so it would be 315 watts per channel in an 8-ohm load or 630 watts @ 8 ohms total.
Would that be sine wave or pink noise?
This company (Peavey) made an amplifier (CS 800) 30 years ago that offered more RMS Voltage Swing than what this amplifier (A CS 2000) can offer yet, it was rated only 240 watts per channel in an 8-ohm load. However, it was tested using sine waves. I’ve examined the Total Harmonic Distortion amongst the two and they are too close to make such a boost in the output in this (CS 2000) model.
Would using pink noise fall into your "real life" why these figures "may be able to put out the claimed 425W per Ch."?
Cheers!
Steerpike said:
It does not say 71 V RMS on each channel it says 71 V RMS.
I arrived to the same sum as well however, divided it into two so it would be 315 watts per channel in an 8-ohm load or 630 watts @ 8 ohms total.
Would that be sine wave or pink noise?
This company (Peavey) made an amplifier (CS 800) 30 years ago that offered more RMS Voltage Swing than what this amplifier (A CS 2000) can offer yet, it was rated only 240 watts per channel in an 8-ohm load. However, it was tested using sine waves. I’ve examined the Total Harmonic Distortion amongst the two and they are too close to make such a boost in the output in this (CS 2000) model.
Would using pink noise fall into your "real life" why these figures "may be able to put out the claimed 425W per Ch."?
Cheers!
Amplifiers' power is not determined only by the voltage swing they can achieve. The voltage swing puts an upper limit on the point at which they clip, but an important factor is the heat generated internally while they are doing this.
Sinus or pink noise ought not to make much difference in an amplifier. The basis of the calculation is measuring the RMS voltage, and computing the power based on a resistive load.
The waveshape doesn't change anything, and in an amplifier, unlike say a speaker, there is no division of duty according to spectral content. The amp works just as hard, no matter what the signal.
Measuring the RMS value of pink noise is a bit more iffy - you need a rather high-tech meter to do it accurately.
Amplifiers that will swing to 70V but not into an 8 ohm load DO have an application, since some PA distribution systems are based on a 70V audio line voltage, In those systems, the speakers are transformer coupled to the line, and present a fairly high impedance. So some amplifiers are designed to be able to do double duty in both types of system.
As mentioned, I think you'd find that with an 8ohm load, the 71V RMS value is not achieved. That is likely a no-load condition, or light load.
Sinus or pink noise ought not to make much difference in an amplifier. The basis of the calculation is measuring the RMS voltage, and computing the power based on a resistive load.
The waveshape doesn't change anything, and in an amplifier, unlike say a speaker, there is no division of duty according to spectral content. The amp works just as hard, no matter what the signal.
Measuring the RMS value of pink noise is a bit more iffy - you need a rather high-tech meter to do it accurately.
Amplifiers that will swing to 70V but not into an 8 ohm load DO have an application, since some PA distribution systems are based on a 70V audio line voltage, In those systems, the speakers are transformer coupled to the line, and present a fairly high impedance. So some amplifiers are designed to be able to do double duty in both types of system.
As mentioned, I think you'd find that with an 8ohm load, the 71V RMS value is not achieved. That is likely a no-load condition, or light load.
Thank you.
I guess "peaks" would be the best way to describe those wattage figures. For the more I look at them, the more I noticed things missing (Continuous Average Power for example) that guaranteed the wattage could be delivered on a long-term basis.
There is even a disclaimer that states, “2-ohm power is time limited by magnetic circuit breaker” that I clearly overlooked. Now that would be something I would really enjoy encountering when conducting a thirteen-hour rave and needed to load eight 8-ohm midrange drivers in the worst-case scenario.
I would imagine a magnifying glass is in order on how amplifiers are measured these days compared to 20-30 years ago.
Cheers!
I guess "peaks" would be the best way to describe those wattage figures. For the more I look at them, the more I noticed things missing (Continuous Average Power for example) that guaranteed the wattage could be delivered on a long-term basis.
There is even a disclaimer that states, “2-ohm power is time limited by magnetic circuit breaker” that I clearly overlooked. Now that would be something I would really enjoy encountering when conducting a thirteen-hour rave and needed to load eight 8-ohm midrange drivers in the worst-case scenario.
I would imagine a magnifying glass is in order on how amplifiers are measured these days compared to 20-30 years ago.
Cheers!
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
Craig
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.
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.
llwhtt said:
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!
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!
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!
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
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
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
Craig
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
Craig
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.llwhtt said:
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.
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!
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!
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