How can I measure the output wattage of my amplifiers? I have this very strong feeling that my Arcam is not 100watts and that its more like 30watts (if not less). Also, I have the very strong feeling that my JVC is hitting 200watts at peak power, but I'd like to measure this to find out. Is there some sort of device that I can connect my speaker outputs to (like some sort of oscilloscope thing?)
How can I measure the wattage of my amp?
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John Duncan
Well-known member
JohnDuncan:Why?
Because I have a feeling the measurements that Arcam quote are not accurate. Or mine is a faulty one.
Because I have a feeling the measurements that Arcam quote are not accurate. Or mine is a faulty one.
In theory, can I not generate a signal at 1khz (using my pc) and then measure the voltage of the amp going through a dummy load of 8ohms? Then times the voltage by two and divide by the impedence to get the continuous wattage?
John Duncan
Well-known member
But I say again - why? I cannot believe you have run a (nominally anyway) 200w amp at peak volume and are still alive. I't about quality, not numbers - you realise that because volume is logarithmic that an amp twice as loud as another needs to be ten times as powerful? Furthermore, it's quite possible that your Arcam sounds quiter than your JVC because it's not distorting the hell out of the signal, thus giving you the perception of being louder?
fatboyslimfast
Well-known member
If you really wanted to (and I really wouldn't advise it), you could put a heatsinked 8ohm resistor across the terminals and measure the voltage across it with a multimeter (set to AC obv). Making sure of course that the resistor can handle the voltage and current you expect to get from the amp. And that you don't touch the leads whilst the test is taking place. BzzzzzT...
You would then need to put the multimeter in series with the resistor and measure the current.
Multiply the two results and you have the power in watts.
But... There are discrepancies with frequency/power so it wouldn't necessarily be a true reading.
And apart from that, as everyone else on this thread has said, why bother? If the arcam isn't powerful enough for your needs, buy a different one. As JD says, a distorting amp will sound an awful lot "louder" than a clean one.
I remember a review by a.n.other magazine, where a 30w cheap amp sounded "louder" than a pair of 250w monoblocks, but only because the monos were so clean and the cheapy so distorted...
And please don't forget that a clipping amp is the quickest way to kill the voice coils on your speakers. If you need PA levels of volume, get a PA amp and speakers...
One more thing before you get bored of me and go onto another thread. It's not just that the Arcam has a lower sensitivity input is it?
You would then need to put the multimeter in series with the resistor and measure the current.
Multiply the two results and you have the power in watts.
But... There are discrepancies with frequency/power so it wouldn't necessarily be a true reading.
And apart from that, as everyone else on this thread has said, why bother? If the arcam isn't powerful enough for your needs, buy a different one. As JD says, a distorting amp will sound an awful lot "louder" than a clean one.
I remember a review by a.n.other magazine, where a 30w cheap amp sounded "louder" than a pair of 250w monoblocks, but only because the monos were so clean and the cheapy so distorted...
And please don't forget that a clipping amp is the quickest way to kill the voice coils on your speakers. If you need PA levels of volume, get a PA amp and speakers...
One more thing before you get bored of me and go onto another thread. It's not just that the Arcam has a lower sensitivity input is it?
John Duncan
Well-known member
fatboyslimfast:One more thing before you get bored of me and go onto another thread. It's not just that the Arcam has a lower sensitivity input is it?
And if it is, change the gain on the channels, since they're all variable on the A32 aren't they?
And if it is, change the gain on the channels, since they're all variable on the A32 aren't they?
fatboyslimfast
Well-known member
Only if by adjusting it you would be going past the overload ceiling. Chances are that you would only be bringing it back into the normal thresholds...
Honestly, I don't listen to music that loud - 10 o'clock on most amps is certainly loud enough! But my Arcam is tending to distort when turned up and seems to deliver more power into one channel (the balance is centered) and therefore wrecks the soundstage.
However, my JVC with its modest 70watts sounds so clean and fresh in comparison and doesn't clip at all even at silly volumes (which I don't listen to normally!).
I think what I should do, is send the Arcam back to my dealer and get them to check if it is working correctly. If it is, I'll be swapping it for something else. My dealer stocks Arcam, Naim and Project, so a simple Naim pre/power combo would be good and a SuperNait maybe...
However, my JVC with its modest 70watts sounds so clean and fresh in comparison and doesn't clip at all even at silly volumes (which I don't listen to normally!).
I think what I should do, is send the Arcam back to my dealer and get them to check if it is working correctly. If it is, I'll be swapping it for something else. My dealer stocks Arcam, Naim and Project, so a simple Naim pre/power combo would be good and a SuperNait maybe...
If you are going to do it right take a look here
http://focus.ti.com/lit/an/sloa068/sloa068.pdf
If you are not then dont bother because the results will be meaningless.
http://focus.ti.com/lit/an/sloa068/sloa068.pdf
If you are not then dont bother because the results will be meaningless.
raym87:
If you are going to do it right take a look here
http://focus.ti.com/lit/an/sloa068/sloa068.pdf
If you are not then dont bother because the results will be meaningless.
Thankyou very much raym87! Great article and greatly appreciated! Many thanks.
If you are going to do it right take a look here
http://focus.ti.com/lit/an/sloa068/sloa068.pdf
If you are not then dont bother because the results will be meaningless.
Thankyou very much raym87! Great article and greatly appreciated! Many thanks.
fatboyslimfast
Well-known member
Now I understand why. Send it back sir - that shouldn't be happening.
And I can heartily recommend a Naim pre/power
And I can heartily recommend a Naim pre/power
fatboyslimfast:Now I understand why. Send it back sir - that shouldn't be happening.
And I can heartily recommend a Naim pre/power
Cheers! What model pre/power should I be looking at? I paid £800 for my Arcam, so in theory if I add £1000 to that for good measure, I'll have £1800 for a pre/power. Is that enough?
And I can heartily recommend a Naim pre/power
Cheers! What model pre/power should I be looking at? I paid £800 for my Arcam, so in theory if I add £1000 to that for good measure, I'll have £1800 for a pre/power. Is that enough?
I've read (in various places) of people complaining that their Arcam amps are supposedly under-powered. Not sure why, as every time I've seen them tested they usually measure well above their stated power figures. The A85 and A90 both measured over 100w, I think the A90 was nearer 110w. Same with AV amps, Arcam's stated figures are always on the low side.
fatboyslimfast
Well-known member
I bought my 102/180 combo for around a grand 2nd hand from a dealer in St.Albans with a 12-month warranty. It's great!
fatboyslimfast:I bought my 102/180 combo for around a grand 2nd hand from a dealer in St.Albans with a 12-month warranty. It's great!
That's funny, my dealer has exactly the same combo, but he's asking £1200 for it. Mint condition though...considering it's the same as the RRP of the Arcam, it could be worth swapping for!
That's funny, my dealer has exactly the same combo, but he's asking £1200 for it. Mint condition though...considering it's the same as the RRP of the Arcam, it could be worth swapping for!
fatboyslimfast
Well-known member
Price will depend on details - phono cards fitted, boxes etc (mine came without the original boxes as a "clearance" deal) so this probably isn't far off.
Be aware that Naim use Din connectors though, and BNC for phono - you don't want to spend all your spondoolies only to get the boxes home and be able to do nothing with them!!! A couple of maplin DIN plugs and a soldering iron (oh, and a burnt finger in my case) and you're away...
Or you could see if they will chuck in a couple of DIN/RCA leads and a couple of RCA/BNC adaptors for the full price...times are hard etc...
Oh, and do you really want that email on your sig - spambots will pick it up in a flash and you'll be getting no end of carp in no time...
Be aware that Naim use Din connectors though, and BNC for phono - you don't want to spend all your spondoolies only to get the boxes home and be able to do nothing with them!!! A couple of maplin DIN plugs and a soldering iron (oh, and a burnt finger in my case) and you're away...
Or you could see if they will chuck in a couple of DIN/RCA leads and a couple of RCA/BNC adaptors for the full price...times are hard etc...
Oh, and do you really want that email on your sig - spambots will pick it up in a flash and you'll be getting no end of carp in no time...
fatboyslimfast:Price will depend on details - phono cards fitted, boxes etc (mine came without the original boxes as a "clearance" deal) so this probably isn't far off.
Be aware that Naim use Din connectors though, and BNC for phono - you don't want to spend all your spondoolies only to get the boxes home and be able to do nothing with them!!! A couple of maplin DIN plugs and a soldering iron (oh, and a burnt finger in my case) and you're away...
Or you could see if they will chuck in a couple of DIN/RCA leads and a couple of RCA/BNC adaptors for the full price...times are hard etc...
Oh, and do you really want that email on your sig - spambots will pick it up in a flash and you'll be getting no end of carp in no time...
Ok, thanks I'll look into that amp system. I have some DIN/RCA leads about the place anyway, so no problem there!
Regarding my signiture, I wanted to create a photo so that it will not be picked up, but I can't find out how to on my signature, it just won't let me. Perhaps I'll have to make a link to a website or something.
Be aware that Naim use Din connectors though, and BNC for phono - you don't want to spend all your spondoolies only to get the boxes home and be able to do nothing with them!!! A couple of maplin DIN plugs and a soldering iron (oh, and a burnt finger in my case) and you're away...
Or you could see if they will chuck in a couple of DIN/RCA leads and a couple of RCA/BNC adaptors for the full price...times are hard etc...
Oh, and do you really want that email on your sig - spambots will pick it up in a flash and you'll be getting no end of carp in no time...
Ok, thanks I'll look into that amp system. I have some DIN/RCA leads about the place anyway, so no problem there!
Regarding my signiture, I wanted to create a photo so that it will not be picked up, but I can't find out how to on my signature, it just won't let me. Perhaps I'll have to make a link to a website or something.
There we go, I inserted an image! Hopefully the spammers won't catch me now! The only problem is, the address takes up alot of characters and the limit is only 200-odd, so I can't contain as much detail anymore. Oh well...
Tony_R
Well-known member
Hughes123:How can I measure the output wattage of my amplifiers?
One quick and reasonably accurate way...
Find a dummy load (non inductive) capable of handling the wattage you wish to measure.
Inject a 1 Khz sine wave, whilst monitoring the output on a scope.
Adjust the gain to just below clipping (this will easily be visible on the scope).
Measure the voltage across the load with an audio voltmeter (most moderm DMM's will measure a 1khz sine wave with 1% or better accuracy).
Multiply the voltage by itself - e.g. if you measure 20v AC then 20x20=400 - divide the result by the impedance of the load - if it's 8 ohms then 400 / 8 = 50w.
This will give you an approxiamate indication of the output power.
I have used resistive wire (in this case recovered from a fan heater) to great effect - I cut it to the resistance I required (note: the impedance won't be exact but close enough) seperated it out to remove the coils (and therefore lower the inductance) and then wound it on an open ceramic former (also recovered from said heater).
To cool it, I suspended it in a bucket of water - a bit "heath robinson" but used to give me good results when testing the 300w beasts I used to build back in the 80's. (belive it or not, suspending it in water had little effect onthe resistance (don't know about the impedance though) but... if you're worried about that, just give it a coating of WD40 before suspending it in the water ;-)
Edit: The wire wasn't wound tightly on the ceramic former - but wound in a very well spaced fashion if that makes any sense..!
Tony.
One quick and reasonably accurate way...
Find a dummy load (non inductive) capable of handling the wattage you wish to measure.
Inject a 1 Khz sine wave, whilst monitoring the output on a scope.
Adjust the gain to just below clipping (this will easily be visible on the scope).
Measure the voltage across the load with an audio voltmeter (most moderm DMM's will measure a 1khz sine wave with 1% or better accuracy).
Multiply the voltage by itself - e.g. if you measure 20v AC then 20x20=400 - divide the result by the impedance of the load - if it's 8 ohms then 400 / 8 = 50w.
This will give you an approxiamate indication of the output power.
I have used resistive wire (in this case recovered from a fan heater) to great effect - I cut it to the resistance I required (note: the impedance won't be exact but close enough) seperated it out to remove the coils (and therefore lower the inductance) and then wound it on an open ceramic former (also recovered from said heater).
To cool it, I suspended it in a bucket of water - a bit "heath robinson" but used to give me good results when testing the 300w beasts I used to build back in the 80's. (belive it or not, suspending it in water had little effect onthe resistance (don't know about the impedance though) but... if you're worried about that, just give it a coating of WD40 before suspending it in the water ;-)
Edit: The wire wasn't wound tightly on the ceramic former - but wound in a very well spaced fashion if that makes any sense..!
Tony.
Tony_R:
Hughes123:How can I measure the output wattage of my amplifiers?
One quick and reasonably accurate way...
Find a dummy load (non inductive) capable of handling the wattage you wish to measure.
Inject a 1 Khz sine wave, whilst monitoring the output on a scope.
Adjust the gain to just below clipping (this will easily be visible on the scope).
Measure the voltage across the load with an audio voltmeter (most moderm DMM's will measure a 1khz sine wave with 1% or better accuracy).
Multiply the voltage by itself - e.g. if you measure 20v AC then 20x20=400 - divide the result by the impedance of the load - if it's 8 ohms then 400 / 8 = 50w.
This will give you an approxiamate indication of the output power.
I have used resistive wire (in this case recovered from a fan heater) to great effect - I cut it to the resistance I required (note: the impedance won't be exact but close enough) seperated it out to remove the coils (and therefore lower the inductance) and then wound it on an open ceramic former (also recovered from said heater).
To cool it, I suspended it in a bucket of water - a bit "heath robinson" but used to give me good results when testing the 300w beasts I used to build back in the 80's. (belive it or not, suspending it in water had little effect onthe resistance (don't know about the impedance though) but... if you're worried about that, just give it a coating of WD40 before suspending it in the water ;-)
Edit: The wire wasn't wound tightly on the ceramic former - but wound in a very well spaced fashion if that makes any sense..!
Tony.
Thankyou Tony! I had a vague idea of how to calculate it (square voltage and divide by impedence) and that I had to use a dummy load, but now I know how to do it! Yay! One question though - How do I know what length of wire I require (ie. how do I know what the impedence of the wire is?) and wouldn't the water get a bit...you know...dangerous?
Hughes123:How can I measure the output wattage of my amplifiers?
One quick and reasonably accurate way...
Find a dummy load (non inductive) capable of handling the wattage you wish to measure.
Inject a 1 Khz sine wave, whilst monitoring the output on a scope.
Adjust the gain to just below clipping (this will easily be visible on the scope).
Measure the voltage across the load with an audio voltmeter (most moderm DMM's will measure a 1khz sine wave with 1% or better accuracy).
Multiply the voltage by itself - e.g. if you measure 20v AC then 20x20=400 - divide the result by the impedance of the load - if it's 8 ohms then 400 / 8 = 50w.
This will give you an approxiamate indication of the output power.
I have used resistive wire (in this case recovered from a fan heater) to great effect - I cut it to the resistance I required (note: the impedance won't be exact but close enough) seperated it out to remove the coils (and therefore lower the inductance) and then wound it on an open ceramic former (also recovered from said heater).
To cool it, I suspended it in a bucket of water - a bit "heath robinson" but used to give me good results when testing the 300w beasts I used to build back in the 80's. (belive it or not, suspending it in water had little effect onthe resistance (don't know about the impedance though) but... if you're worried about that, just give it a coating of WD40 before suspending it in the water ;-)
Edit: The wire wasn't wound tightly on the ceramic former - but wound in a very well spaced fashion if that makes any sense..!
Tony.
Thankyou Tony! I had a vague idea of how to calculate it (square voltage and divide by impedence) and that I had to use a dummy load, but now I know how to do it! Yay! One question though - How do I know what length of wire I require (ie. how do I know what the impedence of the wire is?) and wouldn't the water get a bit...you know...dangerous?
Tony_R
Well-known member
Hughes123:
Thankyou Tony! I had a vague idea of how to calculate it (square voltage and divide by impedence) and that I had to use a dummy load, but now I know how to do it! Yay! One question though - How do I know what length of wire I require (ie. how do I know what the impedence of the wire is?) and wouldn't the water get a bit...you know...dangerous?
Depending on the power output, there can be some localised boiling of the water (i.e. it boils directly around the element - but that is harmless).
My advice is to place the water container a good distance away ( 2 - 3m) from your test rig / workbench - and then run some suitably heavy duty cable to the load - this cable doesn't need to be audiophile stuff - something like the stuff you get from Maplin (resembles the old QED 79 strand cable) is good.
As for the length of the wire - you can either be really technical about it, an cut a sample, measure the DC resistance and then calculate the ohms per foot - or use empirical solutions such as cut / measure / cut / measure (oops too short - pass me some more..)..
It's really as simple as that. I did on occasion use the wire in free air (up to about 100w - but it does glow red.....)
You would also *definately* want to connect a fuse in series with this load, to protect against short circuits - and be absolutely sure to keep the resistance wire well seperated to avoid the probability of any short circuits, or sudden reductions in resistance!
I've also heard of people using large wirewound resistors in series / parallel to reach the correct resistance - however these can be a little too inductive unless you use high wattage carbon (i.e. non wirewound) types, which are both expensive and quite rare I think.
Read this article http://www.aikenamps.com/DummyLoads.htm for some useful info.
In one of my electronics books somewhere, I have a design for a dummy load, using several carbon film resistors in a series / parallel arrangement sandwiched between two layers of GRP PC board - a much safer option..!
Whichever approach you decide to take ** be careful and stay aware of the dangers of high voltages and potentially high currents too **
A 120 w amp can produce a peak to peak voltage swing in excess of 60v p - p so be aware...!
Tony.
Thankyou Tony! I had a vague idea of how to calculate it (square voltage and divide by impedence) and that I had to use a dummy load, but now I know how to do it! Yay! One question though - How do I know what length of wire I require (ie. how do I know what the impedence of the wire is?) and wouldn't the water get a bit...you know...dangerous?
Depending on the power output, there can be some localised boiling of the water (i.e. it boils directly around the element - but that is harmless).
My advice is to place the water container a good distance away ( 2 - 3m) from your test rig / workbench - and then run some suitably heavy duty cable to the load - this cable doesn't need to be audiophile stuff - something like the stuff you get from Maplin (resembles the old QED 79 strand cable) is good.
As for the length of the wire - you can either be really technical about it, an cut a sample, measure the DC resistance and then calculate the ohms per foot - or use empirical solutions such as cut / measure / cut / measure (oops too short - pass me some more..)..
It's really as simple as that. I did on occasion use the wire in free air (up to about 100w - but it does glow red.....)
You would also *definately* want to connect a fuse in series with this load, to protect against short circuits - and be absolutely sure to keep the resistance wire well seperated to avoid the probability of any short circuits, or sudden reductions in resistance!
I've also heard of people using large wirewound resistors in series / parallel to reach the correct resistance - however these can be a little too inductive unless you use high wattage carbon (i.e. non wirewound) types, which are both expensive and quite rare I think.
Read this article http://www.aikenamps.com/DummyLoads.htm for some useful info.
In one of my electronics books somewhere, I have a design for a dummy load, using several carbon film resistors in a series / parallel arrangement sandwiched between two layers of GRP PC board - a much safer option..!
Whichever approach you decide to take ** be careful and stay aware of the dangers of high voltages and potentially high currents too **
A 120 w amp can produce a peak to peak voltage swing in excess of 60v p - p so be aware...!
Tony.
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