I was just looking at the circuit I had for a Pioneer A80 amp I used to own. That was 150 watts RMS into 8 ohms and used a "passive" or normal volume control. The CD input fed straight into this (no preamp).
Some numbers...
150 watts RMS is approx 35 volts RMS. The input sensitivity was quoted as 150 millivolts and the voltage gain of the amp was around 234 (calculated from the feedback resistor network).
So those numbers work well... 150 mv * 234 is 35 volts. Bang on the mark. Now to achieve that the volume control would have to be on full with 150mv as an input.
A CD can be as high as 2 volts RMS for maximum level (which means the highest transient peak on the "loudest CD out there) and so the 150 mv sensitivity means that for normal listening the volume would be around a third of the way round... if that makes sense.
Some numbers...
150 watts RMS is approx 35 volts RMS. The input sensitivity was quoted as 150 millivolts and the voltage gain of the amp was around 234 (calculated from the feedback resistor network).
So those numbers work well... 150 mv * 234 is 35 volts. Bang on the mark. Now to achieve that the volume control would have to be on full with 150mv as an input.
A CD can be as high as 2 volts RMS for maximum level (which means the highest transient peak on the "loudest CD out there) and so the 150 mv sensitivity means that for normal listening the volume would be around a third of the way round... if that makes sense.
These are my first results from testing:
Screenshot of amp spec:
Amp spec:
60W per channel in stereo mode, if I quoted 50W in my other thread this was because it's 50W per channel in surround mode (driving more than 2 speakers).
200mv input sensitivity.
Results of testing:
No load & no input (not connected to input) @ 0db = 0.971v output
No load & connected to 0v input @ 0db = 0v output
No load & 0.70v input @ 0db = 22.59v output
No load & 0.67v input @ 0db = 21.33v output
0db isn't full volume but what I would think of as within spec volume, +db drives into clipping from +4.
Is anyone able to help make sense of these figures for me to help me understand if it's meeting the spec?
22.59v output with an 8ohm load would equate to 63.7W rms?
Screenshot of amp spec:
Amp spec:
60W per channel in stereo mode, if I quoted 50W in my other thread this was because it's 50W per channel in surround mode (driving more than 2 speakers).
200mv input sensitivity.
Results of testing:
No load & no input (not connected to input) @ 0db = 0.971v output
No load & connected to 0v input @ 0db = 0v output
No load & 0.70v input @ 0db = 22.59v output
No load & 0.67v input @ 0db = 21.33v output
0db isn't full volume but what I would think of as within spec volume, +db drives into clipping from +4.
Is anyone able to help make sense of these figures for me to help me understand if it's meeting the spec?
22.59v output with an 8ohm load would equate to 63.7W rms?
I think you are using the words "0 db" to refer to a volume knob position. Your test shows voltage gain, but if you don't have a nominal load on the amp, you don't know if it will put out current or not. Your test results are annotated "no load". The voltages look okay. The voltage on the load is a figure of merit, but without the load it only proves you don't have gross problems. My performance tests of amps use a resistive load simulating the speakers that I actually use. The actual load will draw the current out of the various components, and allow you to determine if there is a problem, and if so, further tests inside the amp will show what component is holding back the current flow.
I believe Mooly said something about modern amps not being able to actually put out the nominal watts, and I believe he warned you not to use a load initially. My obsolete amps will put out something like rated output watts for all day in the case of the tube amps, or an hour or so until the heat sink overheats on the St120. (it actually puts out more than 60w/ch) Which is why I installed fans on the heat sinks of the sT120- in diyaudio, you don't have to put up with the limitations the designer gave you. I don't have enough load resistors to test the CS800s at full power, yet. I'm sure not going to listen to it inside at 360 W/ch. As it trips the breaker at 55 deg f turn on, I suspect I have some electrolytic capacitors that have hit life, and perhaps some consequential damage to semiconductors. The St70 has needed re-capping (electrolytic) 3 times since 1971, the St120 transistor amp once since 1985.
I believe Mooly said something about modern amps not being able to actually put out the nominal watts, and I believe he warned you not to use a load initially. My obsolete amps will put out something like rated output watts for all day in the case of the tube amps, or an hour or so until the heat sink overheats on the St120. (it actually puts out more than 60w/ch) Which is why I installed fans on the heat sinks of the sT120- in diyaudio, you don't have to put up with the limitations the designer gave you. I don't have enough load resistors to test the CS800s at full power, yet. I'm sure not going to listen to it inside at 360 W/ch. As it trips the breaker at 55 deg f turn on, I suspect I have some electrolytic capacitors that have hit life, and perhaps some consequential damage to semiconductors. The St70 has needed re-capping (electrolytic) 3 times since 1971, the St120 transistor amp once since 1985.
Last edited:
That appears to show that 200mv (that will be an RMS figure) is the required input in order to obtain rated output.
I would take that to mean that if you applied 200mv (0.56 volts pk/pk on scope) and turn the volume to full then the output should be 20 volts RMS (56 volts pk/pk on scope).
The 200 mv and 50 watts works out to a voltage gain of 100 which will be with the volume control on full whatever that may show as on the display.
Your measured results seem to indicate a voltage gain of around 33 which does not tally with the spec.
You need to repeat that test with the volume of full and see what the required input voltage is to make the output 20 volts RMS. From the spec it should be 200mv.
So it looks like the overall gain could be low up to now...............
Can I just clarify what you mean by 200mv = 0.56v pk/pk on scope?
I thought 200mv would be 0.2v on my multimeter?
However if I set 0.2v on my scope as pictured (yes it needs a clean
):
I then reduced my source volume (source is my PC running a 100hz test tone over a headphone jack to twin phono lead), so that I measure 0.563 (following your mentioning of a 0.56v input)
I get the pictured output on the scope which is obviously peak to peak showing when the scope is set to 0.2v and the actual input voltage is 0.563 measured on my multimeter:
So I'm a little confused how 200mv is equating to 0.56v?.
I thought 200mv would be 0.2v on my multimeter?
However if I set 0.2v on my scope as pictured (yes it needs a clean
):An externally hosted image should be here but it was not working when we last tested it.
I then reduced my source volume (source is my PC running a 100hz test tone over a headphone jack to twin phono lead), so that I measure 0.563 (following your mentioning of a 0.56v input)
I get the pictured output on the scope which is obviously peak to peak showing when the scope is set to 0.2v and the actual input voltage is 0.563 measured on my multimeter:
An externally hosted image should be here but it was not working when we last tested it.
So I'm a little confused how 200mv is equating to 0.56v?
.Can you also confirm that when you're talking full volume you mean as far as it will go or is 0db correct (goes to +10db)?
The reason I ask is that the voltage output goes to a rediculous level when I set it to +10db (as high as it will go) which equates to about 200W per channel in full distortion.
The reason I ask is that the voltage output goes to a rediculous level when I set it to +10db (as high as it will go) which equates to about 200W per channel in full distortion.
Yes, 200 mv on the meter should be 200mv RMS assuming the meter is ok.
However if I set 0.2v on my scope as pictured (yes it needs a clean
An externally hosted image should be here but it was not working when we last tested it.
I then reduced my source volume (source is my PC running a 100hz test tone over a headphone jack to twin phono lead), so that I measure 0.563 (following your mentioning of a 0.56v input)
I get the pictured output on the scope which is obviously peak to peak showing when the scope is set to 0.2v and the actual input voltage is 0.563 measured on my multimeter:
An externally hosted image should be here but it was not working when we last tested it.
So I'm a little confused how 200mv is equating to 0.56v?
Your attenuator on the scope is set to 200mv/div.
The picture of the trace shows the peak to peak value as 8 divisions. That's 8 * 0.2 which is 1.6 volts pk/pk
The DVM would (should) show that as 0.56 volts... which it is.
You need to set the input voltage (from your PC) to show 0.56 volts peak to peak on the scope which is 200 mv RMS.
So the scope on that setting should be showing the waveform as covering 2.8 squares or divisions...
Set it to +10db. The input voltage of 200mv should deliver 20 volts RMS at the output (56 volts on the scope
) at that volume setting.OK, I obviously need to learn a lot more about my scope in terms of reading voltages.
I've measured 0.199v on my meter from my PC (closest it would get to 200mv).
I turned the volume up to full (+10db) and got a reading of 19.96v on my meter.
This was on the CD input with a stereo output, which according to the spec should be 60W per channel.
I've measured 0.199v on my meter from my PC (closest it would get to 200mv).
I turned the volume up to full (+10db) and got a reading of 19.96v on my meter.
This was on the CD input with a stereo output, which according to the spec should be 60W per channel.
Those results seem to confirm all is OK tbh
The receiver says 200mv sensitivity. You have applied that and measured approx 20vac output which corresponds to 50 watts RMS. The final test would be to make sure the amp hold up into a real load... I'm sure it does. If it didn't it would distort grossly and not just be less loud.
The picture showing the spec mentions "continuous average power (FTC)" and also 50 and 60 watts is mentioned.
Had to look up FTC as it seems something applicable to USA markets,
Audio power - Wikipedia, the free encyclopedia
The only rating that engineers work to is an RMS figure. Audibly you would not tell a 50 or 60 watt amplifier apart.
You might find this interesting,
http://www.diyaudio.com/forums/soli...er-do-you-really-need-domestic-listening.html
input of 0.199Vac & output of 19.96Vac is a gain of +40dB (100 times). That part is upto specification.
Now reduce the input voltage to 0.02Vac (20mVac) and read the output voltage, Volume control still set to maximum.
Add an 8r0 dummy load to the output and read the output voltage.
change to a pair of 8r0 loads giving 4r0 equivalent. Read the output voltage. Change the pair of 8r0 resistor to series connected to give an equivalent of 16r test load. Read the output voltage. All these tests are for an output of ~1W. They will not overheat your amplifier. They will give you an idea of how the output voltage varies with load resistance.
The next bit is more risky. Testing for maximum output power for 1 or 2 seconds. Yes only a couple of seconds. Just long enough to check that the scope still shows an unclipped output signal, then repeat for a second two seconds to get a reading on your voltmeter.
To do that full power testing, you have to develop a test method that does not overheat and possibly/probably damage your amplifier nor your dummy load.
You decide and we can give guidance for a safe method.
Now reduce the input voltage to 0.02Vac (20mVac) and read the output voltage, Volume control still set to maximum.
Add an 8r0 dummy load to the output and read the output voltage.
change to a pair of 8r0 loads giving 4r0 equivalent. Read the output voltage. Change the pair of 8r0 resistor to series connected to give an equivalent of 16r test load. Read the output voltage. All these tests are for an output of ~1W. They will not overheat your amplifier. They will give you an idea of how the output voltage varies with load resistance.
The next bit is more risky. Testing for maximum output power for 1 or 2 seconds. Yes only a couple of seconds. Just long enough to check that the scope still shows an unclipped output signal, then repeat for a second two seconds to get a reading on your voltmeter.
To do that full power testing, you have to develop a test method that does not overheat and possibly/probably damage your amplifier nor your dummy load.
You decide and we can give guidance for a safe method.
So basically if the amp is within spec then it's fair to say that it won't have lost any output volume?
AndrewT could you confirm what you mean by testing maximum output power and why it's more risky? Are you talking about measuring on full with no load? I have already done this, full volume, no load and actually had to wait for a few seconds for the voltage to settle as it steadily increased as the amp got up to temp.
The only load I have access to test it on would be 9ohms (two 18ohm power resistors in parallel), surely if it produces the same output voltage under load then it will be within spec?
So to clarify should I expect the same results as above even with a 9ohm load on or will the load affect the output voltage?
AndrewT could you confirm what you mean by testing maximum output power and why it's more risky? Are you talking about measuring on full with no load? I have already done this, full volume, no load and actually had to wait for a few seconds for the voltage to settle as it steadily increased as the amp got up to temp.
The only load I have access to test it on would be 9ohms (two 18ohm power resistors in parallel), surely if it produces the same output voltage under load then it will be within spec?
So to clarify should I expect the same results as above even with a 9ohm load on or will the load affect the output voltage?
The loading of 8 or 9 ohms should not alter the output level by more than a fraction. The reduction would be due to resistive losses/output inductor etc.
Full power testing caries risks for the unwary. So much commercial gear simply won't survive it for more than a few moments. Not saying that's the case here but it happens.
Andrew like me is playing it safe... the last thing you want is a blown power amp.
And yes, the amp seems to meet it's specs from all you have measured so far and so ultimately it's as loud as it should be
Full power testing caries risks for the unwary. So much commercial gear simply won't survive it for more than a few moments. Not saying that's the case here but it happens.
Andrew like me is playing it safe... the last thing you want is a blown power amp.
And yes, the amp seems to meet it's specs from all you have measured so far and so ultimately it's as loud as it should be
And measure on the output terminals and not the load resistor as thin wire to the load will drop some voltage. That might (might ) explain why you mentioned the output increased over time on full power test. Maybe the load resistors were getting so hot their value increased thereby drawing less current and giving the impression the output increased... maybe !
) explain why you mentioned the output increased over time on full power test. Maybe the load resistors were getting so hot their value increased thereby drawing less current and giving the impression the output increased... maybe !Can I still confirm what you mean by full power testing? Full volume no load for a period of time? I presume because the amp wouldn't be expected to be running at that volume for an extended period of time, it's liable to overheat?
Just so I know for future reference, is there anything in particular that's most susceptible to failing due to overheating or could it be absolutely anything that would be classed as a blown amp?
Thanks for all the help it's been really appreciated and helped me learn a lot for future reference.
Just so I know for future reference, is there anything in particular that's most susceptible to failing due to overheating or could it be absolutely anything that would be classed as a blown amp?
Thanks for all the help it's been really appreciated and helped me learn a lot for future reference.
Full power testing means seeing the amp can maintain it's rated output into the specified load resistance.
So that means setting the amp to give 20 volts at the speaker terminals and monitoring that on a scope. Then connect 8 ohms across those terminals and ideally the scope should show no change.
The only reason we have been saying "full volume" is to determine if the amplifier meets its rated output for a known and specified input voltage. You could apply 2 volts or 5 volts to the input and still test for maximum power output but that wouldn't have told us that the amp also meets its sensitivity spec.
They are two different things...
Testing at full power raises the junction temperature of the output transistors instantly and if that heat can not get away then the amp will fail. Think how hot a 20 or 30 watt soldering iron gets. Now think of that power in a piece of silicon a few millimeters square.
So that means setting the amp to give 20 volts at the speaker terminals and monitoring that on a scope. Then connect 8 ohms across those terminals and ideally the scope should show no change.
The only reason we have been saying "full volume" is to determine if the amplifier meets its rated output for a known and specified input voltage. You could apply 2 volts or 5 volts to the input and still test for maximum power output but that wouldn't have told us that the amp also meets its sensitivity spec.
They are two different things...
Testing at full power raises the junction temperature of the output transistors instantly and if that heat can not get away then the amp will fail. Think how hot a 20 or 30 watt soldering iron gets. Now think of that power in a piece of silicon a few millimeters square.
I read that to mean 60W for stereo mode which is what I've been testing, or 50W for five channel surround mode where the amp has to drive more speakers, which makes sense to me.
But I don't know why it only refers to 60W Continuous Average Power (FTC) in stereo mode, yet theres no mention of FTC in the surround mode spec.
But I don't know why it only refers to 60W Continuous Average Power (FTC) in stereo mode, yet theres no mention of FTC in the surround mode spec.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.