How does one compare Class A power ratings with A/B

[aussievintage]

15 minutes ago, Wimbo said:

If linear gain is 1 volt, then the rms value of that is .707 volt.

 

Gain is not measured in volts.   However a  sine wave of 1 volt peak equals 1÷√2 or approx .707 volts rms.

 

18 minutes ago, Wimbo said:

the rated Class A value is the RMS value

You have something confused here.     Watts are watts.     Class A, AB, or B or whatever, doesn't matter

 

20 minutes ago, Wimbo said:

pure Class A amplifier's RMS value is 20 watts

Are you perhaps using the term 'RMS'  to mean 'power'?  The units are watts, or joules per second.  To calculate it's value for a sinewave, you multiple the rms values of the current and voltage.

[Wimbo]

32 minutes ago, aussievintage said:

 

Gain is not measured in volts.   However a  sine wave of 1 volt peak equals 1÷√2 or approx .707 volts rms.

 

You have something confused here.     Watts are watts.     Class A, AB, or B or whatever, doesn't matter

 

Are you perhaps using the term 'RMS'  to mean 'power'?  The units are watts, or joules per second.  To calculate it's value for a sinewave, you multiple the rms values of the current and voltage.

See, this is where it gets confusing for me. All the amplifiers with a rated power in RMS.

What your saying is this technical measurement is bullshit devised by manufacturers.

34 minutes ago, aussievintage said:

Gain is not measured in volts.   However a  sine wave of 1 volt peak equals 1÷√2 or approx .707 volts rms.

Yes, its logarithmic if I remember correctly.

[sir sanders zingmore]

I really miss @Zaphod Beeblebrox In these sorts of threads. 

[aussievintage]

1 hour ago, Wimbo said:

1 hour ago, aussievintage said:

 

See, this is where it gets confusing for me. All the amplifiers with a rated power in RMS.

What your saying is this technical measurement is bullshit devised by manufacturers.

 

Amplifier power is rated in Watts not RMS.   Those watts are calculated using rms values of voltage and current.  To call the rating Watts rms is incorrect but a shorthand perhaps acceptable to some.

 

1 hour ago, Wimbo said:

Yes, its logarithmic if I remember correctly.

Sorry but it simply a method calculating the average power.   If you use the rms values, you calculate the average power as desired.

 

I think you are still confusing gain with power.  It is gain, measured in decibels that is logarithmic. 

[aussievintage]

1 hour ago, Wimbo said:

All the amplifiers with a rated power in RMS.

 

To quote Wikipedia  "As described above, the term average power refers to the average value of the instantaneous power waveform over time. As this is typically derived from the root mean square (RMS) of the sine wave voltage,^[6] it is often referred to as "RMS power" or "watts RMS", but this is incorrect: it is not the RMS value of the power waveform (which would be a larger, but meaningless, number)."

 

from    https://en.wikipedia.org/wiki/Audio_power#Continuous_power_and_"RMS_power"

[Wimbo]

36 minutes ago, aussievintage said:

Amplifier power is rated in Watts not RMS.   Those watts are calculated using rms values of voltage and current.  To call the rating Watts rms is incorrect but a shorthand perhaps acceptable to some.

Your misunderstanding me. But thats alright. I know power is watts. Basic Ohms law.

[aussievintage]

15 minutes ago, Wimbo said:

Your misunderstanding me. But thats alright. I know power is watts. Basic Ohms law.

Sorry about that.    Maybe have a read of the whole Wikipedia article on Audio Power that I linked.  Just remember rms means root mean square, which means, it's the square root of the average (arithmetic mean) of the squares of a set of numbers representing the signal (sinewave) either voltage or current.

[Colin Rutter]

I have built a few Class A amps
They sound fine both SE and PP
The only theoretical advantage I can see in SS amps is that the devices are running at constant temperature and therefore should be more linear but in practice I don't think they sound "better"
A well designed amp will always be OK
I have SS ( bipolar, Mos, monilithic chip, Class D) and tube.
They all sound fine
As for class A being able to push more power? Once any SS and hits the supply rail volts you get hard clipping.
For the same rated amps to be different
The rail volts must be sagging under load
So it's the power supply not the amp topology causing the sensation

"It's about the music not the electronics"

[davewantsmoore]

2 hours ago, Sir Sanders Zingmore said:

I really miss @Zaphod Beeblebrox In these sorts of threads. 

Why isn't he here?

[Wimbo]

2 hours ago, davewantsmoore said:

Why isn't he here?

I'll ring Rage tomorrow.

 

[Addicted to music]

10 hours ago, aussievintage said:

No not the bias current, but the current draw when producing full continuous  power into a load.

?????

What has adjusting the bias current to overcome crossover distortion has to do with current drawn with full load?  

Current drawn at full load is usually tested after this is done!

 

10 hours ago, aussievintage said:

 

only for a very specific transistor design.   Lot's of class AB valve amps out there.

All  BJT will come under this category.  who gives a fat rats about AB glowing bottles....

10 hours ago, aussievintage said:

 

Tell that to SE amplifier owners

 

Don't care about SE amplifier owners....  

 

10 hours ago, aussievintage said:

 

This is what I meant.  At 300 watts, the current draw is the virtually same.

BS, Same as what?   your comment makes no sense, or this is just argument for argument sake!

 

300W measured at the mains on a A/B SS power amp doesn't mean your doing that at the speaker load!  whether it be class A or A/B.   Do the maths!     Take into consideration that Class A is 25% efficient and Class B is around 70% efficient.

[aussievintage]

1 minute ago, Addicted to music said:

?????

What has adjusting the bias current to overcome crossover distortion has to do with current drawn with full load?  

Current drawn at full load is usually tested after this is done!

Yes, but if you see the comments earlier that lead up to this and it will make sense.  The original comment was about power supply size and ripple from an inadequate design.  Somehow the max current capability discussion got twisted into some other point about biasing, which, as you say has nothing to do with it.  Hence my statement that I was referring to the full current draw, not the bias current. 

 

5 minutes ago, Addicted to music said:

BS, Same as what?   your comment makes no sense, or this is just argument for argument sake!

 

This appears confusing only because of the confusion over biasing vs operation at full load.

 

 

 

7 minutes ago, Addicted to music said:

300W measured at the mains on a A/B SS power amp doesn't mean your doing that at the speaker load! 

Wasn't talking about the mains.  I missed that word in your post, sorry. I was discussing the power supply and ripple when delivering that power to the load.

 

 

 

Bottom line, we have some crossed wires here (forgive the pun).     Apologies.

[Addicted to music]

9 hours ago, aussievintage said:

 

Gain is not measured in volts.   

Gain of an amplifier circuit  is measured with volts, the ratio is Vout/Vin.  

8 hours ago, Wimbo said:

See, this is where it gets confusing for me. All the amplifiers with a rated power in RMS.

What your saying is this technical measurement is bullshit devised by manufacturers.

Yes, its logarithmic if I remember correctly.

 

Watt(s)  just Watts, forget the RMS.   An unless its stated with the usual standard 8 or 4 ohm load forget all the other BS that goes with it!   Don't get me started when I see quotes like how a good amp doubles down when quoting 4 ohms,  good luck on that!

 

Its Logarithm because the human ear isn't linear in its sensitivity.  so to get an amplifier to double the loudness you need a 3db gain, this equates to 10X the power.  you can do the maths and prove me wrong!  Im going to bed!

 

[aussievintage]

9 hours ago, Addicted to music said:

Gain of an amplifier circuit  is measured with volts, the ratio is Vout/Vin.  

Forgive me for the bad wording. Gain is not specified in volts.  Gain has no units, it is a ratio, normally expressed in db. 

[Wimbo]

A lot of good lingo going on here in laymans terms.

[almikel]

On 20/05/2019 at 8:01 AM, Wimbo said:

A lot of good lingo going on here in laymans terms.

 

On 19/05/2019 at 10:46 PM, Addicted to music said:

Gain of an amplifier circuit  is measured with volts, the ratio is Vout/Vin.

 

On 20/05/2019 at 7:58 AM, aussievintage said:

Forgive me for the bad wording. Gain is not specified in volts.  Gain has no units, it is a ratio, normally expressed in db. 

perhaps a bit OT...

Both above are correct - you measure the gain by calculating the ratio of Vout/Vin - but the units are the same top and bottom (volts), so they cancel, and the gain has no units - if Vout was 10V and Vin was 1V, the gain would be 10 (ie output is 10 x the input) - but this is not dB gain...

 

...it gets a bit more complicated - to express this ratio in dB is

Gain (dB) = 20 x log (Vout/Vin)   (log base is 10)

Gain          = 20dB

So a voltage gain of 10 (ie Vout = 10 x Vin) when expressed as dB is 20dB

 

Which is different to comparing power instead of voltage

Power Gain (dB) = 10 x log (Pout/Pin),

or say comparing 2 different amplifiers, one with 200W output vs another with 100W output

Power Gain         = 10 x log (200/100)     (same log base of 10)

Power Gain         = 3dB

the 200W amplifier has 3dB more power than the 100W amp (double the power)

 

I remember which is "10x" vs "20x" by knowing Power = V^2/R, and in log maths Log (V1/V2)^2  becomes 2 x Log (V1/V2) - the ^2 comes down the front changing 10x into 2 x 10=20x...or I Google again...

 

Anything expressed in dB is always a ratio between 2 things (eg power difference between 2 amps, or Voltage out vs Voltage in for an amp), and sometimes the ratio between the thing being measured, and a known reference (eg dB SPL).

 

cheers

Mike

 

 

 

[mwhouston]

On 05/05/2019 at 7:04 PM, andyr said:

 

^^^ What he said! 

 

The larger PS in the Class A can often deliver more current than an AB amp of greater power.  I'm thinking PASS amps which, say, are only 50wpc into 8 ohms - but are known to drive Maggies well.  (Maggies like current.  )

 

 

The only Class A amp I've heard was amazing!  However, I hope to hear another one later this year ... as Hugh Dean is coming out with a 35w Class A amp. 

 

Andy

 

Where has Hugh announced this? On his site?

[almikel]

On 19/05/2019 at 10:15 AM, Addicted to music said:

I will bet if you had a pure class A design it will be consuming at the max rating at idle and lowering as you increase the music signal. 

Serious question - I don't understand why a class A design would consume more power from the power supply/240V outlet for no input signal/no output vs full input signal/full output - I thought the consumption with class A was constant regardless of input?

 

Mike

[mwhouston]

Without reading all of the above posts and some appeared to be way off the mark; 

 

• In Class A operation with the power or output/driving device, tube or transistor, the control grid/gate/base is always throttling back (negative bias) the current flow through that device. In a tube the grid would stay negative compared to the cathode (or filament in a triode).
• In Class B mode the controlling element, in the power device, is more positive and allows higher current flow through the device. With a tube the grid would go positive the same with a NPN transistor. This occurs when the audio signal, being fed to the device, exceeds the devices negative bias. Image the device has a negative (-5V) bias but now the audio signal is plus 6V. The device is being driven beyond its negative bias. 

In Class A/B amps (take transistor amps) most high powered amps will deliver 30 or more watts (the output device remains in negative bias) until the input signal gets to the stage when it is pushing the transistor to higher conduction by sending the base positive (for NPN semi-conductors). 

 

When the bias is so positive it drives the output device into over-conduction, where it cannot handle the current, clipping occurs.  Usually more noticeable in SS devices. 

[mwhouston]

17 minutes ago, almikel said:

Serious question - I don't understand why a class A design would consume more power from the power supply/240V outlet for no input signal/no output vs full input signal/full output - I thought the consumption with class A was constant regardless of input?

 

Mike

My main experience is with Class A tube amps (I’ve built and sold many) but have also built a number of Class A SS AMPS. THE hiragana “Le Monster” Class A is an example but the principle is true for tube and SS. Class A amps draw pretty well a constant current regardless of input signal level or volume plate at.  Not usual for big Class A SS amps to be drawing many amps at turn on and to run very hot with no music on. 

 

Your assumption is correct. 

[Ittaku]

1 hour ago, mwhouston said:

Not usual for big Class A SS amps to be drawing many amps at turn on and to run very hot with no music on.

I think you mean not UNusual?

[andyr]

8 hours ago, mwhouston said:

Where has Hugh announced this? On his site?

 

No he hasn't announced this yet, on his web-site, Mark.  Hugh shows me what he's been working on when we have coffee every month or so.

 

It's a ss Class A, btw. 

 

Andy

 

[mwhouston]

8 hours ago, Ittaku said:

I think you mean not UNusual?

Yes not unusual. 

[mwhouston]

1 hour ago, andyr said:

 

No he hasn't announced this yet, on his web-site, Mark.  Hugh shows me what he's been working on when we have coffee every month or so.

 

It's a ss Class A, btw. 

 

Andy

 

Ta mate, I’ll have a chat with him. Haven’t caught up for a while.

[kranky]

Gent's I think this might be the said Amp.

AKSA LENDER p-mos hybrid Alepha over on DiyAudio.

#3155.

Steve.