Output capacitance question...

[Chr1]

How do you know if an amplifier has sufficient output capacitance?

From what I have read, for an amplifier to accurately recreate sudden transient changes in music, it requires output capacitors that are large enough to be to able provide this needed increase in power.

Is there a way to measure or calculate if an amplifier has this?

Thanks in advance for help understanding this.

 

[sergeauckland]

I think you mean power supply reservoir capacitors, rather than output capacitors. It's these that provide essentially all the power for an amplifier. Output capacitors were used in early solid state amps, but not for the past 40 or so years.

If the amplifier has sufficient continuous power for your needs, with low noise (hum), then the design has sufficient smoothing for whatever transient comes along.

Short-term Dynamic Power usually exceeds the continuous power by a few dBs, but there's no standard for what constitutes a transient, 2mS, 5mS 100mS? that whatever a manufacturer might quote for dynamic power is difficult to compare with another manufacturer's claim.

I don't worry about transients, if the amp can handle continuous output correctly and adequately, that will cover all transient needs too.

S

 

[escksu]

I think you meant power reservoir caps. Yes, i think i can safely say all solid state amps comes with it. Never seen one without. There is no way to measure it. Easiest is to simply take of the cover of the amp. Look for those huge cylindrical electrolytic caps (mostly electrolytics). Those are your power filtering/reservoir caps.

Btw, those caps usually are one of the first to "go"...

 

[solderdude]

Is there a way to measure or calculate if an amplifier has this?

By looking at the schematics or lifting the top and have a look at the capacitors.

Re output caps:
Some older designs actually had output capacitors. This is needed when there is no split supply rails. Too low values means LF roll-off being too high.
Most amps today are DC coupled on the output so don't need nor have output capacitors.

Your description, however, indicates you did not mean output caps but reservoir/smoothing capacitors.
In most cases it's not the reservoir caps being the limiting factor but the whole power supply (transformer/rectifier/reservoir caps or SMPS) + amplifier circuit itself that determines max output power, peak music power into certain impedances.

 

[Chr1]

Thanks and apologies for my use of the wrong terminology there!

I am now curious as to why there would not be an accurate way to measure this. Presumably how an amplifier is able to deal with transient power demands is a very important consideration with amplifiers in general?

Thanks again for the help understanding this.

I started a thread earlier relating to this...
My earlier thread.

 

[solderdude]

I am now curious as to why there would not be an accurate way to measure this. Presumably how an amplifier is able to deal with transient power demands is a very important consideration with amplifiers in general?

because you aren't measuring the capacitance. You are measuring a complete device. Power supply + circuit in specific loads.
It is usually the limits of the circuit and power supply combination.

When you want to know the amps performance you would have to perform a lot of continuous power and various pulse power tests in various loads to fully characterize the amps performance.

When you only want to know how much capacitance is in your amp (which does not say everything) you lift the top of and read the capacitance of the reservoir caps or look in the schematic.
It will not have a direct relation to measured and perceived performance.

 

[sergeauckland]

Thanks and apologies for my use of the wrong terminology there!

I am now curious as to why there would not be an accurate way to measure this. Presumably how an amplifier is able to deal with transient power demands is a very important consideration with amplifiers in general?

Thanks again for the help understanding this.

I started a thread earlier relating to this...
My earlier thread.

There is an easy way to measure this, it's short-term output against continuous output, but the problem is that as there's no standard for 'short-term', or how to measure it, (into what impedance, single channel or both channels, what frequency), different manufacturers will end up with different numbers, so impossible to compare.
I disagree that transient power matters much, as continuous power tells you what an amplifier will do, and if that's sufficient, then there's no need to know about any small increase in transient power. Bear in mind also that amplifiers with stabilised power supplies, whether linear or Switch-Mode, won't have any increase in transient power over continuous power.

S

 

[Chr1]

There is an easy way to measure this, it's short-term output against continuous output, but the problem is that as there's no standard for 'short-term', or how to measure it, (into what impedance, single channel or both channels, what frequency), different manufacturers will end up with different numbers, so impossible to compare.
I disagree that transient power matters much, as continuous power tells you what an amplifier will do, and if that's sufficient, then there's no need to know about any small increase in transient power. Bear in mind also that amplifiers with stabilised power supplies, whether linear or Switch-Mode, won't have any increase in transient power over continuous power.

S

Again, the reason I am curious is that my preferred amplifier is only rated at 50w @8 Ohms, but sounds much better and more powerful than several amplifiers with higher power ratings.
I have recently learned that this is most likely due to a superior power supply. So I am now confused as to how reliable the power rating is on it's own. Accurately reported or otherwise...

 

[solderdude]

Again, the reason I am curious is that my preferred amplifier is only rated at 50w @8 Ohms, but sounds much better and more powerful than several amplifiers with higher power ratings.
I have recently learned that this is most likely due to a superior power supply. So I am now confused as to how reliable the power rating is on it's own. Accurately reported or otherwise...

What you learned may have some grains of truth in it but most likely is not related to capacitance.
If that were the important variable a cheap amplifier with 1,000uF capacitance would suddenly become much better sounding going to 100,000uF (without changing the rest of the circuit or the transformer) which it doesn't. Same power limitations, same continuous output power and probably same peak power. The only difference would be peak power could be delivered a few ms longer.

Differences between amps can be caused by many technical reasons. A bigger capacitance only will not do this.

 

[sergeauckland]

Again, the reason I am curious is that my preferred amplifier is only rated at 50w @8 Ohms, but sounds much better and more powerful than several amplifiers with higher power ratings.
I have recently learned that this is most likely due to a superior power supply. So I am now confused as to how reliable the power rating is on it's own. Accurately reported or otherwise...

Depending on what the amplifier is, the 50w/8 ohm rating may be very conservative, or the amplifier could have good low impedance performance that gives you closer to 100 watts into 4 ohms, possibly 150-200 watts into 2 ohms. Then, if your loudspeakers have an extreme impedance characteristic, it's perfectly possible that your 50 watt amp does a better job than another higher rated into 8 ohms amplifier that can't handle the low impedance your loudspeakers present.

How an amplifier handles low impedances isn't just the power supply, that does have an effect, but it's as much how the design of the actual amplifier is done in terms of current delivery and how and what overload protection exists. Power supply capacitance is only one, (minor) factor in how all this works.

S.

 

[Chr1]

What you learned may have some grains of truth in it but most likely is not related to capacitance.
If that were the important variable a cheap amplifier with 1,000uF capacitance would suddenly become much better sounding going to 100,000uF (without changing the rest of the circuit or the transformer) which it doesn't. Same power limitations, same continuous output power and probably same peak power. The only difference would be peak power could be delivered a few ms longer.

Differences between amps can be caused by many technical reasons. A bigger capacitance only will not do this.

Thanks. If it is not down to larger/better specd reservoir/smoothing capacitors does this mean that it is the specifications of the transformer that are paramount? If not, what other components are important?

Also, are pulse power tests in various loads the only way to accurately measure an amplifiers transient power capability?

Apologies again for all of the rather naïve questions!

 

[solderdude]

Thanks. If it is not down to larger/better specd reservoir/smoothing capacitors does this mean that it is the specifications of the transformer that are paramount? If not, what other components are important?

Everything. Power supply voltage/current/power, circuit design, feedback (amount and type), used components, PCB design right down to wire routing and protection and above all the load itself.
The combination of all of these factors determines performance into specific loads and ultimately if there will be audible differences and under which circumstances.

are pulse power tests in various loads the only way to accurately measure an amplifiers transient power capability?

Basically yes but there are several methods and stimuli. You also need to know the continuous power and test under various (preferably realistic) loads.

Transients in amps are never an issue. The moment you have 20kHz power bandwidth (meaning FR is flat at maximum output power) at realistic loads then the amplifier simply is fast enough to handle the fastest impulses you can throw at it.
Another test is using a square-wave and checking for rounding or overshoot under realistic loads (for amps only).

As mentioned this is never a problem. Transients in music rarely have any frequencies in it above a few kHz which is dead easy for amps.

 

[Chr1]

Everything. Power supply voltage/current/power, circuit design, feedback (amount and type), used components, PCB design right down to wire routing and protection and above all the load itself.
The combination of all of these factors determines performance into specific loads and ultimately if there will be audible differences and under which circumstances.

Great, thanks. So this being the case, presumably this means it is very difficult to predict via specifications and therefore measurement via pulse power tests into various loads is the only accurate way to determine this?

 

[solderdude]

Specifications as provided by manufacturers often leave a lot to be desired and are often not enough to fully characterize an amp but do provide some basic parameters in resistive loads.

It won't tell you how the system will subjectively sound to an owner because the variables in human perception and other circumstances are too big.

A good set of relevant measurements can ensure that the amp will provide a proper (means not too much altered) electrical output signal into specified loads.

 

[Chr1]

Indeed. I have long been very suspicious of manufacturers claimed specifications. My other hobby is motorcycles. Both the weight and horsepower figures claimed relating to sportsbikes most definitely need to be carefully investigated and often are dubious to say the least. As with hifi, there's also a lot of snakeoil involved. With sportsbikes you can see what components racers use and laptimes determine what works best.
Unfortunately I am not yet able to obtain quite as much objective data when it comes to audio!

I guess what I am trying to determine is how one determines the quality/capability of an amplifier without actually listening to it. I think that I have pretty much figured out how to do this for a DAC, as Amir's testing appear to be all that is required. I have my doubts relating to amplifiers however, as I do not think that his testing is comprehensive enough. Given that the relevant specifications and measurements are seldom available, it would seem to me that this is an area that warrants further investigation.

Anyway, thanks for all the help and your patience explaining it to me.

 

[solderdude]

With sportsbikes you can see what racers use and laptimes determine what works best

Wouldn't there be variables that can influence performance namely the driver and circumstances ?
A dyno would probably not lie about parameters found under the same conditions but a wobbly frame or slippery tires can make drastically different lap times.

It's the same with audio in a sense.
The speaker, the used music, the positioning, the room, the mood of the listener, the pre-biasses (sight, knowing what is playing), listening SPL, limits being reached or nearly reached, gear that may have a not obvious defect are all variables.

I guess what I am trying to determine is how one determines the quality/capability of an amplifier without actually listening to it.

You can only determine if an amplifier is suited to properly drive a certain load to desirable levels in a certain room. The actual load, room, speaker and SPL are variables that should be taken into account but rarely are.

What you can do is calculate what power you need in your room to reach a certain SPL. You need dimensions, some circumstances (listening distance, room conditions, placement) and data from the used speakers (impedance plot, efficiency, frequency response, directivity).
From this info you can make a list of data such as needed power in its lowest impedance.
On that number you can select an amplifier that can reach that power in a power bandwidth you need.
When that amplifier has low distortion numbers over the entire usable range (< 0.01%) you will have some form of guarantee the amp is not the limiting factor. Also do not forget the S/N ratio and sensitivity as factors.

That is about the only thing you can do. Another way is selecting an amplifier that can deliver shitloads or power (more than you need) in the lowest impedance your speaker has and you are probably fine.

 

[Chr1]

Yes, you are right. Of course I should have specified that in the motorcycle racing scenario the rider must remain constant, but improvements in setup and components can be determined by improvement in laptimes. Not easy for sure, but there's a methodology.

One thing that I find useful is to note what racers on a budget do and use. Obviously the big factory teams have huge budgets and can throw money at a problem which is irrelevant to most people. Club racers with limited finance tend to have to choose more affordable components that are often a good choice for the hobbyist. (Not race tyres, brake pads... or carbon discs however, please!)

I am definitely of the conclusion that the pro-audio world is similar to the racing world ie Less boutique horseshit and more real world practicality and performance for sure. Unfortunately, I think that in good quality hifi there is quite a lot of crossover and I am trying to figure out how to sort the wheat from the chaff objectively. Not simple unfortunately!

 

[solderdude]

The pro audio world consist of many companies that build cheap devices that are good enough and provide certain functionality over perfect measurements/performance.

In the monitor world there are a few science driven (usually very expensive) brands that make everything from crappy budget stuff to state of the art monitors. While these are excellent art what they do most people are better served with good speakers intended for hifi sound reproduction.
Most equipment designed for professional usage is not nearly as good in performance as hifi equipment designed for sound reproduction.
The focus points are sturdyness, ease of use and connectivity.

 

[Chr1]

The pro audio world consist of many companies that build cheap devices that are good enough and provide certain functionality over perfect measurements/performance.

In the monitor world there are a few science driven (usually very expensive) brands that make everything from crappy budget stuff to state of the art monitors. While these are excellent art what they do most people are better served with good speakers intended for hifi sound reproduction.
Most equipment designed for professional usage is not nearly as good in performance as hifi equipment designed for sound reproduction.
The focus points are sturdyness, ease of use and connectivity.

I think that this is a bit of an over-generalisation personally.

 

[solderdude]

In which shops can you find the most expensive and best spec'd equipment... In a music store or your average high-end hifi shop ?