SOUND ON SOUND

[James Perrett]

Given how complex a good class D amplifier needs to be and that it needs to be partnered with a nearly as complex regulated* and protected PSU it is a wonder to me that they are a popular as they are?

They use lots of cheap parts instead of a few expensive parts.

A proper professional amplifier will have a mains input rating that is higher than its output rating. As an example: the Quad 405 which is rated for 200W total output has a specified mains input power of 30-350W depending on signal level.

[MOF]

A proper professional amplifier will have a mains input rating that is higher than its output rating. As an example: the Quad 405 which is rated for 200W total output has a specified mains input power of 30-350W depending on signal level.

That was my thinking, no amplifier is 100% efficient so I don’t see how 80watts input can be less than the 500watts output. If it was 80watts in to 70watts output I could understand that. Even if it had an industrial grade super capacitor it would eventually run out of power.

[ef37a]

Given how complex a good class D amplifier needs to be and that it needs to be partnered with a nearly as complex regulated* and protected PSU it is a wonder to me that they are a popular as they are?

They use lots of cheap parts instead of a few expensive parts.

A proper professional amplifier will have a mains input rating that is higher than its output rating. As an example: the Quad 405 which is rated for 200W total output has a specified mains input power of 30-350W depending on signal level.

Well yes James, a bit but the most expensive part of any amplifier (apart from maybe the casing) is the mains transformer which you would not fit in a class D amp as you don't want a 50/60 Hz supply.
In any case in a "500W" D power amp I doubt the high speed,high power output MOSFETs are cheap? Class D has made great inroads in even top end monitors.

I'll say again, I reckon the 80W is just for 'legal' reasons. Also, although I have THE GREATEST respect for Acoustical's products, didn't the 405 have a problem in a review with meeting the 'pre heating' temperature rise test? That would to me dismiss it as a "professional" amplifier since such a device should be able to run at full power indefinitely. I don't say the Quad would fail, like "POOF!" but I think it would shut down.

Dave.

[Sam Spoons]

A proper professional amplifier will have a mains input rating that is higher than its output rating. As an example: the Quad 405 which is rated for 200W total output has a specified mains input power of 30-350W depending on signal level.

That was my thinking, no amplifier is 100% efficient so I don’t see how 80watts input can be less than the 500watts output. If it was 80watts in to 70watts output I could understand that. Even if it had an industrial grade super capacitor it would eventually run out of power.

I know Dave is going to pull me up on this but amplifier manufacturers used to quote 'watts RMS'. As a consequence of spending time on here I know that it is a 'made up' unit and doesn't really exist but it was a consistent method of measuring an amplifiers power output, usually IIRC when fed with a 1kHz sine wave.

WRT professional amps the Crown MacroTech 8000's that ran the subs when I worked for the PA company use 13A fused plugs (and we never blew one), my 8 kW shower needs it's own 40A breaker...

The mistake you are making is to assume that like my shower, a power amp playing music is drawing it's full output all the time, in practice it simply does not do so. I had enormous difficulty with this when I started looking into it and still wouldn't claim to have an in depth understanding but I have enough empirical evidence to just accept it.

[merlyn]

I would think the OP wants to get a cab that won't blow when connected to this amp and 500W seems like a lot.

500W into 4 Ohms = 250W into 8 Ohms.

So really it's 250W as most cabinets are 8 Ohms. My friend had an Orange Tiny Terror which is also described as having a 500W Class D power amp. He used it with an Eden 1x12 cab which worked and was plenty loud.

With a 1x12 the rating will be 200 - 300W so to be on the safe side this setup would be best not turned up full tilt. Anything bigger than 1x12 will be around 400W which should be fine.

I had a shot of the Tiny Terror and it was good. Difficult to believe it was so loud and clear while being so small and light.

So pretty much any decent cab but smaller ones can't go up to full tilt, which, if it's anything like the Tiny Terror, would be deafening.

[James Perrett]

The mistake you are making is to assume that like my shower, a power amp playing music is drawing it's full output all the time, in practice it simply does not do so. I had enormous difficulty with this when I started looking into it and still wouldn't claim to have an in depth understanding but I have enough empirical evidence to just accept it.

The whole field of power ratings for audio is filled with fiddle factors and fudges. Unfortunately it is down to the customer to decide what sort of fiddle factor is appropriate to the material that they will be amplifying. For a bass amp, music that relies on highly compressed, continuous bass sound will probably require more power than a slapping and pulling funk bass. The slapping will require higher peak power but the notes are short lived and the spaces between the notes reduce the average power demand.

A sensibly rated amp should really specify things in the way that Quad did with the 405 but music gear is often more about voodoo rather than technology.

[ef37a]

"
WRT professional amps the Crown MacroTech 8000's that ran the subs when I worked for the PA "

Now THAT^ really IS a "professional" amplifier! I cannot find specs for the 8000 but the 5000 gives very detailed figures of sine wave power into various loads and for certain bursts of signal( one cycle, 40mS etc) . Yes it will put out bursts of 5000 watts but only into 4 Ohms bridged and will not run two 2.5kW immersion heaters!

When amplifier reviews were done properly they were tested for volts across a Big Mother load resistor under sine wave drive and under those conditions the mains current draw did keep ahead of the output power. In fact some designs had a strange feature which meant their current draw increased as the test frequency rose quite alarmingly even though the power in the load was constant. Some of the bigger amps WERE sailing close to the 13A limit!


Dave.

[Sam Spoons]

"
WRT professional amps the Crown MacroTech 8000's that ran the subs when I worked for the PA "

Now THAT^ really IS a "professional" amplifier! I cannot find specs for the 8000 but the 5000 gives very detailed figures of sine wave power into various loads and for certain bursts of signal( one cycle, 40mS etc) . Yes it will put out bursts of 5000 watts but only into 4 Ohms bridged and will not run two 2.5kW immersion heaters!

When amplifier reviews were done properly they were tested for volts across a Big Mother load resistor under sine wave drive and under those conditions the mains current draw did keep ahead of the output power. In fact some designs had a strange feature which meant their current draw increased as the test frequency rose quite alarmingly even though the power in the load was constant. Some of the bigger amps WERE sailing close to the 13A limit!


Dave.

The other 'professional' thing about them was the need to employ two 'professional' weightlifters* to move them :D

On a serious note, the MacroTech 10,000 requires a 208VAC/16A three phase supply!

* Preferably Heavyweight and Russian

[BigRedX]

TC Electronic do some "creative" descriptions of the power input/output of their bass amps which coupled with a degree of built-in compression in the signal processing allow them to publish these specifications without shame. If you do a search on either Basschat or Talkbass you will find out exactly how they manage this and how they have been rumbled.

Almost all budget class-D bass amps use the same ICE-Power module so the actual power input/output will be that of the module.

[ef37a]

"On a serious note, the MacroTech 10,000 requires a 208VAC/16A three phase supply!"

The book for the 5000 shows a 30A US plug for 115V operation and so would indicate a 15A supply in Blighty. That it doesn't pop 13A fuses shows it cannot deliver 5000 continuous "heating" watts into a load.

We had a problem with the first Hoover Keymatics. If the motor started at the wrong point in the cycle with the heater on they would blow a 13A fuse. The solution was to solder 15A fuse wire across blown fuses!
Technically naughty but 'Hell hath no fury' like a lady with 2 kids and a hubby on wash day with no machine! They came up with a revised program 'key' eventually I understand.

Dave.

[Sam Spoons]

The book for the 5000 shows a 30A US plug for 115V operation and so would indicate a 15A supply in Blighty. That it doesn't pop 13A fuses shows it cannot deliver 5000 continuous "heating" watts into a load.

That was the point of this discussion I think, that 'music watts' are different from 'heating watts'. A '5000 watt' power amy can deliver 5000 watts when needed for the duration required to allow peaks/transients to be reproduced accurately but music, by it's nature, does not require that amount of power for much of the time and when it does it is for a very short time.

We had a problem with the first Hoover Keymatics. If the motor started at the wrong point in the cycle with the heater on they would blow a 13A fuse. The solution was to solder 15A fuse wire across blown fuses!
Technically naughty but 'Hell hath no fury' like a lady with 2 kids and a hubby on wash day with no machine! They came up with a revised program 'key' eventually I understand.

Dave.

A pragmatic approach to problem solving which seems to have dissapeared in our 'Elf & Safety' society :bouncy:

[MOF]

That was the point of this discussion I think, that 'music watts' are different from 'heating watts'. A '5000 watt' power amy can deliver 5000 watts when needed for the duration required to allow peaks/transients to be reproduced accurately but music, by it's nature, does not require that amount of power for much of the time and when it does it is for a very short time.

No the discussion was about suitable speakers for 80 watts or 500 watts i.e. how much extra capacity to prevent damaging them and then my question that followed on from that was how can the speaker output be so much greater than the amplifier’s power input?

[ef37a]

That was the point of this discussion I think, that 'music watts' are different from 'heating watts'. A '5000 watt' power amy can deliver 5000 watts when needed for the duration required to allow peaks/transients to be reproduced accurately but music, by it's nature, does not require that amount of power for much of the time and when it does it is for a very short time.

No the discussion was about suitable speakers for 80 watts or 500 watts i.e. how much extra capacity to prevent damaging them and then my question that followed on from that was how can the speaker output be so much greater than the amplifier’s power input?

Yes, and that apparent paradox cannot be answered without far more information about that particular amplifier. I think there has been quite a bit of agreement that the 80W is a 'working' figure for the purposes of fusing or the calculation of a rating for say a generator? Then, AFAIK manufacturers are required by law to fit a rating plate?

Any audio power amplifier must draw more power from the wall as the power into the load increases unless it is truly class A but this amp cannot even produce a continuous sine power of the 'suggested' 500 watts, more like 300W into 4 Ohms and unless somebody actually measures it we cannot really be sure of that!

As far as suitable speakers goes? IMHO err on the side of caution as much as pocket allows. A 300W rating at 8 Ohms would seem pretty safe but then if someone touches a jack plug tip with the taps wide open who can say? ***t'Appen.

Dave.

[MOF]

As far as suitable speakers goes? IMHO err on the side of caution as much as pocket allows. A 300W rating at 8 Ohms would seem pretty safe but then if someone touches a jack plug tip with the taps wide open who can say? ***t'Appen.

Yes definitely get a loudspeaker with a Speakon connector.

[Sam Spoons]

I wonder if Dave meant that or, maybe, touching the tip of the guitar lead and the resultant loud buzz we are all familiar with?