Audio amplifier dynamic power explained with demonstration

[@Robjud-u2x]

For some of the more modern music with long sine waves in the bass region you need continuous power, the supply rails will be condtantly loaded and sagged. Something like acdc with a kick drum transient every second or so you benefit from dynamic power, between every kick drum the caps charge up to near idle voltage.

[@BiddieTube]

I remember when amplifiers were rated in RMS watts. That is what all the high end products (the only ones I looked at) were rated in. Also, all the pro sound studio monitor amps were rated in RMS also. Even today, I get studio reference amps for almost all my audio amp needs, and, at least Alesis (the brand I get because they make low power ones) is rated in RMS. I was looking for a consumer 30 watt per channel amp, in a case i was not concerned about top quality, and found many rated at 1000 and more watts that appeared to be around 30 watts channel. I could not find any that seemed to have a sensible power rating, and so just guessed based on the way it looked and the power it consumed. And so, I ended up getting a 1,200 watt amplifer, and indeed, it was 30 watts channel, just what I wanted. But the thing is, no matter how you test it, no matter what testing method one tests with, there is no way one could come up with 1,200 watts, and so IT IS A LIE!! Is false advertising legal these days? Based on my search for a 30 watt consumer amp, it must be legal to false advertise. Another great thing to check out, if one wants to find false advertising, check out home shop vacuums. I found them rated over Seven Horse Power, and yet they plug into a standard home outlet, aka Nema 5-15 outlet which are 15 amps. That motor would need a 230 volt 40 amp circuit. What I say about those products is that they are what everybody has been wanting, Over Unity!

[@bassblaster505]

Look at the cheap car audio industry. brands like BOSS and DUAL that all your high school kids love cause there cheap say BS like 1500W, but only does about 430W. good friend of mine wanted an upgrade from a Sony 500 monoblock, so naturally, went to walmart, got a "2000W" Dual, and was trying to figure out why it wasnt any louder than his sony.

[@martinda7446]

A 7 horsepower motor would need just over 20 Amps on a 230/240 volt mains. Just about do-able. PMPO means nothing and has never been defined unlike RMS which is the heating power of an AC waveform into a specific load. They fiddle with the figures thus, 240V mains supply has a peak to peak value of 678V - if you had a double 240V socket you would have 1357V - thats how dumb the power figures are, but there is always some bonkers math behind it - they would need to explain it to someone occasionally. Are they lying, well yes, but a lawyer might say otherwise. That is how it was 40 years ago. Today, they are probably just lying outright. The only way to rate the power of an amplifier is both channels driven continuously into required load and the RMS power measured.

[@rich1051414]

You touched on the importance of the reservoir cap on the power supply, but it is most important for lower frequencies. With an inadequate reservoir cap on an amp pushed to it's power supplies continuous limit, the volume itself will audibly dip when low frequencies play, and then increase again dramatically when they stop. It sounds absolutely horrible but an easy thing for anyone to fix if they know what the problem sounds like.

[@marianneoelund2940]

Nice job on the videos, John. At 8:50, I was wondering: Doesn't your Rigol scope have vertical cursors that allow you to select a time point for the scope to read the waveform sample at? That's the cursor mode that I normally use on my Tek scope. I like the fast live FFT feature on your scope for finding the precise clipping point.

[@twotone3070]

Very informative, thank you John.

[@PileOfEmptyTapes]

1. One of the more well-known brands to specify dynamic power is NAD, who typically include a factor of 2 (3 dB). 2. 2000 µF caps are very skimpy for a 4 ohm capable amplifier - for a power bandwidth down to 20 Hz, you'd need about 8200 µF. Are your speakers that small? 3. It is not unusual to find a crest factor (peak / average ratio) of 6-10 dB in music. For kicks, I'd be tempted to use a rather wimpy transformer with rather highish (but still safe) voltages at idle plus a fairly massive amount of capacitance, like 2x 22000 µF or so or more, and see how that sounds. And no, large caps won't blow up your rectifier, the winding resistance of a smallish transformer makes for a good current limiter. Back in the late '70s, it actually was not unusual to find fairly big caps (10000-22000 µF), as transistors back then would also be limiting the maximum supplies you could run (SOA wasn't all that great). As the '80s rolled around, parts got better but things also started to be made more and more cheaply but in greater numbers, and build quality really suffered after about '82 or so, including skimping on electrolytics.

[@grandadpop7865]

In answer to your second point, I'm sure John said his power supply used 10,000 µF capacitors.

[@ChrisSmith-tc4df]

A regulated power supply is unnecessary. As a linear series pass regulator, it can only be worse than the worst case droop between AC cycles as it can only dissipate excess voltage - not fill in. If greater power were desired, I'd increase the filter caps - perhaps by allot - and let the amplifier's power supply rejection ration (PSSR) sort out the rest. Adding a series power choke after the full-wave bridge would help raise the minimum DC level as well with a reactive boost in between crests. The crests are useless for this application, so you might as well inductively capture them to fill in the voids in between. The inductor would be physically large in the low mH range.

[@dartrunner4599]

What does it look like with pink or white noise? Any easy way to measure for clipping with that?

[@basshead100]

Hello friends. Such a question. I have 2 monoblock. The first mono pull out 5800 W RMS on static and 11000 W on dynamic test on 1 ohm, and the second 8000 W RMS on 1 Ohm static and the same 11000 W on dynamic 1 ohm test . The difference is only in the price of the amps Going to wire 2 subs 0.7 ohm with total 8000 W rated power.

[@kencohagen4967]

Home audio amplifiers were regulated, but car amplifiers weren't. A continuos sinewave is measured below 1% distortion for home amps. In fact some home amps are rated at .001 % distortion or somewhere in that neighborhood. The important thing is that 1% is were our ears can start to perceive distortion. Car amps on the other hand might be rated at something like 25 watts per channel at 10% distortion. That means it gets load and sound like shit doing it. There are other specs as well, and with most of them the lower number is the better except channel separation, signal to noise ratio, 100 or better is what to look for, frequency response, this should be a minimum of 20 hz to 20,000hz, the range of human hearing. 10hz to 100,000hz is much better, but the minimum requirement usually suffices. Anything less and you'll definitely miss part of the source material. I bought an Am that was rated from 40hz to 20,000hz. It lacked bass. It might have been made with a subwoofer output, but it still left a lot to be desired with the mains. And on the top end, dropping below 20,000hz to say 16,000hz will take away a lot of the transient response, say of a bass drum being kicked. That impact happens very fast and without a way to hear that attack the music will be lacking something. So keep these minimum specifications in mind when you boy any amp!

[@drittal]

Car amps rated at 10% thd? None that I’ve ever ran. US amps were rated at .006%. Newer class D amps have higher THD, with early ones around that 1%.

[@99Duds]

oh maybe you could go into more about how a regulated supply interfaces with a power amp? im always looking to improve my setup.

[@99Duds]

my 12 inch sub is powered by 2 regulated 30V 5A (31.5V no load) power supplies, the amp is a TDA 7293 bass is solid even at very low volumes. I know im only getting about 85 watts RMS but man it sounds like 2 to 3 times that.

[@davekazoroski6548]

Actually, the way sound works, doubling the amplifier's power would make an almost unnoticeable increase in volume. Tripling the power would make a slightly noticeable increase in sound level. This is due to how our ears work, they work on a logarithmic scale - this is how the decibel came about.Takes a massive increase in power to increase loudness, actually takes about ten times the power to get twice as loud. Lots of good reading on this subject on the internet.

[@tolgadabbagh1877]

@@davekazoroski6548 why do i hear almost twice the loudness when i plug in the other 2 channels to my 4 channel amp without making any change to the volume then ? maybe someone made this up and it is only a mostly untested internet legend .

[@mr.amp0076]

Can you make a class g type amplifier??

[@JohnAudioTech]

A lot of amplifier output stages to look at in future videos!

[@jp-um2fr]

I watched a video of a new high power D-Class American amp chip. The CEO was proud to present this new amp and stated the power rating at 10 % distortion. Every PDF sheet I have looked at seems to try and hide the true performance of D-Class either concentrating on ridiculously low power figures or this stupid 10% figure depending on what parameter they are trying to fudge. Over half a century ago I built a pair of Mullard 20 W valve amps. Mullard were proud of 0.05 % RMS distortion into 15 Ohms. They quoted the max at 27 W, I can't remember the RMS value at that - certainly a lot less than an unusable 10%.

[@JohnAudioTech]

Yes, it is annoying. You have to look at the power vs. distortion graphs on the datasheet to see the real performance of the device.

[@abijeetrs6522]

jp PS audio ?

[@limatoshi5845]

Hi JohnAudioTech I love your channel 'cause I have learned a lot and still learning BTW can you do a video on a 2000Watt transistor amp, this will be of great help to me. Thank you.

[@machiElectronics]

Hi Dear Sir please make video How Wind your own Audio transformer or inductor For Audio Amplifier

[@LogicalLokesh]

Late uploaded!!