Switching Regulator for Audio Amplifier

[Eeyore]

20 * 5 / sqrt(2) = 70W

20V pk = 14.14V rms - squared = 200 divide by 4 = 50 W rms. No that bit's OK.

Graham

 

[Eeyore]

Transformers aren't all that expensive. Going a bit over designed on
the transformer will make it run cool.

There is another issue that has been ignored all the way through these
arguments. The actual mains voltage can be 10% either way of the
nominal. The design needs to be done at the two extremes if you want
it to produce the rated power at the low line case and survive the
normal high line case. A thermal shutdown is a very good idea here
too.

This is where professional designers come into play.

Graham

 

[Jan Panteltje]

[....]

But for audio the average power is much lower, at least for music,
so 100VA would be just fine.

Transformers aren't all that expensive. Going a bit over designed on
the transformer will make it run cool.
Agreed.


There is another issue that has been ignored all the way through these
arguments. The actual mains voltage can be 10% either way of the
nominal.

No he did not ignore that.

The design needs to be done at the two extremes if you want
it to produce the rated power at the low line case and survive the
normal high line case. A thermal shutdown is a very good idea here
too.

Thermal shutdown is a very clever idea,
that protect against those 100% sine wave tests

I must say that those toroids hardly ever get really hot in audio amps....

And he should not be too pedantic,
the difference in volume between 45 W and 50 W is not that big.

 

[Fred]

"MooseFET"




20 * 5 / sqrt(2) = 70W

** Huh ????????

Why the root 2 ??

Peak power = double "watts rms" - you dumb asshole.

..... Phil

The chip has a 138 peak output capability. So, instead of creating a
35-40W continues amp with 50W of peak poer, if I make a power supply
capable of supporting 50W continues output, then maybe it will perform
like a 75-90 watt amp with a music signal.

I have a 75W PA that I play my audio through now, and it is
insufficient. I just looked at the speaker efficiency and surprise it
was 93db/W. Maybe I should just get more efficient speakers, like 100
or 101 db/W That would be s 6 to 7 db boost right there.

I doubt it would actually sound 4x louder, although it would probable
be noticeably better.

Fred

 

[Eeyore]

Thermal shutdown is a very clever idea,
that protect against those 100% sine wave tests

I design mine to survive sinewave tests into the rated load ! Why ? Because
highly compressed 'rave' DJ music exhibits almost exactly the same dissipation.

I must say that those toroids hardly ever get really hot in audio amps....

When we went to 2 ohm load ratings I had (auto resetting) thermal switches
installed inside them. They simply killed the signal on over temp. Never had
one do it though and I had a real 'amp torture test' I'm proud of - not to
mention a speaker killer test too.

And he should not be too pedantic,
the difference in volume between 45 W and 50 W is not that big.

About 0.2dB probably.

Graham

 

[Eeyore]

The chip has a 138 peak output capability.

So what ? Under what conditions ? You need to learn about power supply
design. Low line- high line, regulation and ripple for starters. Only THEN
can you make any meaningful calculations.

Graham

 

[Jan Panteltje]

I design mine to survive sinewave tests into the rated load ! Why ? Because
highly compressed 'rave' DJ music exhibits almost exactly the same dissipation.

I usually stop or reduce volume when I smell voice coil.

I duno where everybody lives, but I am sure if I run the Chinese 2x 100W for a whole
afternoon, then either all the young ones come party here, or somebody will complain.
Or both

 

[Eeyore]

I design mine to survive sinewave tests into the rated load ! Why ? Because
highly compressed 'rave' DJ music exhibits almost exactly the same dissipation.

I usually stop or reduce volume when I smell voice coil.[/QUOTE]

DJs don't !

I duno where everybody lives, but I am sure if I run the Chinese 2x 100W for a whole
afternoon, then either all the young ones come party here, or somebody will complain.
Or both

The average Chinese amp is crap down to its very foundations.

Graham

 

[Jan Panteltje]

DJs don't !

Too bad for them

The average Chinese amp is crap down to its very foundations.

Graham

That Olympic opening and closing was pretty impressive from a technical POV.
They have a space walk planned for the coming month.
And I know some other Chinese products that impress me.

Face it, it is all over

 

[Eeyore]

DJs don't !

Too bad for them [/QUOTE]

They have too many drugs in them to notice.

That Olympic opening and closing was pretty impressive from a technical POV.

Playing light orchestral or whatever is a piece of shit. Any sodding smp can do that.

They have a space walk planned for the coming month.
And I know some other Chinese products that impress me.

Face it, it is all over

No it isn't. We just need to pick ourselves up and execute people like Thatcher and the
Bushes. It's called a 'revolution'.

Graham

 

[Martin Griffith]

They have too many drugs in them to notice.



Playing light orchestral or whatever is a piece of shit. Any sodding smp can do that.



No it isn't. We just need to pick ourselves up and execute people like Thatcher and the
Bushes. It's called a 'revolution'.

Graham

Steve Bell cartoon
http://www.guardian.co.uk/politics/cartoon/2008/sep/03/if.margaret.thatcher

martin

 

[Fred]

I usually stop or reduce volume when I smell voice coil.

I duno where everybody lives, but I am sure if I run the Chinese 2x 100W for a whole
afternoon, then either all the young ones come party here, or somebody will complain.
Or both

You mentioned spice before. The trouble I have had with using spice
for this is modeling the transformer in a practical way. It has been
long learning curve compared most everything else.

I just worked out a simple method to model them so that I get the
rated amps at the rated voltage and the proper no-load rise. Now I
can do some realistic ripple studies.

Fred

 

[Eeyore]

Now I can do some realistic ripple studies.

Ripple is piss easy.

You're relying too much on simulation tools and ignoring basic fundamentals like dV/dt = I/C

Graham

 

[Fred]

Could you elaborate upon dv/dt = I/C?

Fred

 

[MooseFET]

On a sunny day (Wed, 17 Sep 2008 06:52:49 -0700 (PDT)) it happened MooseFET [....]

The design needs to be done at the two extremes if you want
it to produce the rated power at the low line case and survive the
normal high line case.  A thermal shutdown is a very good idea here
too.

Thermal shutdown is a very clever idea,
that protect against those 100% sine wave tests

A square wave is worse. Slowly run its amplitude up towards just
about 50% for best results. :>

[...]

And he should not be too pedantic,
the difference in volume between 45 W and 50 W is not that big.

Agreed.

 

[MooseFET]

20V pk = 14.14V rms - squared = 200 divide by 4 = 50 W rms. No thatbit's OK.

Yes you are right. I must have been asleep.

 

[Eeyore]

Yes you are right. I must have been asleep.

It happens.

Graham

 

[Fred]

It happens.

Graham

I suppose you were making some kind of reference to the interaction
between the mains impedance, winding resistances of the transform, the
diode drops, and the ESR and capacity of the filter caps.

Fred

 

[Jan Panteltje]

I see my Chinese amp simply uses a _huge_ torroid, 250W? ...... and normal transistors,

a temp controlled fan, stereo, all in a nice 19 inch rack, with separate volume controls
for left and right, with clipping warning indicator LEDs, with power switch, cinch AND XLR
connectors on the back....

So here are some pictures from the PA3000 inside, the transformer is 220VA.

Discrete is simple and no, it is not MOSFETs, the power transistors seem to be
2SA1943 (PNP) and 2SC5200 (NPN).

 

[Fred]

So here are some pictures from the PA3000 inside, the transformer is 220VA.

Discrete is simple and no, it is not MOSFETs, the power transistors seem to be
2SA1943 (PNP) and 2SC5200 (NPN).

Pictures, what pictures?

What is this equation called V * T = C * I, and what is is supposed
to do?

I is supposed to make sure the output maintains a certain amp
capacity?

I've been reading that calculations of ripple current a really just a
technical excersise, because the ESR of both the filter caps and the
transformer will only be know after build time. The rule of thumb
that was presented was to size the filter caps with an ESR rating of
about 3.5 to 4.5 the output current depending on the size of the
transformer.

On the capacity side, were the sightly contradictory suggestions of
aminimum capacity to reduce ripple voltage to <= to 10% of supply
voltage, and 2000uf per ampere of output current.

Fred