Transformer flux imbalande solutions

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Reminds of when as a kid i saw an amplifier rated at 100 W that was 2" by 5" BY 8". Then i saw that the rating was PMPO. But that was 40 years ago. A lot of such ratings today are "marketing magic" of the same kind

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Not to be picky or anything, but who uses an output transformer any more? High output units? Who can dissipate hundreds of watts inside a dashboard?

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Yup, and a large chunk are engineers.

Wow, I didn't know they used PMPO that long ago. That's hardly out of the tube age. I thought marketing was just discovering "watts RMS" back then!

Just to be sure, we've been talking about the switching supply's output transformer. But actual audio outputs? Those went out of style in the

Last beast I saw with real iron must be my dad's Mcintosh something power amplifier -- good for over 300 real watts into any kind of load you want. He bought it in the 70s. They put autotransformers at the end, so the amplifier always drives around 3 ohms, and you can connect anything from 2 to 32 ohms.

One might theorize this is the reason why Mcintosh hardware sounds "so good" (in the tubophile sense) -- the only fundamental difference between your average tube and SS amps is the output transformer.

Well, those 1kW+ amps are fairly hunky, and they have a lot of aluminum to hold in the heat from peak loads (class B giving ~60% efficiency, that's easily 1.6kW input and 600W dissipated). Definitely not continuous duty, last one I saw used fullpack TO-3P outputs. Hardly 50W capacity in one of those. There were 8 of them, not quite enough for all that dissipation, especially after ten or twenty seconds when the chassis starts getting really hot.

But that's more of a floor-of-the-trunk environment, too. I don't know if they make in-dash radios over 50W (being the 12V bridged into 4 ohm rating).

Tim

Naah... in some ways, that was the "pyrite age" of PMPO ratings. Fantastically-optimistic PMPO ratings were common, especially in lower-end-of-the-market consumer stereos.

PMPO ratings became less common after the FCC enacted the regulations which stated that home-audio amplifier power ratings were required to be in RMS-continuous-into-8-ohms, with well-specified test and warmup conditions.

PMPO (or equivalent) continued to be used for car-stereo amps, I believe, and in more recent years a lot of computer-type "amplified speaker" systems have used them.

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Why are you jerking us around, never mind, you are just a jerk.

Naw, not until the 1970's

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Transformer? Who do you think you are.

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rating).

I built such an amplifier set for my '77 280Z. With a bridge each for left and right, it's quite nice! I used a Panasonic AM/FM tuner as the front-end.

...Jim Thompson

The 12V is actually 14.5V, and the ICs typically go within 1V from the rails. So "12V BTL @ 4 Ohm" is about 19.5W of the undistorted sine wave. They usually specify the power at 10% THD, which makes the nice looking number of 25W.

The problem with the boosted rails is that it is very difficult to pass the conducted EMI requirement for the OEM market while keeping the cost and size reasonable. I made the amp with R-R output; it makes 100W into

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

I specify my stuff at "real" power, sitting still, car not running. Besides, in AZ, car running, temperatures as they are, "12V" is usually only about 13.3V.

I was driving a pair of 6" x 9" ovals

BTW, Distortion of approximately 0.003% ;-)

I didn't boost, I bridged ;-)

...Jim Thompson

At what frequency? :-) Besides, this number probably indicates the deep feedback; every audiophile knows that the feedback is very bad :-)

Do you know of any special reason why they don't make the R-R ICs for the audio amplifiers?

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Except it wasn't. I have _the_perfect_ AB bias scheme that I disclose to no one, so don't ask. (It was really the Monster Cables that made the difference ;-)

I have no idea. Haven't been involved in audio since around '85, when I was designing sub-bass systems for discos ;-)

...Jim Thompson

But, wait! Those are *audio* watts, and you're talking "regular" watts. Audio watts are like regular watts on steroids, so you get to use much bigger numbers. :-)

Ed

...Jim Thompson

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As far as i know they have been for many years. However doing a rail-to-rail power amp for automotive use sounds challenging. You may be up for it, but i am not.

And besides, that's 36W square wave. It's still "RMS", so it can still be sold as "watts RMS", eh? ;-)

Oh, and don't forget "Sears Watts"!

Tim