A stupid idea

[DcibeL]

I was thinking of this idea the other day and I am no expert at amplifier design, but I can't think of any reason why this wouldn't work. For a high power amplifier design, what if it didn't have a transformer?

What if I took the 120V straight from the wall, rectified it, filtered it, and designed an amplifier around the resulting rail voltages. The end result would be a high power amplifier that would be cheaply build due to the lack of one of the most expensive parts, and it would also be smaller and lighter for easy transportation.

Would this be a stupid idea? I just figured that there would have to be something wrong with it if nobody has built one yet.

[SY]

Deathtrap. Deadly, deadly dangerous. Don't even think about it.

[ocool_15]

Originally posted by SY


Deathtrap. Deadly, deadly dangerous. Don't even think about it.

I've heard that too, Youd have (120Vx1.414)-.6=169V DC so 85V rails. I think that would mean more signifigant power disipation on the output stage (especially at lower volumes)if im correct....

Correct me if I'm wrong that tube amps often run at higher voltages? They have a transformer ect to limit current of course.

[Stocker]

To elaborate a bit:

In a common amplifier with an isolation transformer, if the following failure modes occur, the worst that happens is you blow a bunch of transistors or fuses:

Power lead short to ground or chassis(forgot/overlooked in wiring)
Circuit failure leads to output swinging to one power rail
power rail shorted to output terminal (don't laugh it can happen)

In the proposed power supply topology, all these lead to mains voltages AND current capabilites on either the chassis or the speaker wires (or speaker chassis)

= death to touch an innocent-looking piece of kit.

avoid.

[Variac]

If it makes you feel any better, this idea comes up every 6 months.
BUT its not worth dying for!!!

[ActiveX]

How if one can use electronic transformers which are used for Halogen lamps, usally they are cheap and easyly available in locally, they range from 50W to 100W.

[Eva]

If transformer-isolation is not used for the power supply, then it must be used for each signal input and each speaker output due to safety issues. So, actually, there is no advantage in supressing power supply transformer.

Furthermore, you will have to buy expensive mains isolation transformers in order to experiment with and test such an amplifier. Note that you can't connect an oscilloscope directly to live circuits (due to ground issues), and that multimeters give erratic results when measuring on high-impedance or small-signal live circuits (this happens due to unexpected capacitances from probes and multimeter body to earth).

The way to go for light weight and small size in high power amplifiers is switched mode power supplies. They allow for very small PSU transformers while still providing mains isolation and other useful features.

[jacco vermeulen]

Originally posted by DcibeL
What if I took the 120V straight from the wall

I still dont understand why the member count of this forum is going up, not down !

Ever considered the transformer to be a big help in keeping the rotten stuff out ?
Fools like me even use several giant isolation transformers to prevent all kinds of weird frequencies entering audio circuits.
It's not every 6 months, more like every 2, why not tell 'm to go for it next time ?

[SY]

why not tell 'm to go for it next time ?

Though there is a certain Darwinian appeal to that, there are certain foul objects known as "lawyers" who make a living collecting money from others for the stupidity of their clients.

[jacco vermeulen]

Originally posted by SY
there are certain foul objects known as "lawyers"

Partypoopers
Suggestion : as from today every person asking this question will be considered a lawyer !

Eva darling,
can you tell me if it is possible to connect a 3-phase toroidal transformer to single phase 220 volts ?
(on several switchboard fuses of course, they are 5000va models)