Power Supply +-50V @12A?

[pandaemonium]

I'm in the process of building an audio amplifier and I need a power supply for it outputing +-50V @12A. What I'd like to do is avoid using huge, heavy and expensive transformers. Does anyone know of a reliable switch-mode circuit? Maybe someone has another suggestion?

 

[audioguru]

Hi Panda,
Why such a high current?
Only 100V will power an amp that produces 140W at clipping into 8 ohms, single-ended. Is the amplifier 4 or 5 channels like this?

If the amps are bridged, then they would produce about 500W at clipping into 8 ohms. Is the power supply for a mono amp like this?

Will you be operating the amp at clipping or beyond, continuously?
Then you must dig deep into your pockets to pay for a nice expensive torroid power transformer, if you can find one somewhere. :lol:

 

[pandaemonium]

Its two channels at 230W each in to 8 ohm, I won't be operating it at full output constantly, but it would be good to have the option to do so if I want.

 

[pandaemonium]

Oh, I just noticed that I miscalculated a little (+-) but I also calculated after rectification. around 6.5 amps will probably do. Thats better. But still, I would like another solution if there is one.

 

[Oznog]

Powered by what? 110VAC or 12VDC?

 

[pandaemonium]

110VAC.
I keep forgetting details, I should try sleep some time, I heard it works wonders.

 

[Nigel Goodwin]

Its two channels at 230W each in to 8 ohm, I won't be operating it at full output constantly, but it would be good to have the option to do so if I want.

To provide 230W into 8 ohms requires supplies of around +/- 70V, +/- 50V won't provide that much power.

BTW, why such a strange requirement?, I could understand 200W or 250W, but why 230W?.

The simple answer is to use a large toroidal transformer, and large capacitors - a switch-mode supply is going to be difficult and expensive to build. You might also notice that most quality amplifiers do it this way!, switch-mode PSU's for audio are still in their infancy.

 

[audioguru]

What kind of whats?
230 Whats "peak" or "maximum" power (like car radio marketers advertise) is 115 Watts RMS into 8 ohms at clipping, and is easy to get from a + -50V supply.
230 Whats peak music power (like some companys advertise, is with horrible-sounding 10% distortion and measured for only a moment) is possible from only a + - 33V supply. It is really only 60 Watts RMS at clipping ino 8 ohms.

Watch out for your mains voltage. My "110V" measures 121V and is supposed to be 117V nominal. Most transformers over here are rated with 120V on their primary. :lol:

 

[pandaemonium]

Nigel: The 230W isn't a requirement, its an existing design, Ive always liked this amplifier, so I'm building another one now that I need another, and substituting the obsolete transistors and thought a different power supply would be nice. The original used a toroidal and two large caps. The total weight of this amp is 40 lbs. and is 7 inches high, so stacking a few quickly becomes problematic. I guess I'll just stick with toroidal transformers.

audioguru: The specifications are: 230 Watts continuous average sine wave power @ 8 ohms < 0.05% THD, @ 1 kHz. THD: 0.005% @ 50 Watts, 8 ohms, 1kHz. 0.01% @ 150 Watts, 8 ohms, 20Hz to 20kHz.

Oh, and my mains measures 115.1V.

 

[audioguru]

What are you going to do with 230 real Watts per channel?
It will blow off your clothes and your ears, just before your speakers blow up!
Bye, bye windows and your best leaded-crystal china!

Haven't you been following the Memorex cassette tape and now CDR commercials? :lol: :lol:

 

[Joel Rainville]

It will blow off your clothes and your ears, just before your speakers blow up!

I played guitar in a band a few years ago, and I ended up thinking I needed a 100 Watt tube amp in order not to be buried by the drums and the bass player. I got one. That amp was so loud the vibrations from it could move the drums across the room at 10Mph... I had to leave that amp at home :lol:

 

[audioguru]

Yeah, my computer speakers move fairly fast too. They have ports on the rear that puff with a lot of force. :lol:

 

[Nigel Goodwin]

I played guitar in a band a few years ago, and I ended up thinking I needed a 100 Watt tube amp in order not to be buried by the drums and the bass player. I got one. That amp was so loud the vibrations from it could move the drums across the room at 10Mph... I had to leave that amp at home :lol:

Valve/tube amplifiers are exceptionally loud, because they are commonly over driven and distorted, so a 100W amplifier will sound louder than a 200/300W transistor amplifer, because you can't over drive the transsitor amp (because the odd harmonic distortion sounds so bad!). However, the transistor amp will be a lOT! lighter to carry, and should be far more reliable!.

To match a drum kit, a 20W or 30W valve/tube guitar amp is plenty! - or you could just turn the 100W one down? - why can't guitarists find the volume control?.

Acoustic drums are usually considered to provide about 60W, for a recent TV recording of my daughters band **broken link removed**, we used purely acoustic drums, a 60W transistor amp for guitar, a 120W transistor amp for bass (bass needs more power than guitar!), and 400W (200W per channel for vocals). This gave a good balance, for a normal gig I DI (Direct Inject) the bass and guitar through the 400W PA, plus mike the drums through it as well.

BTW, the TV appearance is due end of September, beginning of October, on Sky One, as part of a documentry about 'Hoodie Culture' in the UK - hopefully featuring Easily Amused and 'The Hoodie Song' which my daughter Melissa wrote!.

 

[pandaemonium]

audioguru: Funny you should mention windows, the first time I used this amp (about 20 years ago), I figured, 230W a channel? so what. So I turned it up full to see what it would do. I guess the room I used it in was to small, because the frame of the window in the room popped apart and the window broke!

I did a modification on the amp and got it to go fairly clean down to 5Hz, thats why I want that much power. Mind you, it can be annoying when a sudden change in air pressure in a room causes your ears to pop.

 

[Joel Rainville]

To match a drum kit, a 20W or 30W valve/tube guitar amp is plenty! - or you could just turn the 100W one down? - why can't guitarists find the volume control?.

Why can't engineers come up with amps that sound the same at either full blown volume or bedroom pratice level?

That's basically why guitarists own multiple amps, because although there are master volume controls on all of them, touching that knob changes the sound so much it ruins the settings you took hours to set and adjust. So you buy different amps that driven hard enough will provide a suitable sound/volume ratio for different purposes/venues. Guitar amps that sound good at low volume are quite rare. And when they do, they usually sound even better at higher volumes

In some venues, you want your amp quieter so you don't overpower the PA, in others, you want your amp to compensate for the crappy PA. When you have the luxury of having a good soundman with decent equipment on site, more and more musicians will use some kind of D.I. box, which makes the whole band a lot easier to balance. You set your gain on the D.I. box, the soundman adjusts your volume, everyone's happy

I once did a show with my amp face down on the floor, miked from behind :lol: Sounded great actually.

 

[Joel Rainville]

BTW, the TV appearance is due end of September, beginning of October, on Sky One, as part of a documentry about 'Hoodie Culture' in the UK - hopefully featuring Easily Amused and 'The Hoodie Song' which my daughter Melissa wrote!.

Too bad I won't be able to see that. I love live music. We have a great 1h30 TV show of live music here in Quebec, once a week. Full blown rock band, sax, trumps, keyboard & piano, and invited guests, from the pro studio musicians no one even heard of, to comedians who can barely sing, to rock stars, to local songwriters... A show made in big part for musicians. Most non-musicians can't stand the long close-ups on individual players :lol:

 

[audioguru]

Is a "hoodie" a new kind of "hippy"?

 

[pandaemonium]

Engineers have come up with amps that sound the same at any volume level: The transistorized amplifier!

Alot of musicians use tube type amplifiers which distort nicely when over-driven. If distortion is the goal, and you don't like the sound of a good distortion pedal, then you can try a transistorized amp and an over-driven tube type pre-amplifier.

 

[Joel Rainville]

Engineers have come up with amps that sound the same at any volume level: The transistorized amplifier!

Indeed. They sound like crap from 0 to 10

Seriously, more and more transistor amps on the market sound just as good as big, heavy and expensive tube amps. I suspect tube amps will completely disappear in a very near future.

But for now, there are still a few generations of guitar & bass players you'd have a hard time convincing solid state amps are any good.

Line6 and Tech-21 NYC make very nice tube-like transistor-based products.

 

[Joel Rainville]

then you can try a transistorized amp and an over-driven tube type pre-amplifier.

Yep, like this one from **broken link removed**. Tried it once in a music store, pretty nice.