Hey guys, I'm new to the forum. I haven't been working with electronics very long and I have just started building simple amps from schematics I find online. i'm planning on using a tda2050 for a surround sound system. The last thing I built was a portable amp powered by a small 12 volt battery, but this new amp needs around 20 volts and I would like to be able to plug it into the wall.

So, what's the best way to reduce the voltage from a wall outlet so I can get 20v safely running to the amp?

Thanks!

 

Plain 120VAC:24V transformer + rectification, filtering and a regulator. The thing is that IC needs both + & - 22V max to get the maximum output but will run as single ended.

I hate to say it but I think there are quite a few better ICs out there. The THD is terrible.

I'm sure our local Guru will probably have a better suggestion.

Just offhand here's a few simple examples but there are better: http://circuitdiagram.net/50w-power-amplifier-with-ic-tda7294.html
http://www.national.com/appinfo/audio/files/BPA-200_Application_Note.pdf

Darn, I really do like that National IC idea now that I've read a bit through it.

 

http://diyaudioprojects.com/Chip/DIY-TDA2050-Hi-Fi-Chip-Amplifier/
This has +25V and -25V power supply to go with TDA2050 amplifier.

 

Yea, but that TDA2050 is 10% THD

 

What about the TDA1514?

 

Yea, but that TDA2050 is 10% THD

Read the datasheet!
All amplifiers produce 10% distortion when the volume control is turned up too high so the amplifier is clipping its head off. It makes the power number appear to be higher. If the volume control is turned up so high that the output is square-waves then the power number is double what it is when the amplifier is barely clipping with low distortion. Most amplifier ICs have their power number shown when the distortion is 10%.

The datasheet for the TDA2050 shows that with an 8 ohm load and a plus and minus 22V supply the power output is 32W when the distortion is 10%, the power output is 25W when the distortion is 0.5% and the output power is 22W at 1kHz when the distortion is typically 0.03%.

The LM3886 is an excellent amplifier IC that is newer than the TDA2050.
Its datasheet has graphs of power output vs distortion and one graph shows the output power is 85W when the distortion is 20%, the output power is 75W when the distortion is 10% and the output power is is 60W at 1kHz when the distortion is only 0.002%.

 

You're right but it does seem to be a chip that claims to be the best thing since rice crispies when I know there are tons of others out there now that do so much better even from a single ended supply which can be far friendlier to the beginning hobbyist.

The LM3886 are nice amp ICs but I think if I ever build anything new I'll be going with true Class D or tube monsters but I've got more high end audio gear around than I'll ever use in practice. I figure that if I crank my high current H-K up with full JBL towers for the fronts, large JBL bookshelves for the rear, one of their better centers and something like a 300W powered sub of theirs placed out properly and equalized to the room (which came out to be virtually flat anyway) it's far more than I'll ever need for the main system as you can hear it a block away. Worked great out in the country when I had to mow a couple of acres, around here it's just overkill but at least with most of the high end JBL or Infinity speakers I've used or specified over the years they still sound just fine at lower volume levels.

I sure did enjoy that article I linked from National about using the LM3886 in parallel, they even kindly included a parts list at the last page for the high power design they came up with. I think it's a great candidate for a hobbyist even if you simple use them as singles.

http://www.national.com/mpf/LM/LM3886.html#Overview

Description

The LM3886 is a high-performance audio power amplifier capable of delivering 68W of continuous average power to a 4 load and 38W into 8 with 0.1% THD+N from 20Hz-20kHz.

The performance of the LM3886, utilizing its Self Peak Instantaneous Temperature (°Ke) (SPiKe™) protection circuitry, puts it in a class above discrete and hybrid amplifiers by providing an inherently, dynamically protected Safe Operating Area (SOA). SPiKe protection means that these parts are completely safeguarded at the output against overvoltage, undervoltage, overloads, including shorts to the supplies, thermal runaway, and instantaneous temperature peaks.

The LM3886 maintains an excellent signal-to-noise ratio of greater than 92dB with a typical low noise floor of 2.0µV. It exhibits extremely low THD+N values of 0.03% at the rated output into the rated load over the audio spectrum, and provides excellent linearity with an IMD (SMPTE) typical rating of 0.004%.

Can't argue with this chip either: http://www.national.com/mpf/LM/LM4780.html#Overview

and either will operate with a single supply so long as you can get a half decent voltage to them. There are .pdf links to the full data sheets in the upper right corner of the overview pages I linked to. Having the built in advanced protection features is a blessing to a beginner, just wish they'd have included some PCB diagrams but I'm sure many have built with them so there are probably plenty to be found on the internet. Neither require a ton of external components which is also a plus.

 

The LM3886 IC costs only $7.30 at Digikey today. They have nearly 10,000 in stock.
A guy in New York makes a stereo amp using two that sells for $4000.00.

 

The LM3886 IC costs only $7.30 at Digikey today. They have nearly 10,000 in stock.
A guy in New York makes a stereo amp using two that sells for $4000.00.

$4k may be a bit overkill depending one what he is using for an enclosure, such as pure silver heatsinks or something.

The part that most people forget about amplifiers is 50% or more of the board space and components will be in the power supply for a good amplifier. If you start out with a crappy/saggy power supply, no matter what IC you use, you will have crappy sound.

 

So, what's the best way to reduce the voltage from a wall outlet so I can get 20v safely running to the amp?

Thanks!

Like the guys have said, you're going to need a good power supply with + and -20v rails, you might think about building that in a seperate case because it's always handy to have a good power supply available.

And you really must think about the case for the amplifier because that might affect the size of the transformer/design etc.

Another point, the 2050 sounds OK with a decent power supply, perhaps not so much when the wick is turned up. So if you invest in a decent transformer, perhaps the 2050 is not the best choice. And another problem, the 2050 suffers from "wide sample variation". I build novelty amps with recycled components and mount them in tin-cans or some novel container, I've used most of the TDA's up to 2050, they're ok for Television sound and surround sound but not for serious hi-fi.