Diy stereo amplifier with laptop charger

Hello all,

If we build a DIY stereo amplifier class AB, and if we use a regular Laptop Charger as power supply, what is the maximum power (watts) per channel we can get ???

Secondly, is ther any disadvantage in terms of audio quality by using laptop charger as power supply ??

Thanks in advance,
Naveen
 
Hello all,

If we build a DIY stereo amplifier class AB, and if we use a regular Laptop Charger as power supply, what is the maximum power (watts) per channel we can get ???

power == sqr(Vrms) / load

If you run it single ended ...
approximately (19v / 2) X .707 == 6.7 volts RMS
(6.7 X 6.7) / 8 == 5.6 watts.

if your run it in BTL mode ...
19v X .707 == 13 volts RMS
(13 X 13) / 8 == 22.5 watts.

Secondly, is ther any disadvantage in terms of audio quality by using laptop charger as power supply ??

If you mean "external SMPS power supplies" my answer is "Yes".

The thing is that SMPS (Switch Mode Power Supplies) work at relatively high frequencies and are tightly regulated. So you are getting high purity DC that does not ripple or hum under load.
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
Laptop power supplies are generic quality SMPS devices with an emphasis on reliability - but perhaps only for a few years in constant daily use. They can work fine with audio devices provided that there is adequate input filtering to reduce the likely high frequency switching artefacts remaining on the DC. There are already quite a few HT amplifiers and good quality amplifiers of class D, AB and even a few class A amplifiers that come with SMPSs and have been for quite some years. There aren't many reasons why you can't use them other than the limitations of their power rating and single polarity, fixed 19V supply.

However, they do generate a lot of switching noise and it's hard to attenuate once it enters the metal case of even a well constructed amplifier. Filtering the DC output first, can begin with something as simple as clipping a large ferrite suppression bead on the cable or better, by constructing a proper low-pass filter and also fitting that before it enters the amplifier's metal shield case. Filtering the HF hash of a SMPS
 
However, they do generate a lot of switching noise and it's hard to attenuate once it enters the metal case of even a well constructed amplifier.

That's why you use an external supply. The switching noise is thus, not in your equipment's cabinet.

Take an RF Sniffer and scan it around the newer SMPS bricks... they're pretty darned quiet these days.
 
Definitely i will drop the idea of using a laptop charger. I'm looking forward to get a DIY amp made with around 50w per channel. And i don't want to compromise on audio quality.

Thank you so much all of you for detailed explanations !!!!

A 24 volt supply running BTL amplifiers (lots of AB and D chip amps around for that) will give you a very reliable 35watts on 8 ohms or 50 on 4.

For example... THIS little guy will give you a very clean 35 watts per channel, all day long, at about .01% distortion with a -3db response from 8hz to at least 30khz. And it runs on a 24volt brick.

The audio world is changing, good audio is getting cheaper... and cheap audio is getting better.
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
I think the 50W amplifier the OP is planning on will likely be a traditional, discrete class AB DIY design that needs around +/- 30V supplies for 50W/8R. A dual rail SMPS is certainly doable with some adjustable modules that are available online but this opens a safety issue, covered generally in note 3 of the forum rules. What do you say, Naveen?