personal audio amp

[baftab]

here is the schematic
wat type of amplifier is this IC??

 

[madmikejt12]

here is the schematic

there is nothing posted :?: :?:

 

[audioguru]

That audio amp has the lowest noise and distortion that I have ever heard. (Seen?)
As audiophiles say, its sound is very transparent! :lol:

Even if we could see its schematic, what is an amplifier's type?
1) Cheap or expensive?
2) Lousy or excellent?
3) Tooobes (valves) or solid-state?

We will just wait for its schematic to be attached then see that it is a Cmos inverter self-biased as a linear amplifier or sumpthin'

 

[baftab]

i found its data sheet
it is a Qusai AB type amplifier

will this circuit work?
i'll start working on it from tomorrow

can u explain its working a bit?
the 2 capacitors in parallel..what is it called?

 

[Nigel Goodwin]

i found its data sheet
it is a Qusai AB type amplifier

As are the vast majority of transistor audio power amplifiers. The circuit you posted actually uses two amplifiers in a bridged configuration, to give twice the power to twice the impedance of a single amplifier.

will this circuit work?
i'll start working on it from tomorrow

I don't see why not?.

can u explain its working a bit?
the 2 capacitors in parallel..what is it called?

It's called two capacitors in parallel! :lol:

It's done because the decoupling effect of the large electrolytics will be less at higher frequencies, so adding a small non-electrolytic capacitor in parallel can improve decoupling at high frequencies.

 

[audioguru]

The LM3875 is an excellent audio amp IC. Look at its product folder:
**broken link removed**
In the folder is a link to its datasheet that you should have. It has details about heatsinks and stuff. :lol:

 

[baftab]

thnx guru

 

[baftab]

dual power supply
how will i check my project at home?
i hav a dual power supply in univesity...
not at home....
ne shortcuts?
or how do i design a +-25 volt power supply?

 

[audioguru]

Why use shortcuts when building an excellent power amplifier?
If its supply was a single polarity the the amp would need the problems of a huge output coupling capacitor.

Wait a minute! This is a bridged amp. It will work fine without an output coupling cap if you properly bias the inputs so it can use a single +50V supply. It might have a pretty big "bang" when it is turned on or off unless you plan to have its input coupling cap charge and discharge slowly.

I started reading all the artilces and comments about these "Gainclone" amps on the web. Some are hillarious.

 

[audioguru]

The 2nd amp amplifies the distortion of the 1st amp, so maybe the 2nd amp should be inverting and get its input directly from the input. :lol:

 

[Nigel Goodwin]

Why is the very bottom resistor 24K?.

 

[audioguru]

Why is the very bottom resistor 24K?.

Hee, hee. :lol: What 24k resistor? :lol:
The original was wrong.

 

[baftab]

ok..i am making a dual power supply for it too
it'll earn me more marks

i found a schematic for it

if tht output is less than 25 say...23 or 22..will by power amp work?
or should i make a supply with a wider range? say till + - 35?
how can this one be improvised?
using a higer rating transformer?
ne other changes?

 

[Nigel Goodwin]

ok..i am making a dual power supply for it too
it'll earn me more marks
i made a dual power supply before....but..it is 15 to -15 volts
any way of improving it so tht it could work from +25 to -25?

You only need a very basic supply, just a center tapped transformer, something like 18-0-18 (bit too high) or 15-0-15 (bit too low), a bridge rectifer, and two large electrolytics.

 

[baftab]

check the schematic i attached...is it fine???

 

[audioguru]

ok..i am making a dual power supply for it too

if the output v is less than 25 say...23 or 22..will by power amp work?

Its datasheet shows how much lower its output power will be with a lower supply voltage.

should i make a supply with a wider range? say till + - 35?

Its datasheet shows how much higher its power supply current will be and how much more its output power and heating will be.

how can this one be improvised?

I don't know since you are just copying the circuit.

using a higher rating transformer?

You must plan the entire design of a power supply, not just its voltage.
The datasheet shows that with a 50V supply, two bridged LM3875 ICs driving 80W into an 8 ohm load causes the amps to heat with a total of 66W. That heat must be dissipated by a huge heatsink.

Since 66W must be dissipated as heat and an additonal 80W is dissipated by the load then the total power from the power supply is 146W.
Simple arithmatic shows a power supply current of 2.92A which is way higher than the max from the little regulators in the power supply circuit you found.

Why use regulators? They aren't needed with a huge 37V/4A transformer and 10,000uF of filtering. The amp won't be operating at max power continuously so a 2A or 3A transformer will be OK. Double its current for stereo.

 

[Nigel Goodwin]

check the schematic i attached...is it fine???

You don't need anything in that circuit to the right of the two 4700uF capacitors, and you need a lower voltage transformer as I mentioned above.

A 15-0-15 transformer would work fine.

 

[audioguru]

The circuit will drive an 8 ohm speaker to 60W with a 15V-0-15V transformer and the supply current will be 2.4A max. A 50VA to 100VA (1.7A to 3.33A) transformer would be fine.

 

[baftab]

i made the power supply and it works +35 to -35

but...but...i counldnt find the IC LM3875 so tht project is no more
now am looking for something else to submit to my professor
10 watt amp or a 20 watt amp....easy to make as i dont hav much time left saturday is the date for submission

 

[Nigel Goodwin]

i made the power supply and it works +35 to -35

I thought you wanted +25V and -25V?.