Weird Science

Constructing a Simple Audio Power Amplifier

Polish ver­sion is here

If you’re a begin­ner elec­tro­nics hob­by­ist, buil­ding even a sim­ple ampli­fier like the one pre­sen­ted in this article can be an excel­lent lear­ning expe­rience. This cir­cuit can serve as your first fully func­tio­nal, self-built audio power ampli­fier. It can also be use­ful for various expe­ri­ments descri­bed on this site. I enco­u­rage you to explore this stra­i­ght­for­ward design, which is based on linear inte­gra­ted cir­cuit tech­no­logy.

For more prac­ti­cal appli­ca­tions, the pro­vi­ded sche­ma­tics allow you to build fully ope­ra­tio­nal and effi­cient ampli­fiers. They are sui­ta­ble for use in car audio sys­tems (the inten­ded appli­ca­tion of the IC) and can also serve as repla­ce­ments for dama­ged power ampli­fier sta­ges in com­mer­cially pro­du­ced audio equ­ip­ment.

Let’s Get Star­ted!

The ampli­fier pre­sen­ted here is sim­ple because most of the essen­tial com­po­nents are inte­gra­ted into a sin­gle IC. As a result, it requ­i­res only a few exter­nal com­po­nents. The IC used is the TDA­7377.

Ilustracja

Source: http://www.don­berg.fr/pics/t/tda_7377.jpg, acces­sed: 01/23/2015

A deta­i­led descrip­tion with spe­ci­fi­ca­tions can be found in the data­sheet ava­i­la­ble here. Let’s look at the dia­gram sho­wing its inter­nal struc­ture:

Ilustracja

As you can see, the TDA­7377 actu­ally inte­gra­tes four sepa­rate ampli­fiers! Nota­bly, two of these ampli­fiers have non-inver­ting inputs (+), while the other two have inver­ting inputs (−). This design allows for various ampli­fier con­fi­gu­ra­tions. Addi­tio­nally, the IC inc­lu­des a standby input: when con­nec­ted to gro­und, it disa­bles the ampli­fier. For con­ti­nu­ous ope­ra­tion, this input can be con­nec­ted to the posi­tive sup­ply rail.

The input con­fi­gu­ra­tion (inver­ting and non-inver­ting) allows you to easily build three dif­fe­rent ampli­fier types:

The data­sheet inc­lu­des exam­ple appli­ca­tion cir­cu­its that you can fol­low. I powe­red my ampli­fier with a 12V sup­ply, but 18V is more sui­ta­ble for higher per­for­mance. The power sup­ply sho­uld deli­ver suf­fi­cient cur­ren­t—at least seve­ral amps.

4-Chan­nel Ampli­fier

Ilustracja

This cir­cuit requ­i­res only a few exter­nal com­po­nent­s—just a hand­ful of capa­ci­tors and pos­si­bly a resi­stor. It can be used to expe­ri­ment with sim­ple sur­ro­und sound sys­tems.

Brid­ged Ampli­fier

Ilustracja

In this con­fi­gu­ra­tion, each spe­a­ker is con­nec­ted between the out­puts of two ampli­fier­s—one inver­ting and one non-inver­tin­g—ra­ther than between an ampli­fier out­put and gro­und. This results in a gre­a­ter vol­tage swing across the spe­a­ker and, con­se­qu­en­tly, much higher power out­put. Out­put capa­ci­tors are not nee­ded in this design.

Ste­reo Ampli­fier with Brid­ged Sub­wo­o­fer

Ilustracja

This cir­cuit com­bi­nes the pre­vious two: two ampli­fiers ope­rate in stan­dard mode, each dri­ving a spe­a­ker, while the other two are con­nec­ted in a brid­ged con­fi­gu­ra­tion to deli­ver suf­fi­cient power to a sub­wo­o­fer.

Test Cir­cuit

I nee­ded a sim­ple ampli­fier for some expe­ri­ments, so I chose the TDA­7377 in its brid­ged ampli­fier con­fi­gu­ra­tion. It per­for­med so well that I’ve used it repe­a­te­dly since then (and still do). The pro­to­type was built on a piece of per­fbo­ard:

Ilustracja:

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The large fil­te­ring capa­ci­tor is pro­mi­nent in the fore­gro­und. The rema­i­ning capa­ci­tors are either par­tially hid­den under the heat­sink or moun­ted on the under­side of the board. The black wire is gro­und, the red wire is the power sup­ply input, the white and blue wire pairs are the two out­put chan­nels, and the input signal is sup­plied thro­ugh a thin twi­sted-pair cable visi­ble at the rear. A heat­sink is essen­tial at higher power levels, tho­ugh even then, the IC doesn’t gene­rate exces­sive heat.

Enjoy expe­ri­men­ting with this edu­ca­tio­nal and prac­ti­cal pro­ject! :)

Fur­ther rea­dings:

Marek Ples

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