Making Amplifier With LM1875

The Audio amplifier is the most favorite circuit category for me in my electronic DIY activities.

Because it's a very useful device for everyday life while viewing YouTube materials or playing MP3 files with a PC.

Therefore, I had introduced several amplifier circuits in the previous Instructables.

Here, I'm also showing one of the basic and small output power (Around 20Watt) of an audio amplifier using LM1875.

Previously introduced amplifiers are utilizing now obsolete TDA2030 and TDA2050 audio power amplifier IC chips.

But LM1875 is still produced by Texas Instrument and the component is easily purchased from any online or offline shop.

Also, many DIYers are suggesting their ways of audio amplifier making ideas with the chip.

Among the many ideas for making divers amplifiers, I'm utilizing the circuit introduced on the following website (Elliott Sound Products).

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https://sound-au.com/project72.htm

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Used to I had made several transistor amplifiers that are introduced on the website.

Also, very detailed technical explanations are available along with schematics of the audio amplifier circuit.

Let's look at more details of the audio amplifier.

As the schematics of the amplifier and power supply circuits in the Elliott Sound Products webpage, it's not a complex amplifier as seen in the drawings above.

With LM1875 and several common RLC components, you can easily make the power amplifier by yourself.

The followings are key and noteworthy parts of the audio amplifier.

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-     2.2uF coupling film capacitor (More than 100V)

-     220pF mica (or ceramic) capacitor for bypassing RF interference to ground

-     20K dual-gang potentiometer for volume control

-     0.1uF film capacitors for power supply bypassing and Zobel network support

-     220V input and dual 15V AC output toroidal transformer

-     4,700uF AC power filtering electrolytic capacitors

-     Diode bridge rectifier

-     And other Resistors and Capacitors included in the schematics

-     Universal PCB, metal supporters, bolts/nuts, and Acrylic boards

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When comparing other LM1875 amplifier circuits, the schematics I used require relatively less number of components for making the power amplifier.

Someone said making the LM1875 amplifier is a kind of schoolish project.

As he means, this chip supports a very typical power amplifier circuit making.

Although the circuit is simple and common, the outcome of the project is not simply fair as it can drive a 4ohm or 8ohm speaker with a powerful output.

Although many analog audio IC chips support 10~20Watt are obsolete, LM1875 is the last survivor and seems very stable for manufacturing and distribution to end-users.

I had made two amplifier units with the chips.

By utilizing different RLC components, the sound quality between the two amplifiers seems a little bit different.

One uses the Vishy 2.2uF coupling capacitor, WIMA film capacitors, and the audio quality of 4700uF capacitors produces crisper and more powerful sound than the other.

When other schematics are used, I suppose more interesting results can be attained and experienced.

As shown amplifier circuit using TDA2030, the overall wiring diagram is similar for the LM1875 as shown in the previous Instructable.

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https://www.instructables.com/Audio-Amplifier-Using-TDA2030A/

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The wiring diagram above is used for the amplifier that sound quality is a little bit low than another.

Maybe the reason for the amplifier producing less sound quality is that probably I had used salvaged common RLC components from other old amplifier circuits.

When you look at the YouTube videos about sound quality comparison among TDA2030, TDA2050, and LM1875, usually slight oscillation is created by LM1875 at high note audio signals.

I'm supposing that symptoms are increasing when you use comparatively less quality RLC components for making amplifier.

As shown in the previous Instructable, I'm using the same split (+19/-19V) power supply circuit for both LM1875 amplifiers.

The sound quality of the other LM1875 amplifier is crispier for the high note audio signals and likely heard more dynamically.

For making this better sound supporting amplifier, I had used brand new and higher quality RLC components.

The picture above is showing the wiring result of a less performing amplifier.

I remember the Solen coupling capacitors are soldered to a certain amplifier and subsequently desoldered for reuse.

The most of RLC components are salvaged from other old amplifier circuits.

By several times of soldering and desoldering, excessive heat is supposedly degrading the quality of these RLC components.

As a result, the overall sound quality of this amplifier is a little bit less performing than the other.

As details about amplifier components wiring and assembling methods are explained in the previous Instructable (Audio Amplifier Using TDA2030A), I will not mention the same contents in this story.

The overall sound quality of the other LM1875 amplifier is better such as resolution (detail of sound) is the more clear and highly dynamic rhythm of hip-hop songs is replayed more actively.

I'm comparing the sound quality of two LM1875 amplifiers by interfacing the SELECTOR circuit that is explained in the previous Instructable.

For making the medium power (> 25Watt) range of amplifier, maybe this project can be the last one.

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Thank you for reading this story.