DIY Smallest LM1875 Gainclone Amplifier

In this post, I will share the building process of the smallest LM1875 Gainclone amplifier. This is including the toroidal transformer in one casing. To make this amplifier looks simple inside, I will not using any PCB, instead all components connection is done by point-to-point wiring. Let's take a look shall we?!

 

This amplifier will build using the high quality components such as Takman resistors, both WIMA MKS and MKP film capacitors, and Panasonic FC capacitors for power supply capacitors and the Elna Silmic for signal coupling capacitors.

Because the secondary output from the toroidal transformer are 2 separate AC 18 volt, I shall mention about the rectifier diode bridge using here is quite special. There are 2 rectifier diode bridge that each rectifier handle for one single supply AC from the toroidal transformer. Then the DC output from the rectifier are combine together to become dual differential fully rectifier DC output.  This will assure the output DC are more cleaner compares to using the single rectifier diode and central-tap transformer design.

 


I am using pure solid cooper wires for all internal cables. The reason for this is I found using solid wire will give better sound quality compares to the multi strands cable.

In the photo above also show the big brown capacitor on the left side of each LM1875 are the signal input coupling capacitor using the new-old-stock Japan made Elna Silmic ARS. Although they are rated only 2,2uF/50v but the size are huge compares to the bottom capacitor which also from Elna Silmic, the newer production from Thailand which is smaller but rated way larger, about 22uF/50v. The reason I using this big Elna Silmic ARS for input coupling capacitor is because it sound better compares to the new production Elna SIlmic capacitor outside the Japan manufacture.

The toroidal transformer I am using here is the 200 VA rating, dual 18 volt secondary output. The weight for this transformer is about 3 kg and it is imported. The sound quality of the amplifier is really determine from what power supply components you are using. 

 

After the main components are installed, then the next steps is installing input output terminal along with the cables.

 

To make this amplifier look sleek and simple, I am using the volume control potentiometer that built in the power ON-OFF switch. This potentiometer is the new-old-stock from Panasonic Matsushita potentiometer.

 

I also make a simple delay circuit relay for speaker output to prevent pop noise when powering ON OFF this unit. This pop noise is a typical issue for every LM1875 amplifier.

This amplifier build is almost finish. It takes so many hours which I didn't notice that the sun start to dawn.

Look how small this amplifier size comparing to a CD case above it. This is a nice looking amplifier and the sound quality is wonderful.

 

Disclaimer: Any statement and photos in this article are not allowed to copy or publish without written permission from the writer. Any injury or loss from following tips in this article is not under writer responsibility.