DIY LM1875 Gainclone Amplifier (Part 4) The Amplifier Section

This is my first post that showing the steps of making this Gainclone amplifier by point-to-point connection between components. The inspiration to making the amplifier like this is when I saw the internal of the vacuum tube amplifier. I just thinking why I cannot do the same with the solid-state amplifier?

So here it is, the building process of the amplifier section by point-to-point connection.

To make connection between components by this method is need steady hand and experienced to work with small parts. The most important is using brand new components and preferable have a long leads for easy connection to others components.

I continue to this build, the first step is attaching the resistors to the main component is the LM1875. The first resistor attached is the 22 kilo ohm for feed-back resistor. I am doing it by bending the lead of feedback resistor like the photo below.

Then I solder it directly to pin 2 and 4 of LM1875.

The next components to install is the series 1 kilo ohm resistors and 22 uF capacitor.

They will be install like the photo bellow.

The next step is install the components for the Zobel network. They are the series of 1 ohm resistor with 100 nF Wima capacitor.

I need something sticky to keep the Zobel capacitors on its position, then I am using Faber Caster - Tack It to attach them on chassis. It stick firmly to the chassis.

The next step is installing the input resistors, 22 kilo ohm and I bending them just like this.

I joint the input resistor to the pin 1 and the other to the ground. This pin 1 will be the signal input point.

Next step is preparing the power supply capacitor, parallel with Wima capacitor 100 nF.

Now it will be much interesting. The space is become limited, while the components installed are become larger.

The last step is installing the input capacitor which the biggest of all components installed before.

At this point, the amplifier circuit is all done and ready to connect all the wires to the input and output terminals.

Previously I have installed speakers cable to the switch and connectors, then I will joint them to the pin 4 of the LM1875 as the speaker output.

The power cable that connect between the LM1875 to the power supply using 3 stains of 18 AWG cable. They braided together not just to look nice, but this will minimized the noise from the cables.

Each channel are have their own power cable to make sure the power transfer are both optimal.

The power cables goes to pin 3 and 5 of each LM1875. This section is very critical and required attention for the correct polarity and avoid short circuit.

All power supply cables are now installed perfectly.

The last step is connect the signal input cable. I will using the Canare cable L2B2A series.

Each channel using single cable for minimal cross-talk between channel.

Then I connect to the potentiometer for the volume control before to the LM1875.

Connect the output from potentiometer to the input capacitor in at the LM1875. At this moment, this amplifier is totally finished.

I powering ON the amplifier, put the multi meter to check the DC output at the speaker terminal.

Left channel has -20 mV which is very low DC offset.

Right channel show about -32 mV which is also very low DC offset.

This project is now done and ready to put in my audio system.

This is a beautiful amplifier inside-out.

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.