LM1875 Gainclone Amplifier With First Watt B1 Buffer Pre-amplifier

Building an amplifier is fun.

Like we are all into this hobby because it is fun. Especially when we can make something like this, we starting from the idea and planning, gather all components to make it a piece of, and when the result is beyond expectation, the excitement is deeper.

Same like the background when I plan to build this amplifier. I tried to combine the First Watt B1 buffer pre-amp with the Gainclone LM1875 amplifier. First, I like sound of the LM1875 amplifier and I also like the idea behind the First Watt B1 buffer pre-amplifier, is to lowering the output impedance to feed to the amplifier.

So how if they are combine in one box?

A short brief about this LM1875 amplifier, I think this is the most relaxing sound amplifier. The music presentation is very mellow and warm, at the same time it can be deliver fast and dynamic enough with maximum power of 20 watt per channel. More than enough for normal listening at home.

The First Watt B1 buffer amplifier is the simplest pre-amplifier design. It is using 2 JFET 2SK170 per channel and without feedback in the design. The goal when using this B1 is as per stated on the First Watt manual is to get the impedance matching between the input to the amplifier. As you might know that we want the lowest impedance to feed to the input of the LM1875 amplifier.

Building the amplifier like this is not always necessary involve with the hi-grade components. Like what I did it, it is using China made toroidal transformer, a combination from generic Taiwan resistors and Germany Roedenstein resistors, also WIMA MKP capacitor together with Elna electrolitic capacitors. For the power supply section, the filter capacitors is standard Panasonic type and the input capacitors is critical, is using Elna Silmic capacitor.

 

The amplifier and the power supply section are separate by aluminum heat-sink to minimize the noise from power supply section goes to the amplifier section.

We have two eye-catching capacitor there which they are oversized value capacitor far above the requirement from the First Watt B1 Buffer circuit power supply. They looks beefy in this amplifier.

I am using LM317 adjustable regulator power supply to feed clean DC voltage to B1 buffer circuit. The output is set to 18 volt as required by the First Watt B1 circuit.

When this amplifier finished, I test and thinking that this combination will generate little bit hum noise to the speakers, but in fact it is not. The amplifier is very silent, dead quiet when it idle. Once the music play, the combination of B1 and LM1875 makes the music play wonderful. I never thought I will get such this great result by only combining those 2 circuit.

Nice combination, good components and nice build equal to great music.

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