Lepy LP-2020A Modification of Input Circuit

I decided to modify the input section of the Lepy LP-2020A because the audio output was just not loud enough for my taste. These digital amplifiers are supposed to pack a much bigger punch, but this one was not even a contender. Looking at the input section we see these huge 10 kΩ SMD resistors (103 marking). These are way too large, what was the designer thinking? RCA signals are weak enough as they are. Imagine you have an audio signal at approximately 0.7 Vp-p, and sometimes even less due to travelling through cheap cables. It is then further attenuated by large 10 kΩ resistors. This is why I have to have my Walkman volume control on full just to make it slightly louder...

U3 is the JRC4558D dual operational amplifier IC, and all the resistors around it are 10 kΩ. This designer sure likes his 10 kΩ resistors, or perhaps there was a sale on...

Usually the resistor at the input is around 1 kΩ, and if memory serves, the earlier Lepai LP2020A+ also had 1 kΩ input resistors, which is why all the knob-polishing "experts" declare it to be louder. However, in my modification, I have decided to use 220 Ω which is the extreme minimum I have seen used in commercial high-end Akai and Panasonic amps.

After the input resistor, there is the 47 kΩ to ground, which looks right, but I am not so sure about the capacitors C40 and C41. I would expect to see electrolytic types with the value of 4.7 µF or thereabouts. Hence, they have to go as well.

As you can see here, I replaced resistors R36 and R37 with 220 Ω SMD, and also removed C40 and C41. For the capacitors, I did not have the values I needed in SMD, hence I soldered conventional 4.7 µF capacitors.

Ideally I would prefer 1 kΩ to 2 kΩ input resistance, when using standard RCA connections, however with just 220 Ω, the input signal will be so strong (at full volume) that it will drive the power amplifier to its supply rail limits. With digital amplifiers, usually when the audio output power reaches the supply rail power, it starts to intermittently cut out. At that point, the only options are to reduce the volume, or increase the supply rail power to meet the demands. However, I did this input circuit mod just as an experiment to see how much louder I could make it. I also have some older equipment that does not provide much signal from the RCA sockets; hence it might be useful there as well.

Here, you can see the conventional capacitors I soldered. It sounds so much louder and nicer that they appear as if they are dancing. Probably Blue skies...

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