Luxman LXV-OT7 Clone Build

This new amplifier build is a clone from the original Luxman amplifier kit that was sold in Japan. This kit was came as bundled with the magazine, it is the Luxman LXV-OT7, a hybrid amplifier using tube as an audio buffer and a stereo IC amplifier.

The power output from this amplifier is small, just 3 watt per channel at 8-ohm, but good enough to drive my 88 dB sensitivity speaker. The tube is use for audio buffer before the amplifier and this what makes this amplifier looking good and sound special.

I make this clone with all components packed in a small amplifier case. Of course, with the improvement on the power supply section that has direct effect to the sound improvement.

Let's check the build.

The original schematic is come along with the kit.

If you check the power supply line, it using an external single 15-volt DC power supply from cheap SMPS adaptor. This is the major component that need to replace with the linear power supply for better sound quality.

This single 15-volt DC line supply all power requirements to this amplifier. It powering the IC power amplifier BA5417 with R-C filter: 0.47-ohm resistor and 3300 uF capacitor. Then it goes in series with another R-C filter: 15-ohm resistor and 1000 uF capacitor, it reduces the voltage to about 12-volt to supply the tube anode supply and the filament supply.

Those R-C filter in the SMPS adaptor basically enough to fight against high-frequency ripples. This is because the DC output is regulated but in high frequency. You will not hear the 60 Hz hum at the speaker output, but it effected so much on the sound quality with this kind of SMPS high frequency noise, makes the sound harsh and thin.

So, in this build, I separate the power supply requirements, one supply for audio power supply which is the BA5417 and the anode of 6DJ8 tube (not 12AU7). It supplies with regulated LM1085 IC regulator for 15-volt output. The other power supply is only for 6DJ8 tube filament using 7806 IC regulator for 6-volt output.

The reason I changed the tube from 12AU7 to 6DJ8 is because I had this tube on my drawer already.

I using high-quality 30 VA transformer with dual AC output at 10-volt and 15-volt. This high quality-transformer consumes most of the spaces in this small aluminum amplifier case. The AC output goes to individual diode rectifier and then goes to the PCB module where all components are packed into this board.

The PCB module is using universal PCB but the size is customized based on the overall amplifier case size.

This limited space inside this case is makes this amplifier build challenging. Not to mentioned that I using large Panasonic FC capacitors on it, but also the ceramic tube socket also packed in this case.

The most time consuming in this build is to measure and reorientating all components layout to fit inside with the shortest path.

Once I finished with the layout, now the components placement can be start installing on the PCB.

The challenge is to make the internal of this amplifier looking good.

I end up with only capacitors at the top of the PCB, while others components, such as resistors, film capacitors and ICs are locate at the bottom. This case also acts as the heat-sink to all IC.

Once the board is on place, now the speaker terminals can be installed, together with the potentiometer and RCA input.

At these stages, things get more complicated.

A small flaw, as you can see, I am using standard quality potentiometer.

This potentiometer works well but not so great compare with my favorite and good sounding ALPS blue potentiometer. But using this might be temporary, to make sure this amplifier finished without delay, since many of my import order are still on delivery, including for this potentiometer.

Check this out, I using Hosiden circuit breaker instead of a fuse. This is my first time using it in my amplifier build and I think it works really well.

That's all for the building process of this Luxman LXV-OT7 clone.

Very challenging especially to put all components together inside this small amplifier case.

It sounds beautiful, and to be honest, it is far from my expectation for the amplifier like this can perform this good.

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