Check out this beautiful Luxman M-4000 power amplifier I’ve just serviced. This classic vintage beast needed a little work, let’s take a look.
The Luxman M-4000 power amplifier is a fairly compact, dense, 180 Watt per channel bipolar amplifier. It’s the predecessor to the M-4000A, which looks very similar, but is substantially different design-wise and even rarer. I completely restored an M-4000A for a customer a couple of years ago.
The M-4000 and others in this series share a lovely wooden case, out of which slides the immensely heavy for its size amplifier unit. This is a true dual mono design, with two big transformers and separate filter capacitors and diode bridges for each channel.
Specifications (courtesy HiFi Engine)
Power output: 180 watts per channel into 8Ω (stereo)
Frequency response: 3Hz to 100kHz
Total harmonic distortion: 0.05%
Input sensitivity: 1V
Signal to noise ratio: 108dB
Dimensions: 485 x 390 x 175mm
Year: 1975 – 1979
As always, there’s additional information on the Luxman M-4000 at The Vintage Knob.
This M-4000 was presented to me with one channel out of service. I was able to get her working again by attending to the basics. In this case, I checked all of the 20+ fuses, and no I’m not kidding, there are actually at least 20 fuses in the Luxman M-4000. Many are standard M-205 glass fuses. A few are board mounted and some are soldered to the boards.
All the fuses must be checked of course because any one open fuse will kill the deal. This takes time because of the need to remove each board, pull the fuses, test them and the soldered fuses too.
It’s good practice to pull and clean fuses, it helps re-make the connection between the fuse and fuse holder and allows you to feel if the end caps have come loose. Few people bother, but it’s necessary.
I took the opportunity to clean the board card edge connectors whilst testing those fuses. After checking fuses and reinstalling cards, I gradually powered up the amplifier for testing and to make some adjustments.
To my surprise, both channels now worked well and I spent some time setting DC offset and bias current. I also took the opportunity to clean the chassis, fascia and beautiful wood case.
Service & Repair
If you would like a video summary, watch my M-4000 video on YouTube. Otherwise, read on!
Those who follow along will know I’m a little fussy about cleaning. This Luxman M-4000 needed a clean and didn’t escape my little fetish. Here she is, after a clean and wax.
If you live in Perth and you’d like me to service your Luxman amplifier, get in touch and we can arrange an inspection.