Yamaha CX-1 Preamplifier Service & Repair

You may have seen the article I wrote recently about repairing a gorgeous Yamaha MX-1 power amplifier. This time I’m servicing a Yamaha CX-1 preamplifier, which matches the MX-1 and is part of the same set.

Yamaha made some really superb hi-fi gear back in the day, as I’m sure many of you know. There were the B series VFET amps like the B-1 and B-2, the legendary NS-1000 monitor loudspeakers, the perhaps even more (studio) famous NS-10 monitors, awesome MX-10000, CX-10000, and many more. Later came the MX-1 power amp, and Yamaha CX-1 preamp featured here, arguably the last really good two-channel gear they produced, until recently.

For more on the Yamaha MX-1, check out my repair article and the video I made, on my YouTube channel.

As you’ll see, the Yamaha CX-1 is a proper stereo preamp, with mostly discrete circuitry, on nicely laid out boards with high quality components. The controls are aluminium, also nicely laid out, with volume and input selectors accessible on the front panel, and less frequently used controls hidden behind an aluminium flap.

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Under the flap…
Yamaha CX-1 Specifications, courtesy of HiFi Engine:

Frequency response: 20Hz to 20kHz
Total harmonic distortion: 0.002%
Input sensitivity: 0.1mV (MC), 2.5mV (MM), 150mV (line)
Signal to noise ratio: 90dB (MC), 95dB (MM), 107dB (line)
Channel separation: 70dB (MM), 65dB (line)
Output: 150mV (line), 1.5V (Pre out), 8V (Pre out Max)
Dimensions: 438 x 86 x 405mm
Weight: 8.8kg
Accessories: remote control transmitter, remote control cable
Year: 1992

Design & Build

Let’s take a look at some of the design features I like about the CX-1.

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Here she is, before any work. The layer of tar is not easy to see, but you can smell it.
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The chassis is very nice, these are solid aluminium side panels that come off first, stamped steel lid underneath. The fascia is also a thick aluminium piece, possibly an extrusion.
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First look inside. Immediately obvious are the high-quality ALPS rotary controls, minimal wiring, board-mounted buss bars, large transformer and high-quality filter and other capacitors.
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Some of the circuits, like phono gain and EQ, are on sub-boards. These had a few dry joints that I repaired. Note the premium caps, with silicone and tape vibration countermeasures, and custom Yamaha controller IC.
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Two x 10,000uF filter caps is what you would normally find in a power amp, not a preamp! These are premium Nichicon ‘audio-grade’ parts too.
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Transformer, plus regulation semiconductors on a nice big heatsink.
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These are the low impedance buss bars I mentioned. Why use them? Well, generally they would be associated with high current flow in a power amp, but in a preamp, they lower power supply source impedance and provide super-low impedance ground return pathways, to lower hum and noise.
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These things could handle many amps, which they don’t in this use-case!
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Neat layout, clear board designators and more buss bars! There’s a lot to like about this design and build.
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High-quality electrolytic caps, discrete transistors, film caps, board-mounted switches and buss bars. This is the phono preamp.
Service & Repair

This CX-1 came to me from a customer who now owns the stunning MX-1 power amp I repaired recently. Like the MX-1, the CX-1 wasn’t working properly and was suffering from years in a smoke-filled environment. The sub-controls under the aluminium flap were noisy and some weren’t working at all. I noticed that the unit had been to a TV repair place previously. That is not usually a good sign, I made mental note and got to work.

The first thing I always do is thoroughly inspect every accessible part of a unit like this. I strip and remove parts, panels, boards, controls etc. This is fiddly and time-consuming, but helps to get equipment working properly.

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With front panel and controls/knobs removed, I cleaned and lubricated everything, checked all the cables and connectors, removed and re-worked boards etc. I found a ribbon cable from the front panel, disconnected where it should plug into the mainboard. This would account for certain controls not working and was likely caused during the previous trip to the TV repair place.
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I cleaned and treated all of these ALPS controls with a premium contact cleaner/lubricant, standard in my services.
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This is the standby power supply board. I wanted to eyeball it, because this is where I found issues in the MX-1 power amplifier. In this case, there were no problems with this board.

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Everything done, cleaned, serviced and back together. Now for the chassis clean…
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Umm… yeah. This is what smoking does to a unit that’s only ever been inside, in a cabinet.
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Several doses of paper towel and foaming cleanser later and the CX-1 was much cleaner.
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By the way, no plastic knobs here, they are solid, milled and spun aluminium, and quite heavy. Knobs like this always feel so much nicer to use, but they are expensive to make.
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She’s really a very pretty unit, the combo of CX-1 and MX-1 would form the foundation for an excellent hi-fi system.

And that’s a wrap, I hope you’ve enjoyed this look inside the Yamaha CX-1 stereo preamp and discussion about servicing and repairing it.

If you like me to look at any of your Yamaha equipment, don’t hesitate to get in touch.

Feel free to leave a comment and share your thoughts!