2019/06/12

Nakamichi CA-5 pre amplifier Repair - 1

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Repairing the pre amplifier "Nakamichi CA-5" now!

I could easily obtain Nakamichi CA-5 Service Manual from the web.

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When I looked at the electrical schematic in service manual, it seems to be a simple discrete circuit configuration.
Since it was a product of the mid-1980s, no surface mount components were used, and it was not a lead-free solder with a high melting point, so I seemed easy to replace components.

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First of all, I checked the flat amplifier section of the main board, so I was relieved that it was working properly. This was probably due to the small number of parts, and the fact that heat stress was hardly added to the electronic parts by the proper component placement design.

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Then, I examined the cause of the interruption of the left channel sound. The main variable resistor (NOBLE) was normal, but the balance variable resistor(ALPS) was found to be very unstable, causing contact failure even at the center position.

Once the balance variable resistor was bypassed and the input signal was sent directly to the main variable resistor, it became possible to reproduce without any problems. As I also cleaned the contacts of the signal connector, the sound freshness also increased.

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The failured parts was ALPS Mini-dent resistor (RK27 series, MN type). It was easily obtained because of the audio parts currently being manufactured, but it did not the exist same resistance value parts.

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When I replaced the balance variable resistor to new one, there was no break or noise in the playback sound, and it was played with a good sound.

Probably because the sound was made in the flat amplifier section, I felt that the low frequency range was very rich and dense, and the resolution was very high. It is a little different from the realistic monitor sound that can be heard on the Nakamichi's high-end tape deck.

Because I used a pure class A amplifier (Accuphase) as the power amplifier, it might have become a warm dense sound image that is the opposite of the cool realistic sound of my reference full digital amplifier (FOB SD05 - Feedback less power DAC).

The contact cleaning of the main variable resistor and switches need to be disassembled, so I will use it in my sub audio system for a while under this condition.

After a while, I will try to tune the sound while checking the details of this amplifier.

posted by toons at 23:59 | Audio