この展示は番外です。
我が家にはオーディオ装置が無かったので、LPレコードを聴けるようにステレオ再生装置を製作することに(1971～72)。貯めた小遣いで口径6インチ半のBTS規格スピーカーユニットを購入し、家にあったラワン板材と合板を使ってエンクロージャを製作。RIAAカーブのイコラーザーや、数ワット出力のステレオパワーアンプは手持ちの球（6CA7など）を使い見様見真似で自作しましたが、一番の問題はターンテーブルとその回転駆動機構でした。これは精密機械の類で大人でも自作は困難でしたから、適当な出来合い品を探すしかありません。
そんな時、市内の電気販売店でパイオニア製のターンテーブルモジュールを発見。当時の主流はベルトドライブ式でしたが、それはシンクロナスモータとリムドライブの旧型で値段は格安と、自分にとって正に渡りに舟でした。偶々その当時家を改築中だったので、大工さんに頼んで檜の木っ端を貰い、それを鉋掛け・ニス塗装してそのモジュールを載せる木製台を製作。
リムドライブはゴロが出るのでHiFiマニアには嫌われますが、単純な構造だから耐久性が高く、愛用し始めて50年以上経ちましたがクリーニングと給油のみで今でも当時と同じように動いています。何台も製作した当時のアンプ類やスピーカーシステムはもう何も残っていなくて、古いレコードと木目のきれいなこのプレーヤだけがあの時代の空気を保存してくれています。
(ダイレクトドライブ式が主流になり、スラスト軸受けの付いた専用サーボモータが容易に入手できるようになったのは、1970年代後半になってからでした。)
Since we did not have any audio equipment at home, I decided to build a
stereo audio system so that I could listen to LP records between 1971 and
1972. First, I purchased a BTS-standard speaker units with a diameter of
six and a half inches, and built an enclosure using lauan boards and plywood
that I had at home. Next, I built my own RIAA curve equalizer and a stereo
power amplifier with several watts of output, using tubes I had on hand
(6CA7, etc.). The key point was the turntable and its rotary drive mechanism.
This was a precision mechanical component that was difficult even for adults
to make themselves, so I had no choice but to find a suitable ready-made
product.
At that time, I found a turntable module made by Pioneer Corp. at an electronics
dealer in my town. The mainstream at the time was belt-driven, but this
was an older model with a synchronous motor and rim drive, and the price
was very reasonable, so it was a perfect match for me. As it happened,
my house was being remodeled at the time, so I asked a carpenter to give
me a piece of cypress wood, which I cut, planed, and painted to make a
wooden base for the turntable module. I think it was just barely passable
for a junior high school woodworker.
Rim drives are disliked by HiFi enthusiasts because they produce noise
in low frequency below 100Hz, but their simple construction makes them
highly durable, and although it has been more than 50 years since I started
using them, they still work as well as they did then with only cleaning
and lubrication. There are no more amplifiers or speaker systems left from
those days when I built several of them, and only the old records and this
wood-grained player preserve the atmosphere of that era.
(It was not until the late 1970s that the direct-drive type became mainstream
and dedicated precision servo motors with thrust bearings became more readily
available.)
