マルツ パーツまめ知識 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
ヘッドホンアンプの製作 |
|
|
|
|
|
|
DHP-1 改善編 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2011年9月 KY |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
◎TR1部の計算ミス |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
先日製作しましたヘッドホンアンプ「DHP-1」にてTR1部の増幅度計算ミスがありました。 |
|
|
大変申し訳ありませんでした。 |
|
|
|
|
|
|
|
http://www.marutsu.co.jp/contents/shop/marutsu/mame/170.htm |
|
|
|
|
|
(ヘッドホンアンプの製作 ディスクリート編 その1 2011年7月 KY ) |
|
|
|
|
|
|
|
|
|
|
|
|
|
動作的には問題無いのですが、計算ミス部とその改善方法について追加レポート |
|
|
します。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
◎TR1部の増幅度がマイナスになっていた |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
図100のようにTR1は「エミッタに抵抗があるタイプの増幅回路」です。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
この回路の電圧増幅度Avは(100式)で計算出来、R5とR3が同じ値(1.5K)ですから |
|
|
増幅度はマイナスになってしまいます。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
TR1部がマイナスの増幅度でも動作的に問題無いので気づきませんでしたが、 |
|
|
|
せっかくの増幅部ですから、プラスのゲインとなるように改善を行います。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
◎TR1の負荷を上げる |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
増幅度を上げるには(100式)から、「RL>REの関係」にすればよいわけです。 |
|
|
|
|
|
|
|
|
|
|
|
|
★TR2のhieを上げる |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
RLは今回の回路ではR3とTR2のhieとの並列合成になり、バイアスの関係からR3の値を |
|
|
いじることが出来ません。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
そこで、TR2のhieを増加させてR3との並列合成値が大きくなるようにし、TR1の負荷を大きく |
|
|
して増幅度を上げます。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
hieはベース電流値で決定され、小さいほどhieが大きくなります。 |
|
|
|
|
つまり、図102のように動作電流を変えないでhieを大きくするにはhFEの大きなトランジスタ |
|
|
を用いれば良いわけです。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
前回はTR2に2SC1815Yを用いました。 |
|
|
|
|
|
|
Yランクの場合hFEは120〜240で、BLランクは350〜700です。 |
|
|
|
|
主なBLランクのトランジスタを以下に示します。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
hFE |
|
|
|
|
|
|
|
2SC1815-BL(F) |
350〜700 |
|
|
|
|
|
|
|
2SC2240-BL(F) |
350〜700 |
|
|
|
|
|
|
|
2SC2459-BL(F) |
350〜700 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
今回はこの中から2SC1815-BL(F)を用いました。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
★R4,R5の定数変更とバイアス抵抗変更 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
TR2にBLランクを用いることでTR1の交流負荷を大きくすることができました。 |
|
|
|
次にR4,R5の値を小さくして、さらに増幅度を上げます。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
図103に変更後の回路を示します。これにより負帰還後の利得は+12dBです。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
(定数変更) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
R1,R4,R5,C3 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
(部品変更) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
TR2 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
★調整 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
バイアスを変えましたので、再調整が必要です。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
前回と同じですが、図104に再掲します。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
◎電気的特性確認 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
TR1の増幅度アップに伴い、全体の負帰還前 |
表1 33Ω負荷 Rch |
|
|
|
の増幅度が上がりました。 |
|
|
出力(mW) |
改善前 |
改善後 |
|
|
|
|
|
|
|
10 |
0.00270 |
0.00120 |
|
|
これにより負帰還後の特性(ひずみ率、SN比) |
20 |
0.00360 |
0.00100
|
|
|
が向上します。 |
|
|
|
30 |
0.00440 |
0.00107
|
|
|
|
|
|
|
|
40 |
0.00520 |
0.00140
|
|
|
表100およびグラフ100にひずみ率特性を示し |
|
50 |
0.00600 |
0.00152 |
|
|
ます。 |
|
|
|
|
60 |
0.00670 |
0.00167
|
|
|
|
|
|
|
|
70 |
0.00740 |
0.00183
|
|
|
今回の改善によりひずみ率が大幅に改善 |
|
80 |
0.00820 |
0.00200
|
|
|
されていることが分かります。 |
|
|
90 |
0.00890 |
0.00226 |
|
|
(グラフ100の赤部が改善後) |
|
|
100 |
0.00960 |
0.00245 |
|
|
|
|
|
|
|
110 |
0.01000
|
0.00268 |
|
|
なお、SN比については約1dBほどの改善度 |
|
120 |
0.01100 |
0.00293 |
|
|
でした。 |
|
|
|
|
130 |
0.01200
|
0.00316
|
|
|
|
|
|
|
|
140 |
0.01300 |
0.00350 |
|
|
|
|
|
|
|
150 |
0.01400
|
0.00370 |
|
|
|
|
|
|
|
160 |
0.01520
|
0.00406 |
|
|
|
|
|
|
|
170 |
0.01600
|
0.00448 |
|
|
|
|
|
|
|
180 |
0.01780
|
0.00500 |
|
|
|
|
|
|
|
190 |
0.01940 |
0.00554 |
|
|
|
|
|
|
|
200 |
0.02190 |
0.00617 |
|
|
|
|
|
|
|
210 |
0.02530
|
0.00706 |
|
|
|
|
|
|
|
220 |
0.03370 |
0.00926 |
|
|
|
|
|
|
|
230 |
0.03870 |
0.01100 |
|
|
|
|
|
|
|
240 |
0.06200
|
0.02050 |
|
|
|
|
|
|
|
250 |
0.11700 |
0.04450 |
|
|
|
|
|
|
|
260 |
0.21500
|
0.06300
|
|
|
|
|
|
|
|
270 |
0.27800 |
0.14700 |
|
|
|
|
|
|
|
280 |
0.48400 |
0.18600
|
|
|
|
|
|
|
|
290 |
0.60000
|
0.34900 |
|
|
|
|
|
|
|
300 |
0.99700
|
0.52200 |
|
|
|
|
|
|
|
310 |
1.24000
|
1.05000
|
|
|
|
|
|
|
|
320 |
1.83000
|
1.35000
|
|
|
|
|
|
|
|
330 |
2.50000
|
1.99000
|
|
|
|
|
|
|
|
340 |
3.18000
|
2.69000
|
|
|
|
|
|
|
|
350 |
3.53000
|
3.05000
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|