大部份中低档带卡座的功放都用一支按键开关作音源转换(如图1),这类电路使用一段时间后大多容易出现接触不良等故障。为此,笔者用4099微型继电器设计制作了如图2所示电路,不仅消除了接触不良的情况,还让音源转换实现了“自动化”。当未对卡座进行操作时,机芯开关K呈断开状态,晶体管9013截止,继电器不动作,其触点接通 Most low-end cassette deck amplifier with a key switch for audio conversion (Figure 1), such circuits are mostly prone to poor contact after a period of failure. To this end, I used 4099 micro-relay design produced the circuit shown in Figure 2, not only eliminates the poor contact, but also to achieve the conversion of the audio “automation.” When the deck is not operating, the movement switch K is off, the transistor 9013 is turned off, the relay does not move, the contact is turned on