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Balanced Line Technology （平衡线路技术）
http://www.douglas-self.com/ampins/balanced/balanced.htm
5）准浮动输出。参见图 6。
这种输出近似模拟浮动变压器绕组；如果热输出和冷输出都驱动信号线，则输出是平衡的，就像使用中心抽头输出变压器一样。然而，如果冷输出接地，则热输出的幅度加倍，因此总电平不变。这种情况是由 75R 输出电阻外部的电流感应反馈检测到的，驱动到短路冷输出的电流会自动降低到不会引起问题的低电平。
类似地，如果热输出接地，则冷输出的幅度加倍并保持异相；总的冷热信号电平再次保持不变。该系统的优点是它可以为平衡或不平衡输入提供相同的电平，而无需重新连接连接器。然而，损失了 6 dB 的动态余量。
5) Quasi-floating output. See Fig 6.
This kind of output approximately simulates a floating transformer winding; if both hot and cold outputs are driving signal lines, then the outputs are balanced, as if a centre- tapped output transformer were being used. If, however, the cold output is grounded, the hot output doubles in amplitude so the total level is unchanged. This condition is detected by the current-sensing feedback taken from the outside of the 75R output resistors, and the current driven into the shorted cold output is automatically reduced to a low level that will not cause problems.
Similarly, if the hot output is grounded, the cold output doubles in amplitude and remains out of phase; the total hot- cold signal level is once more unchanged. This system has the advantage that it can give the same level into either a balanced or unbalanced input without rewiring connectors. 6 dB of headroom is however lost.
当驱动不平衡输出时，准浮动输出可用作接地消除连接，抑制接地噪声的效果不亚于真正的平衡模式。这需要冷输出在电缆的远程（输入）端接地。在不利条件下，这可能会导致高频不稳定，但总的来说，这种方法是合理的。如果您使用的是特别长的电缆，那么明智的做法是检查一切是否正常。
如果冷输出本地接地，即在电缆的发送端接地，则它作为简单的不平衡输出工作，没有噪声抑制。当不平衡使用准浮动输出时，冷脚必须接地，否则共模噪声将使本底噪声降低至少10 dB，并且可能存在其他问题。
When an unbalanced output is being driven, the quasi- floating output can be wired to work as a ground-cancelling connection, with rejection of ground noise no less effective than the true balanced mode. This requires the cold output to be grounded at the remote (input) end of the cable. Under adverse conditions this might cause HF instability, but in general the approach is sound. If you are using exceptionally long cable, then it is wise to check that all is well.
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发表于 2023-4-27 19:17
