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Re: High Output Impedance On Line Output = BAD DESIGN (but passive preamps)

I am amazed.

The term "high output impedence" is relative. The higher the input impedence of the following stage relative to the output of the previous stage, the better because both the source impedence and transmission line (interconnect) become less of a factor. This is the reason cathode follower and emitter follower output stages are used in the first place. For a power amp with a 10k input, a 1.8k preamp output could be a problem. For a power amp with a 200k inupt, a 1.8k output should not be a problem. The lower the output impedence of the source and the higher the input impedence of the load the less the effect of the impedence of the interconnect has as well. This is straightforward network analysis. The concept of a so called "passive preamp" is a terrible idea as can easily be seen from the way its impedence interacts with both the source and the load not to mention how it is affected by the connecting wire. OTOH, a 50 or 100 meg audio tapered pot buffered between two active gain stages with barely inches of wire connected to it is not a problem.

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