Thanks for the excellent input, George.
An additional point everyone should be aware of is that how objectionable a given low ratio is likely to be depends not only on the ratio itself but also on how much variation that ratio has over the frequency range.
For example, if the ratio is say 3:1 at the worst case frequency (i.e., at the frequency at which the ratio is lowest), but the impedances that are involved don’t vary much over the frequency range, and hence the ratio doesn’t vary much over the frequency range, the consequences would be a slight and inconsequential reduction in gain; an increased sensitivity to cable effects (especially if the low ratio is due mainly to a high output impedance of the component providing the signal); and perhaps a small degradation in the distortion performance of the component providing the signal.
However if the low ratio involves the kind of output impedance characteristic that occurs in the case of many tube-based components, where the output impedance may be a few hundred ohms in most of the spectrum but may rise in the deep bass region to a few thousand ohms at 20 Hz, the consequences of that same 3:1 ratio (at 20 Hz in this case) will include significant deep bass rolloff as well as frequency-dependent phase shifts in the bass region. Which are likely to be much more noticeable and objectionable than the effects described in the preceding paragraph.
Or putting it all another way, 3:1 may be fine in some cases, while 8:1 may be unacceptable in some cases, depending on how the impedances and consequently those ratios vary over the frequency range.
Regards,
-- Al
