"Ken Winokur" wrote in message
oups.com...

What's so important about good mic pre's? Is there something intrinsic
in an excellent mic pre that can't be made up with the proper choice of
mic (with a decent mic pre)?

What are the components that make up the sound of a mic p frequency
response, distortion, noise, slew rate? Are there others?
[snip]
I have always thought that the combination of mic and mic pre (as well
as other components in the system) was what really counted, not that
there was anything special in the mic pre itself.

This is a whole 400-level course that it's impossible to really do justice
to in a few paragraphs -- but what the hell. Here goes.

First off, frequency response and distortion are indeed involved in the
sound of a preamp. Noise, if the preamp is competently designed, shouldn't
be an issue; a good preamp adds only a few dB to the intrinsic noise of the
mic. And these days slew rate is seldom an issue; except for some
ultra-cheapies, the circuits in most preamps have adequate slew rate.

The other issue that is important to the sound of a preamp is the load it
places on the microphone. Some mics (not all) will change their behavior
significantly with different load impedances. So you're right that the
combination of mic and mic pre counts, but I don't think it's the only
thing.

When we talk about distortion, it's not enough to specify a number and say
that this is the quantity of distortion. It is also important to specify the
*type* of distortion: in a harmonic distortion measurement, it's important
to note which harmonics are generated, and how the harmonic spectrum changes
with level and load. In an IM-distortion measurement, it's equally important
to note whether the preamp produces only first-order IM products, or
higher-order ones, again noting how the behavior changes with level and
load. It's been my experience that preamps with a harsh sound, even though
the total distortion level may be low when lab-tested, tend to have
distortion spectra with higher levels of high-order distortion products,
while preamps that don't sound harsh tend to measure with distortion spectra
comprised entirely of low-order distortion products.

Then there are "colored" preamps, designed to impose a particular sound via
irregularities in frequency response, distortion mechanisms, or transformer
hysteresis, but those are something of a separate ball-game. Other issues
include rejection of radio-frequency interference (RFI), which can cause IM
problems even when there's no overt breakthrough of disk jockeys into the
mic feed, and susceptibility to ground-loop weirdness.

That's just scratching the surface, of course, but it'll give you some idea
of the issues involved. Your Bellari, for example, has a godawful IC in its
output circuit, the source of much of the harshness, and a cruddy
transformer to boot. Clean those things up and you'll have the nucleus of a
good preamp.

Peace,
Paul