Paul Sherwin wrote:
Jon Noring wrote:

I'm very interested in building such a tuner to match with
audiophile-grade tube amplifiers and pre-amplifiers now being built
by hobbyists (as well as those sold by commercial vendors.) There are
quite a few nice kits now being marketed for audiophile quality tube
amps/pre-amps, such as those made by diytube (http://www.diytube.com/
-- there are many others like diytube.) So why not similar kits (or
workable designs) for a tube-based AM tuner?

No offence Jon, but I think you're nuts.

No offense is taken, and yes I may be a little nuts. :^)


Most hifi listeners (never mind audiophiles) wouldn't dream of using
*FM* for serious listening, because of the level of optimodding and
other sound processing that goes on. Quite a lot of commercial
stations even adjust the playback speed of their music to make the
station sound more 'lively' and to squeeze in more commercials.

Nevertheless, there are those hifi/audiophile listeners, such as
myself, who still wish to connect both AM and FM tuners to their audio
system, to listen to various broadcasts. Not everything audio is found
on CD/vinyl.

On FM, especially among alternative FM stations, one often finds very
unusual musical programs being broadcast of music which the listener
does not have in their collection (it helps them to expand their
horizons and maybe go out and purchase said music on CD/vinyl.) In
addition, there are sometimes live broadcasts of concerts which will
never appear on CD/vinyl. (In Salt Lake City, the alternative FM
station I am thinking of is KRCL, http://www.krcl.org/ . Really a fun
station to listen to, especially the late Sunday night program
broadcasting 1920's to 1940's era recordings.)

On AM there are certainly broadcasts which interest different people
for different reasons at different times. Live sports events not found
elsewhere, news, of course the venerable talk radio, and for some of
us, we like to spin the dial at night and see what distant stations we
can pull in.

Thus, if we do connect AM and FM tuners to our system, we want the
tuners to deliver the highest audio quality signal to our amplifiers.
That is, the tuners should not taint the broadcast signal any more
than it already is tainted as it leaves the broadcaster's antenna.

(Btw, aren't there alternative FM stations which do not play these
games of distorting the sound, and only broadcast the purest possible
signal?)


AM has all that, plus very high levels of signal compression and an
effective HF cutoff of about 3.5kHz. You can't improve this by
extending the IF bandwidth, because the stations just don't transmit
anything above this.

Well, maybe in the U.S. most stations cutoff at 3.5khz. Then that's
where they cutoff. However, the AM tuner design is intended for the
world, and as Patrick Turner noted, in Australia many broadcasters
have a much higher rolloff because of the "open highway" they have
on the BCB -- fewer stations spread farther apart.


There's nothing wrong with building your own high quality AM tuner,
either solid state or tube, but no matter how many gold lettered
Telefunken ECC83s you use it won't sound very good.

Agreed in principle. The AM tuner must deliver the highest possible
fidelity as broadcast, that's all. It must have very low distortion.

One question to ask is in various areas of the world (including the
U.S.) what is the distribution of HF cutoff among the many broadcast
stations? I doubt in the U.S. every broadcaster rolls off HF at
3.5khz, but maybe most do -- are there any AM stations in the U.S.
which have a much higher HF rolloff than 3.5khz? Note again Patrick's
comment on Australian AM broadcasters.

Jon Noring