Thursday, May 26, 2011

Pioneer 9500II question

I just posted this to FMtuners Yahoo Group:

As part of my newest adventure into Pioneer tuners, I got a TX-9500 II. To
connect it to my usual #1 antenna (a folded dipole, just like #2, but in
different location) I needed to connect it to a 75 ohm cable. So I brought out
the same piece of cut RG-6 I used for testing a Marantz 20B last year.

The sensitivity was horrible, I couldn't get college stations at all, and my
usual KPAC was way noisy, noisier even than the 20B which I tested (or
mis-tested) last year. Very poor quieting.

But then I got the idea of connecting to the 300 ohm terminals, simply by
extending the twinlead from Antenna #2 a few feet by soldering in a section of
twinlead. This brought a massive improvement, though I still find the 9500II is
not as quiet in stereo as my quietest digitally tuned tuners (which feature
advanced MPX chips and technologies, I never bothered with any of the lousy
ones), and I know this is true because I've now done an A/B test with a Kenwood
KT-6040, which was much quieter. From memory, the 9500 II seemed in the same
ballpark, maybe even better than KT-8300 (though I haven't tested the 8300 in a
few years).

I'm worried that my hacked RG-6 is either bad or I am not terminating the
connection properly. It always seems tricky to me to have to cut a piece of
RG-6, clamp the shield down, and then run the signal wire to a screw. The
pictures always show a piece of RG-6 that has braided shield, whereas all the
ones I've ever cut have a foil-and-wire type shield, which doesn't lend itself
to being folded back as pictured, so I simply twist the foil and wire into a
wire and bend it back over the section of RG-6 that is being clamped. Perhaps
that is the wrong way to do this.

Another possibility, mentioned here before, is that there might be an internal
75 ohm balun that has gotten fried. Does anyone know if TX-9500 II has a balun
to convert 75 ohm inputs to 300 ohms which is actually sent to the front end,
whereas the 300 ohm balanced passes right into the front end? Or do both inputs
go through some sort of balun or impedance matching devices to yet another
impedance like 110 ohms or something.

I've always suspected that tuners lacking an F connector are more optimized for
the 300 ohm connection and the 75 ohm connection needs to go through an internal
impedance matching device, whereas tuners having an F connector are optimized
for 75 ohms, and the 300 ohm connection has to go through internal impedance
matching device. Though there is no logical reason why this would have to be
so, or there might have been some shift that occurred over time (like in the
late 1970's) rather than related specifically to the kind of 75 ohm connection

Perhaps I should go back and retest the Marantz 20B also. It might have been
more sensitive than I thought (I can't remember if I tried direct 300 ohm
connection with it, or I might have handicapped it slightly by using external
balun to convert 75 ohm cable, thus requiring signal to pass through two
baluns). My antennas #1 and #2 are very close on KPAC 88.3, with the #1
possibly having about 1dB more strength according to meter on Kenwood 600T (64
vs 65 dBf).

The 9500II midrange is quite nice. The "buzz" sound in Stereo which I now
believe to be station error of some kind, is not audible at all, instead there
is more noise. So while the 9500II has no buzz, it has a grainy background
hiss, and the 6040 has hardly any hiss but very clear buzz. Unless I engage the
High Blend on the 6040 to kill the buzz, the 9500II is more pleasant to listen
to. The high filter switch on 9500II seems to cut highs in a way I don't like.

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