Radio Road Which tuner to get and getting the most from it. Thank God, for the radio!

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RE: When does a tuner need an alignment?

Posted by Timbo in Oz (A) on September 30, 2018 at 03:14:26

In Reply to: When does a tuner need an alignment? posted by fastcat on September 29, 2018 at 12:16:45:

"How do I know if my Tuner is in alignment??
In a previous posting, someone asked the above, VERY good question.
I didn't find a response and believe that one IS deserved! Let me
make an initial stab and PLEASE feel free to comment or correct as
you see fit.
In an FM tuner the circuits that can be aligned fall into three broad
categories - the "Front End"; the "IF/Detector Strip" and the "Stereo
Multiplex Decoder Section". Each of these sections has a different
job to do and when not "working" correctly can contribute a different
set of potentially audible artifacts.
Fortunately most tuners allow the Multiplex section to be bypassed
via a mono-stereo switch, causing the same information to come from
both the left and right channel outputs. Forcing the tuner to mono
should eliminate any audible problems from that section so we can
concentrate on potential problems in the other two.
Switch the tuner to mono and find "clean", "strong" station that
is "by itself" hopefully in the middle of the band. Let me try to
define "strong" by differentiating it from "weak". With no station
tuned in you should hear a rush of noise - assuming that you have and
can defeat any muting circuits which are designed to "shut off" the
output when no signals are present. When you tune in a "weak" signal
you will hear background noise mixed in with it. As the signal
strength increases the noise will be rejected and above a certain
level you should hear only signal and no noise. By "clean" I mean a
station that does not add anything to the music like compression or
peak-limiting (to supposedly increase their coverage area). This
eliminates most commercial stations (OK, I'll except some of the too-
few wonderful classical/jazz stations in certain metropolitan
areas). Look for a college radio station - most in my area my area
don't futz with the signal. "By itself" means that you should try
and find a station that has no strong "neighbors" or strong signals
on either side.
To isolate potential problems with the IF/Detector Strip, turn the
tuning knob "through" the signal. There should be a clear audible
peak where the signal sounds the least distorted. If your tuner has
a center channel tuning meter, it's center indication should
correspond to this peak. If your tuner has some kind of signal
strength indication, this indication should also correspond with the
peak. If not, something could be mis-aligned in the meter or the
Detector circuitry.

There could also be a misalignment problem with the IF/Detector section if the signal sounds OK on soft passages but distorted on loud. As you tune away from either side of peak, the signal should distort and noise begin intrude EVENLY. Noise and/or distortion occurring more on one side of peak than the other could indicate misalignment of the IF section. Misalignment in the RF section is tougher to isolate but can be indicated by signals appearing to be louder or less distorted at one end of the FM band versus the other.
After you spent some time listening to and becoming familiar with the
sound of the tuner in mono, switch back to stereo. On a strong
stereo station you should, of course, hear differences from each
channel but no other spurious sounds. If you hear added noise or a
tone which may change pitch as you tune through the peak, something
is probably mis-aligned in the Multiplex section.
In older tube tuners, the ability to separate the left and right channel of the stereo signal even with the circuits optimally aligned varied all over the place, and could vary significantly with frequency with the separation degrading at higher audio frequencies.
Many tuners have/had circuitry added at the end of the multiplex section to "blend" the higher audio frequencies of the left and right channel together in an attempt to minimize perceived noise on weaker
stations. If your tuner has this function try switching it on and
off to see if there is an audible difference - if not maybe it's not
adjusted properly.
With good ancillary amplification and speakers which can exploit the
sound; a good, aligned tuner, set to a station that cares about the
sound, can reproduce a three-dimensional (left/right, front/back)
sound stage that approaches the source material.
{ NB CK is SO right here, live direct OB's of acoustic concerts, simply miked to real stereo, are a high end source especially if sans any dynamic range compression / or done gently! }
The progression of FM tuner technology has markedly reduced the
number of alignment adjustments and hence things that can go wrong
due to the ravages of time.
To give an example; in the Scott 310E tube tuner, there are 12 possible adjustments in the Multiplex section versus as little as one or two in "modern" tuners, and 10 adjustments in the IF/Detector section versus as little as one or two today. Appreciate that in older tuners most of these adjustments interact and take a LOT of time to get right, and DON'T SQUABBLE about a $150 realignment done by someone who HOPEFULLY knows what they are doing.
EVERY tube tuner that has crossed my path and not been touched in a while ......
has audibly benefited from re-alignment. < < < < < < < <-------------- NB

Even changing a tube in some of them can change the sound.
Charles King "


Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger

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