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Radio Road Which tuner to get and getting the most from it. Thank God, for the radio! |
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Radio Road Which tuner to get and getting the most from it. Thank God, for the radio! |
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In Reply to: How does one know when a tuner needs alignment? posted by barondla on October 4, 2022 at 18:09:18:
o FM Stereo Tuner "Alignment by Ear"
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 accept 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, its 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.
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. Even changing a tube in some of them can improve.
Charles King
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Follow Ups
- Try This? - stellavox 10:13:11 10/08/22 (1)
- RE: Try This? - barondla 21:53:49 10/23/22 (0)
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