"I can change a cartridge and set up the replacement in twenty minutes. If I change the headshell on the one tonearm I have that uses interchangeable headshells, it takes about 10-15 minutes including the set-up of the new cartridge (the SME 309 headshells don’t allow for individual overhang: that must be set by moving the arm"
Good skills! There is no way most people could change/setup a cartridge on a fixed arm in 20 minutes. My friend knows how, has the tools, but waits for me, I supervise, he does it. Takes longer that way.
And, a heck of a lot of people do not have any cartridge mount/align skills,
the fixed arm comes with factory aligned cartridge, UNTIL ,,, stylus is worn.
If MM, switch stylus, the cartridge body remains in-place/aligned, takes seconds.
IF MC, everything must be mounted/all alignments, with a few inexpensive tools, and some skills practiced enough to be confident. Or have a friend or hired person do it. Give yourself a lifetime gift by learning/doing it yourself.
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As you say, some arms, you move the base in/out.
Typical ’standard’ removable headshell with slots, (allowing prior overhang and null points adjustments) stay aligned, change the headshell in seconds: all that is needed: verify azimuth (headshell fitting allows minor azimuth adjustment prior to final tightening, takes seconds) then set tracking weight and anti-skate: (altogether less than 5 minutes).
I buy headshells with allen key clamps, allowing the initial azimuth adjustment while in the arm fitting. Micro-Seiki 505 arms allow you to adjust the fitting on the arm for azimuth, a terrific feature.
Alternate Mono Cartridge; Alternate Stereo Cartridge: same as MC: mount/overhang/2 null points/azimuth/vta/ all pre-aligned once. simply adjust tracking weight/anti-skate when you want to use that pre-aligned cartridge.
The majority get anti-skate wrong, re-builders and makers say the majority of stylus they check are worn on one edge only! Using Hudson Hifi alignment LP with other side blank allows easy and accurate anti-skate to be set with visual confirmation, very quickly.
Arm Height: VTA. Refined VTA is for perfectionists, most of us get very good results with ’parallel arm method. Tonearm parallel to LP when stylus is in the groove (cantilever flexed by tracking weight), that is why it is important or very important to have an arm with easy height adjustment.
For me: changeable headshell/easy height adjustment, I haven’t seen anything as easy and smooth as the Acos Lustre GST-801.