STP distance. Is it critical ?

This might help:

http://www.audioasylum.com/audio/vinyl/messages/77287.html

You can see in numbers what difference there is.

I think the effective length of the arm will change if it is mounted somewhere other than its designed location. I might be wrong, but it makes sense that the arm would swing through a slightly different arc. The manufacturer's template would not line up quite right.

This might help:
The link did not come through correctly.

Here's another attempt:

http://www.audioasylum.com/audio/vinyl/messages/77287.html

Yes, it is critical. When you want to have the specs from the manufacturer to get the best result of this calculated Arm. Some Arms work also with differences (Loefgren and Baerwald are not the only valid datas), but then you need a different alignment System. Otherwise you will ruin the grooves sooner or later. Analog reproduction is precision.

Dear Smoffat: Everything is almost critical in cartridge/tonearm set up depending what you are looking for.

In a cartridge/tonearm set up you can't change the effective length: the distance from stylus to tonearm pivot center.

All the geometry calculations/equations were made with this effective length parameter with a fixed/permanent value and inner/outer most grooves distances.

Baerwald, Löfgren or Stevenson set up calculations take all those three values to obtain mainly : overhang, offset angle and STP distance.

You can find through the net all these geometry calculators where the only parameter that you need give to the " Calculator " is tonearm effective length to have all the set up parameters.

Even you can choose between DIN or IEC standards or even you can make tyny changes on the inner/outer most distance values.

In all cases you will have all the parameters need it to cartridge/tonearm set up and you can use any one of them with your Phantom and decide which works fine for you or wich one you prefer.

With any of these kind of geometry set up calculations the tonearm can be placed anywhere if you respect the effective length at null points.
Yes 1.0mm-2.0mm makes a difference and not for the better.

As Syntax point out: " Analog reproduction is precision. "

Regards and enjoy the music,
Raul.

Smoffat, making a couple of assumptions about the tone arm you can see what the results might be by using the calculators available at VinylEngine. Let's assume that to set up for Lofgren's A (Baerwald) alignment with an effective length of 235mm and spindle-to-pivot distance of 217.5mm that the corresponding overhang would be 17.5mm with an offset angle of about 23.4 degrees. (If you know the actual offset angle/overhang you can get more accurate results.)

The calculator will indicate the effect of moving the tone arm +/- 1mm of the specified STP while maintaining the specified offset angle and effective length of the tone arm. (Overhang is changed by +/- 1mm to accomodate change in STP and keeping effective length constant.) The graphs display the resulting tracking distortion.

If your STP distance is 1mm closer at 216.5mm ("Custom"):

http://www.vinylengine.com/overhang_shift_calculator.php?el=235&oh=17.5&oa=23.4&ty=s&n_oh=18.5&submit=calculate

If your STP distance is 1mm farther at 218.5mm ("Custom"):

http://www.vinylengine.com/overhang_shift_calculator.php?el=235&oh=17.5&oa=23.4&ty=s&n_oh=16.5&submit=calculate

However, you may be able to accomodate the needed change in offset angle by rotating the cartridge within the headshell slots. For example, if you change effective length by 1mm to 234mm (STP is 1mm too close), you may be able to achieve Lofgren's A (Baerwald) alignment by rotating the cartridge so the offset angle is now 23.5 degrees. The alignment will be very close, depicted as "Original"/"manufacturer":

http://www.vinylengine.com/tonearm_alignment_comparator.php?m_el=234&m_oh=17.5&m_oa=23.5&compare=i&submit=calculate

Tom