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RE: Fidelity Research FR64S

Posted by John Elison (A) on June 30, 2020 at 14:33:03

In Reply to: RE: Fidelity Research FR64S posted by mulveling on June 30, 2020 at 13:54:19:

Okay, Baerwald and Loefgren A are one and the same. The Loefgren A parameters for the IEC modulated groove envelope with a tonearm mounted at 230-mm are as follows:

Effective Length: 246.74-mm
Mounting Distance: 230.0-mm
Overhang: 16.74-mm
Offset Angle: 22.25-degrees
Inner Null-Point: 66.00-mm
Outer Null-Point: 120.89-mm

> My point is that hitting the Loefgren A IEC curve at 230 mm P2S requires a slight modification to the offset angle

You're right! The offset angle of 22.25-degrees in the above scenario is slightly greater than the 21.5-degrees specified for the FR-64S tonearm. However, if you want to increase P2S so the offset angle will equal 21.5-degrees, you will need to extend P2S significantly farther than 231.5. Here are the tonearm parameters for that scenario.

Effective Length: 254.96-mm
Mounting Distance: 238.80-mm
Overhang: 16.16-mm
Offset Angle: 21.50-degrees
Inner Null-Point: 66.00-mm
Outer Null-Point: 120.89-mm

The only thing I can think of that would justify a mounting distance of 231.5 is if a different headshell had a 1.5-mm longer distance from its bayonet mount to its headshell slots. That would require mounting the tonearm farther from the spindle to maintain a 15-mm overhang.

On the other hand, it's more likely that someone simply made a mistake in thinking that by increasing mounting distance they were also increasing overhang thereby making the FR-64S more compatible with IEC Loefgren A. Unfortunately, by increasing mounting distance you are actually reducing overhang. Consequently, they should have specified a mounting distance of 228.14-mm to increase overhang to 16.86-mm for IEC Loefgren A as indicated by the tonearm parameters below:

Effective Length: 245-mm
Mounting Distance: 228.14-mm
Overhang: 16.86-mm
Offset Angle: 22.42-degrees
Inner Null-Point: 66.00-mm
Outer Null-Point: 120.89-mm

Best regards,
John Elison

Edits: 06/30/20

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