Part of the "fun" of owning an analog playback system is living with the doubt that it is appropriately tuned and set-up. For we anal retentiveness types (the largest proportion of audiophiles?) this is a difficult uncertainty to live with. Am I missing some notes? Can I really hear the rosin across the bows? And I am certainly not of the "if it sounds right, leave it alone" school. Our ears 'betray us', and the only real way of system verification is through measurements. But as most test records are things of the past, it is a little difficult to accomplish this.
Thus began my long sojourn of purchasing test records though eBay. In the end, I acquired a considerable collection, including several un-opened copies of a most useful test record, the CBS STR-112 "Square wave" test record. This record is very well documented and is extremely useful. "The STR-112 permits detailed study of the tracking capabilities of stereophonic phonographic pickups. The square wave modulation allows rapid appraisal of stylus-tip mass, damping, and tracking. Low frequency compliance and tracking are determined by means of 300Hz bands of progressively increasing amplitude. Intermodulation distortion measurements are made possible by graduated 200 Hz and 400 Hz intermodulation test bands. Furthermore, all of these tests are provided in left-right or lateral-verticle modulation modes. The STR-112 has been cut with verticle angle approximating 15deg., which is representative of current recording practice. It replaces the now-obsolete STR-110 and STR-111 Test Records."
CBS STR-112
AT-33ANV tracking 1000Hz Square Wave
[Tested in my SME 20/2a with Breuer Dynamic 8C MkII] The first cartridge that I tested was my Audio Technica AT-33ANV , a cartridge similar to the AT-OC9 that John Ellison likes (and has tested) so much. This test is supposed to create a square-wave, for a perfect velocity sensitive cartridge, but I never saw anything but triangles being reproduced -- it is cut as a triangle on the record.
Here is snapshot of a track from the DIN 45542 PHONO CARTRIDGE DISTORTION TEST RECORD LP" -- this is an interesting test for Frquency intermodulation (though I actually didn't measure or quanitify this FIM -- I was more interested in just getting a feel for the capacity of the cartridge and to see the how my setup checked out -- I was specifially looking for symetry in both channels -- it did beautifully.) All tests where done with a VTF of 1.8 grams.
The Side B is recorded with 45 degree flanks and a vertical modulation angle fixed at 15 degrees -- there is a 300Hz+3000Hz modulated signal for 33rpm, which tests for nonlinear distortions with stereo pick-ups. 0dB: f1=300Hz with velocity 8cm/s, f2=3000Hz with velocity 2cm/s, i.e. velocity rate is 4:1 for 300Hz/3000Hz (11cm/s:2.8cm/s for nearly 400Hz/4000Hz). Playing with 33.3rpm, frequency intermodulation distortion (FIM) can be measured by determining the degree of frequency modulation of f2 by f1 (FIM can be read as flutter component around 300Hz) - Ortofon often declares these data for their cartridges as FIM distortion at recommended tracking force.
AT-33ANV tracking side B of the DIN 45542 PHONO CARTRIDGE DISTORTION TEST RECORD LP
Here is another screen capture of the Audio Technica AT-33ANV tracking yet another cut of the DIN 45542 test record. This one is from side "B" I believe, and is a sequence of tests at different velocities to test VTA. Once again, I was mostly interested in using it as tool to determine if cartridge was tracing both sides of the grove and generating an equal amplitude.
AT-33ANV & DIN 45542
AT-150MLX Azimuth Test -- 2 deg tilt towards spindle.
Here follows one of the more compelling reasons to invest in an O'scope to analyze your phono cartridge setup. At left you will see the first trace of an AT-150MLX tracking the Cardas Audio Test record (engineered by Stan Ricker) track 9 -- NAB "0db" 1Khz@7cm/sec. In the following sequence, I will adjust the headshell azimuth in order to align the cartridge stylus/diamond shank into the disk.
There are two things ones needs to check before this -- You need to calibrate your O'scope probes with the typical self calibration tools that the manufacturer provides, and you need to measure the relative channel performance of your RIAA phono stage, using a HAGTECH (or home brew) inverse RIAA filter to check to see if the phono channels are balanced.
In this capture, we see that the magenta trace (the right channel) has less amplitude than the left (yellow) channel. This is because I have the the top of the headshell (a Sumiko HS-12) torqued over from perpendicular by about two degrees towards the spindle pivot.
Here is an example of the type of measurement that one needs to perform before attempting this test -- here is a snapshot of my modified HagTech Bugle Phono stage, measured with ARTA , where I am sending a MLS impluse through a HagTech Inverse-RIAA: the channels are with 0.1 dBv of one another for the bulk of the spectrum, and almost identical at 1KHz.
HagTech through iRIAA
In this capture, we see that the magenta trace (the right channel) has more (greater) amplitude than the left (yellow) channel. This is because I have the top of the headshell (a Sumiko HS-12) torque over from perpendicular by about two degrees away from the spindle pivot. The opposite of above.
AT-150MLX with 2 degree cant in other direction
The best that I could do
Here is the very best alignment that was possible after several iterations of changing the azimuth. The result was actually a little off perpendicular (right angles to the surface of the record), which means that the diamond stylus shank was not perfectly perpendicular as it relates to the cartridge body -- which is the case in almost all of the cartridges that I have ever owned, tested or installed for customers.
An important point in making these measurements is to use a high-pass filter to filter your discs rumble -- the predominate rumble came from the vinyl itself, not necessarily the turntable -- at least in the case of my non-vacuum hold-down turntable. The waveforms wavered up and down with the micro-warps and surface imperfections that the stylus was traversing -- not even the extra thick 180 Cardas Frequency Test Record was immune to these fluctuations.
