Ohm Loads for cartridges

The theory of playback of Vynyl LP recordings is well documented in several professional publications. it is in fact quite complicated. I will try to explain it in simple terms. Fitst, the frequency response on the recording is done to the RIAA recording curve, where the low frequencies are reduced in level and the high frequencies boosted to follow this frequency curve or frequency response. On playback, the frequency response of the Pick-Up Pre Amplifier is the exact opposite providing the RIAA Equalisation or Compensation to end up with an overall flat playback frequency response of the original recorded material. Unfortunately, there are losses in this process, and this is where things get tricky. The recording is done with a "Chisel" shaped stylus having fairly sharp corners. The Playback Stylus is either Spherical (Round) or Elliptical and cannot follow the original cut groove exactly which will cause some loss of high frequencies. A loss which differs from cartridge to cartridge, and dependent on the stylus diameter and type. The stylus assembly in the Pick-Up cartridge also have a mechanical resonant frequency, usually at a frequency higher than the highest frequency of interest, but in some cases involving inferior products unfortunately not. Electrically, the coil on a conventional Moving Magnet cartridge forms an inductor. The technique for best playback results is to "Tune" the cartridge at a suitable frequency by considering the cartridge coil as an inductor, and the cable on the Pick-Up Arm together with the input capacitance of the Pre-Amplifier as a parallel tuned circuit which will resonate at a particular frequency. Better types of Pre-Amps have selectable C to allow this to be done. The tuning will result in a distinct peak in the high frequencies which is then damped out by resistive loading to give an overall flat playback frequency response up to a maximum high frequency determined by the stylus diameter, and the stylus assembly in general. Very tricky to do and requires patience, basic test instruments and a calibrated frequency response test record. By the way, test records only last a few playbacks before they suffer loss of high frequency information. Fortunately, most reputable Pick-Up Cartridge manufacturer do specify the optimum capacitive and resistive loading for each type of cartridge. These specifications only hold good provided the cartridge is fitted with the correct original manufacturers stylus assembly, and that this is in "Good Health". For brand "X" aftermarket stylus assemblies, the situation could be completely different, my advise, for replacements, even if it costs more, purchase the proper manufacturers replacement stylus assembly.

Actually, the first part is wrong. The RIAA curve cuts the high frequencies before it goes to the cutting amplifier during proeduction, and the highs get reboosted on playback of the end product thru equalization in the phono stage. This is widely known. The stylus could not track the groove if the hf was as loud as the lf.

If any of you guys remember J. Peter Moncrieff's International Audio Review ( IAR ), he spent quite a bit of time in a few issues charting and documenting what worked best with dozens upon dozens of cartridges. While this was quite a while ago and he obviously couldn't have covered the current models of today, his findings on many of those was that what worked optimally in terms of frequency response and noise characteristics RARELY matched the manufacturers suggested loading characteristics. He produced charts showing the both of these specs with the factory specs and with a few others for you to draw your own conclusions from. Sean >

You got that backwards Carl. In the RIAA system, records are cut with a constant amplitude up to 500Hz, a constant velocity between 500Hz and 2120 Hz, and a constant amplitude again above 2120Hz. A phono cartridge is a velocity transducer, not an amplitude transducer. So for a flat response the records would be cut with a constant velocity at all frequencies. But that would result in very large groove excursions at low frequencies, which (amongst other things) would necessitate a very large spacing between the grooves. By attenuating the bass frequencies (in the constant amplitude region), the grooves can be cut closer together. By boosting the high frequencies (in the constant amplitude region again) the signal to noise ration is improved. Brian

Okay everyone, I have been reading all the words regarding cartridge loading on this msg. board but I am still a bit confused. I keep getting conflicting information from different sources regarding "cartridge loading" so I hope someone can clear my misconceptions up. Correct me if I'm wrong but I thought that a resistor with a higher value, ie. 10K ohms reduced more current than a 500 ohm resistor. If so, does it not follow that placing a 10K ohm resistor to "load" a cartridge would alter the signal from the cartridge, ie., reduce the bandwidth and lower the high frequency signals, etc., more so than a 500 ohm resistor. If this is so than how can a resistor with a lower value, say 500 ohms be said to offer more "loading" on a cartridge than a 10K ohm resistor? This is what Mr. Fremer suggests and yet I have dealers telling me this is wrong. I am confused.