Ohm Loads for cartridges

For what it's worth here are my observations. I am running a Koetsu Onyx Platinum (.2mv, 5ohms) into a BAT VKP10 phono stage into a BAT VK5i into VK60 monoblocks biamped with Llano Trinities. The P10 has gain settings of 50 and 55 db in its direct all tube mode (6 6922 for gain) and gains of 67 and 73db if you switch in the stepup transformer. Loading of 100, 1000, 10,000 and 47,000 is builtin. To me the Koetsu sounds best at 55db all tube loaded at 47k. I believe there is some ringing at the higher frequencies which can be cured by going to 10k but with the loss of some dynamics. Going under 10k turns everything to mud and syrup. The volume at the preamp is generally at 50 I(unity is 62) so there seems to be sufficient gain and no loss of dynamics. The bass is satisfactory but see below. My guess is that the best loading would be around 25k. When I switch in the steup (sounds best at 73db) the sound to me takes on the characteristics of a CD: fast, dynamic, and a bass with terrific extension and control; however I lose all the midrange delicacy and air and timbre and so I go back to the all tube mode. This is loaded at 100 ohms and the sound would probably improve by going even lower. At 47k it is unlistenable. However the volume setting on the P10 is now around 30 which probably is not a good thing--losing music to the resistor. So all this means to me is that loading is very dependent on whether or not you are going into a stepup or all tube. I noticed that the Rowland phono stage only offers loading of 200 and 400 and I believe this is true of other solid states and hyrids. Now if I could only incorporate the stepup bass with the all tube mids and highs....

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