Ohm Loads for cartridges

Hi Carl. I have experimented with cartridge load in the Aesthetix IO phono, and the hand trimmed resistor provided by Lloyd Walker (Walker audio) was an improvement over the standard one. As far as other places in the circuit, I agree that any resistor that parallels the signal path will effect the sound. On subsonic filters, the IO does not have one. My previous unit, the Elliott Magnum Opus Phono (previously the Counterpoint SA-9, less the Infinity caps and tweaks), did have a subsonic filter, and it was adjustable in two positions. I think it was 30 HZ and 10 HZ, but I may well be wrong on those numbers. My experience with the subsonic filter (either position) was negative in my system, but that could be due to the design of the filter in that particular preamp. I previously used a 28K Vishay for loading the Benz Ruby in my system, when it was my reference cartridge. The specifications had called for the Ruby to load at 49K. My Koetsu Rosewood Platinum Signature is running at 1K Ohms, and was determined by the (selectable) choices on the rear of the IO. After that load number was determined, I tried the hand trimmed resistor provided by Walker. The improvement was very nice, considering the little money and time spent for the change.

1000 ohms seems very high for such a low output mc like that Koetsu. According to the Guide, it's output is .2 millivolts at 5 cm/sec rms lateral velocity. My Lo4 is much higher at .85 millivolts, and seems to sound best at 384 ohms. Again, Fremer never sways from his experience, that very low output cartridges sound best when loaded (even well below 100 ohms). I don't doubt that you are getting excellent performance from your Platinum Signature, though. I also don't doubt that a subsonic filter would have a signature on the music, but feel that it'd still be nice to "switch one in", when needed, otherwise you're unnecessarily straining the power amplifier, asking it to reproduce a noise artifact that isn't part of the recording...and a very loud artifact it can be, even with slight warpage that's common in the pressing of brand new records.

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.