Cartridge Loading for a phono pre amp

Dear @imhififan : We can run several kinds of tests but the real, important and critical issue for any audiophile ( not a fully technical oriented person. ) is if load impedance in a LOMC cartridge changes its frequency response and J.Carr proved it does not and this fact is what we need to know:

• Kleos electrical model (9uH, 5.4ohm, 8pF)
• Lyra Phono Pipe Very Low Capacitance tonearm-to-phonostage cable 120cm actual measurements (0.75uH, 0.325ohm, 32pF)

What these tell me (among other things) is that, all else being equal, changing just the interconnecting cable (each of which has a different capacitance characteristic), changes the optimal resistive load; and if you can afford to bring up that peak in the MHz to something <10dB then you can bring up resistive loading to about 500-1K ohms even with a highly-capacitive cable; and finally, you are not really affecting the audible high frequencies with any resistive load shown. "

He followed:

" To claim that the loading affects the measurable frequency response of the cartridge is bogus. However, if inappropriate loading bathes the phono stage in copius amounts of high-frequency noise, it may start to distort (unless the designer implemented various techniques to make sure that this won’t happen), and the result will likely be intermodulation distortion. IMD products can go low enough to fall within the audible band (even when the stimuli are ultrasonic), and IMD nearly always is not harmonically related to the signal, making it particularly grating to the ear. ""

All those was confirmed in the same old thread by an expert engineering of Analog Devices Co. when he stated with facts:

" certainly not on tracking which is demonstrably false based on IM tests on tracking performance that I have incidentally performed as a function of load. While mechanical impact does occur as a result of electrical load- there is some back emf necessarily generated by the signal current that affects the mechanical motion, but a quick back of the envelope calculation using Lenz’s law and the 10uH cartridge suggests a 2 orders of magnitude difference between the generated signal and the back EMF for a 100 ohm load at 20kHz- certainly not enough to cause tracking issues . By the way, I constructed a model for the cartridge back EMF using Lenz’s law and incorporated it into my simulations.
For those who are interested, the simplest version of the law is V(t)= -LdI/dt.
In this case the parameters can be measured (the LC100A meter from Ebay is a great way to do it) and the back EMF acts to oppose the voltage developed in the coil. The fractional change (attenuation) in the signal voltage is easy to calculate as it approx. equal to -L*2*pi*frequency of interest/Rload. So, it’s inversely proportional to the load R and proportional to the frequency. "

The other issue is if 47k is the standard load for a LOMC cartridge and the evidence showed in " all " active high gain phono stages proved that 47k is not the standard load impedance for LOMC cartridges and along those evidence/facts are the coments of the manufacturers/designers of those phono stages as J.Curl , M.Huber, J.Carr and others. As a fact if exist an standard load for LOMC cartridges this is not 47k but 100 ohms ( some say between 100 ohms-500 ohms. ) but as designers/reviewers/audiophiles know and say the LOMC loading is up to each audio system and owner MUSIC priorities.

Those both issues are already quite clear.

Now, if you want to " see " if load could change cartridge tracking abilities then use the Shure ERA V test record. I understand that you own an active high gain phono stage, this means with no SUT. There are other cartridge tracking test records as Telarc that’s very good. To make this kind of test through a test record you must be sure that the cartridge/tonearm overall alignment/set up is accurated and that the test record and the stylus tip are clean and optimal condition and the run the test and make the load changes you want it.

For me everything is already clear: load impedance does not affects cartridge frequency response and 47k is not the standard for LOMC loading. The test could be only for " fun ". Just do it.

R.

If anyone wants to do a simple experiment on how loading affects a magnetic circuit, one can use a speaker. It’s similar to a MC cartridge circuit wise as the coil of a speaker moves in a magnetic field just like an MC cartridge.

Start with an open circuit (speaker disconnected from amp) and lightly push the woofer, it should move freely. Then (as an extreme example) try wiring a jumper across the + and - terminals of a speaker (make sure the amp is disconnected). Try pushing the woofer, it will resist all movement. Then, try wiring a resistor at 10x the impedance of your speaker. You will notice some resistance trying to push in the speaker compared with the open circuit. Then try a resistor 100x, then a 47k resistor.

This will demonstrate how loading affects the effective stiffness of the cantilever under various loading conditions.

I have the Benz Glider Gold and regarding @Blackdoghifi on loading recommendations, the Benz do like higher loading. I have found 1K to work the best after running through other lower options using my Fosgate Signature phono amp. Try them all but I’ll bet you will find the 1K to sound best.

@rauliruegas To be clear, at no point have I stated that loading affects the frequency response of a LOMC cartridge. Your statements to the contrary are false. Please cease and desist. When you engage in such statements and then debunk them, you are engaging in a logical fallacy known as a strawman. Logical fallacies are inherently false.

How does one safely send a square wave through a cartridge? Just curious as I have no intention of trying it.

Apparently PS Audio did their homework.

I suspect if you put too much energy through the cartridge you might be able to damage the magnetic field generated by the magnet structure, so your reticence is wise. I used a square wave generator set to a very low output. I put the cartridge in series with a nominal resistance so I could read the square wave across the resistor- essentially if the coil of the cartridge were a problem for the square wave, it would be readily visible. The signal was low enough (I have to admit I was a bit concerned about damage to the cartridge when I did this the first time) that the cartridge was unaffected. This meant the scope was at a very high gain setting.

Note that a load to the cartridge would be a resistance in parallel with the cartridge, not in series. Anyway, I found that the cartridge could pass a square wave at any frequency- even 20KHz, with no ringing at all.

This surprised me at the time, since the reason for doing this was to create a box that would allow you to plug in the cartridge and easily determine the ideal load (this was about 35 years ago). When I saw that the cartridge could pass a perfect square wave at any audio frequency, I realized that the loading was not affecting its frequency response so something else was afoot.

One of the side issues associated with this topic is that of ticks and pops. If the phono section has good RFI immunity and if it also has good high frequency overload margins, that peak at 1 or 2MHz won't overload the input of the phono and you'll get less ticks and pops. I had this graphically demonstrated to me when an employee complained of a noisy LP he had bought. His LP played fine on the shop system so he brought in his preamp and there were the ticks and pops, sounding for all the world as if they were on the LP surface.

How that works is the energy of the cartridge can set off the electrical resonance, even though that peak is well outside of the audio band. This phenomena is known as 'excitation' in the radio world. Once the peak has gone into excitation, it puts out a signal at its resonant frequency which is applied to the input of the phono section. Since its a good 20-30dB higher than the cartridge signal, it can overload some phono sections if they have not taken this phenomena into account.  I suspect such phono sections are a lot more common than we like to think- that preamp I mentioned earlier was a Toshiba and Toshiba is a supplier of semiconductors so you would expect good engineering... this has led me to think this problem was an epidemic back in the 1970s and 80s. 

@imhififan ​@fundsgon  friends: As I said not only the Shure or Telarc test records are really good but other as Ortofon are great as the CBS Laboratories series and the Stereo Review and we have not forget the B/K and Vanguard.

I own in mint condition/almost new around 15-20 vintage test record.

The Ortofon are special because there is no analog recorder in the recording process due that are D2D and the Telarc neither because is a digital recording test LPs. We can find out almost any test we can make not only tracking or resonance issues.

I bougth all through ebay and the overall recording proccess of any of those old test LPs even for today " standards " are second to none.

R.