Cartridge Loading for a phono pre amp

holmz asked:

" Wouldn’t loading it down to 250 ohms from say 47k make it softer as the back EMF os gone that “would have been” stalling the motor? "

his answer was: " EMF?. No...." the same answer on other 2 subject treads different forums where was proved that it’s EMF:

"Yes, it really is back EMF- it’s calculated using Lentz’s law and is a consequence of Faraday’s Law of Induction and it occurs as a result of the change in current through the coil- that’s where the frequency dependent term comes from (the derivative). The term is subtracted from the voltage generated by the cartridge and in that way it acts to reduce the output voltage and hence the current, so there’s a degree of negative feedback. "

and in this thread you can find out the equations used. In this and the other threads your " man " "just " dead silence " against that EMF analysis the engeenering did it, not a single comment.

Thanks @rauliruegas

Are these the equations you are referencing?

 

My Sonic Lab Ultra Eminent BC: 0.6Ω output 0.29mV

 

Voltage Input: At 0.29 mV, the Wizard determined the optimal gain level at +70 dB of gain. This setting has audible hiss coming from the speakers at 30% volume without any record playing. On careful listening, the gain level was sufficient. Optimal loading was determined to be 180Ω by the Wizard.

 

Current Input: At 0.6 Ω, the Wizard determined the optimal gain level to be I/V + 20 dB, but based on listening test I preferred a much lower setting of I/V + 5 dB.

 

According to Ohm’s Law where I = V/R, Current = 0.29 / 0.6 = 483 Micro Amps, a very sufficient level of gain based on the low impedance of the cartridge.

 

Clearaudio Goldfinger Statement (GFS): 50Ω output 0.9mV

 

Voltage Input: At 0.9mV, the Wizard determined the optimal gain level to be 70dB of gain on the Voltage input. On listening test, I preferred +60 dB of gain, a much lower setting. Optimal loading was determined to be 330Ω by the Wizard.

 

Current Input: At 50Ω, the cartridge required IV+ 20 dB of gain.

 

According to Ohm’s Law where I = V/R, Current = 0.9/50 = 18 micro amps, the GFS’s high input impedance resulted in a very low level of gain regardless of the Goldfinger’s output of 0.9mV, which is relatively high for an MC cartridge.

If that is the case I still appear to need feeding to compute the back EMF.
Luckily you stated:

I think that all forum participants has a responsability and is not spread false information with no real evidence. That responsability comes by the fact that Agoners forums have different knowledge levels gentlemans and everyday comes rookies looking for advise looking for help so the higher knowledge level participants in the forums have all a higher responsability about that’s exactly that: give help and good proved advises.

Well… I am the rookie that needs some help.

Ralph stated that the cantilever gets stiffer as the impedance goes down,

you stated this most recently:

"Yes, it really is back EMF- it’s calculated using Lentz’s law and is a consequence of Faraday’s Law of Induction and it occurs as a result of the change in current through the coil- that’s where the frequency dependent term comes from (the derivative). The term is subtracted from the voltage generated by the cartridge and in that way it acts to reduce the output voltage and hence the current, so there’s a degree of negative feedback. "

and earlier this:
 

@holmz : " He never posted that loading to hard a cartridge will cause stiffness to the cartridge cantilever enough to mistracking. "

I was who posted that only to clarify that J.Carr never support those false statements by atmasphere. Tha’s all.

 

" to which answered " with false statements. Good for you if that is what you was looking for.

 

I paste all those information coming for true experts for we audiophiles can learn and don’t believe in what " some one " is spreading every where with out facts.

I would have assumed that the higher impedance was making it more difficult to push the current, and that the low impedance would allow it to flow easier and result in a lower voltage at the phono stage.

But Ralph says it is the other way, and another gentleman as well.
(Hence the statement I made about needing a real physicist.)

I would like to understand how the loading affects the voltage at the phone stage as well as the stiffness change at the cantilever/stylus.

Dear friends @holmz : Here and in other threads I told you that you read but sometimes you did not because those equations ( not all the development but help you. ) are twice posted in this thread.

Look something interesting:

" 1-

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. ""

That came from J.Carr and next what was posted by other expert gentleman around EMF and tracking that involves IM too:

" 2-

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. "

R.

Why ARC featured such function in their reference phono stage that serve no purpose? So they can charge more?🤔

We have a loading strip on our preamps too, and I advise customers with LOMC cartridges to not use it. But if you have a higher output cartridge, the loading strip can be quite handy! Because of their higher inductance, high output cartridges have that electrical peak at a lower frequency, which can be at the high end of the audio band or just outside of it. The winding of a higher output cartridge tends to have a lower Q value so loading can be helpful to reduce ringing. 

" The industry spec is 47K for all cartridges.  " where is the " official " announcement about, say by the AES that coul confirm it? where?

@rauliruegas 

Cripes. If one is grounded in audio history then this is obvious. ARC SP6: 47K phono input impedance; similarly H/K Citation 1, Marantz 7, Conrad Johnson PV12, etc., etc.

"  less able to trace high frequencies. " again: where are the white papers that can confirm it.

It has to be published to be real?? Since JCarr published something, you're not challenging his statement (despite the obviously recursive aspect of that argument...), you're employing a double standard. In order for the cantilever to not get stiffer a fundamental rule of physics (law of energy conservation https://energyeducation.ca/encyclopedia/Law_of_conservation_of_energy) has to be violated. IOW you would have free energy and the world's energy issues would be solved 😂 

So no papers needed- just a grounding in basic physics (high school level), in particular how alternators and generators work. A 'Sheesh!' is in order here.

That is ridiculous and with no facts or diagrams/equations that shows exactly that. I That " can easily get you outside of this target window ( ideal resonance frequency range. ) " is not proved here or in any other subject threads. Again: only IMAGINATION.

Ohm's Law and the power formulas are not a figment of someone's imagination 😁

The cartridge is being asked to do just under 2 1/2 orders of magnitude more work with the example you provided:

47,000/100 = 470

-meaning 470X more current is drawn from the cartridge; because 47K is so high a resistance value relative to the impedance of the cartridge winding, the output voltage is essentially unaffected so the current increase also represents the wattage increase).

Anyone with an elementary school education can work out the math here. Perhaps, knowing that, you can tell me where that current is coming from??  If you can answer that, a bonus question: what is the consequence of that current flow?

This is such simple math I don't see why a paper needs to be written about it, but maybe even though its basic, some people simply haven't thought it thru. Or didn't do so well in math.

Please do answer the questions.

These only 2 of your examples about that 47k input impedance:

SP6

50K ohms, all inputs. (Magnetic phono may have any value from 10 ohms to 100K ohms substituted. Also has provision to add input capacitance for matching certain magnetic cartridges.)

PV12

• Frequency Response: 2Hz to 100kHz
• Distortion: 0.25%
• Gain: 49dB (mm), 16.5dB (line)
• Input Sensitivity:
• Signal to Noise Ratio: 78dB (mm)

" In the PV12 with phono stage, this input provides the amplification and equalization required by moving magnet and high output moving coil cartridges. " This information came by CJ directly, not mine.

One of them not even handled LOMC cartridges that’s the real issue.

Useless that you insist about. No one active high gain phono stage came or comes by default with fixed 47k input impedance, no one. I posted here around 8-9 today phono stages ranging in price from 3K to 95K that’s is not only enough evidence but a true evidence and not as your CJ or SP6 and the like.

In the other side you did not gave us the answer to what you posted before:

" can easily get you outside of this target window ( ideal resonance frequency range. ) "

where are those cartridges that with today decent medium mass tonearms shows what you said coming from 100 ohms to 47k or the other way around. We need to see/read those numbers out of the ideal frequency range due to loading. Where ? and don’t try to distract with other kind of information or other question: JUST SHOWS THOSE NUMBERS AND LOMC CARTRIDGE MODELS WITH TONEARMS.

R.