Cartridge Loading.....Part II

Dear @intactaudio  : This is part of the J,Carr w.papers ( I never seen any from atmasphere. ) that I'm sure you are aware of it:

• 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. "

 

Yes he said too that a phono stage could be overloaded by the inductance, load impedance and cable capacitance if the designer does not took in count this issue and when that happens appears as IMD. Today SS designs comes with really high overload/headroom margin/level.

You said:

" Moncrief suggests (and shows) that for MC carts, IMD distortion levels are directly related to applied cartridge load. "

but atmasphere that has that IAR 5 posted:

" did not show is where the IMD was coming from..."

So, if PM did not shows from where comes the IMD only JC is rigth?

Because exist a big difference in both assertions what you said that PM showed means that always appears the IMD when what JC said is that the IMD sometimes could appears when the phono unit design was not designed tooking in count that " issue ". 

I think that you need re-read the PM w.papers or pasted here for all we can learn and most important to answer my question to you.

 

R.

 

 

So, if PM did not shows from where comes the IMD only JC is rigth?

I would say no since the two loadings  PM shows for his IMD are 5Ω and 100Ω both of which will surely damp any possible LC resonance which would then eliminate the whole RFI aspect.   I will note that the cartridge used has a 30Ω internal impedance so the 5Ω and 100Ω values are odd but that is secondary to demonstrating the effect.

 

Dear @intactaudio  : Re-reading several posts here and in other forum about the loading issue I tend to agree with you. Please let me explain:

first JC works graphs here were not to prove nothing about IMD or frequency changes because MC loading.

That's why he posted that " FR changes is bogus " when he posted this to a forum member who asked about the FR effects of cartridge loading: brigth vs dark sound. Doing his thread answer ( JC ) made a comment about IMD but was only a comment to re-afirm/confirm that exist no FR changes because loading. A time comment and nothing more than that.

PM confirmed no FR chnages with cartridge loading and all these is the only true  about cartridge loading and FR.

The JC advise is the lower cable capacitance the better.

@larryi pointed out:

" One position is that low loading is preferred because it CAUSES distortion that is perceived as high frequency information and people have grown accustomed to, and prefer, the distortion. "

 

According what you said PM posted:

" finally proposes that the excess IMD caused by a lightly loaded MC cart is often perceived as high frequency detail that many have grown accustomed to and the "dark" sound of heavily loaded cartridge can be due to a system being tuned for the typical lightly loaded case. "

 

@hagtech  posted with no other significant comment:

" 

reset the loading to 47K, buttoned things up and called the wife in for a listening session.  Sure as heck both of us noticed the highs were crisper "

 

 

All those post coincide in that specific regards.

 

Now, I can remember that over 30 years now I almost always recomended to load highly the MC cartridges at around 100 ohms and doing what larry posted: move the volumen position to recover the SPL and with this simple " even SPL " the dark sound just gones and the sound will shines with lower distortion levels that at 20k-47k.

 

Today with your help of those PM works and the other gentlemans help I confirm that over the years my take about those 100 ohms loading is just rigth and as a fact that's the load impedance that I used and use with dozens of LOMC cartridges that I owned and own in my active high gain phonolinepreamp and when I'm using a SUT in my unit I set up the MM load at 100k. Everything works excellent.

 

Thank's to you all to share a critical information for me. Good !

R.

 

R.

 

 

 

 

 

Dear friends @intactaudio  : I made an extensive search looking for documented/measured information about the JC comment on IMD and looking for too if JC mentioned a second time that issue and he never did it, at least I can't find out.

Btw, here information from experts, first by @hagtech :

 

"" As mentioned earlier, the peaking is best damped by lowering the load resistance. This is why MC cartridge manufacturers often request loading of about 100 ohms. The next plot shows the 5mH 10 ohm cartridge loaded with 200pF and a variable resistance. ..................... Most MC cartridges have less inductance than this example (chosen to highlight the issue), and so the typical loading value of 100 ohms is usually quite reasonable. "

 

Next comes by the designer/manufacturer of SUTs as intactaudio:

 

" Most modern moving coil cartridges have a source impedance of about 10 ohms and the “load impedance ten times the source impedance” rule suggests 100 ohms is a good choice for load impedance ...... This is well in line with the recommendations from many cartridge manufacturers. Anything above 100 ohms should be equally suitable.
Does the cartridge's tonal balance change with load impedance? It certainly does if the cartridge is a moving magnet type, but low output moving coil cartridges are much less sensitive to changes in the load impedance. Users sometimes claim that higher load impedances produce a brighter sound than lower ones, but cartridge manufacturers tend be non-specific about recommended load impedances, often recommending a wide range or simply anything above a minimum impedance.
The recommendation of Rothwell Audio Products is in line with Ortofon, Audio Technica and most other cartridge manufacturers - that 100 ohms is a good value for most cartridges, and that the exact value is not critical as long as it is well above the cartridge's source impedance.
One thing is certain, and that is that the load impedance should not be equal to the cartridge's source impedance. That would produce a 6dB loss of signal (when there's often only a few hundred microvolts to start with) and seriously compromise the signal-to-noise ratio.  "

 

R.

I would say no since the two loadings  PM shows for his IMD are 5Ω and 100Ω both of which will surely damp any possible LC resonance which would then eliminate the whole RFI aspect. 

@intactaudio FWIW 5 Ohms as a load is so low that most cartridges will produce measurably less output whereas at 100 Ohms the output would hardly be affected. At least this is true of any LOMC cartridge I've measured (a cartridge of 30 Ohms would be affected by both). Knowing that, when I saw the 5 Ohm value in Moncreif's measurements I was forced to take his conclusions with a grain of salt. I think he would have produced better science with 75 Ohms as his lower limit.