Help with cartridge loading.

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#21
I am unconvinced that compensating for a falling mechanical response by peaking the electrical response works very well. About 40 years ago I designed a video amplifier for a project I was working on and the bandwidth was a little below specification. In retrospect I should have replaced the transistors with better ones that had higher cut off frequency (higher gain bandwidth product) but instead decided to use a peaking coil to compensate for the early fall off in response. It worked well on sine waves but it messed up the phase response and on square waves produced overshoot and ringing. I concluded the peaking coil was a bad idea but had spent too much time and money to redo the design with better transistors. I think that peaking the cartridge electrical response creates the same problem.
 
#22
Electrical compensation for a falling mechanical response might not work well, but I suspect it works better than not compensating for a falling mechanical response.

Any sharp cutoff filter will produce ringing on square waves, because all the frequency components which would cancel the ringing are no longer present. You are seeing the effect of things which are missing, not things which the filter has added - it took me years to realise this!
 
#23
Hi,

I´m wondering why MM cartridge loading is typically done by switching on additional capacitance, as this effects bandwidth negatively.
The capacitive base load formed by the cabling and amp input capacitance is often on the edge already, sometimes even too much.
In such cases additional capacitance is of no positive use.
Why aren´t -similar to MC cartridge loading- resistors used instead (or also).
Seems that slightly pointed highs pickups like reported from the AT-440mla would profit more from higher loading (~39kOhm) and darker sounding pickups like Shures or Grados preferred less R-load (~68kOhm), combined with the lowest capacitive load possible.

jauu
Calvin
 
#24
Calvin said:
I´m wondering why MM cartridge loading is typically done by switching on additional capacitance, as this effects bandwidth negatively.
Click to expand...
Whether the capacitance is additional depends on what is already there. It is true that some cables plus some preamps already provide more capacitance than some cartridges recommend. One solution is to use Ortofon MM, which almost always need lots of capacitance.

Too much capacitance affects bandwidth negatively, but so does too little capacitance. The right amount gives a little electrical HF boost to counter the mechanical HF droop.

Changing the resistive load would have less effect, and could increase HF noise.
 
#25
rayfutrell said:
I am unconvinced that compensating for a falling mechanical response by peaking the electrical response works very well. ... I concluded the peaking coil was a bad idea but had spent too much time and money to redo the design with better transistors. I think that peaking the cartridge electrical response creates the same problem.
Click to expand...

Fortunately, the engineers at companies like Shure have done the hard work of demonstrating this. It works very well IF you follow their loading recommendations- they published a very nice paper on this in Audio some years back. Deliberately ruining the frequency response by not following their recommendations because of something to do with video amplifiers is not something I'd recommend.

MMs have gotten a bad rep among audiophiles, and this is almost entirely due to not loading correctly, whether wittingly or unwittingly.
 
#27
If the Q is less than 0.5 (critical damping) you will not have ringing. However to get a peak in the electrical response the Q has to be over 0.707 (maximally flat condition) and the circuit will ring on transients. The peak in the electrical response is directly proportional to the Q. The more the peaking the more the ringing.
Sy,
Do you have a link for that Audio article?
 
#29
rayfutrell said:
If the Q is less than 0.5 (critical damping) you will not have ringing. However to get a peak in the electrical response the Q has to be over 0.707 (maximally flat condition) and the circuit will ring on transients.
Click to expand...

No. The overall damping comprises both electrical and mechanical, much in the same way as a loudspeaker and crossover. In a similar sense, Qts vs Qes and Qms.

Sorry, I don't have a link to the article, but it was discussed (and the critical figures reproduced) in Linear Audio vol 6, p 163.
 
#30
Hi,

on hagtech.com/loading.html there´s a nice article explaining loading on pickups.
It shows the effects of capacitive loading and resistive loading and the difference between both.
Beeing a sim it doesn´t account for the mechanical resonance of the pickup and its related effect on amplitude response.
For most pickups this resonance is located between 10kHz and 30kHz.
The right amount gives a little electrical HF boost to counter the mechanical HF droop.
Click to expand...
Yes, but C-loading affects the bandwidth alot more than R-loading.
Especially with ´louder´ pickups, featuring increased R and L values of their coils, the bandwidth limit may be close to 10kHz with a -12dB/8ct drop above.
As sims show the high inductance pickups show less amplitude variation/less peaking, resp. they allow for wider capacitance variation in this regard.
On the other hand lower inductance pickups amplitude peaking is higher but associated with higher peaking frequencies.
See attached LTSPiceIV sim file.
The sim also shows, that keeping C low and varying R rather dampens the peak amplitude, preserving more bandwidth/high peaking freq.
It seems to me that the pickups would profit rather more from R-loading than C-loading. :scratch:

jauu
Calvin
 

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#34
Not necessarily. The source MM has mechanical issues. The inductor MM is just a slightly lossy (and hummy?) inductance so you can't assume the same bandwidth. This is because there will be only weak coupling between the mechanical and electrical aspects.

If your problem is too much capacitance for your cartridge with your chosen phono preamp then you have to change one of them.
 
#35
There are several articles looking into cartridge loading. Here are two. However, neither of them get the formula for the Q right.
Website of Wayne Stegall - Phono Termination Calculations and Calculator
http://www-f9.ijs.si/~margan/Audio/Ironing_RIAA.pdf

I don't believe the dynamic loudspeaker is good analogy to the MM phonograph cartridge. A loudspeaker is reversible. If you put a voltage into the coil the diaphragm will move and if you move the diaphragm a voltage is generated in the coil. Moving the cartridge stylus generates a voltage in the coils, but putting a voltage into the coils is not going to move that stylus and generate a back EMF because the stylus is restrained by the groove.
 
#36
rayfutrell said:
A loudspeaker is reversible.
Click to expand...

So is a cartridge. The laws of E&M don't distinguish between a magnet moving past a wire or a wire moving past a magnet.

Whether you accept that the mechanical and electrical response combine to give an overall response and that the electrical should be adjusted for an overall flat response is irrelevant- the people who design and manufacture cartridges are well aware of it and make their recommendations accordingly. There's a lot of nonsense out there, unfortunately, just because of this sort of narrow view which doesn't consider the transducer as an electromechanical system.
 
#38
DF96 said:
If your problem is too much capacitance for your cartridge with your chosen phono preamp then you have to change one of them.
Click to expand...

Oh to have pockets deep enough for that...🙂
I had to replace my 35 yr old Plinius amplifier due to lightning strike !
I upgraded to something that brought me into the digital era though with a very mediocre phono stage.

I auditioned and purchased a new cartridge that was well reviewed and suited my listening preferences.

Then I unearthed the phono stage I had been building for the last decade and finished it. 🙂

Unfortunately the Nagaoka MP-150 is not a match for my Supra Phono stage.🙁

The Supra phono preamp has input capacitance of 280pf and the Nagaoka recommends 150pf max.🙁 (without tonearm and interconnect cabling 😱)
(surely Shure, Ortofon, and Grado build for the real world where capacitance in circuits and cables define options rather than other manufacturers who design for ideal conditions or their own in-house electronics ??)

So...until I can afford to replace the cartridge (12-18 months) I have to find a solution that allows the household 🙂D) to enjoy the 10,000 LP library. 🙂

Our next cartridge may well be an Ortofon, Grado, or MC, all of which are happy or immune to capacitive loading...😀

Meanwhile in order to ameliorate the current condition i have adopted the workaround here... Near-zero capacitance effect for phono cables - method - Vinyl Engine
and can report a very happy household !, WAF !, and a voracious trolling through the collection ! 😀
LPs, once again spin our wheels !..
Thanks to all posters for your guidance and comments.
I am enlightened, happy, and grateful.
 
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#40
Found a paper on cartridge loading with actual measurements, not simulations, on page 2. As you see when the capacity is reduced from 1000 pF the Q (peak) is reduced and the bandwidth (3 dB frequency) is increased, as expected. However when the capacity is reduced to 60 pF the response decreases the goes back up. Is this the tip resonance showing up as the bandwidth is increased? I seem to recall reading that the Shure V15-V tip resonance was around 30 kHz, well above the audio range.
http://www.filmaker.com/papers/pap_RM-Phono C-load & balance.pdf
 
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