Cartridge impedance loading question

* The correct loading for any cartridge will be such that it does not ring at audio frequencies- IOW if you run a squarewave through it, a squarewave will come out with no ringing.*

Ringing at audio frequencies might be a your criteria for loading an MP-1, but there are certainly other considerations for the rest of us, and I would think for MP-1 users as well. That is the sound, irrespective of RFI.

That bit about squarewaves is cute, but would leave a lot of people scratching their chin and changing load. I'm not saying your criteria is irrelevant, but it's not the ONLY criteria.

* With any LOMC cartridge ever made, this will be the case at 47K. So why do we hear differences? It has not so much to do with the cartridge and **everything** to do with the phono preamp. If the preamp is sensitive to Radio Frequency Interference, then loading the cartridge will affect tonality as it detunes the RF circuit formed thus*

Changing load does not necessarily affect tonality. The highest value or 47K is often not the most desirable. BTW, why stop at 47K, why not 1M or infinite?

The answer has to do with how the phono stage reacts to RFI as I have pointed out.

Designers also have to be pragmatic about what sort of input impedance is needed to control noise! If it were to be high as you ask about, controlling noise becomes a major problem in a high gain circuit! So 47K was derived as a reasonable compromise decades ago- it allows low noise and a moderate, easy load for almost any phono cartridge.

Ringing at audio frequencies might be a your criteria for loading an MP-1, but there are certainly other considerations for the rest of us, and I would think for MP-1 users as well. That is the sound, irrespective of RFI.

To be clear, 'Ringing at audio frequencies' is no more a consideration for our preamp as any other, as such only occurs with high output moving magnet cartridges. For them, the inductance is much higher and so loading is important.

Regarding the sound, it cannot be considered 'irrespective of RFI': in plain and simple terms if the circuit has RFI problems **the sound will not be right if RFI is present!!** If such is the case then loading will have a beneficial effect.

In more detail: if the circuit is sensitive to RFI, due to poor layout, lack of input stopping resistors, RFI filters, bad grounding (IOW anything that can cause RFI sensitivity), etc., the result will be that RFI will adversely affect the sound. The RFI is generated by the pickup and cable itself: it is not a matter of shielding from radio stations.

Until this fact is understood loading will remain mysterious and a matter of debate.

Ringing and squarewaves is not just cute, it is part of the toolkit one uses to do circuit analysis. It might interest you to know that many years ago I tried to make a box that one could simply plug in the phono cables from the arm and the box would sort out what the right loading was. It was during experimentation to gather data that I saw that LOMC cartridges don't ring at any frequency anywhere near the audio range- in fact even with a 100KHz squarewave to 'ring' them, they still just pass the squarewave perfectly. Once I understood this fact, I was then able to make changes to our preamp design to make it more RFI resistant at its input, which had the effect of making the low impedance loading resistors nearly irrelevant and also improved the sound at the same time- that latter bit of course is what we are all after.

So loading is not about LOMC cartridges and it is entirely and 100% about good circuit design in the phono preamp.

*The answer has to do with how the phono stage reacts to RFI as I have pointed out.*

Loading encompasses more than RFI as I have pointed out.

*Designers also have to be pragmatic about what sort of input impedance is needed to control noise! If it were to be high as you ask about, controlling noise becomes a major problem in a high gain circuit! So 47K was derived as a reasonable compromise decades ago- it allows low noise and a moderate, easy load for almost any phono cartridge.*

1M doesn't seem to be much of a problem with Herron phono stage, but that's beside the point. 47K became a default standard for HO carts, not LO carts. For 4-ch it was 100K, but that's low gain. Look at vintage preamps and see what the loading options are.

*Regarding the sound, it cannot be considered 'irrespective of RFI': in plain and simple terms if the circuit has RFI problems **the sound will not be right if RFI is present!!** If such is the case then loading will have a beneficial effect.*

If a circuit does not have RFI problems then loading can still have a beneficial affect.

*The RFI is generated by the pickup and cable itself: it is not a matter of shielding from radio stations.*

Novel way of looking at a generator, or is it a transmitter? The oscillation or ringing occurs in the preamp because of the extraordinary amount of gain needed.

The tiny voltage of a LOMC still has inductance, which combines with cable and preamp capacitance and can cause HF ringing, but is only a problem with extremely low output carts with high resistance/inductance. I think such occurrences are beyond the bandwidth of your phono stages.

Saying RFI is generated by the cart is misleading. It is not. There are other loading considerations with MC's, none of which are about noise or tonality. You assume the higher the load, the better. I beg to differ. Such things as imaging, stage, dynamics, detail, and focus can all be affected by load, while tonality is unchanged.

Loading is very much about the cart and particular preamp.

Fleib, I recommend you do some design work and see if you still say that. You might also do a search on some of the comments by the Jonathan Carr (Jcarr) who is active on this forum.

If a circuit does not have RFI problems then loading can still have a beneficial affect.

Loading of LOMC cartridges has no effect whatsoever so far as the cartridge is concerned. There is a slight benefit to loading as low impedance terminations of cables reduces cable artifact, particularly with high capacitance cables. This is better realized if the cartridge is operating in the balanced mode (as it is a naturally balanced source) and the signal is carried through a balanced line. Then the cable will have no artifact at all. 600 ohms will be sufficient to eliminate the cable artifact.

Novel way of looking at a generator, or is it a transmitter? The oscillation or ringing occurs in the preamp because of the extraordinary amount of gain needed.

The cartridge/cable combo acts as both. It does not matter that the phono section has no bandwidth at the resonant frequency, which is usually several MHz. The gain has nothing to do with it.

The tiny voltage of a LOMC still has inductance, which combines with cable and preamp capacitance and can cause HF ringing, but is only a problem with extremely low output carts with high resistance/inductance. I think such occurrences are beyond the bandwidth of your phono stages.

I wonder if there is a semantic issue underpinning this conversation. In the above quote you are correct in almost every way except that there are no LOMC cartridges with high inductance... if it is assumed that by 'tiny voltage' you are referring to about 1.0mV or less. The inductance you thus refer to is the inductance in question, the frequencies are those in question, and no phono section I know of can go that high, but they don't have to- they only need to have an RF sensitivity and then you suddenly hear loading making a big difference.

Saying RFI is generated by the cart is misleading. It is not. There are other loading considerations with MC's, none of which are about noise or tonality. You assume the higher the load, the better. I beg to differ. Such things as imaging, stage, dynamics, detail, and focus can all be affected by load, while tonality is unchanged.

But here in your next paragraph you seem to contradict the earlier paragraph in the first sentence. I did not nor do I assume that the 'higher the load the better': I said the correct load and most designers design for 47K.

I agree that loading affects these things if your preamp has RFI problems! I don't know if you have ever heard what RFI can do to an audio circuit outside of a phono situation but the effect it can have on soundstage, background noise, detail and the like can be profound. As a result all I can assume from your reactions here is that the phono sections where you have tried different loading options are all having trouble with RFI; that is why you heard a difference! RFI has big effects on audio gear if not tamed.

I do however agree with your closing statement as loading has a lot to do with both the cartridge and the individual preamp, for the reason that the inductance of the cartridge and the resulting RFI affects different preamps differently. In our case since we got a handle in this some years back it has almost no effect which is good- its more plug and play. But we originally included the loading strip on our preamp (which is still there) because in the old days we heard differences with nearly every preamp we auditioned.

Here are some links that you may find interesting:

http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1281468389&openflup&18&4#18
and further down on the same thread:
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1281468389&openflup&22&4#22
pay attention to post number 3 at this link:
http://www.whatsbestforum.com/showthread.php?15077-Cartridge-Loading-A-Misnomer

Atmasphere,
I see you brought back up. The LOMC I was referring to are some of those coreless designs with very low output and high inductance/resistance relative to other MC. It was J Carr who told us about the HF oscillation/noise that could occur.

Regarding the notion that higher value loads are necessarily better, consider this:
If 500 ohms sounds good, and one tries 47K and it also sounds good but different, and both loads seem equally quiet, why is 47K better?
You're saying it is and you're wrong IMO.
Regards,