Urika 2 cartridge loading

[13th Duke of Wymbourne]

There are many ways to skin the RIAA cat even in the analog domain - whether to buffer between each time constant or combine them and whether to apply some of the filtering in a feedback network. Throwing in digital filtering gives more choices and splitting some time constants between analog domain and some in digital is possible and it seems that is Linn's choice.
I do want to follow-up on your comment that you cannot apply all the RIAA filtering in digital - it can be done safely. The link below is to an AES paper by Rob Robinson of Channel D, who makes a range of phono pre-amps. He has been a proponent of digital RIAA for many years and has an RIAA bypass switch in his phono amps to allow this. And he happens to write software to do the digital RIAA too. The paper is a little involved so here is my TLDR summary -
The obvious concern with sending an un-equalized signal to an ADC is that the RIAA-boosted treble will eat up the dynamic range and the low frequencies will be captured with low resolution. As a recap, the RIAA pre-emphasis applied to the cutting head cuts the lowest frequencies by 20dB (10x) compared to 1kHz and the highest frequencies are boosted by 20dB compared to 1kHz. But these concerns turn out not to be significant problems.
Though the lowest bass frequency signals might be reduced by a factor of 100 at the ADC input (if treble sets the voltage peak) they are still captured with full resolution. This is because bass frequencies are effectively over-sampled by a large amount, which makes up any loss in resolution due to the lower amplitude. If the ADC is sampling at 96kHz that is 2x oversampling for 20kHz but for a 20Hz signal that is 2000x over-sampling.
The highest frequencies turn out not to be as much of a problem as first expected because the energy in music rolls off above ~1kHz. So, even though RIAA boosts the treble, when combined with the natural treble roll-off the maximum levels of high frequencies are only about 6dB (2x) higher than 1kHz and not the expected 20dB. In the paper Mr. Robinson presents a study of many records where he has recorded peak amplitudes and their frequency distributions to reach that conclusion. So, typically the treble will use up a bit more ADC range than mid-band but only by about 1 bit, which is not a lot.

Finally, Mr. Robinson postulates that having the treble set the largest signal seen by the ADC is a better solution than applying RIAA de-emphasis before the ADC. In the former, the higher frequencies are captured with the fullest resolution and, we know that the lower frequencies are taken care of by progressively more over-sampling. If RIAA de-emphasis is applied first the largest peaks will come from mid-band so they will use up most of the ADC range and the treble frequencies will not be captured with as much resolution.

http://www.channld.com/aes123.pdf

 

[pirov]

Interesting to compare the different default loading settings in Konfig for Linn and Lyra cartridges:

 

[13th Duke of Wymbourne]

MC loading is something I have mused over but don't have much experience with. I spent decades with a phono amp with fixed 100 ohm resistors so I never got to experiment.
From an electrical point of view, the inductance of an MC coil will resonate with the loading capacitance (cable + phono amp input) but I would expect that to be way above the audio bandwidth (probably up in the MHz region). Loading resistance will damp out that peak, 1k might still show that peak by 100 ohms should damp it out completely.
From an electro-magnetic point of view there is something called Lenz's Law that states that 'the current induced in a circuit due to a change in a magnetic field is directed to oppose the change in flux and to exert a mechanical force which opposes the motion' (thank you Wikipedia). I don't know EM theory as well as I'd like but it implies, to me, that as the cantilever moves the coils in the magnetic field the current flowing in those coils will create their own magnetic field to oppose the movement. So, this could act as mechanical damping. If you load at 100 ohms compared to 1k then 10x the current will flow. But I don't have a sense for the magnitude of this effect - taking it to the extreme if there was no resistance in the circuit would the induced current completely oppose the original movement and the cantilever won't move at all? Very low resistance cartridges connected to transimpedance phono amps (effective loading less than 1 ohm) still work so, maybe, the Lenz Law effect is not so great.

I mentioned Channel D in my last post, they make transimpedance phono amplifiers and show a picture of the output from a cartridge through a voltage phono amplifier compared to a transimpedance amplifier and the latter is obviously less distorted. They claim it allows the cartridge to track better - whatever the reason, there is something going on with more (smaller resistance) loading.
https://www.channld.com/seta/linoC2.html

Something that will happen will smaller loading resistance is that the reactance of the coil will become a larger proportion of the total resistance of the circuit so the potential division between the coil reactance and the loading resistor will cause a lowering of bandwidth, though unlikely to affect the audioband.

 

[pirov]

MC loading is something I have mused over but don't have much experience with. I spent decades with a phono amp with fixed 100 ohm resistors so I never got to experiment.
From an electrical point of view, the inductance of an MC coil will resonate with the loading capacitance (cable + phono amp input) but I would expect that to be way above the audio bandwidth (probably up in the MHz region). Loading resistance will damp out that peak, 1k might still show that peak by 100 ohms should damp it out completely.
From an electro-magnetic point of view there is something called Lenz's Law that states that 'the current induced in a circuit due to a change in a magnetic field is directed to oppose the change in flux and to exert a mechanical force which opposes the motion' (thank you Wikipedia). I don't know EM theory as well as I'd like but it implies, to me, that as the cantilever moves the coils in the magnetic field the current flowing in those coils will create their own magnetic field to oppose the movement. So, this could act as mechanical damping. If you load at 100 ohms compared to 1k then 10x the current will flow. But I don't have a sense for the magnitude of this effect - taking it to the extreme if there was no resistance in the circuit would the induced current completely oppose the original movement and the cantilever won't move at all? Very low resistance cartridges connected to transimpedance phono amps (effective loading less than 1 ohm) still work so, maybe, the Lenz Law effect is not so great.

I mentioned Channel D in my last post, they make transimpedance phono amplifiers and show a picture of the output from a cartridge through a voltage phono amplifier compared to a transimpedance amplifier and the latter is obviously less distorted. They claim it allows the cartridge to track better - whatever the reason, there is something going on with more (smaller resistance) loading.
https://www.channld.com/seta/linoC2.html

Something that will happen will smaller loading resistance is that the reactance of the coil will become a larger proportion of the total resistance of the circuit so the potential division between the coil reactance and the loading resistor will cause a lowering of bandwidth, though unlikely to affect the audioband.

Yikes, this is complicated. So just to be clear for dimwits such as me, are you saying that 10x the current will flow with a loading of 100 ohms compared to 1000 ohms? I was under the impression that the higher the number, the less the loading (damping?), so that at 1k the cartridge is 'wide open' (lighter loading with more current flowing) than @ 100 ohms?

 

[pirov]

MC loading is something I have mused over but don't have much experience with. I spent decades with a phono amp with fixed 100 ohm resistors so I never got to experiment.
From an electrical point of view, the inductance of an MC coil will resonate with the loading capacitance (cable + phono amp input) but I would expect that to be way above the audio bandwidth (probably up in the MHz region). Loading resistance will damp out that peak, 1k might still show that peak by 100 ohms should damp it out completely.
From an electro-magnetic point of view there is something called Lenz's Law that states that 'the current induced in a circuit due to a change in a magnetic field is directed to oppose the change in flux and to exert a mechanical force which opposes the motion' (thank you Wikipedia). I don't know EM theory as well as I'd like but it implies, to me, that as the cantilever moves the coils in the magnetic field the current flowing in those coils will create their own magnetic field to oppose the movement. So, this could act as mechanical damping. If you load at 100 ohms compared to 1k then 10x the current will flow. But I don't have a sense for the magnitude of this effect - taking it to the extreme if there was no resistance in the circuit would the induced current completely oppose the original movement and the cantilever won't move at all? Very low resistance cartridges connected to transimpedance phono amps (effective loading less than 1 ohm) still work so, maybe, the Lenz Law effect is not so great.

I mentioned Channel D in my last post, they make transimpedance phono amplifiers and show a picture of the output from a cartridge through a voltage phono amplifier compared to a transimpedance amplifier and the latter is obviously less distorted. They claim it allows the cartridge to track better - whatever the reason, there is something going on with more (smaller resistance) loading.
https://www.channld.com/seta/linoC2.html

Something that will happen will smaller loading resistance is that the reactance of the coil will become a larger proportion of the total resistance of the circuit so the potential division between the coil reactance and the loading resistor will cause a lowering of bandwidth, though unlikely to affect the audioband.

Yikes, this is complicated. So just to be clear for dimwits such as me, are you saying that 10x the current will flow with a loading of 100 ohms compared to 1000 ohms? I was under the impression that the higher the number, the less the loading (damping?), so that at 1k the cartridge is 'wide open' (lighter loading with more current flowing) than @ 100 ohms?

 

[13th Duke of Wymbourne]

An MC cartridge is like a voltage source - it produces a voltage across the coils given by the groove modulation velocity. The Lyra Etna SL is specified as 0.25mV peak for a groove velocity of 5cm/s peak. Just to put that in context the largest groove velocity is of the order of 50cm/s so your cartridge could give out a peak voltage of 2.5mV in the extreme case. The Lyra internal resistance is ~ 1.5 ohms (the resistance of all the wire in the coils). The amount of current that flows in the coils depends on the total resistance in the circuit and that depends upon the load resistance. If you use 1k ohm then when the cartridge generates 0.25mV peak the current that will flow is 0.25mV/(1k + 1.5) ~ 0.25uA (pretty small). Making the load resistance 100 ohms will increase the current flow to ~ 2.5uA (so 10x more). The smaller the load resistor, the more it loads down the cartridge. As the Etna has such a small internal resistance that it hardly 'sees' a 1k load (almost no load) and 100 ohms is no trouble. To answer your question, more loading means a smaller load resistor that means more current.

The downside to lowering the load resistor is that the voltage output will decrease but in your case going from a 1k load to a 100 ohms will only reduce the output by 1.3% so nothing to worry about. If you went all the way down to a 10 ohm load you would lose 13% of the signal (1.2dB) so you have room to play.

As an aside, I mentioned transimpedance phono amplifiers earlier (aka current mode). Some reviewers say these treat an MC cartridge like a current source - this is not correct. An MC cartride is always a voltage source, but if you load it heavily (small value load resistance) you'll get a lot of current out of it.

 

[sktn77a]

My own experience with MC cartridges and SUTs somewhat validates the above discussion. I had a Denon 103D cartridge ("output impedance" 35 ohms) and a Denon AU320 SUT (3 ohm/40 ohm). The 103D would sound normal (great!) in the 40 ohm position, but way too loud and dull/boomy in the 3 ohm position. Fast forward to my Linn Asaka ("output impedance" 3.5 ohms) sounded great in the 3 ohm setting but quiet and toppy in the 40 ohm setting.

 

[pirov]

I'm not sure how/whether my subjective experience squares with the theoretical discussion above. In short, the main difference I hear when selecting (say) 100 ohms against 1k ohms is that the musical presentation sounds subtly more restrained and less dynamic (possibly better with recordings that tend to be thin/bright, but not as good at 'lifting the veil' with the majority of good recordings). There is no appreciable difference in volume.

Anyway the cartridge is definitely improving with more hours on the clock (I've settled on an IR of 820 ohms which I'll stick with for the foreseeable future).

 

[Wenge1]

I'm not sure how/whether my subjective experience squares with the theoretical discussion above. In short, the main difference I hear when selecting (say) 100 ohms against 1k ohms is that the musical presentation sounds subtly more restrained and less dynamic (possibly better with recordings that tend to be thin/bright, but not as good at 'lifting the veil' with the majority of good recordings). There is no appreciable difference in volume.

Anyway the cartridge is definitely improving with more hours on the clock (I've settled on an IR of 820 ohms which I'll stick with for the foreseeable future).

You might want to think about bringing your signature up to date to reflect your new cart

 

[sktn77a]

My own experience with MC cartridges and SUTs somewhat validates the above discussion.

I would add, however, that passive SUTs and active phono preamps are two separate considerations.