MC cartridge loading

[Varun]

Mike Reed asked me what phono stage I was using.

I have a passive Plinius phonostage- a box with a volume knob which I had felt was enough-but then was persuaded to go powered and active. I have included an image of the fascia of the Phono-Preamp.

The knob on the R deals with cartridge loading. When taking these pics I realized that I had left the cartridge loading untouched at 470, which was set for my Koetsu. Just shows how these little things need attention and matter.

The point here is that these parameters also matter and if I moan about Koetsu being lush- overblown, then I remember that that was happening on 47K- not the right setting for that cartridge as I realized.

Varun

[Mike]

The point here is that these parameters also matter

Hell yes!

Cartridge loading can make or break the sound of an MC cartridge! And then again, I've heard one or two that don't seem to be even slightly bothered.

[Barry]

I wish a lot more phono preamplifiers had such an easily accessible impedance selector. On all of mine, the impedance can only be changed by going inside the amp and either physically replacing resistors or manipulating horrid little DIP switches.

Koetsu recommend a loading of 50 to 1000Ω for the Black. 470Ω would seem to be just right. The coil resistance is 5Ω, so the load impedance is 94x the coil resistance. Any value greater than 10x is usually OK. I don't know what the coil inductance is, but it will be something like 5mH. If the coil resistance is sufficiently small that it can be ignored relative to the load impedance, then the series combination of coil inductance and load resistance will have a -3dB point at R/(2πL) or in this case 470/(2π 5.10 ̄-³) = 15kHz. This is one reason to choose a higher resistive loading.

However, like the setting of VTA, one shouldn’t become hide bound by these things – if it sounds right to your ears then it is right.

[Varun]

That is high knowledge Barry-magnificent. As I am listening to Dynavector XX-1, I changed the loading yesterday to 47K- NO GOOD, so it is at 1K at the moment- it was warm yesterday for my liking but as I did not have a problem with 470 before, I may have to return to it.

Cheers

Varun

[Alex Nikitin]

I wish a lot more phono preamplifiers had such an easily accessible impedance selector. On all of mine, the impedance can only be changed by going inside the amp and either physically replacing resistors or manipulating horrid little DIP switches.

Koetsu recommend a loading of 50 to 1000Ω for the Black. 470Ω would seem to be just right. The coil resistance is 5Ω, so the load impedance is 94x the coil resistance. Any value greater than 10x is usually OK. I don't know what the coil inductance is, but it will be something like 5mH. If the coil resistance is sufficiently small that it can be ignored relative to the load impedance, then the series combination of coil inductance and load resistance will have a -3dB point at R/(2πL) or in this case 470/(2π 5.10 ̄-³) = 15kHz. This is one reason to choose a higher resistive loading.

However, like the setting of VTA, one shouldn’t become hide bound by these things – if it sounds right to your ears then it is right.

Barry,

Your calculations are correct, however your estimate of an MC cartridge coil inductance is way off. Even high output MC have much lower inductance, for example Goldring Eroica H is only 0.2 mH. Low output MC cartridges inductance is in the uH range, Goldring Eroica L is only 3 uH and AT OC-9 is 50 uH. In this respect even for the Goldring Eroica H load of 100 Ohm would produce only about 0.25 dB drop at 20 kHz.

Alex

[Varun]

Thanks Alex for your input,

How would you calculate the ideal load for my high output Dynavector XX-1, may I please ask?

Thank

Varun

[Mike Reed]

VARUN,

Barry is right in that different carts. have different loading flexibities. My Helikon is very unfussy, but the three botton Koetsus (Blk, Red T & Red K Sig.) all prefer to see around 100 ohms. Having said that, my Black sounds very good through the 560 ohms my Prefix is set at.

Can't see a gain control on your Plinius, so I guess that is set for m.c. however, passive phono stages are something I have no knowledge of.

Why can't you just twiddle the loading knob until it sounds right? Am I missing something? Surely a high output m.c. is akin to a m.m. and would benefit from the 47 kohms (+mm setting).

[Alex Nikitin]

Thanks Alex for your input,

How would you calculate the ideal load for my high output Dynavector XX-1, may I please ask?

Thank

Varun

Varun,

I would probably follow Mike's advice:

Why can't you just twiddle the loading knob until it sounds right?

As far as I understand there is no hard and fast rule on this matter. The load of MC cartridge does not really affect the frequency response - however it does affect two other things - the output and the mechanical damping of the coils - the lower the load, the higher the current through the coils and consequently higher the damping, as the magnetic field created by the current will produce a force trying to slow down coils movement. In this respect some cartridges may benefit from increased damping and some will not. However it is just a guess.

Alex

[Barry]

Barry,

Your calculations are correct, however your estimate of an MC cartridge coil inductance is way off. Even high output MC have much lower inductance, for example Goldring Eroica H is only 0.2 mH. Low output MC cartridges inductance is in the uH range, Goldring Eroica L is only 3 uH and AT OC-9 is 50 uH. In this respect even for the Goldring Eroica H load of 100 Ohm would produce only about 0.25 dB drop at 20 kHz.

Alex

Hello Alex,

Thanks for pointing out the somewhat large (up to three orders of magnitude!) error in my estimation of a moving coil cartridge’s inductance. At the time I thought the figure seemed high and I was worried by the subsequent calculation of a –3db roll-off at 15KHz. Surely if that was true then it would have commented on in almost any review.

In my defence, my estimate (and that’s all it was) was made on the assumption that since moving coils typically have 1/10 of the output of that of fixed coil designs, the coils of an MC have 10x fewer turns. Since the inductance of a coil of n turns is proportional to n², then the inductance will be 100x less. Fixed coil cartridges typically have an inductance of 500mH (sometimes more, sometimes less), so this is how my figure of 5mH was derived. Clearly I have also made the (perhaps gross) assumption that the magnetic flux remains unchanged.

Actually my greatest sin was not to have a check on Google to see exactly what the typical MC inductance would be. I have paid my penance by writing out 500 times:

‘I must not quote estimates with an air of authority, without checking the facts.’

Having now done a bit of research I can confirm your quoted figures, to which I can add:
Goldring Eroica LX, 12μH; Goldring Elite 200μH

Denon 103, 56μH; Denon 103SA, 380μH; Denon 110, 380μH; Denon 160, 490μH and 304, 50μH

Audio Technica AT-31E, 30μH; AT-33E, 70μH; AT-33PTG, 70μH; AT-33EV, 22μH; AT-33ANV, 22μH and AT-33R, 70μH

Van den Hul ‘Frog’, 63μH.

Unfortunately I could not find any information on Ortophon or Koetsu, however as you rightly point out with such low inductances the –3dB point is very high: for the Denon 103 loaded by 390Ω it is 1.1MHz, increasing to 1.3MHz if the load is increased to 470Ω.

So thanks again and apologies to Varun for the miss-advice: I have yet to earn the appellation ‘-magnificent’ and anyway I would feel uncomfortable with it, had I earned it.

Regards

[Varun]

Colleagues,

I seem to have missed this highly interesting debate.

Mike:- I agree-the XX-1 High output should be 47K worthy. The Phono-Preamp has a gain control on the L- the knurled knob. It is set on Low. Please look at the image. Now for Koetsu - I did find 470 the best setting upon listening. So that is how I chose it. As I said - I completely forgot to set the loading when the cartridges were changed and obviously it did not matter too much. I have tried 47K since posting the thread and I do not like it. So I am going to let it run at 1K and make changes if I need to.

The weather is not conducive to listening, what with the Class A amp acting as heater-and my life long intolerance for hot weather.

After selling my EAR 802, I went through a phase when I wanted simplicity. I was using EAR 804 with the 509s, I then decided to try passive phonostage. As I say it has no circuitry just a volume knob and input and outpout jacks. It is a long story. I still have the passive phono stage- if any one is intersted?

Varun