LOMC loading into SUT vs head amp

[orangejello]

I have seen manufactures specify different cartridge loading values for SUTs vs head amps. For example here is the spec for the Lyra Delos. There is a significant difference in this case. I have also seen general rules of thumb - loading should be 3x to 5x cartridge output impedance for SUT and > 10x for head amps. Can anyone explain this?

FWIW in my experience LOMCs need to be properly loaded at least when used with a SUT. Without loading there is too much sizzle in the high end and transients have too much of an edge.

 

[watchnerd]

I have seen manufactures specify different cartridge loading values for SUTs vs head amps. For example here is the spec for the Lyra Delos. There is a significant difference in this case. I have also seen general rules of thumb - loading should be 3x to 5x cartridge output impedance for SUT and > 10x for head amps. Can anyone explain this?

FWIW in my experience LOMCs need to be properly loaded at least when used with a SUT. Without loading there is too much sizzle in the high end and transients have too much of an edge.

I ignore it.

Instead, I just make sure the reflected impedance from the SUT is >= 10x internal impedance of the cart.

 

[LTig]

I have seen manufactures specify different cartridge loading values for SUTs vs head amps. For example here is the spec for the Lyra Delos. There is a significant difference in this case. I have also seen general rules of thumb - loading should be 3x to 5x cartridge output impedance for SUT and > 10x for head amps. Can anyone explain this?

FWIW in my experience LOMCs need to be properly loaded at least when used with a SUT. Without loading there is too much sizzle in the high end and transients have too much of an edge.

This is strange:

Output voltage: 0.6mV@5cm/sec., zero to peak, 45 degrees (CBS test record, other test records may alter results)
...
Recommended load directly into MC phono input: 97.6ohm ~ 806ohm (determine by listening, or follow detailed guidelines in user manual)Recommended load via step-up transformer: 5 ~15ohm (step-up transformer's output must be connected to 10kohm ~ 47kohm MM-level RIAA input, preferably via short, low-capacitance cable)

With 0.6 mV output voltage you'll need a 1:10 SUT, which means it will increase the voltage by a factor of 10 (= 6 mV) and reduce the input impedance of the phono stage by a factor of 100. The theoretical input impedance of the SUT then would be 100 - 470 Ohm. Don't know how they come to 5-15 Ohm.

 

[SIY]

This is strange:

With 0.6 mV output voltage you'll need a 1:10 SUT, which means it will increase the voltage by a factor of 10 (= 6 mV) and reduce the input impedance of the phono stage by a factor of 100. The theoretical input impedance of the SUT then would be 100 - 470 Ohm. Don't know how they come to 5-15 Ohm.

It may be garbled. 5-15 ohm is a reasonable range for an MC's source resistance for a typical 1:10 stepup.

 

[LTig]

It may be garbled. 5-15 ohm is a reasonable range for an MC's source resistance for a typical 1:10 stepup.

Yep, that makes sense. My VdH MC1 special with 0.65 mV output voltage has 9 Ohm (+/- 10%) source impedance and a recommended load impedance of 200 Ohm.

 

[antennaguru]

If you have LOMC cartridge with a low internal impedance, then you will probably be happiest with a high transformer ratio from an SUT, say 20:1 or an electronic step-up with a loading of say 100 ohms. The cartridges that fit this bill are from Lyra, Koetsu, ZYX, Ortofon, etc., with an internal impedance of 12 ohms or less.

OTOH, if you have a LOMC cartridge with a high internal impedance, then you will be probably be happiest with a low transformer ratio from an SUT, say 10:1 or an elecronic step-up with a loading of say 400 - 800 ohms. The cartridges that fit this bill are from Denon, Dynavector, and Hana, with an internal impedance of over 30 ohms.

There are actual mathematics behind this, if there is interest...

 

[watchnerd]

If you have LOMC cartridge with a low internal impedance, then you will probably be happiest with a high transformer ratio from an SUT, say 20:1 or an electronic step-up with a loading of say 100 ohms. The cartridges that fit this bill are from Lyra, Koetsu, ZYX, Ortofon, etc., with an internal impedance of 12 ohms or less.

OTOH, if you have a LOMC cartridge with a high internal impedance, then you will be probably be happiest with a low transformer ratio from an SUT, say 10:1 or an elecronic step-up with a loading of say 400 - 800 ohms. The cartridges that fit this bill are from Denon, Dynavector, and Hana, with an internal impedance of over 30 ohms.

There are actual mathematics behind this, if there is interest...

My LOMC ART-9XA has an internal impedance of 12 ohms:

https://www.audio-technica.com/en-us/cartridges/line-series/art-series/at-art9xa

I can't say I think it sounds better through either of my SUTs, whether the Hashimoto HM-7 (15x or 30x) or Lundahl 1931 (16x)

 

[LTig]

My Van den Hul MC One special has 9 Ohm coil resistance - not sure whether this is also the internal (output) impedance. However it has 0.65 mV output voltage and hence 20 dB gain (10) is more than sufficient. Therefore I think one should use the output voltage to chose a SUT and not the internal impedance.

 

[SIY]

My Van den Hul MC One special has 9 Ohm coil resistance - not sure whether this is also the internal (output) impedance. However it has 0.65 mV output voltage and hence 20 dB gain (10) is more than sufficient. Therefore I think one should use the output voltage to chose a SUT and not the internal impedance.

I would agree and note that for any given cartridge source impedance, the transformer can be optimized with a properly chosen series RC across the secondary irrespective of the step-up ratio (within reason, of course!).

 

[antennaguru]

In audio almost every connection between devices uses a low source impedance connected to an input impedance at the other end that is at least ten times higher than the source impedance. This is to derive a full power transfer over the connection.

For electronic step-up devices used with LOMC cartridges this is very easy math. If your cartridge is say a Koetsu with 5 ohms internal impedance you will be happiest with the sound when the electronic step-up device is set to at least 50 ohms impedance, more typically 80 - 100 ohms impedance sounds best. Trying different settings is a nice way to dial in the sound you like best.

A Step-Up Transformer used with LOMC cartridges is a little different math because the cartridge is looking through the turns ratio of the SUT at the input impedance of the MM phono stage - which is typically 47K ohms input impedance. The way the math works is that 47K divided by the square of the turns ratio of the SUT, for what is seen by the cartridge and which typically sounds best when it is at least 10 times the internal impedance of the cartridge.

In the case of a higher internal impedance LOMC a lower turns ratio SUT usually sounds best. For example, a Dynavector 17D2 has an internal impedance of 32 ohms. Using a 10:1 turns ratio SUT the impedance that the cartridge sees is 47,000 / (10) (10) = 470 ohms. This should sound good because 470 ohms is at least 10 times 32 ohms, or 320 ohms. However, if one were to substitute a 20:1 turns ratio SUT the impedance the cartridge sees is 47,000 / (20) (20) = 117.5 ohms. Here the 117.5 ohms is far less than 10 times 32 ohms, or 320 ohms, and the sound will typically be bass-shy and lean.

Most of the complaints I hear of with SUTs are people trying to use high internal impedance cartridges like the Dynavector cartridge I mentioned, or the even more popular Denon DL-103 cartridge which has an even higher internal impedance approaching 40 ohms, with too high a turns ratio Step-Up Transformer.

Generally, the lower internal impedance LOMC cartridges are more forgiving with the turns ratios of the SUTs because the math almost always works out to be at least 10 times the internal impedance of the LOMC cartridge!

All of this has to do with tonal response, which is affected by the impedance the LOMC cartridge looks into. There is also an aspect of system matching here as well. Not everyone's taste in tonal response is the same so YMMV.

 

[LTig]

I would follow the 10:1 rule only if the manufacturer of the pickup does not specify a recommended load impedance. My MC ONE special is specced for 200 Ohm so this is what I use in my DIY phono preamp.

I have no SUT and don't intend to use one since I can choose load and gain independently. With a SUT you can reduce the load with additional resistors in parallel but you can't increase it.

 

[antennaguru]

I would follow the 10:1 rule only if the manufacturer of the pickup does not specify a recommended load impedance. My MC ONE special is specced for 200 Ohm so this is what I use in my DIY phono preamp.

I have no SUT and don't intend to use one since I can choose load and gain independently. With a SUT you can reduce the load with additional resistors in parallel but you can't increase it.

The VDH MC ONE has an internal impedance of 9 ohms so an electronic step-up gain stage with 200 ohms resistive loading is a good recommendation as it is well above 10X the internal impedance of the cartridge. You could actually try slightly lower value loading resistors and see if you like the way that sounds even better since it's a DIY phono stage.

Some people prefer a passive Step-Up Transformer as there is no shot noise, which is inevitable with an active gain stage. I use both approaches on different systems.

 

[Bob from Florida]

Rothwell has a decent explanation here - http://www.rothwellaudioproducts.co.uk/html/mc_step-up_transformers_explai.html

 

[Pegwill]

Hi

You might also find this of use.

Regards

http://www.hagtech.com/loading.html

 

[antennaguru]

Rothwell has a decent explanation here - http://www.rothwellaudioproducts.co.uk/html/mc_step-up_transformers_explai.html

Good article, but a very long one that agreed with what I said with a lot fewer words. Must be that I don't type so well and keep it short...