Thinking about MC cartridges

[rothwellaudio]

I think I'll add to the test list the realities of what, in most cases, varying load impedance actually does to the response of an MC cartridge.

There was post here on AK a while ago where someone had done a frequency response sweep of his LOMC cartridge with a 100 ohm load and a 47k load and the difference was miniscule. It might be a struggle to find the thread though.

 

[rothwellaudio]

The Denon manual states, use the “40 ohm” selection 1:36 turn ratio for the standard DL 103, using this calculator http://www.hagtech.com/loading.html that’s a 36.3 ohm rating the “3 ohm” selection 1:10 is a 470 ohm rating, as pointed out by @rothwellaudio

The Denon manual I have says the turns ratio for the 40 ohm setting is 1:10. It doesn't state a turns ratio for the 3 ohm setting (though 1:36 would be a reasonable figure). The specs are on page 8.
https://www.hollandlink.eu/Denon-AU320-manual.pdf

Denon’s labels on several SUTs isn’t the actual loading, it’s just a suggested selection option based on the internal ohm rating of a particular cartridge (lower internal ohm or higher internal ohm)

Yes, the labelling refers to the source impedance, not the load impedance.
Btw, the frequency response plot shows what a good, wide bandwidth performance the transformer has.

 

[JP]

There was post here on AK a while ago where someone had done a frequency response sweep of his LOMC cartridge with a 100 ohm load and a 47k load and the difference was miniscule. It might be a struggle to find the thread though.

Even better, Scott Wurcer did a test by shorting one coil while playing a square wave track - no affect to the other channel. I re-read that one just this morning but am unable to find it again.

 

[adnick]

The Denon manual I have says the turns ratio for the 40 ohm setting is 1:10. I doesn't state a turns ratio for the 3 ohm setting. The specs are on page 8.
https://www.hollandlink.eu/Denon-AU320-manual.pdf

Yes, the labelling refers to the source impedance, not the load impedance.
Btw, the frequency response plot shows what a good, wide bandwidth performance the transformer has.

Yes my backwards personally, meant to write it the other way around I’ll edit my mistakes…

The “general rule” for loading is 10 x the cartridge internal rating, but to get specific one would have to consider interconnects and wiring , so using ones ears is a simple alternative and if based on a general understanding of SUT turn ratios and such it can a fun and pleasing experience.


I’ve always said my 103R sounds better with the RCA MI 12399 SUT than it does with the AU 320, and that’s supported by the numbers, about 1/2 of what the AU 320 does at the recommended setting.


I’d hazard a guess that many are just using whatever system they have and if it sounds good to them, then it’s “good”.

VR
Andy

 

[rothwellaudio]

The “general rule” for loading is 100 x the cartridge internal rating.

10x is the more usual recommendation.

I’ve always said my 103R sounds better with the RCA MI 12399 SUT than it does with the AU 320, and that’s supported by the numbers, about 1/2 of what the AU 320 does at the recommended setting.

I'm not sure what that means. What numbers? Half of what?

 

[adnick]

10x is the more usual recommendation.

I'm not sure what that means. What numbers? Half of what?

Oops extra zero….

The RCA MI12399 is 1:14 so it’s about half way in between (239 ohms) the setting available setting on the AU 320, that’s all I meant….

Andy

 

[AvFan]

Does the output of a MC cartridge change with different loads?

 

[flavio81]

Does the output of a MC cartridge change with different loads?

Yes, when the output impedance is equal to the input impedance (the transformer "load" for the cartridge), the voltage will be diminished, in theory to half, if i'm not mistaken.

If the load is even lower (in terms of ohms), the output would be reduced even further.

That's why Cafe Latte and Rothwellaudio recommend "10x", to avoid the loss.

 

[ctjetta]

RCA MI 12399 SUT

Just found a pair of those on ePay. GULP! I won't be purchasing these any time soon. And THEN I would need someone to configure them if I did.

EDIT- to add emoji ( seemed necessary)

 

[rothwellaudio]

Does the output of a MC cartridge change with different loads?

Yes, when the output impedance is equal to the input impedance (the transformer "load" for the cartridge), the voltage will be diminished, in theory to half, if i'm not mistaken.

If the load is even lower (in terms of ohms), the output would be reduced even further.

That's why Cafe Latte and Rothwellaudio recommend "10x", to avoid the loss.

That is correct. With an active amplifier the gain and load impedance are (generally) completely independent of each other, so the load can be set to anything without affecting the gain of the amplifier. However, low values of load impedance (aka the input impedance of the amplifier) will cause the output of the cartridge to fall. The source impedance and load impedance form a simple potential divider.

With a transformer things are a bit more complicated. A higher turns ratio will present a lower load impedance to the cartridge, so the cartridge's output drops, but that is offset to some extent because the higher turns ratio steps up the cartridge's output more.

Really, striving for a particular load impedance isn't the transformer's objective. The transformer is there to raise the output voltage from the transducer. The change in load impedance is incidental, though not entirely inconsequential.

 

[adnick]

Just found a pair of those on ePay. GULP! I won't be purchasing these any time soon. And THEN I would need someone to configure them if I did.

EDIT- to add emoji ( seemed necessary)

Yeah they have gone up, well sorta, paid $50 each for two that have messed up labels and built the box….

However I’d recommend the Denon AU 320 for several reasons, it sounds good, gives flexibility of 2 arms and cost….

Edit: Also for those who would like to build their own SUT, the Stromberg Carlson TM8A has the same 9 pin configuration as the RCA MI 12399 so it’s wired the same. I’ve purchased these for as little as $30 a piece….they are a good starting option, because if a reasonable pair of RCAs come up, one can switch them out.

Andy

 

[AvFan]

That is correct. With an active amplifier the gain and load impedance are (generally) completely independent of each other, so the load can be set to anything without affecting the gain of the amplifier. However, low values of load impedance (aka the input impedance of the amplifier) will cause the output of the cartridge to fall. The source impedance and load impedance form a simple potential divider.

With a transformer things are a bit more complicated. A higher turns ratio will present a lower load impedance to the cartridge, so the cartridge's output drops, but that is offset to some extent because the higher turns ratio steps up the cartridge's output more.

Really, striving for a particular load impedance isn't the transformer's objective. The transformer is there to raise the output voltage from the transducer. The change in load impedance is incidental, though not entirely inconsequential.

I have a switch that can apply five different loads to the primary side of the SUT (1:15 Hashimoto HM-7) while my WP MM preamp has a 1Mohm load resistor. If I have done my math right the cartridge load is only 3 or 4 ohms less than the resistor value on the primary side of the SUT. The range of load to cart impedance values is between 6 and 15 with resistors between 82ohms and 180ohms and the cartridge has an internal impedance of 12ohms. When I switch between loads I swear I can hear the volume change. So not my imagination?

 

[adnick]

Simply Multiply the turn ratio by the cartridge output voltage of the cartridge, for the passive transformers….also this site which was posted earlier http://www.hagtech.com/loading.html also allows one to figure out resistor value for a desired load….

Edit: Before the peer review starts—OF course the website is based on a 47k preamp


VR
Andy

 

[AvFan]

Simply Multiply the turn ratio by the cartridge output voltage of the cartridge, for the passive transformers….also this site which was posted earlier http://www.hagtech.com/loading.html also allows one to figure out resistor value for a desired load….

Most of the SUT load calculators including Hagerman are based upon only loading the secondary side with the MM's load resistor and the added resistor. The added resistor in my case is on the primary side. The cart sees the added resistor as is but the 1Mohm resistor is on the secondary side and has to be factored in. 1/(1,000,000/15^2) So it reduces the load just a few ohms. I just thought it odd that I could hear a difference in volume between load values.

 

[adnick]

Most of the SUT load calculators including Hagerman are based upon only loading the secondary side with the MM's load resistor and the added resistor. The added resistor in my case is on the primary side. The cart sees the added resistor as is but the 1Mohm resistor is on the secondary side and has to be factored in. 1/(1,000,000/15^2) So it reduces the load just a few ohms. I just thought it odd that I could hear a difference in volume between load values.

Yeah, wasn’t responding to your post, that’s the reason I made sure to point out it’s based on the common MM 47k preamp…

Believe you should probably be able to hear a slight change, but I’m not familiar with your setup, except for the excellent transformers


Andy

 

[rothwellaudio]

The range of load to cart impedance values is between 6 and 15 with resistors between 82ohms and 180ohms and the cartridge has an internal impedance of 12ohms. When I switch between loads I swear I can hear the volume change. So not my imagination?

Between 6 and 15 ohms?

I just thought it odd that I could hear a difference in volume between load values.

Not surprising that you can hear a difference in volume. As the load impedance gets down to about 3 x the cartridge impedance the drop in volume will be very noticeable.
The load impedance should be about 10x the cartridge impedance to minimise the loss of signal. You can go down to around 3x the cartridge impedance if you think it sounds better before you start to lose more than a few decibels.

 

[rothwellaudio]

Simply Multiply the turn ratio by the cartridge output voltage of the cartridge, for the passive transformers….

Yes, that works (to a good approximation) for low turns ratios and cartridges with low source impedances. However, with higher turns ratios and higher source impedances, it isn't accurate.
Take for example a cartridge with a source impedance of 40 ohms and a SUT with a turns ratio of 1:30. Say the cartridge has an output voltage of 0.2mV, and lets assume the transformer is perfect and therefore doesn't have any resistance in the coil windings, and it's fed into a phonostage with a 47k input impedance.
A step-up ratio of 1:30 and an output voltage of 0.2mV should give an output from the SUT of 6mV, right?
No, the output is actually only 3.4mV. The reason is because the cartridge sees a load of only 52 ohms and its own internal impedance is 40 ohms.

 

[adnick]

Yes, that works (to a good approximation) for low turns ratios and cartridges with low source impedances. However, with higher turns ratios and higher source impedances, it isn't accurate.
Take for example a cartridge with a source impedance of 40 ohms and a SUT with a turns ratio of 1:30. Say the cartridge has an output voltage of 0.2mV, and lets assume the transformer is perfect and therefore doesn't have any resistance in the coil windings, and it's fed into a phonostage with a 47k input impedance.
A step-up ratio of 1:30 and an output voltage of 0.2mV should give an output from the SUT of 6mV, right?
No, the output is actually only 3.4mV. The reason is because the cartridge sees a load of only 52 ohms and its own internal impedance is 40 ohms.

Yes Hagerman stops it’s examples of “standard step up ratios: at 1:30 and even though the Altec Peerless K241 series can be wired at ratios like 1:50, not many choose over 1:23 for 47k preamp SUTs

 

[cafe latte]

To be honest I am not much of a SUT fan. Now that I think about it I did dally with a SUT for a bit during the time I owned the modified 103R, but it was not memorable. At that time I used the Liberty B2B-1 phono stage which handled low output cartridges quite well. So does my current Esoteric E-03 phono stage.

The only SUT I own are the Ortofon T2000 and T5000, and that is because I have the matching cartridges. They are low enough in output that a SUT is mandatory. My Esoteric can run the MC3000 II and MC5000 reasonably well, but there is some performance abilities that are not achieved. The SUT achieves that.

I was not a huge fan of the 103r what I had for ages. I was nice but bass was muddy and and it was not a clean and fresh as my best other carts.
Then a friend loaned me a Denon Sut, I tried the Denon again and I also selected a more appropriate headshell (heavy) and the Denon sounded lovely, the bass was transformed and everything just snapped into place. Mine is retipped with Boron and Micro ridge, I have some too with adjusted suspension for lower effective mass arms which also sound great. I think these carts with a decent heavier arm and a retip can sound really good, with a new body they can really perform. I think the reason for the divide on this cart is they need very specific set up and loading to sound there best.
Chris

 

[Mister Pig]

I was not a huge fan of the 103r what I had for ages. I was nice but bass was muddy and and it was not a clean and fresh as my best other carts.
Then a friend loaned me a Denon Sut, I tried the Denon again and I also selected a more appropriate headshell (heavy) and the Denon sounded lovely, the bass was transformed and everything just snapped into place. Mine is retipped with Boron and Micro ridge, I have some too with adjusted suspension for lower effective mass arms which also sound great. I think these carts with a decent heavier arm and a retip can sound really good, with a new body they can really perform. I think the reason for the divide on this cart is they need very specific set up and loading to sound there best.
Chris

From the images I have seen it looks like the coils and frame are well done with the Denon. The body is not exceptional, and some folks think the diamnond can be approved. While others like the presentation of a conical. Its interesting. Hotrodding one isn't terribly expensive and I suspect you get a good cartridge for the money.

Speaking of conicals. I have the Charisma Audio Charm in for a listen. A new cartridge with a modest but good body, and a low impedance coil assembly. Looks quite promising.