Load resistor for MC-3440A/DL-103D SUT

[Rallen]

Hey there

I am planning to build a MC SUT based on the Cinemag CMQEE-3440A transformers that I want to use with my Denon DL-103D cart.

https://www.studioelectronics.biz/sunshop/index.php?l=product_detail&p=1740

This is my first venture into MC SUTS. I have read plenty of articles about the subject, but still have a little hard time to understand everything.

My DL-103D seems to want a load impedance of > 100 Ω. It's output is supposed to be 0,25 mV.

The transformers impedances are listed as 37.5, 150, or 600 ohms; the secondary impedance is 50k. Gain ratio is 1:37, 1:18.5, or 1:9.25.

I suspect I should use the 1:9.25 amplification for my cart. Would this be a good match?
Also, to tune the load impedance, I have tried using an online SUT calculator and came up with the result that I need a resistor of around 11kOhm (my phono stage as 47kOhm load)

Is this all correct? Thanks!

Also - I seem to find carbon film resistors mentioned everywhere, but metal films ones at 1 % are easier to find. Any reason not to use these?

 

[cobbers]

Why not just use 18.5 turns and keep it simple ,will give you a load of about 135R and give you an output of about 4.6mV.
Load quoted is for a minimum of 100R.

 

[Rallen]

Why not just use 18.5 turns and keep it simple ,will give you a load of about 135R and give you an output of about 4.6mV.
Load quoted is for a minimum of 100R.

Thanks! That would definitely be a possibility. To be honest I think I read somewhere at some point that 1:10 would be great for this cart, so I kinda only focused on using that
Out of interest - are my other thoughts and calculations correct? Would 1:9.5 and 11kOhm resistor theoretically do the trick as well?

 

[krenzler]

Hi Rallen.

Have you read the thorough walkthrough of the interplay between MC's and SUT's over at Vinyl Engine? If not, I'll advise you to read this through carefully at least 10 times.

https://www.vinylengine.com/step-ups-and-mc-cartridges.shtml

I've used DL-103R (0.25mV/14 ohm) with a prebuilt 3440a and it sounded great at 1:18.5/137 ohm. 103D is slightly different being 33 ohm. But if you try the 1:9.25 turns ratio you'll get less than 2.5mV to the MM stage.

 

[GT]

Forget about the loading when using a SUT. It's pretty much irrelevant when using a SUT. Just concentrate on getting the correct amount of MC gain. Most cartridge manufacturers assume you will be using a solid state phono stage, because these are much more common than a valve/tube phono stage, so you can tune (or curb) the rising frequency response of the MC cartridge in the system using different values of loading resistance. To do this in a solid state phono stage you can just put a resistor of a different value to 47K ohms directly across the cartridge input, which is the loading value the cartridge manufacturers are quoting. Some of the better cartridge manufacturers quote 2 values. One for solid state phono stages and one for when an SUT or a valve/tube phono stage with an inbuilt SUT is used.

Depending on the gain of your phono stage and the output voltage of the MC cartridge will depend on how much MC gain you will need for your cartridge. A good starting point would be a SUT with a 1:10 ratio (20dB of gain) and this will present about 470 ohms (AC wise) to the cartridge. Another option would be a 1:20 ratio (26dB of gain) and this would present about 117ohms (AC wise) to the cartridge.

 

[Rallen]

Forget about the loading when using a SUT. It's pretty much irrelevant when using a SUT. Just concentrate on getting the correct amount of MC gain. Most cartridge manufacturers assume you will be using a solid state phono stage, because these are much more common than a valve/tube phono stage, so you can tune (or curb) the rising frequency response of the MC cartridge in the system. To do this in a solid state phono stage you can just put a resistor of a different value to 47K ohms directly across the cartridge input which is the loading value the cartridge manufacturers are quoting. Some of the better cartridge manufacturers quote 2 values. One for solid state phono stages and one for when an SUT or a valve/tube phono stage with built in SUT is used.

Depending on the gain of your phono stage and the output voltage of the MC cartridge will depend on how much MC gain you will need for your cartridge.

Thanks. Sounds like you are on the 1:18.5 team? Phono stage is Lesbox yaqin ms-23b if that makes a difference

 

[GT]

Thanks. Sounds like you are on the 1:18.5 team? Phono stage is Lesbox yaqin ms-23b if that makes a difference

Ultimately it will depend on the gain of your phono stage (not including the SUT) and how much signal to noise you need. My phono stages produce about 48dB of MM gain. Other MM phono stages will be different, most will be less than 48dB so you may need a higher gain in your SUT.

 

[cobbers]

For a 33R MC I would tend towards 9.25 - would give a load of about 500R and an output of about 2.4mV - so gain and noise of the MM stage will become more important.