Advice on SUT for Koetsu Rosewood - EAR MC-4, Slagle/EMIA, other

If the cartridge needs additional loading that should be placed at the primary of the SUT to load the cartridge directly. I find secondary loading to make a cartridge behave under various situations to be a sonic band-aid.

Years ago I found it interesting that people who use active gain stages tend to find their MC cartridges insensitive to loading and those who use SUT's can get fanatical about it.

FWIW the loading doesn't do anything for the cartridge at audio frequencies except reduce its output. The loading is audible though, but that is because it detunes the RF resonance caused by the cartridge inductance and the tone arm cable capacitance.
If the preamp is insensitive to RFI the loading doesn't do anything. 47K is therefore an effective load. I've heard loading make a difference but when you get the RFI problems sorted at the phono input, that difference goes away.

While the Jensen is one of the best SUTs available, being best isn't the same as being right for all cartridges for the reasons Dave mentions above. Quality and application are two different things!
But in Stu's system, the problem he described sounded very much like any phono section that isn't getting enough signal. Dynamics wake up, the sound is more vivacious when that is rectified. So comparing the Jensen which is set up for a low boost to a transformer set up for a lot more may not be about the transformers so much as it is the amount of signal presented to the input of the phono section. For that you would have to have both set up as much as possible the same way.

My largest concern here is that it sounds like it is the optimal to build the sut to suit one cartridge so when/ if you do the cartridge square dance ideally you would need change sut too?

No. You simply have to load it correctly for that cartridge.

I still don't believe you :-)

That's a bit of a surprise- your response on AudioAsylum lead me to believe otherwise. I can point you to a number of other examples should you need more proof.

A SUT or line level transformer driving a gate/grid of an active device is a different situation where any load or network required is a function of a compromised transformer design and not part of the transformers "job description"

SUT's typically drive the input of a phono section, where the input standard is 47Kohms. In this situation, the inductance of the cartridge and the capacitance of the interconnect cable form a resonant circuit. This resonance might have to be snubbed else it can cause troubles for the preamp, if the preamp has poor RFI immunity. That's what the loading resistor is for. However, driving a SUT with its additional inductance this peak is a bit different.  If you don't deal with it it might cause the transformer's response to not be flat- depends on if the transformer is designed specifically for a certain cartridge, but if the transformer is mounted in the preamp as is the case with this thread where the transformer is expected to work with *any* cartridge then loading should be set up. 

  I have found that when operating as balanced care must be taken with the cable layout to adhere to the balanced standard and simply attaching an XLR connector to an existing tonearm wire is hit or miss when it comes to hum pickup.  

Actually you treat it like any other balanced source. The '+' and '-' outputs of the cartridge travel in a shielded twisted pair, the shield is the tone arm ground (pin 3 on DIN connections, pin 1 on XLR connections). If you set it up this way (assuming that the arm itself is actually connected to the ground) there will be no hum whatsoever. 

Ralph, I will ask Dave Slagle what he thinks about my setup and loading. The original sound tradition Hashimoto hm-7 I tried had an even higher winding ratio such as 1:30 I think. It sounded pretty amazing with 29dB gain. But it was a little too big and "in my face." This will be 26 dB on top of 46 dB of my linestage, which seems reasonable.

Dave didn't believe me when I commented on AudioAsylum some years back that interwinding capacitive coupling is affected by loading, and thus to get flat frequency response loading is a pretty important aspect of transformer use. He's a believer now. BTW his updates on the H/K Citation 2 are excellent.

Hang on guys, some transformers have multiple taps and others do not. You have to check on the wires coming out of the transformer. Most are color coded. While having multiple taps gives you flexibility. I think but I am not entirely sure that a single ratio transformer is theoretically better. Ralph may be able to comment on this. Sowter has multiple tap transformers but I have always avoided them. May be just a knee jerk assumption. My brain hates unused wires.  

Multiple taps don't do anything to degrade performance, but they do allow you to use the transformer in a more flexible manner. The Jensen transformers in the OP's preamp have as commented earlier three different setups that can be used. The wires don't hang unused- they have to be connected together to form either parallel or series arrangements. This affect they way they respond to inter-winding capacitance so the loading requirements change as well.


A nice little side note: All phono cartridges are balanced sources and most of the time are run as if they are single-ended. But when you do this you wind up with that odd 'ground wire' that other single-ended sources don't seem to need. That ground wire is pin 1 of the XLR if you were running balanced. All transformers are capable or running balanced or single-ended input or output, so if you have an SUT you can run balanced from the tone arm to the transformer and single-ended from the transformer output if your phono section is single-ended. The advantage here is that the tone arm interconnect cable ceases to be as critical in the overall system sound; if you had to audition this cable to find the right one for your system you know exactly what I mean.  So you can take another step closer to neutrality by doing this, although you will have to find a place to install the XLR connections to the transformers... again, a fun little fact :)

Ralph, you would think the transformers would be designed for a 47K load which is pretty standard for MM phono stages. If not 47K how would you figure out what it was? Just a meter? Also why the capacitor. Wouldn't just a resistor do? I know you might have to change capacitive
loading for a MM cartridge but why the transformer?

@mijostyn They are designed for 47K, but any transformer designer worth his salt knows that the transformer isn't going to work perfectly with that- and that it will also change depending on what cartridge is used. IOW they know that it has to be loaded correctly (if they don't, they are leaving performance on the table). The capacitance has to do with the fact that you will likely get a peak somewhere that might not show up from simple ringing of the transformer with a square wave.


@montaldo If you don't get the transformer loaded correctly, you will hear differences but they won't tell you anything about which transformer is better! On top of that 20:1 is very different from 8:1.


To get to the right loading values for the transformer you have to talk to the manufacturer of the transformer. The only way I know to do this empirically on the bench is to  apply a square wave in series with the cartridge and look at the output of the transformer on an oscilloscope and vary its load to get a very slight amount of overshoot.


The problem here is that the capacitance of the tone arm interconnect cable is a variable, as well as the capacitance of the cable at the output of the square wave generator, and you run the risk of damaging the cartridge by deguassing it.


This is why I like working with Jensen, as they have demonstrated over and over again that they know and care what they are doing. Most SUT manufacturers can't tell you how the unit works with every cartridge out there.

Thank you Atmasphere! the Berning preamp has loading plugs for the moving coil section but if I understand what you're saying correctly those are for the INPUT side whereas you think the Jensen transformers themselves may need loading on the output side. Is that correct?

I can't speak to the Berning as I'm not familiar with its innards but to the last question, any and all SUTs should be loaded on the output side and the cartridge should never be loaded at all since the SUT is doing all the loading via its ability to transform impedance. So when its loaded correctly (with the cartridge at its input) there is simply no need to load the cartridge.

As an additional note, cartridge loading is for the benefit of the preamp not the cartridge. If the preamp has good RFI immunity no cartridge loading will be needed. When the SUT is used, it blocks RFI generated by the cartridge inductance and tonearm cable capacitance, so no need for cartridge loading. Clear as mud? 


An additional note: the amount of gain you ask of a transformer also degrades its performance. So the least amount of gain you get from it will always be the best. Also, if you use a different turns ratio the correct loading will change.


Until you are able to sort out this loading issue, its quite pointless to compare transformers!!! Some transformers are designed to be fairly well loaded when presented with a 47K load and a nominal cartridge resistance, others are not (IMO Jensens fall into the latter category; they assume that you are going to pay attention and get the loading right). In a nutshell you would then be comparing apples to oranges. Any SUT comparison needs to have the SUTs on an even playing field; both need to be properly loading which will not be the same values! The transformer manufacturer should **always** be able to to supply you with the correct loading values (which will usually be a combination of a resistor and capacitor).

My system is a Koetsu Rosewood Signature (.4mv), Jelco 850M on a Sota Star Sapphire, Berning all-tube bespoke capacitance coupled preamp (46 dB gain on the MM stage, Jensen transformers on the moving coil stage), Quicksilver v4 monos, Verity Audio Pafisals.

Jensens are some of the very best SUTs made anywhere at any price.

They are Jensen JT-347-AXT Step Up transformers (1:12 ratio configured). Given these and overall MC gain of only 64dB, does this explain my lack of dynamics with the Koetsu Rosewood Signature (.4mv)?

@montaldo
-And that is one of the best that Jensen makes.

Now there are some things you should know about when you use an SUT and this applies to all of them: SUTs need to be loaded correctly in order to perform correctly. Not to go into it with too much depth but transformers have an input side (primary) and output side (secondary). If they are not loaded at all, the inter-winding capacitance comes into play and the transformer will not have proper bandwidth- it will look like a flattened bell curve. If the transformer is loaded too heavily, the output will be rolled off!


The cartridge itself doesn’t need any load if an SUT is employed! IOW **never** attempt to load the cartridge if a Step Up Transformer is in use!! Instead, you load the output of the transformer, and the correct loading values change depending on which cartridge you are using.


Again, this applies to all SUTs. BTW cartridge loading is a different topic but in a nutshell for this conversation the impedance of the cartridge is what is requiring the loading of the SUT to change depending on the cartridge.


Now in the case of Jensen, they’ve sorted out what the correct loading values for most cartridges actually are (including the Rosewood Signature). If you contact them they can advise you on the proper loading the JT347. You’ll have to talk to David about how to install the loading in the preamp.


Seriously, the Jensen is excellent! But to unlock its performance you **have** to pay attention to proper loading, and this will be true no matter what transformer you use!!