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

Indeed the 47K is there for MM inputs to properly load a MM cartridge. The 47K value is not a liability for an active MC stage but when the turns ratio of a SUT is considered things change. The 47K value reflects to the Cartridge as 47K/Turns ratio squared. The perfect example of where this becomes an issue is with the Altec 4722. This is a 30/200:40K mic transformer that found a cult-like following because it is a great match wired 1:18 (120:40K) for a denon 103. The interesting thing with this combo is you get essentially the same gain out of a 103 in both the 1:18 hookup and the 1:36 hookup. This happens because assuming 47K, the reflected load of the 1:18 is 145Ω which is fine for a 103 but moving to 1:36 nets a 36Ω load which is less than the 40Ω internal impedance of the 103 which results in a 6dB loss which roughly offsets the 6dB gain from doubling the turns ratio. If the 47K resistor were increased to say 200K suddenly the increase of gain by doubling the turns ratio would be returned however the transformer behavior would also change which may be better or worse. It is interesting to note that some people do prefer the sound of the 1:36 connection with the 103 which has two possible expanations. 1) the transformer has no ringing and is critically damped. 2) loading a cartridge with its internal impedance reduces IM distortion and increases high frequency tracking (Peter Moncrief IAR #5)

Since with the SUT connected the secondary of the transformer serves the purpose of the grid resistor, it can in theory be removed completely. The problem with this is if the SUT is external and the interconnect gets unplugged or has a fault the phono stage can immediately become unstable and wreak havoc with a system with the tweeters usually becoming a casualty. The better solution is to increase the 47K value to the largest value that still keeps the phono stage stable with an open input. This becomes a situation where it is wise to open a dialog with the manufacturer and then have a competent tech change the value retaining the original part to replace if the unit is to ever be resold. I should also point out that increasing the value from 47K serves no purpose if the SUT is relying on that value (and possibly an additional Zobel) for controlled response.

I install a 300K at the input of my LR phono and I believe shindo used 100K so no everyone adheres to that antiquated 47K value.

dave

Dave
Thank you very much indeed, something even my poor simple head can grasp and comprehend!
Dialog with Manley will commence!

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 :)

I think I was better off when I knew nothing at all.... At least I was blissful in my ignorance!

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?
Ming boggling.....

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.

I still don't believe you :-)

I think this was in reference to a transformer inside an ampex deck that showed different behavior than I had seen from other line level transformers.  This particular transformer showed a critically damped but rolled off top end and when loaded the midband gain was reduced without effecting the high frequency corner which in "extended" its bandwidth.   I still believe that designing for the specific situation is the best approach and only rely on the load to control things if it is the main purpose of the transformer.  Power delivery to a speaker necessitates a load, working in a 600Ω professional environment also necessitates a load.  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"

I have seen the age old 'all cartridges are balanced' along with the 'all cartridges are current generators' and rather than bicker about a technical definition, I look at the primary as a two terminal generating device that inherits its mode of behavior from whatever you hook it up to.  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.  

dave