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

The K&K link does not "back" what Ralph says.  Ralph states (correctly) that for any given source there is one load that will make the transformer act in the manner for which it was designed.  The K&K link assumes the transformer to be a perfect device that simply reflects an impedance and has no other impact on the sound.  It is my belief that SUT's should be designed to work optimally in an unloaded situation with 47K input resistor and ~100pf of cable capacitance being the worst case situation.  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.  I then went through the process of playing with loads on both the primary and the secondary of various SUT's and found that loading the secondary had a much more profound effect on the sonics.  If the transformer were ideal then a 100Ω load should be a 100Ω load independent of whether it is at the cartridge directly or reflected through the transformer.  Since the differences were not subtle I came to the conclusion that the load on the secondary was altering the sound of the transformer as much or more than  it was the cartridge.  This goes a long way to explain the "black art" label attached to loading SUT's since loading the secondary changes both the sound of the SUT and the sound of the cartridge at the same time.  

dave

Dave I am confused on the second variable.  Or what you can do to the transformer to make the cartridge  not need loading.

Let's say you have 5 ohm cart.  We use the 10x rule so 50 ohms is a ballpark load.  We have no input resistor on the phono amp.  Can you build a transformer say 1 to 20 to meet that 50 ohm need.

Or to put it another way on a 1 to 20 step up,  what is the load  variance window you can get by material and or winding?

Thanks Tom

Hey Tom,

Transformer "misbehavior" (ringing etc) is a function of source and load values.  With a known source (cartridge impedance) and load (47K+||100pf) the transformer can be wound such that it gives the desired behavior.  This is a completely different concept than loading the cartridge and much of the confusion in the topic comes from lumping everything together into an "ideal black box"

For your 5 ohm cartridge and a need for 20X gain, a 1:20 can be done to have a low Q resonance of 3-5dB above 100Khz loaded only by the test rig.  Adding the actual input impedance of 47K+ and 100pf for cable capacitance will damp this behavior down to an extended well behaved top end.    Lets assume you want the cart to se 50Ω and the input resistor is 300KΩ.  The turns ratio of 20 will give an impedance ratio of 400 so that 300K becomes 750Ω.  Placing a 54Ω resistor at the cartridge in parallel with the reflected 750Ω will net a 50Ω load with minimal effect on the transformer behavior.  From the transformer primary viewpoint, the 54Ω resistor will lower the 5Ω source impedance to 4.6Ω.   The change in source impedance from 4.6 to 5Ω  is well within the range of source impedances that will work for a given design.  It is when you start changing the source or load impedances by a factor of 2 or more from the "design center" that transformer behavior starts to dominate the sonic signature.  Take the peerless 4722 that works nicely with a denon 103 and drive it with a 2Ω SPU and that controlled top end suddenly turns into a 10+dB peak @ 22Khz.  Fix that 10dB peak with a 10K secondary load and you end up with syrup.

The important thing to understand here is that the load the cartridge sees and the turns ratio of the SUT do not need to have any relationship to each other and simply mathematically attaching them to each other as a ROT generally leads to inconsistent sonic results.  

Reporting back on the effect of adding Dave slagle's 1:20 Copper SUT to my Berning pre and Koetsu Rosewood Signature. In short, everything is back. The gorgeous tonal balance and graceful top end of the Bernng remain,  but now all the Dynamics have been restored and the engagement and involvement is stunning.  the difference is not subtle.  it's as if every component of system were upgraded.

 am I am I right that this huge difference can be attributed to some sort of better loading match between the Transformer and the cartridge?  and maybe it is aided by the additional gain but not primarily driven by that?

Thanks Dave

It is one more variable in the 100's so we can black art our way to audio nirvana.  If you are out at a west coast event let the forum's know.  To hear your modified stacked 57's would be a delight!!!

Enjoy the ride 
Tom