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.
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.