How to select the most suitable Hashimoto step-up transformer.

Selecting the correct step-up transformers is really difficult in the beginning for most readers so it seems. The “scrambled” information that Hashimoto supplies with their transformers does not help either.

We have found the most accurate information about selecting/working with step-up transformers on the Rothwell audio website.
http://www.rothwellaudioproducts.co.uk/html/mc_step-up_transformers_explai.html
Please read this information a few times to fully understand.

After reading the information on the Rothwell website this is the way to select the correct (Hashimoto) step-up transformer.

The Hashimoto transformers show with a load of 47K on the secondary side (the input impedance of almost all phono stages) only a very mild ringing/overshoot. There is really no need to optimise the transformers with added capacitance on the secondary side.

As can be read from the Rothwell information (and we agree on this): you don’t want to load the step-up transformer (and MC-cartridge) more then necessary.

The recommended transformer/cartridge selection method
(Found on the Rothwell Audio website)

Rothwell (and our) recommended procedure for selecting the right step-up transformer is to work initially with a cartridge's output voltage rather than its source impedance. The method is to calculate what the cartridge's output signal will be after it has been stepped up by the transformer. A cartridge with an output of 0.35mV and a step-up transformer with a 1:15 turns ratio will give an output of 5,25mV. This is about the right signal level for the input of a moving magnet phono stage. Too high a voltage will compromise headroom (though bear in mind that valve designs have huge headroom), and too low an output will result in compromised signal/noise ratio. 5mV is a good target figure, but anything in the range of 2.5mV to 10mV is within acceptable limits. In fact your complete audio system plays a role here. When you have a system with high internal gain (for example high gain in the line stage and/or a highly sensitive power amplifier and/or high efficiency loudspeakers), you probably want less gain from the step-up transformers. The opposite can also be the case. When you have a system with low gain (low gain phono stage, very low efficiency loudspeakers) a little extra gain from the step-up transformers can be helpful.

Having found a good match for cartridge voltage output and transformer turns ratio, check that the transformed impedance is acceptable. 47K is virtually the universal input impedance of moving magnet phono stages, dividing this figure by the square of the turns ratio will give the load impedance that the cartridge sees. With a 1:10 transformer, the load impedance seen by the cartridge will be (47000/ (10x10)) = 470 ohms. Is this within the cartridge manufacturer's recommended range? Please check the cartridge specifications to make sure.
A 1:20 transformer will present a load impedance to the cartridge of 117 ohms and a 1:30 transformer will present a load of 52 ohms. 1:30 is best reserved for the few remaining cartridges that outputs 0.1mV or 0.2mV.

Some examples
Take for example the Ortofon Xpression. Output voltage (at 1Khz, 5cm/sec) is 0,3mV. Internal impedance 4R. When used with a 1:20 transformer, the 0.3mV output will become 6mV, which is ideal for an MM phono stage. The 117 ohm load on the cartridge is clearly compatible with Ortofon's recommendation of anything above 10 ohms.
The figures for the Denon cartridges look slightly odd compared to the rest of the table. If the figures are correct, the output voltages seem a little low for the higher than normal source impedances of 40 ohms (possibly due to the use of relatively weak magnets and more turns of wire on the coils), nevertheless a 1:20 transformer would give an output voltage of 5mV with the DL-103R and present it with a load of 117 ohms. The voltage is again ideal for a MM phono stage and the impedance is only very slightly higher than Denon's recommendation, which is probably only meant to be a guideline anyway.

Ok, but what to do when this calculated load on the MC-cartridge is way above the manufacturer recommendation? In that case we can use an extra resistor at the primary side of the step-up transformer. Take for example the Ortofon SPU Synergy GM. Output voltage (at 1Khz, 5cm/sec) is 0,5mV, impedance 2R. When used with a 1:15 transformer, its 0.5V output will become 7,5mV, which is still within the recommended range for an MM phono stage. The resulting load on the cartridge (47000 / (15x15)) = 208 ohm. This is above Ortofon's recommendation of 10 to 50 Ohms. However we can add a resistor in parallel to the primary side and lower the loading on the cartridge. When using a 200R resistor the resulting load will become ((R1 x R2)/ (R1+R2) = (208 x 200) / (208 + 200) = 102R. Using a 62R resistor, the load will become 48R.

We would advise to first listen to familiar music without any added resistors. When the sound is to bright, forward, light and lean, then some extra loading is needed. After adding an extra primary loading resistor, listen again. When the sound becomes slow, dark, recessed and compressed, you know you added too much load to the cartridge.

What would happen when we want to keep the manufactures recommendation without using the primary loading resistor? In that case a transformer with a turn ratio of 1:30 has to be used. This transformer will load the cartridge with (47000/ (30x30)) = 52R. However with this step-up transformer the output voltage after the step-up will become 15mV. This value can cause overload problems within a transistor phono stage, but the most heard issue is that there is now too much gain in the total system and only a slight turn of the volume control will cause the system to play very loud.

Our preferred method is to select a step-up transformer which will amplify the cartridge output to a value between 3 and 10mV and add a loading resistor parallel on the primary (step-up) winding when you find it necessary. However, in our experience this is seldom the case.