to select the most suitable Hashimoto step-up transformer.
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.
have found the most accurate information about selecting/working
with step-up transformers on the Rothwell audio website.
Please read this information a few times to fully understand.
reading the information on the Rothwell website this
is the way to select the correct (Hashimoto) step-up
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.
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.
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.
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.
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.
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.
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.
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.
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.