The Rialto is phonostage pre-amp compatible with both moving magnet and
low output moving coil cartridges. Discrete transistor circuitry is used
throughout for maximum fidelity and lowest noise, and audiophile
polypropylene capacitors are used for both the RIAA equalisation and
signal coupling.
The
Design Brief
Although this is our first new phonostage for several years, phonostage
design is nothing new to Rothwell. The first phonostage to bear the
Rothwell name was designed as far back as 1989 and was debuted at the
London Hi-Fi Show of 1990 (it was an expensive valve design with many of
the features subsequently adopted by other manufacturers, like a large
outboard power supply and selectable cartridge loading). Since then there
have been solid state moving coil and moving magnet designs from Rothwell,
some sold as Rothwell products and some designed for third parties. More
than twenty years of design experience has lead to an understanding of
what really makes an impact on sound quality and what merely looks good on
paper (or indeed just adds to the cost). The goal when designing the
Rialto was to achieve high-end performance without the high-end price
tag. To this end, every effort was put into maximising sound quality and
everything that has no bearing on sound quality was sacrificed. For
example, the ability to switch between mm and mc modes of operation via an
external switch might be convenient, but internal switches allow the
signal path to be kept as short and direct as possible, so internal
switches are what were chosen.
There's even a separate switch for each channel to keep the signal path
short. The gain and input impedance for mm and mc operation could have
been made adjustable, but that would have been an unnecessary expense for
virtually no benefit in terms of sound quality, so fixed values for gain
and input impedance were chosen (42dB and 47k for mm, and 62dB and 100
ohms for mc). The budget saved on unnecessary adjustability is better
spent on power supply filtering - seven stages in total are used in the
Rialto to maximise channel separation and inter-stage separation. Even the
power on/off switch was deemed unnecessary since the total power
consumption is so low (less than most domestic equipent in standby mode).
The result is truly audiophile sound quality at a very affordable price.
Zero
Global Feedback A moving coil phonostage typically has a gain of about 60dB, but due
to the RIAA equalisation curve it actually has more like 80dB at the low
end of the audio spectrum. 80dB is huge amount of gain and is best spread
over more than one gain stage. Many designs employ two gain stages, but
the Rialto has three to allow each gain stage to operate with less gain
for improved performance. Each gain stage uses just two discrete
transistors and employs local feedback to achieve extremely low
distortion. The high linearity of each gain stage means that overall
global feedback (widely acknowledged to be good for achieving good THD
figures but bad for perceived sound quality) can be eliminated.
Audiophile
Components The Rialto uses a passive circuit to create the RIAA curve (accurate
to better than 0.5dB) and employs multiple audiophile grade polypropylene
capacitors which not only allows non-standard capacitance values to
achieved (to obtain the accuracy in the RIAA curve) but also to act as
mutual bypass capacitors, minimising ESR (equivalent series resistance)
and maximising audio performance.
The transistors too are audiophile devices, carefully selected for maximum
fidelity and minimum noise. Different transistors are used in the moving
magnet section of the Rialto and the moving coil section so that both
moving coil and moving magnet cartridges are amplified by gain stages
optimised for their specific requirements.
Low
Noise Performance Low noise cannot be achieved merely by using expensive components. The
circuit design has to be right and the circuit board tracks have to be
very carefully routed. Both these aspects of design have been meticulously
addressed in the Rialto so that background noise is as low as
possible. The power supply goes through seven stages of filtering so that
the circuit is operating from a perfectly clean voltage supply, allowing
the music to appear out of silence, unsullied by residual hum, buzz and
hiss.
Don't be fooled by the Rialto's affordability. This is a top-flight
phonostage.
Specifications:
gain
mm
mc
input impedance
mm
mc
output impedance
sensitivity for 500mV o/p
mm
mc
headroom
signal/noise
power supply
mains voltage
power consumption
dimensions
weight
packed weight
42dB
62dB
47k + 150pF
100R
75R
4mV @ 1kHz
0.4mV @ 1kHz
20dB
>87dB (mm), >69dB (mc)
24 volts DC, center +ve
100V - 250V AC
<1W
60 x 155 x 92 mm
570g (exc. psu)
770g (inc. psu)
The Upgrade Path
For audiophiles looking for future upgrades, we don’t recommend the usual
path of changing to a larger power supply. A power supply capable of
delivering more current is of no benefit to a class A circuit which draws
constant current, and the extensive supply filtering and storage within
the Rialto means that changing the power supply would yield only marginal
benefits. For audiophiles looking to get the absolute best performance
from a moving coil cartridge, we recommend using one of the Rothwell
step-up transformers (see links on
main Rothwell products page) in
conjunction with the Rialto in moving magnet mode. This will push the
Rialto’s performance from Hi-End standard into the Super League.
Order a Rothwell Rialto MM/MC
Phonostage (free shipping to the UK and European Union. If you live
outside of these areas, please
contact us before ordering for a shipping
quote): £379
(Please note that we do
not offer the 30-day trial period on the Rothwell products - although they
can of course be returned if there is any fault.)
Please allow up to 14 days before dispatch
for Rothwell products
