http://www.hi-fiworld.co.uk SEPTEMBER 2019 HI-FI WORLD 73
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usical Fidelity A100
amps come my way
quite often. Given
that my local area in
Kent is not exactly
rich in hi-fi shops
or for that matter a thriving audio
community exchanging costly pieces
of equipment and selling off that
which is on the bottom end of the
current upgrade chain, it is almost a
strange amp to be so popular here.
I would expect the Denons and the
NADs and the Marantzs – but not
Musical Fidelity's A100. I can only
assume that at the time the A100
was a particularly interesting amp
and many of them found their way
into the listening circles spread
across Britain's South East and that
they are now something of a cult.
Perhaps not, but you never know
as I have seen quite a few over the
years – usually owned by people
I wouldn’t expect to have them.
That maybe is creating an image of
a stereotypical purchaser but the
common personal circumstance
is always much the same. The son
or daughter or the brother with
one of these has rescued it from
the loft of a distant relative who
brought it new and loved it. But it
now has problems.
The A100 suffers due to the
heat it creates, because it is biased
further into Class A than other
amps of a similar output, to give
more classic Class A famed sound
quality. Given that these amps are
now getting on in years I find all
sorts of faults but most can be
cleared very easily just by changing
all the capacitors associated with
the power amp from input to
output.
There is little point in being
selective about these capacitor
changes. All of those associated
with the power amp are liable to
be, if not dried out, then at least
under-performing. It is always
best to replace them all in one
operation. They all need to be
higher temperature 105 degree
types as the original 85 degree ones
are not going to last all that long.
The preamp circuits tend to
be fine and I have yet to find much
wrong with the main smoothing
capacitors in the power supply. I
generally keep some appropriate
main smoother types just in case
but haven’t – as yet – had to change
any in this model. This is probably
due to their close proximity to the
fans which are pulling in cool air
over them then passing it through
the hot circuitry and away from the
amps themselves.
Worst damage to the printed
circuit board occurs around the
12v zener diode but unless there is
anything else going wrong a clean
up of the soldering, removal of the
scorch marks on the board and it
will run fine.
Biggest component supply issue
I have found in the A100 is a lack of
replacement fans. They are rather
specific to the amp and I have had
problems finding ones that fit when
they fail. It's always one that fails- never both – although I always
replace the pair. There will come
a time when a different cooling
scheme will be required but at
the moment it isn’t too much of a
problem. The cooling is however
very important and must be fitted.
The mains switch was held in with
superglue and a match of one unit,
so that had to be changed too.
So with all those capacitors
changed do they sound better?
Different perhaps? Well it is always
difficult to tell, as never having
heard an original one that is factory
fresh from the box, there is nothing
to compare it with. A working but
well used one isn’t going to sound
the same as it did 15 years ago,
such is the way components age- especially when subject to heat.
So there is most likely a serious
change over time that the owner
might realise – but not something
that would be immediately obvious
with nothing to compare it against.
I can usually say that the basic
process of capacitor change is
a change for the good. There is
something in the midrange and low
treble that gains clarity that I have
never studied too closely – but is
there. Capacitors are about the
only component in any audio device
that have a definite sound. Caps can
be selected to warm up a sound or
to add detail. They can add bass end
wallop too – all without altering
the actual values of the initial
design or for that matter changing
the frequency response.
Sometimes it can be as simple
as a single item that defines the
sound. The A100 is not as warm a
sounding amp as you might have
expected from its biasing. It has
quite a clear mid and top end but
I have heard amps of more classic
Class AB that have a similar sound,
so the A100 isn’t exactly unique.
It isn’t in the Technics Class AA or
Quad 44/405 sound either.
With new capacitors you
might be able to hear what they
are doing, but only if you compare
directly the before and after
sound – which again isn’t all that
helpful since A-B comparison isn’t
possible. New capacitors take time
to burn in so it might be a couple
of hours or even weeks before the
effectiveness of the replacement
shows in the sound. That adds all
sorts of consequences into the mix
when you do repairs.
With their minimalist controls
and unflashy finish Musical Fidelity
A100s are not exactly an AV
receiver – but they still seem to
please my customers.
Dave Tutt
"the basic process of
capacitor change is a
change for the good"
HI-FI SERVICE & REPAIR
Dave Tutt
+44 (0)7759 105932
[email protected]
http://www.tutt-technology.co.uk