Once the design started coming together,
there was a lot of wiring to be installed. Screened
audio cable for the line level signals between each
amplifier and the rear panel, mains wiring for each
amplifier. It doesn't sound like much wiring but
once you start putting it together, things become
crowded very quickly. All wiring was twisted into
pairs where possible, for wiring carrying AC this is
important to help reduce the chances of hum pickup
(this is the reason that valve heater wiring was
always twisted in the old days). I also twisted any
groups of wiring which were carrying DC voltages,
this isn't necessary for noise reasons - there's no
chance of picking up interference from wires
carrying smoothed DC - but it doesn't hurt to keep
everything neat.
The assembly part proved a
nightmare, I tried to stay away from connectors as
much as possible, thinking of heat and degradation
of the audio signal - in a few places I had to use
connectors, luckily only on some of the power lines.
It got to a point where the amps became almost
impossible to work on, one time I had to alter
something and it took an extra 2 hours work just to
replace 2 components.
Routing the wiring proved a major
headache, with most line inputs being around a Volt
they are quite well protected but with a sensitive
phono input of around 4mV, even 0.5mV of induced hum
coupled with the low frequency boost of the RIAA
equalisation would cause one hell of a hum which
would easily make itself heard over the music. At
this level, interference is very easily induced into
the low level circuits if they pass near to mains
wiring.
The chassis fitted together really
well, I had to alter it in a few places but on the
whole it went together without trouble and once it
was bolted together it looked almost like a factory
finished product.
|
Putting things together. Huge amount of
work to do, wiring runs going everywhere. It
took several evenings work just assembling them. |
The cabinet
This was relatively straightforward,
just a box made from MDF and softwood but without
any front or back. It was glued and screwed
together, sanded smooth and then coated inside and
out in matte black paint to make a neater finish and
to help the covering stick. The covering was fabric,
fixed on with spray contact adhesive and trimmed. I
wanted to fit some ventilation to the top to sit
directly over the valves, this was made from a pair
of round metal bezels and a pair of cut down chrome
computer fan grilles. Finally a set of handles and
feet were added.
|
Test fit after building the cabinet. Looks
a bit ugly at the moment.. |
On to part 5
