Thursday 10 September 2015

Project X Part IV, Rationing the sound

Just been enjoying some Nielsen here on what has been a dry sunny but cool  day.
The amplifier is working rather well but one issue is the output from things like a cd player or my digital audio players line out is a lot higher than its input stage can handle so I have to turn the volume way way back and it sounds a bit strained on very loud passages.

It's a common problem cause by the strange decision in the early 1980's to standardize the output from digital to analogue converters typical found in cd players to around 2 volts where in the past it was rare for any device to have an output over 0.75 volts r.m.s. and often around  .250 to 0.5 volt which devices were and still are designed to 'see' into.
In simple terms, it means it's likely the very first stages of an amplifier are likely receive so much signal from such a source that they distort before the volume control can ration it, sounding harsh.
I've ordered up a pair of high quality 10db inline attenuators by Rothwell to put between the signal lead and the switching box which should cure that and allow it to use more of the volume controls rotation. 
They use 'audiophile' grade metal oxide resistors in a padded network in a plug enclosure to achieve that without compromising the transparency of the sound while being neat. 
Postscript: They arrived the next day from Bacup, Lancashire, England and it cured it leaving to sound very impressive playing a 96/24bit HD version of Rush's a Farewell To Kings on Closer To The Heart and the Christian Ferras recording of Sibelius's Violin Concerto (with BPO/H v Karajan on DG) via a Fiio X1 digital audio player's line  output.

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