Cambridge Audio 840A bypassing pre-amp?


Standard Member
Hiya, im looking to use my 840a as a power amp & it has a 'fixed input mode' function but i'm not sure if this actually bypasses the pre-amp or not?
You can set 'fixed mode' at any level so i assume not

The manual says:

"Completely separate pre-amp and power amp toroidal transformers and circuits make the 840A effectively a pre and power amplifier combination in one chassis"

"The 840A features separate transformer secondaries for left and right
channels, twin rectifiers and separate PSU's for dual mono operation of the
left and right power amplifiers. A separate transformer supplies the preamp
making the 840A effectively a Pre and Power amp combination in one box"

"Fixed level inputs

Any input of the 840A is able to be set for fixed gain. Whenever this input
is selected the gain will automatically go to this value and will not be
adjustable by the volume control. This feature allows the 840A to be
effectively used as a stereo power amplifier (for that selected input only)"

Im basically looking to use my DAC as the pre-amp, 840a as power amp, as i hear this will improve sound quality, but i can't see it improving anything unless the 840a's pre-amp is actually bypassed in 'fixed input' mode?

Thanks in advance for any help

Last edited:


Distinguished Member
Fixed level inputs bypass some of the 840A's preamp, not all of it - for example it does not bypass any of the switching, and it permits gain setting. The 840A does not offer power-in connections.

Whether using the variable level output of your DAC will improve the overall sound compared to using its fixed level output and the 840A's volume control is a different question. It would make sense for you to try out both options rather the relying on what you've gathered from other sources. Since you already own the pieces, comparison is easy to organize.


Standard Member
Cheers mate, i guess the best way is to just test & see what sounds best

I also want to use a sub on my 840a's preout so probly wise to use the 840a's pre-amp, or i imagine i'd have to turn the gain down quite a bit on my sub if my 840a was used in a power amp fashion (output set to 0db & fixed)

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