In article , Dave Plowman (News)
wrote:

If it were me I'd probably buy one of the cheap kits I used for
http://www.audiomisc.co.uk/HFN/HeadDAC2/HeadDAC2.html

I don't know if the board is laid out for gain, but your headphone amp
shows a unity-gain circuit only. I can't imagine they failed to make
provision for gain, though.

Something always worries me about using a 5 volt single supply for line
level audio - assuming it is used neat. In the old days, 24v was the
sort of norm for pro stuff. Admittedly line level is higher with that.
But when ICs came along was +/-15v or more.


The HeadDAC2 situation has the max input level set by the DAC I chose.
Which is also powered by the same circa 5V line. It doesn't clip early in
practice.

In other circumstances I prefer a twin-rail. So I've used the same kit as a
basis for a heaphone amp and HF filter for my ARMX6, but in this case using
+/- 5V. Again, I know what the max input level will be.

Remember reading a criticism of the Quad 33 pre-amp citing its 12v as
being too low.

That really depends on factors like if there is an active gain stage before
any volume controls and what else might limit the max input, what the
clipping behaviour is like, etc. The problem here in general commercial kit
is to guess what the user will connect. I've had a case of someone
connecting mains power to a LS output, which isn't what the designer
expects to have to cater for! 8-]

The 33 also comes from an age well before the CD audio standard of 2V
signals. But does offer the magic of the 'keymatic'...

FWIW In the Armstrong 700 preamp I used +/- 21V rails and had a volume
control before the active stages. (Except for RIAA, which also has +/- 21V
rails.)

Sadly that didn't stop a reviewer talking nonsense about its clipping
levels. But then, that's magazine reviewing, innit! 8-]

Jim

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