"Pete Cross" wrote in message


1. it amazes me how the digital era of audio appears to
be going, I saw a report recently of a new Logitech
speaker that was getting rave reviews saying "it has no
distortion at all" reading the reviews it became clear
they where refering to be able to play at max vol with an
ipod as the input without it distorting....a look at
logitech.com found me the spec 20wrms @ 10%thd ! sheesh!
that got me wondering too about the mp3 source, compared
to the orig CD wav what wouth the thd of the mp3 work out
at ? can it be measured ?

You're making a very common mistake when you read that spec. Does this
equipment have 10% THD as typically used? Probably not. There's a
long-standing (and self-defeating) tradition of rating the power of
equipment in this class @ 10% THD. This practice boosts the number of watts,
that's all. Basically, the electronics are clipping like crazy because the
gain was turned too high. Back of the volume to typical levels and the THD
might be very low.


2. a few yrs back I got samples from Analog Devices of a
low noise audio switch and a dc controlled vol chip (
0.002% thd ) I knocked them together with a couple of
5532's and have been enjoying them since ( from tv/dvd or
Technics CD into 4 x 75wrms mosfet amps and onto a pair
of ILP TL4's, ground/door and window shaking stuff and
very clear, or so I thought..... last week I got hold of
samples of National's LM4562 and replaced the 5532's, the
attack on drums is now much better and everything sounds
tighter.

Anybody who thinks that a LM4562 sounds better than a NE5532, both in
well-designed circuits, is suffering from specificaion-induced
constructor's ear. They are both free of audible distortion unless someone
screws up the design.

As it was chucked together I used 7815 & 7915
regs, I had a trouble with rf on the -ve rail which could
be heard as a faint hiss, so I thought whilst it's in
bits I'll go over the power supply , no need! it's now
silent, better rejection ?

More than likely you screwed up the design by not properly bypassing the
5532 power pins in the origional design. Conventional wisdom is that a
suitable cap (classic 0.05 uF ceramic for example) between the power supply
pins will settle them down.

More than likely National idiot-proofed the 4562s.

anyone else tried these LM4562's ?

The probable justification for National coming out with the 4562 was the
fact that 5532s were thoroughly commoditized. Too many people making them
and selling them for highly competitive prices.