Hi,

In message , Des
writes

Ok. I'm the first to admit that I'm no audiophile. My 25 year old
Rotel 810 amp is showing definite signs of packing up.
Yeeeeeehaaaaaaaaaa. A stone-cold *need* to buy a new amp. Joy, joy
joy... etc.

I'm prepared to pay a suitable wedge for the replacement - if it lasts
anything as long as the Rotel, I'm going to be stuck with it for long
time.

I'm thinking about an Arcam A85. It seems to be very well thought of.
I lifted one off the shelf at a local hi-fi store and nearly strained
a muscle - I think Saddam has been hiding depleted-uranium inside
them.

Now this thing costs nearly £800. 'Precious'? I'm positively friggin
paranoid! I do NOT want to cock this up, or I will have a very long
time to regret it. If it sounds bloody-awful compared to the one I
reviewed in the store, I want to find out pronto, so that I can return
it.

I won't pass comment on the merits (or not) of burning in, other than to
say I've never bothered. However, there's nothing at all wrong with the
A85, it's a bloody good amplifier in my view. If you're spending that
much wonga, it's definitely worth asking for a 'sale or return' so that
you can audition it at home - things never sound the same in the shop.
Most good audio shops will let you do this; at least, I've not been
refused yet.

--
Regards,
Glenn Booth

"Des" wrote in message
...
Reviewers often comment that it takes about 100 hours before a new amp
settles down and start to sound like it 'should'.

In this case, what constitutes 'burning-in'? Is it sufficient to just
leaving the power on for a week? Or does it have to be driving a load
(the neighbours are going to just love that)?

IMHO yes leaving the power on helps, but it would be better if you listened
to music 'from cold' to find out if you can hear any differences as things
warm up. If not, then save some electricity and leave it off when not in
use!

I can think of some areas where changes occur in an amplifier over time.
These may be minor and in most amps inaudible, but it depends on the design
and the listener.

1. Electrolytic caps in PSUs. These 'form' over a very long time (weeks).
Would lead to better performance (ie better smoothing, more DC like
voltages) over time.

2. Temperature effect on electrolytic caps. In switched mode supplies too
much heat dries them out and they lose effectiveness. If you look at specs.
they quote life of say 10,000 hours. Most supplies last a lot longer than
that!

3. For coupling capacitors between stages (ie in the analogue audio path)
effects 1. & 2. would effect slightly the characteristics of the capacitor
to how well if passes signals of different frequencies. May or may not be
audible.

4. Transistors warm-up. Again for analogue stages the transfer function of a
transistor will vary with temperature, depends on the design how well this
is compensated for.

HTH, no 'rules', just listen with open ears.

Regards,
John

"John" wrote in message
...
"Des" wrote in message
...
Reviewers often comment that it takes about 100 hours before a new amp
settles down and start to sound like it 'should'.

In this case, what constitutes 'burning-in'? Is it sufficient to just
leaving the power on for a week? Or does it have to be driving a load
(the neighbours are going to just love that)?

IMHO yes leaving the power on helps, but it would be better if you
listened
to music 'from cold' to find out if you can hear any differences as things
warm up. If not, then save some electricity and leave it off when not in
use!

I can think of some areas where changes occur in an amplifier over time.
These may be minor and in most amps inaudible, but it depends on the
design
and the listener.

1. Electrolytic caps in PSUs. These 'form' over a very long time (weeks).
Would lead to better performance (ie better smoothing, more DC like
voltages) over time.

2. Temperature effect on electrolytic caps. In switched mode supplies too
much heat dries them out and they lose effectiveness. If you look at
specs.
they quote life of say 10,000 hours. Most supplies last a lot longer than
that!

3. For coupling capacitors between stages (ie in the analogue audio path)
effects 1. & 2. would effect slightly the characteristics of the capacitor
to how well if passes signals of different frequencies. May or may not be
audible.

4. Transistors warm-up. Again for analogue stages the transfer function of
a
transistor will vary with temperature, depends on the design how well this
is compensated for.

HTH, no 'rules', just listen with open ears.

Regards,
John



Capacitors and their effects - apart from long-term drying out and the
inductance of very large values - also fall into snake oil IMHO.

However one thing that can have effect is heat. Most amps have some sort of
temperature sensing in the output stages that are designed to stabilise the
biasing which will inevitably change with temperature. The old way used to
be a small signal transistor either glued into or onto the surface of the
heatsinks - the Japs now build specialist transistors that have this
transistor fitted internally with external access. Leaving the amp on for
perhaps an hour before use will allow the heatsinks - and thus the bias -
to thermally stabilise which could lead to reduced crossover distortion -
the main effect of poor biasing.

Poorly designed amps that run close to instability in the first place (the
exact opposite of inherently very stable designs like Quad - and there are
enough of those around in the esoteric-fi areas) may, when cold, have
relatively significant crossover distortion which can lead to listener
fatigue and perceived 'edginess' to the sound.


--
Woody

In article , harrogate
wrote:


Capacitors and their effects - apart from long-term drying out and the
inductance of very large values - also fall into snake oil IMHO.

There are various effects. However I'm not personally convinced they are
audible as reviewers seem to assume.

However one thing that can have effect is heat. Most amps have some sort
of temperature sensing in the output stages that are designed to
stabilise the biasing which will inevitably change with temperature. The
old way used to be a small signal transistor either glued into or onto
the surface of the heatsinks

e.g. 'Rubber zener' used to set the bias, and clamped thermally to the
output devices and drivers (ideally). The problem here is due to the times
taken for temperatures to equalise between devices. To some xtent you can't
win here as the output devices will have junction/channel temperatures
which are very different to such a bias control device in another package.
Also possible problems with asymmetric musical waveforms where the
junctions temperatures differ.


- the Japs now build specialist transistors that have this transistor
fitted internally with external access.

Neat idea. Wish I'd had these in 1980. ;- I envy modern designers for
some of the devices they now have. However I also pity them for some of the
'reviews' that have to put up with after years of hard work. That's show
biz, I guess. :-/


Leaving the amp on for perhaps an hour before use will allow the
heatsinks - and thus the bias - to thermally stabilise which could
lead to reduced crossover distortion - the main effect of poor biasing.

In some cases warm-up might make things worse. Depends upon the situation
that gives best performance and if the amp was setup warm or cold, etc.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

In article , John
wrote:


IMHO yes leaving the power on helps, but it would be better if you
listened to music 'from cold' to find out if you can hear any
differences as things warm up. If not, then save some electricity and
leave it off when not in use!

I can think of some areas where changes occur in an amplifier over time.
These may be minor and in most amps inaudible, but it depends on the
design and the listener.

1. Electrolytic caps in PSUs. These 'form' over a very long time
(weeks). Would lead to better performance (ie better smoothing, more DC
like voltages) over time.

This is one area where I can see that such a 'burn in; change may occur.
However it is possible to design an amp that is fairly insensitive to the
rail fluctuations. Hence with good designs I'd hope this wasn't happening
to any audible extent.

2. Temperature effect on electrolytic caps. In switched mode supplies
too much heat dries them out and they lose effectiveness. If you look at
specs. they quote life of say 10,000 hours. Most supplies last a lot
longer than that!

Again, if the unit is properly designed this should not be a factor in my
view.

3. For coupling capacitors between stages (ie in the analogue audio
path) effects 1. & 2. would effect slightly the characteristics of the
capacitor to how well if passes signals of different frequencies. May or
may not be audible.

Do people still use electrolytics as signal path coupling caps these days
in 'audiophile' equipment? I know that other types show charge storage
effects, but this should, I hope, not be audible with decent designs
handling musical signal patterns.

4. Transistors warm-up. Again for analogue stages the transfer function
of a transistor will vary with temperature, depends on the design how
well this is compensated for.

This might explain a change during the first few tens of mins of use.
Beyond that, I'd expect it to vary with the musical dynamics, not show a
one-off 'burn in' during the first few hundred hours of use. Again, with a
decent design, I'd hope this wasn't audible.

Thermal effects in output stages are certainly a possible problem. Indeed,
i've just put up some new webpages on one aspect of this. ;-

The difficulty I have with the above mechanisms is that I'd hope that by
now decent designs would avoid them all as a source of one-off 'burn in'.
(Possible exception being forming of reservoir caps, but even this can be
dealt with by suitable design, I would hope.) Hence I find it odd that such
claims by reviewers tend to appear when reviewing expensive 'audiophile'
units. Cheap and cheerful, I can see being a problem. But where such claims
are made with expensive audiophile items, I'd be inclined to avoid the
units in question as it undermines my confidence in the designer/maker.

My own experience is that I don't recall encountering audible 'burn in'
with the equipment I've used/built. This despite having often measured
changes in electrolytics (and power line variations) with use. Mind you,
with items I've built this may be due to my fiddling about with all sorts
of circuit changes during the relevant period, so I may have missed this in
the rush. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

On Mon, 14 Jul 2003 09:12:51 +0100, Jim Lesurf
wrote:

Do people still use electrolytics as signal path coupling caps these days
in 'audiophile' equipment? I know that other types show charge storage
effects, but this should, I hope, not be audible with decent designs
handling musical signal patterns.

Plot the AC signal path of an amplifier's output stage and you will
find that the supply decoupling electroloytics are in series with the
speaker - they function as speaker coupling caps. I am not aware of
any design that has done away with this topology yet.

d

_____________________________

http://www.pearce.uk.com

"Don Pearce" wrote in message

On Mon, 14 Jul 2003 09:12:51 +0100, Jim Lesurf
wrote:

Do people still use electrolytics as signal path coupling caps these
days in 'audiophile' equipment? I know that other types show charge
storage effects, but this should, I hope, not be audible with decent
designs handling musical signal patterns.

Plot the AC signal path of an amplifier's output stage and you will
find that the supply decoupling electroloytics are in series with the
speaker - they function as speaker coupling caps. I am not aware of
any design that has done away with this topology yet.

It makes a big difference whether the caps are inside or outside the
feedback loop.

On Tue, 15 Jul 2003 21:26:05 -0400, "Arny Krueger"
wrote:

"Don Pearce" wrote in message

On Mon, 14 Jul 2003 09:12:51 +0100, Jim Lesurf
wrote:

Do people still use electrolytics as signal path coupling caps these
days in 'audiophile' equipment? I know that other types show charge
storage effects, but this should, I hope, not be audible with decent
designs handling musical signal patterns.

Plot the AC signal path of an amplifier's output stage and you will
find that the supply decoupling electroloytics are in series with the
speaker - they function as speaker coupling caps. I am not aware of
any design that has done away with this topology yet.

It makes a big difference whether the caps are inside or outside the
feedback loop.

Doesn't change the fact that they couple current into the speakers.
And of course everything, including the speakers themselves, is inside
the feedback loop.

d

_____________________________

http://www.pearce.uk.com

"Des" skrev i melding
...

In this case, what constitutes 'burning-in'? Is it sufficient to just
leaving the power on for a week? Or does it have to be driving a load
(the neighbours are going to just love that)?

There is one slight danger in leaving any amp permanently switched on. A
friend of mine has it in his head that his HiFi sounds better if it is kept
"warm" all the time, so he leaves it switched on all the time. The only
disadvantage is a slight increase in his electricity bill (or so he
thought). Then one night there was a serious spike in the power supply
which blew both the poweramp and preamp.... He complained to the
electricity company but got nowhere.


--
Andrew Walls
Near the Arctic Circle
Norway

On Sun, 13 Jul 2003 20:22:12 +0100, Des
wrote:

Reviewers often comment that it takes about 100 hours before a new amp
settles down and start to sound like it 'should'.

More evidence, in case we didn't need it, that "Reviewers" don't know
a lot about engineering ... amplifiers are pieces of consumer
electronics: you don't "run in" a new fridge, or microwave, or
television, or ...

In this case, what constitutes 'burning-in'?

Its definable precisely as the time it takes you to get used to how
your new amp sounds compared to your old one. If an amp *really*
starts to sound different* after its been used for X hours, this is
almost certainly a case of very poor design engineering :-)

Julian

* i.e., for a given input, the output at time t is measurably
different from that at time 0.

--
Julian Fowler
julian (at) bellevue-barn (dot) org (dot) uk