Is Hi-Fi delusional?
 

"Andy Evans" wrote in message
...
Pretty much - except there is no secondary. It is a big tapped choke
rather than a transformer. The turns ratio still applies to get the
output voltage, though. Picture the way a volume control works, and
substitute an inductor for the resistor and you have it.

Thanks, Don. Two questions:
- Is this how a transformer volume control works - is it a variac or an
isolation transformer?
- How come my variac goes up to 270v - the analogy is the famous volume
control
that goes up to 11!

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

Yes a variac is a single tapped winding, and so gives no protection from the
mains. Yes you really can get 270VAC from most variacs:-)

Modern transformer volume controls have a 1:1 ratio, and
tapped secondary. 24 taps seem to be common.

These tend to sound a lot better than a passive stepped attenuator.

Iain

Is Hi-Fi delusional?
 

On Thu, 21 Oct 2004 10:59:40 +0300, "Iain M Churches"
wrote:


"Don Pearce" wrote in message
...
On 18 Oct 2004 13:49:49 GMT, ohawker (Andy
Evans) wrote:

Single-ended designs like a SET are a different matter, and possess
none of the desirable attributes of power line rejection.

My amps are PP, but without global negative feedback. How does this rate?
Incidentally, my speakers are quiet, no pops or squeeks. Thanks for the
information - it's good to get help on this ng. Andy

Not really enough info - if PP refers only to the output stage, you
could still be prone to a bit of hum at least - but your ears will
tell you about that.

d
Pearce Consulting
http://www.pearce.uk.com


Hum in a push pull amplifier appears at opposite
phase in the two halves of the output stage, and so cancels.

Absolutely, but in many valve amps it is only the output stage that is
PP - the earlier stuff is single ended, and this is where power line
hum can creep in. Valve amps don't have the advantages of current
mirrors and complementary polarities to help.

On large broadcast valve amps, back in the sixties, the HT voltage for
the power stage was taken straight from the reservoir capacitor, and still
there was no hum.

Not surprised - the voltage gain of a power stage is pretty minimal,
so there is no reason for hum to get in at that point.

Whether you agree with its use or not, NFB does have the benefit of
reducing the noise floor of an amplifier. In valve amps (my field of
interest) one can achieve total silence in the speakers from a
100W amp with the CD source on pause. On a good amp you
should be able to hear the digital fades on a CD.

I'm all for NFB, and it can be applied far more effectively in a solid
state amp because you don't have to worry about the low frequency
phase shift of a transformer. I haven't yet come across a valve amp -
even a high end one - that didn't have that slight residual "liveness"
if you put your ear to the speaker.

Pops, squeaks, hum, line noise, and other gremlins can be
greatly improved by the use of a balanced line input.


Well, the line noise we were discussing was really that coming through
the power supply into the amp, so this doesn't really apply. As for
the stuff on the inputs, there is really no reason for any of this to
be getting onto line level inputs in a domestic setting. I'm all for
balanced feeds on low level microphone signals, but otherwise, no - it
isn't necessary. Certainly my Hi Fi has no extraneous noises even
without balanced feeds.

d
Pearce Consulting
http://www.pearce.uk.com

Is Hi-Fi delusional?
 

"Fleetie" wrote in message
...
"Keith G" wrote
(Björk - Telegram)

(Note to Fleetie - You need bigger bass drivers or a sub, not a bigger
amp....)

I'd tend to disagree, Keith.

It's painfully evident that my current valve amp has insufficient
headroom to handle Bjork's obsession with deep bass. A 150W amp
would allow me to play some of her songs with the vocals at a
decent level, without the bass clipping to ****. Which is what happens
now if I try to listen to some of her tracks at such a volume that
the vocals are loud enough to sound really good.

A sub would *not* improve matters.

I know for a fact I need a bigger amp. If you could come here and
hear it, I think you'd know what I mean.

Anyway, I'm gonna have to wait until I can afford a bigger power
amp. :-(


Martin


You do not mention the power of your valve amp, but a 25W PP
amp driving a decently sensitive pair of speakers can be very loud:-)
It may be that your valve amp has poor output transformers, or a lowish
damping factor, which aggravate the problem.

Care to give us more info?

Iain

Is Hi-Fi delusional?
 

"Andy Evans" wrote in message
...
Recreating fine detail, faithfully timbre in music is all very well but
you
want those dynamics too - its all part of the listening experience. Good
live unamplified music is anything but boring surely?

Maybe I'm not describing this correctly - the dynamics are there, but what
is
absent is the reproduction of sounds 'larger' than they are in real life
through added reverberation and hash in the hifi reproduction system. Take
away
this added 'presence' and the original experience remains. If you are used
to
resonances of various kinds enlarging the sound, then the effect is of
removing
something or making the sound smaller. One example is a listening test I
did
with three types of ICW capacitors (47uF) which increased in size and
power
rating (160 to 630v) as the film used got thicker. The smallest was about
an
inch diameter, the biggest the size of a coffee cup. The biggest was the
most
acoustically dead, and the sound was as I describe - more focussed and
less
lively. However, though I preferred the large cap, an audio designer
sitting
next to me preferred the middle one, saying it was more lively and
interesting.


=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

47µF is not a large capacitor. I remember from my student days being taught
that
the working voltage of an electrolytic should be rated at 1.4 times the
voltage across
it (providing that it will always operate under loaded conditions) and that
elctrolytics
with a working voltage rating much higher than the actual voltage across
them gradually
loose their ability to operate at the higher voltage.

The reason you liked the second capacitor better may be that it had a
better
electrical performance. There are so many factors beside just capacitance
and DC voltage working. for example ESR, Impedance, and Ripple factor.

Iain

Is Hi-Fi delusional?
 

"Mike Gilmour" wrote in message
...

"Mike Gilmour" wrote in message
...

"Andy Evans" wrote in message
...
Recreating fine detail, faithfully timbre in music is all very well but
you
want those dynamics too - its all part of the listening experience. Good
live unamplified music is anything but boring surely?

Maybe I'm not describing this correctly - the dynamics are there, but
what is
absent is the reproduction of sounds 'larger' than they are in real life
through added reverberation and hash in the hifi reproduction system.
Take away
this added 'presence' and the original experience remains. If you are
used to
resonances of various kinds enlarging the sound, then the effect is of
removing
something or making the sound smaller. One example is a listening test I
did
with three types of ICW capacitors (47uF) which increased in size and
power
rating (160 to 630v) as the film used got thicker. The smallest was
about an
inch diameter, the biggest the size of a coffee cup. The biggest was the
most
acoustically dead, and the sound was as I describe - more focussed and
less
lively. However, though I preferred the large cap, an audio designer
sitting
next to me preferred the middle one, saying it was more lively and
interesting.


=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

I can understand the component differences but try and get hold a good
recording of a live event that you've attended (before mastering if
possible) and use that plus your own memory (which is unreliable at the
best of times but it's the best you've got) use that as your reference.
Remember if its a dry acoustic recording then mastering may well add
reverb, compression and additional processing which muddles your
objective. Using that original gives you a reasonable chance imo of
component selection.

It helps to know a recording eng ..and most importantly get permission
from the artists, say its for your own tech use - some may refuse.

Most recording engineers cannot take the risk.
Most artists would not agree.
No record company would agree - they are paranoid about bootlegging :-)

Iain

Is Hi-Fi delusional?
 

47µF is not a large capacitor.

It is when it's polypropylene! I use all polypropylene caps in crossovers. andy

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

Is Hi-Fi delusional?
 

Global negative feedback has become one of the realities of reproduction, but I
prefer the sound without it, in fact when I took it off I could have cried for
joy - the music just seemed to relax and come alive. If you use good
componants, low distortion valves and a simple circuit, you can get it to sound
good, and in fact it doesn't measure too badly either (I've had distortion
tests done on various amps). This is just an observation, not a recommendation
- I just like it myself. And of course, there is feedback in places, just not a
global loop. Andy

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

Is Hi-Fi delusional?
 

"Jim Lesurf" wrote in message
...
In article , Andy Evans
wrote:
Contrary to what Stewart and others think, I've spent 35 years building
and tweaking hifi with one aim in mind - to make the hi-fi system sound
like live music. I didn't use measurements for this, I used my ears
since I've been a professional musician for most of my life.

Well, I've used both my ears *and* measurements. I find the measurements
to
have been very useful in helping to identify what to do when my ears
weren't happy. Saved me a lot of 'flailing about' and helped me to get an
understanding of what it happening.

As both an engineer and a musician, I like the above approach.
When I build something that sounds especially pleasing, or perhaps
not sop pleasing, I take it to the workshop to find out why:-)

Over the years, several interesting factors have come to light.
Extended bandwidth (DC to daylight:-) is not necessarily a prerequisite
for a good sounding amplifier.

As regards distortion, I have found that the amount of THD is not
so important as the distortion content - the way the THD is made up.
For example amplifiers with a small amount of 3rd harmonic sound
less pleasing than amplifiers with a larger amount of 2nd harmonic.

My main interest is in high quality valve amplifiers, which IMO
are much more of a challenge for a designer than SS
(I also happen to like the way valve amplifier can sound)

It is probably true that measurement is not the complete story, as
amplifiers
are designed to play music through loudspeakers, not reproduce sine waves
and spectral noise into oscilloscopes and spectrum analysers. But being
able
to see what is going on, does tell one a great deal, and points one in the
right
direction.

Iain

Is Hi-Fi delusional?
 

On 21 Oct 2004 08:42:27 GMT, ohawker (Andy
Evans) wrote:

Global negative feedback has become one of the realities of reproduction, but I
prefer the sound without it, in fact when I took it off I could have cried for
joy - the music just seemed to relax and come alive. If you use good
componants, low distortion valves and a simple circuit, you can get it to sound
good, and in fact it doesn't measure too badly either (I've had distortion
tests done on various amps). This is just an observation, not a recommendation
- I just like it myself. And of course, there is feedback in places, just not a
global loop. Andy


Interesting I guess you can remove global feedback on a valve amp,
because it is just an add-on, nor central to the design as in a SS
amp. But how did you then apportion local feedback to the various
stages to restore overall gain?

d
Pearce Consulting
http://www.pearce.uk.com

Is Hi-Fi delusional?
 

"Don Pearce" wrote in message
...
On Thu, 21 Oct 2004 10:59:40 +0300, "Iain M Churches"
wrote:
Hum in a push pull amplifier appears at opposite
phase in the two halves of the output stage, and so cancels.

Absolutely, but in many valve amps it is only the output stage that is
PP - the earlier stuff is single ended, and this is where power line
hum can creep in. Valve amps don't have the advantages of current
mirrors and complementary polarities to help.

But one still gets cancellation in a PP stage

On large broadcast valve amps, back in the sixties, the HT voltage for
the power stage was taken straight from the reservoir capacitor, and still
there was no hum.

Not surprised - the voltage gain of a power stage is pretty minimal,
so there is no reason for hum to get in at that point.

The point here I think is that on a large valve power amp, the signal
at the input of the PP power stage might be 70V. The hum from
a large reservoir cap might be about 2mV. That's 90dB even without
cancellation.

I'm all for NFB,

Good man:-)

and it can be applied far more effectively in a solid
state amp because you don't have to worry about the low frequency
phase shift of a transformer.

Nothing good comes easy:-) I have found that high
frequency phase shift is much more of a problem.
Without correction, negative feedback turns into positive
feedback at frequencies outside the audio
band. A carefully designed NFB network can be made to avoid this,
and tailor the bandwidth to have a 3dB point as required.


I haven't yet come across a valve amp -
even a high end one - that didn't have that slight residual "liveness"
if you put your ear to the speaker.

Come over to my place (I'm in Helsinki) I will be pleased to offer you
a large Finnish vodka, after you have put your ear to the speaker and
found there is nothing - just inky black silence. I have built several amps
in use by studios and prof musicians, they all tell me the same - total
silence.


Well, the line noise we were discussing was really that coming through
the power supply into the amp, so this doesn't really apply. As for
the stuff on the inputs, there is really no reason for any of this to
be getting onto line level inputs in a domestic setting. I'm all for
balanced feeds on low level microphone signals, but otherwise, no - it
isn't necessary. Certainly my Hi Fi has no extraneous noises even
without balanced feeds.

It has taken a long time for balanced line to filter down from the broadcast
and studio environment to domestic applications. But there are signs that
it
IS happening. Many CD players have both an AES/EBU digital output on an
XLR plus a pair of analogue balanced line outputs on XLR/M. Also
people often seem to have a turntable and a (valve) RIAA
stage at one end of the room, and the rest of the equipment at the other.
In a situation like this, balanced line working is an excellent solution.

Iain