Is Hi-Fi delusional?
 

On 19 Oct 2004 23:42:16 GMT, ohawker (Andy
Evans) wrote:

You beat me to it! But you have to imagine an olde worlde wirewound
volume control. :-)(SP)

Hello Stewart. My pal Chris (ex Bill Beard, as was the variac) is of the
opinion that the benefit of the variac is lowering the impedence, which in turn
should clean up some of the treble hash. Does this figure?

Since it will actually *increase* the source impedance at 100% output,
that doesn't make sense. It can only lower the impedance if you lower
the output voltage, which in itself could have much larger influence
on the power supply.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Is Hi-Fi delusional?
 

On 19 Oct 2004 20:26:17 GMT, ohawker (Andy
Evans) wrote:

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?

It's a 'variac', aka multi-tapped autotransformer.

- How come my variac goes up to 270v - the analogy is the famous volume control
that goes up to 11!

Because the input side isn't tapped at the end of the coil.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Is Hi-Fi delusional?
 

In article , Stewart Pinkerton
wrote:
On 19 Oct 2004 23:42:16 GMT, ohawker (Andy
Evans) wrote:

You beat me to it! But you have to imagine an olde worlde wirewound
volume control. :-)(SP)

Hello Stewart. My pal Chris (ex Bill Beard, as was the variac) is of
the opinion that the benefit of the variac is lowering the impedence,
which in turn should clean up some of the treble hash. Does this
figure?

Since it will actually *increase* the source impedance at 100% output,
that doesn't make sense. It can only lower the impedance if you lower
the output voltage, which in itself could have much larger influence on
the power supply.

Above is also my experience/understanding.

The point of the variable 'transformer' variacs is to let you dial up a
mains voltage. For some tests this can be useful as the mains isn't always
spot-on the nominal value. Overvolts can be used for test purposes and to
coax full nominal voltage out of a low mains.

But unless you wind the output well below 240/250V you won't get a lower
source impedance. It will usually be higher.

In effect, the variac shoves some extra resistance and inductance in the
way of the mains. It also may saturate, so this added impedance rises when
you try to draw a lot of current.

Hence it may alter the PSU and amp, but in ways I'd wish to avoid in normal
(non-variac) use. Can be useful as a diagnostic, but has to be interpreted
with care beyond the "Whoops! What's going on here?" stage... :-)

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

Is Hi-Fi delusional?
 

As for a transformer volume control - I'm not sure what that is.

Hello Don - see this http://www.stevens-billington.co.uk/page102.htm

Much beloved of current hifi tweakers.

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

Is Hi-Fi delusional?
 

Andy Evans wrote:
As for a transformer volume control - I'm not sure what that is.

Hello Don - see this http://www.stevens-billington.co.uk/page102.htm

Much beloved of current hifi tweakers.

Both the S&B and the Sowter version are transformers, not autoformers,
and also allow balanced input and single ended output, as the diagram
lower down the page you provided a link to shows.

- How come my variac goes up to 270v - the analogy is the famous volume control
that goes up to 11!


Because thats where the volume control analogy falls down, it does
indeed go to 11, or whatever ratio you wish.

Take for a example, a easy way of making a 115 to 230 volt conversion is
to take a center tapped torroid, join the two primary sections in
series, feed 115 into the center tap and common, and take 230 from the
other half of the primary and common.

--
Nick

Is Hi-Fi delusional?
 

"Ian Bell" wrote in message
...
tony sayer wrote:

Unless you make
your own recordings, that is the situation you are stuck with and you
just have to make the best of it.


Very good point and sadly..all too true....


Sad, no, an opportunity, yes. There is nothing more satisfying than
making
and listening to your own recordings. I have been doing it for 40 years.

Ian
--
Ian Bell


I have too. But I am just a "new kid" compared with you. I have been doing
it for only 30 years. One of the most interesting things about acoustic
recording
(orchestral etc) is that one can sit in the studio and listen to the
rehearsals,
and then compare this reference with what is coming out of your speakers in
the control room.

Iain

Is Hi-Fi delusional?
 

"Andy Evans" wrote in message
...
you've wasted your time. The decision as
to whether what comes out of your Hi Fi has been made long before any
piece of
media reaches your hands

Hello Don - yes, I expected this observation which is largely but not
entirely
correct. Yes, of course, volume and placement of instruments (at least..)
are
choices of the producer. But the microphones still pick up the sounds of
the
instruments and the voices - the producer has to be remarkably ham fisted
to
ruin that (not that it can't be done). So yes, we have to make the best of
this, but no - maximising one's hifi is never a waste of time. Why else
would
we read these pages? (I'm tempted to say - "to find a convenient argument
to
take part in"...)

=== Andy Evans ===


Hello Andy.

You are confusing the realms of responsibility here. The volumes and
placement
of the instruments (both physically in the studio, and in the recorded
soundstage)
are the responsibility of the engineer, not the producer.

I have been a professional recording engineer for thirty years.
Iain

Is Hi-Fi delusional?
 

"Don Pearce" wrote in message
...
On 18 Oct 2004 12:27:16 GMT, ohawker (Andy
Evans) wrote:

Bear in mind that every single piece of Hi Fi kit you own has an isolation
transformer built in. Adding more doesn't increase the
isolation in any way

I'm in the middle of trying to read up on this, but so far I have come
across
arguments for 'more iron' i.e. a very large isolation transformer. Haven't
yet
read why. I'm googling on "isolation transformer" and finding sites like:
http://www.smpstech.com/qa/qa0002.htm


Well, I see what they say, and you can check for yourself if you need
better isolation. Disconnect all the inputs from the power amp, and
turn the volume control right down. Now have a listen to the speakers
and check what you hear. A bit of hum is normal, and unaffected by
better isolation. Likewise a bit of hiss will be there, and is nothing
to do with isolation. On the other hand, if you hear random pops and
squeaks they may - just may - be coming along the mains.

This would be very unlikely though, because not only does the power
supply in the amplifier do a hugely successful job of eliminating
mains-borne crap, but the amplifier itself is designed to reject any
signals appearing on the power line. Between the two of them you will
be hard-pressed to find a need for work on the British mains.

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

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


Hello Don.

You wrote:

Well, I see what they say, and you can check for yourself if you need
better isolation. Disconnect all the inputs from the power amp, and
turn the volume control right down. Now have a listen to the speakers
and check what you hear. A bit of hum is normal, and unaffected by
better isolation. Likewise a bit of hiss will be there, and is nothing
to do with isolation.

If you connect a shorting plug to the input connector, turn the gain
control to zero, and put your ear to the speaker, you should hear
absolutely
nothing from a high-end amplifier - just inky black silence.

But you do use a balanced line connection don't you? It's an excellent
way to block the gremlins.

Iain

Is Hi-Fi delusional?
 

"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.

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.

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.

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


Iain

Is Hi-Fi delusional?
 

On Thu, 21 Oct 2004 10:44:44 +0300, "Iain M Churches"
wrote:


"Don Pearce" wrote in message
...
On 18 Oct 2004 12:27:16 GMT, ohawker (Andy
Evans) wrote:

Bear in mind that every single piece of Hi Fi kit you own has an isolation
transformer built in. Adding more doesn't increase the
isolation in any way

I'm in the middle of trying to read up on this, but so far I have come
across
arguments for 'more iron' i.e. a very large isolation transformer. Haven't
yet
read why. I'm googling on "isolation transformer" and finding sites like:
http://www.smpstech.com/qa/qa0002.htm


Well, I see what they say, and you can check for yourself if you need
better isolation. Disconnect all the inputs from the power amp, and
turn the volume control right down. Now have a listen to the speakers
and check what you hear. A bit of hum is normal, and unaffected by
better isolation. Likewise a bit of hiss will be there, and is nothing
to do with isolation. On the other hand, if you hear random pops and
squeaks they may - just may - be coming along the mains.

This would be very unlikely though, because not only does the power
supply in the amplifier do a hugely successful job of eliminating
mains-borne crap, but the amplifier itself is designed to reject any
signals appearing on the power line. Between the two of them you will
be hard-pressed to find a need for work on the British mains.

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

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


Hello Don.

You wrote:

Well, I see what they say, and you can check for yourself if you need
better isolation. Disconnect all the inputs from the power amp, and
turn the volume control right down. Now have a listen to the speakers
and check what you hear. A bit of hum is normal, and unaffected by
better isolation. Likewise a bit of hiss will be there, and is nothing
to do with isolation.

If you connect a shorting plug to the input connector, turn the gain
control to zero, and put your ear to the speaker, you should hear
absolutely
nothing from a high-end amplifier - just inky black silence.

But you do use a balanced line connection don't you? It's an excellent
way to block the gremlins.

Iain



Which line connection are you talking about here - line as in line
input, or line as in mains?

If you are talking about line input, it doesn't make any difference
what it is when the volume is turned all the way down. If you are
talking about mains type line, then every Hi Fi amp in existence (that
I am aware of) uses a balanced system - the transformer provides the
balancing.

As for the degree of hum and hiss with the volume down - yes, "inky
black" silence would be very nice, but it does depend on exactly where
in the chain the manufacturer has placed the volume control. For best
headroom it should be placed early, but that does have a residual
noise penalty. The usual balance is to choose a point where you can
just hear some noise if you put your ear to the speaker. If you can
hear absolutely nothing, then probably the front end will be lacking a
bit of headroom.

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