120V vs. 240V which is better for audio?
Don Nebel
the option of using single ended or balanced inputs. I have been told
that balanced inputs offer better noise characteristics because of
common mode rejection. I had read in a magazine article that the same
(common mode rejection) can apply to a amplifier power supply. Now I
have another option to choose from, do I use a single ended power source
(120 volt) or a balanced source (240) volt. Could there be a measurable
or audible difference between 120 volt and 240 volt as a primary voltage
supply for audio? Don Nebel
Geoff Wood
want to take your amp. Noise in power amps, be it line-bourne or thermal,
has not really been a cause of worry for well over 20 years ...
geoff
"Don Nebel" <DVN...@webtv.net> wrote in message
news:26829-3CC...@storefull-2116.public.lawson.webtv.net...
Larry Brasfield
Don Nebel (DVN...@webtv.net) says...
> I am planning to build a amplifier for my home stereo. The amplifier has
> the option of using single ended or balanced inputs. I have been told
> that balanced inputs offer better noise characteristics because of
> common mode rejection.
Balanced inputs eliminate one source of
extraneous noise, namely ground loops.
They can also reduce field induced noise
pickup, although that is not typically
a real problem for line level signals.
> I had read in a magazine article that the same
> (common mode rejection) can apply to a amplifier power supply.
I doubt it. (I don't doubt you read it,
but I don't know how, as an experienced
EE, to make any sense of that concept.)
> Now I
> have another option to choose from, do I use a single ended power source
> (120 volt) or a balanced source (240) volt.
A normally wired 120 VAC circuit will not
have any effect on a circuit powered by a
properly designed power supply. (Geoff's
advice is perfectly sound on this.)
> Could there be a measurable
> or audible difference between 120 volt and 240 volt as a primary voltage
> supply for audio?
Sure, if somebody really screws it up
badly. For example, somebody might get a
hair up their *** and decide the neutral
and safety ground should be connected
right at the power supply. Without the
neutral, (as with 240 VAC), that would
not be a possible screw up.
Is there likely to be a measurable (or
audible) difference? No. Just be sure
whoever designs the line input circuit
is not an idiot and understands usual
and safe practise.
--
-Larry Brasfield
(address munged)
Carroll Conklin
transformer it with a 2-3 kW transformer. You can get 115 V@30-40 Amperes.
This makes an audible difference with Solid State amps and also with tube
amps. I have done this more than once with instantly recognizable results. I
also beleive that noises, i.e. refridgerator turn-on, which happen on one
leg are reflected equally on the other leg and naturally eliminated in the
transformer primary.
Try it,
Carroll
Larry Brasfield <larry_b...@snotmail.com> wrote in message
news:MPG.17327bcc...@news.qwest.net...
Geoff Wood
never had problems with fridge, dimmer noise, etc on my solid state power
amps. Maybe you have a different problem in your house.- maybe a bad ground.
I can't imagine what sort of amp you are running that benefits from a 30-40
amp mains supply - a stadium PA rig perhaps ?
geoff
"Carroll Conklin" <acon...@rcn.com> wrote in message
news:aackkq$37v$1...@bob.news.rcn.net...
Geoff Wood
;-)
geoff
"Geoff Wood" <ge...@paf.co.nz-nospam> wrote in message news:pImy8.1970
Larry Brasfield
Carroll Conklin (acon...@rcn.com) says...
> I have to disagree. If you bring 240V the listening room and isolation
> transformer it with a 2-3 kW transformer.
Is that a complete sentence?
> You can get 115 V@30-40 Amperes.
Around 4 KW for a home stereo? I guess you
live in a different universe from the one
where my answer applies.
> This makes an audible difference with Solid State amps and also with tube
> amps.
I expect that if you had 4 KW being dumped
anywhere, even a resistance heating element,
you would be able to hear it. Since you do
not specify the two situations that produce
"an audible difference", I cannot assign any
useful meaning to your assertion.
> I have done this more than once with instantly recognizable results.
Well that proves it. Now, what is that?
> I
> also beleive that noises, i.e. refridgerator turn-on, which happen on one
> leg are reflected equally on the other leg and naturally eliminated in the
> transformer primary.
You have a 240 VAC refridgerator in a place
where 120 VAC operation is a normal option?
Or are you claiming that turning your 120 VAC
refridgerator on produces little imbalance
between opposing 240 VAC phases? Please
forgive my skepticism either way.
> Try it,
I'll have to decline for now since I cannot
tell what you are claiming. This difficulty
adds to my reluctance due to sheer skepticism.
Perhaps you would like to explain how any kind
of line sag is "eliminated in the transformer
primary". I have to confess that makes no
sense to me whatsoever. Please explain in
terms an EE should hope to understand.
...
Anton Elron
balanced power with guys like Dick Sequerra, et al, fitting toroidal
redistribution transformers to provide 120V balanced (i.e.
60-0-60)power. Your house, if you are an American home owner who has a
house built since Truman was President, already has 120-0-120 balanced
power with one 120 volt leg providing power to half the 120 outlets
and both legs providing 240 to clothes dryrs,ranges, air
conditioners,et al. The pole pig is center tapped on its secondary and
the center tap is connected to ground.
The 240 route has to be the better way to go.
Note this does not mean European 240 users have it better-their 240
is "single-ended" to ground, everything in the house is on it, and
since the voltage is doubled, the currents needed are halved-so is the
amount of copper in all the wires.
gins...@catskill.net
run on 240 (US) a piece at a time. I have a tetra-amped system and
have converted 2 Marantz 8b tube amps, a couple of Haflers (220 and
500), a tube head amp, etc. In my rural location where the ac power
seems pretty clean, there was an obvious, audible improvement. I did
it because of the aforementioned recording studio practice and I can't
wait to do my preamp. I'm now setting up a sequencer to drive
solid-state relays and the whole thing will be hard wired, except for
the Marantz amps which I installed power cords.Check your equipment,
you might find, as I did in some of mine, that they were supplied with
so-called universal power transformers and a simple rewiring sets them
up for 240. As for the earlier post, why spend $$$ for isolation when
less money gets direct 240 operation just by changing a power supply
switch or installing a new power trannie.
Badmuts
> Balanced inputs eliminate one source of
> extraneous noise, namely ground loops.
Balanced inputs DO NOT eliminate ground loops. They only eliminate the
symptoms.
The only way to eliminate a ground loop is not to create one, by
thoughtfully ground-lifting equipment, or using isolation transformers in
the audio line.
Bm
Larry Brasfield
Badmuts (bad...@spemblok.tonewheel.demon.nl) says...
I'm afraid your notion of what "ground loops"
are is not even close to industry usage.
Furthermore, yours is a useless definition.
The term is used in electronics to refer to
the situation where different signals become
combined due to shared (ground) return paths.
The term does NOT refer to ground topology
in which a loop can be found. If loops of
that nature were inherently detrimental for
some reason, coaxial shields would be bad
and ground planes would be pure disaster.
The critical distinction is not whether a
loop can be found but whether, because of
the ground topology, signal current from
more than one nominally independent signal
flows through the same ground conductor.
Balanced signalling inherently avoids shared
return paths because zero or negligible signal
current flows anywhere but in the balanced pair.
The mitigation methods you mention can be used
to break ground loops, but they can be avoided
altogether with differential signalling.
Ironically, using signal isolation transformers
is one way of converting a single-ended input
into a balanced input.
--
-Larry Brasfield
(address munged, s/sn/h/ to reply)
Carroll Conklin
I was replying to the Power side of the question not the signal side. I
think I should try to use complete sentences to convince you about my
Isolation/step-down/line voltage transformer theory. Here it goes.
Let's take a 100 Watt Solid state amp for an example. It will have a power
transformer that steps down line voltage (117V) to some lower AC voltage to
create +/- 40V DC. This step down ratio is not substantial when it comes to
current step-up. So if you use a typical 117V circuit @15A you may have 12
usable amps without power factor correction. Stepping it down results in
getting back to 15 amperes.
Typically, after rectification comes filtering in the form of huge
electrolytics. These are notorious for slow delivery of current during
transition. So, when the amp is looking for current it sees over the filter
and straight through the secondary right back to the line, first. With a
117V 15A service, it is current starved and relies on the filter caps which
slowly start to give up their energy. This results in boomy non-defined bass
which veils the lower midrange.
Take 240V@15A step it down to 120V at 30A and you have a completely
different current capability.
I have used Signal DU-3 transformers to do this twice. The results are
phenominal!
Really Larry, try it.
Carroll
Larry Brasfield <larry_b...@snotmail.com> wrote in message
news:MPG.1733a32bd...@news.qwest.net...
Geoff Wood
You can easily have electrically isolated (transformer coupled) circuitry
and still manage to achieve non-signal ground loops through mains, racks,
chassis, and between adjacent channels shields. These may not have a direct
effect on the signal at that point, but may contribute to a problem
elsewhere .
geoff
"Larry Brasfield" <larry_b...@snotmail.com> wrote in message
news:MPG.17370d217...@news.qwest.net...
Larry Brasfield
Carroll Conklin (acon...@rcn.com) says...
> Larry,
[Cut intro and gobs of quoted text following.
The discussion concerns the results to be
expected from using 240 VAC versus 120 VAC
to power an audio amplifier or audio setup.]
...
> Let's take a 100 Watt Solid state amp for an example. It will have
> a power transformer that steps down line voltage (117V) to some lower
> AC voltage to create +/- 40V DC. This step down ratio is not
> substantial when it comes to current step-up. So if you use a typical
> 117V circuit @15A you may have 12 usable amps without power factor
> correction. Stepping it down results in getting back to 15 amperes.
The voltage step-down will result in about
a 3-to-1 current capacity increase. But
since this is not really germane, I am
not going to quibble with your numbers.
> Typically, after rectification comes filtering in the form of huge
> electrolytics. These are notorious for slow delivery of current during
> transition.
Electrolytic capacitors supply current at
the frequencies used by switching power
supplies, so I think the notoriety you
invoke is not a law of nature. Also,
the electrolytic capacitors used in DC
power supplies are there to supply
energy to the regulator or load during
times when the line is below the level
that would forward bias the rectifier.
> So, when the amp is looking for current it sees over the filter
> and straight through the secondary right back to the line, first.
That is only true at low frequency and
during the 1/6 line cycle (or less) that
the rectifier is conducting. At all
times, the electrolytics will present a
lower impedance to load currents than
the rectifier/transformer except at
very low audio frequencies. At the low
frequencies where load current has much
effect on the filtered DC, the feedback
around the amplifier will be maximally
effective in eliminating an output effect.
> With a 117V 15A service, it is current starved and relies on the
> filter caps which slowly start to give up their energy. This
> results in boomy non-defined bass which veils the lower midrange.
Such effects upon the amplifier output
could occur only if the rectified DC
were depleted enough to eliminate the
headroom required by the output stage.
At the onset of audible effect, there
would be severe distortion problems,
not just some boominess or veiling
(whatever that is).
> Take 240V@15A step it down to 120V at 30A and you have a
> completely different current capability.
Clearly there is more raw power to be
had from a higher input voltage at the
same current. The question is whether
this will affect any reasonably designed
audio equipment. (And remember, this
started with a home audio setup.)
> I have used Signal DU-3 transformers to do this twice. The
> results are phenominal!
I don't deny that some phenomena may be
associated with your trial. However, I
doubt very much that anything outside
the bounds of your skull was affected.
> Really Larry, try it.
Thanks, but I'll pass. If I had an amplifier
with such poor power supply rejection that
its frequency response depended on the mains
connection, I would put it into the trash.