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  #41   Report Post  
Kevin Aylward
 
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Scott Dorsey wrote:
Kevin Aylward wrote:

Oh dear...you want to mess with the collector resisters to have an
offset on the input? Ahmmm... and just how many amplifiers do you say
you have actually designed?


Sure, you can have all the offset on the input that you want! After
all, there's a DC blocking cap!


But one doesn't do that by tinkering with the collector resistors of the
input transistors. That's, dare I say, just plain daft, and don't work.

Its like nails scratching nails down a blackboard to us analogue
designers. There are so many reasons not to try this. Indeed, in my
current designs, there arnt any, its all current sources.

(Note that by input I was referring
to the negative-going input on the differential pair that is used for
feedback, but of course if you offset one side of the differential
pair, you offset both of them)


You also offset the output, which don't do very nice things to the
speaker.

To further clarify, if you offset the + input, the negative input will
follow. If you offset the - input, you have to force the + input to
follow. By itself, it will stay just where you set it.

To do what you suggest requires having the + input as usual, that is
connected to Ov in order to ensure that the output is also zero. The
bypass capacitor is then offset with a voltage and fed via a resister.
The junction of the resister and cap would then be bypassed solidly to
the 0v reference point to minimise distortion and hum loops. Since we
now have two caps, it would be simpler to just wire them in series back
to back without the bias circuit at all.

Again, I have never seen a power amp using an offset bias in this
manner. I cant believe its done until I see some evidence for it. I
certainly don't see it gaining anything from a technical point of view.


hint: http://www.anasoft.co.uk/EE/index.html


Sorry, I tried to look at the "very low distortion amp" circuits, but
the resolution was very poor and they were pretty much unreadable,


Strange, it aint that good, but its certainly readable on my system.

so
I can't judge anything either way.


Well, if you download SuperSpice, I can send you the proper schematic so
that you can simulate it.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.


  #42   Report Post  
Paul Stamler
 
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"Kevin Aylward" wrote in message
...

The problem with specs is that often the spec are wrong or misleading.
The specs tell the story if they are correct and fully understood.


Trouble is, they never are. Never. Proper specs would include full harmonic
spectra at high *and* low levels, into various loads, and various two- and
three-tone intermodulation spectra. For example, I've measured some
sound-cards that tested wonderfully on every harmonic-distortion test I
tried, no problem. Then I tried three-tone high-frequency IM tests and,
whoa, some tested really well and some didn't. Manufacturers don't publish
those specs.

Selling a two channel mic amp for $1500 is snake oil. There is zero
chance that its value for money.


Excuse me, but that's tommyrot. I suggest you spend some time with a Great
River preamp and a cheaper preamp with as close a frequency response as you
can find. Do some listening tests, making sure you match levels carefully.
You will almost certainly hear the difference. Then use both for ten years,
and see which one is broken. More expensive preamps usually do sound better,
and they're also better built, which is part of what professional gear is
about.

But then, if it tests so well that you know you won't hear a difference, you
probably won't hear a difference. You will, however, notice the scratchy
pots and busted switches ten years down the road.

There is a sensible limit. Anything better is worthless. You cant get
any better then the weakest link in the chain. This is the speakers. To
get distortion lower then 1% costs you an arm and a leg. To get speakers
flat to 1db, costs the other arm and leg.


The latter points are quite correct. The former is not. The facts of
information theory are that the total chain is always *worse* than its
weakest link. If there is degradation of the signal in the early stages of
the chain, generating harmonic and intermodulation distortion products,
these products will generate further distortions downstream in addition to
the distortions generated by the original program material. Cleanliness is a
virtue even with imperfect devices at the end of the chain. And cleanliness
means keeping the distortions that are most annoying to the ear out of the
chain. Which is why that amp with .001% THD may still be a stinker, if the
distortion harmonic is 9th or 11th, and it produces IM at low levels.

Specs are useful things, but until we've found specs that correlate
perfectly with human hearing, and use them, they're at best an imperfect map
of the behavior of electronic devices.

Peace,
Paul


  #43   Report Post  
Kevin Aylward
 
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Scott Dorsey wrote:
Kevin Aylward wrote:
Just considering a 1% distortion of a speaker for 1% verses 1.01%
should tell one something about how dubious to be able to detect
0.01% differances.


If the 1% is all second harmonic distortion and the 0.1% is high order
non-harmonic trash, it's not dubious at all.


I addressed this in another post. Its why I use the figure of 0.01%. I
don't claim that this figure is necessary, but I do claim that it is
sufficient.

Again, we have to compare this with the Doppler distortion of the
speakers themselves, in addition to harmonic distortions and
intermodulaton. That is the distortion cused by HF sounds being
generated by a source that is moving at some LF, say 100Hz.


High end audio is a scam to make money. Its that simple.


Much of it is, but what does that have to do with anything?
--scott


Because someone made an assertion of:

I can give you two amps with similarly low high-level distortion
figures, which sound audibly different in a very obvious way


I disagreed with that assertion.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.


  #44   Report Post  
Arny Krueger
 
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Scott Dorsey wrote:
Kevin Aylward wrote:
Peter Larsen wrote:
Kevin Aylward wrote:

For example, its not uncommon to have a single electrolytic
cap in the feedback network of a power amp putting out +/-70V.
I can assure you that such a cap typically allows for the amp
to have 0.001% thd.

Kevin, have you tried replacing that cap with something relevantly
non-electrolytic and listened?


If the distortion is 0.001%, I see no reason to comparison listen

to
them at all, and I don't.


I can give you two amps with similarly low high-level distortion
figures, which sound audibly different in a very obvious way, and
which have
very different looking outputs on a scope given a 1 KC square wave
input.


Well yes, but at last one of them is a bad amp. Most modern amps have
good nonlinear distortion performance at both low and high levels.



  #45   Report Post  
Arny Krueger
 
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Frank Stearns wrote:
"Kevin Aylward" writes:

If the thd/imd is below say, 0.01%, and say power BW of 50Khz, and
the amp is competently designed, i.e. no spurious dynamic biasing
issues, stable etc, then they all sound the same. Period.


Kevin -

Thank you for your observations, but please -- could you describe

your
room where you're making these peceptual observations -- LEDE? RFZ?
Hybrid? Other? Any acoustical treatment at all?


Let's make it easy and do our listening tests with some really-pretty
good headphones - say HD 580s.




  #46   Report Post  
Frank Stearns
 
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"Kevin Aylward" writes:

but please -- could you describe your
room where you're making these peceptual observations -- LEDE? RFZ?
Hybrid? Other? Any acoustical treatment at all?


Name any room you like. It matters squat. Its a dead issue.


Oh my. Kevin, you're expressing perhaps unintentional gross ignorance
here. I'm speaking of rooms that properly control early reflections,
balance decay times, and mitigate LF problems as a way to help make
otherwise subtle elements and changes audible and unambiguous. Such rooms
are tools, just like a stone chisel -- or a laser milling machine.

You might try mixing or mastering a project in your untreated spare
bedroom v. Capital Records, Abbey Road, the old A&M Mastering studios or
Masterfonics, The Mastering Lab, or any other 1000s of studios
world-wide that have recognized the importance of this and built their
rooms accordingly.

Sure be nice if we didn't have to bother with this stuff (it can get
expensive and exasperating at times), but you can't change the laws of
physics.

And yes, transducers do distort more than any other component but that
does *not* mean that lesser problems are always obscured by this. As one
exmple, to some degree humans can readily hear a signal that is enveloped
in noise. (It's evolution, as you say -- the cave guy, with the waterfall
nearby, still manages to hear something and looks up and gets out of the
way of a charging sabertooth.)

- snip -

Such rooms also help solidly eliminate imagined differences.


High end audio is a scam to make money. Its that simple.


High-end consumer audio mostly is, agreed. But higher end pro audio, when
implemented properly, can make large differences in how our clients and
their listeners can more fully enjoy the art that has been captured and
reproduced. The general public doesn't give a damn whether there was a 741
in the signal path or a 2134, but one will most likely sound a leetle more
pleasant than the other.

Frank Stearns
Mobile Audio
--
  #47   Report Post  
Scott Dorsey
 
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Kevin Aylward wrote:
Scott Dorsey wrote:
input transistors. That's, dare I say, just plain daft, and don't work.

Its like nails scratching nails down a blackboard to us analogue
designers. There are so many reasons not to try this. Indeed, in my
current designs, there arnt any, its all current sources.

(Note that by input I was referring
to the negative-going input on the differential pair that is used for
feedback, but of course if you offset one side of the differential
pair, you offset both of them)


You also offset the output, which don't do very nice things to the
speaker.


No. There is a capacitor in the way. That's the point. You want that
offset on the capacitor.


To further clarify, if you offset the + input, the negative input will
follow. If you offset the - input, you have to force the + input to
follow. By itself, it will stay just where you set it.

To do what you suggest requires having the + input as usual, that is
connected to Ov in order to ensure that the output is also zero.


No, the + input is also floating above ground. There is a DC blocking
cap between the input jack and the + input. If you raise the voltage
of one input, you raise the voltage of the other.

The
bypass capacitor is then offset with a voltage and fed via a resister.
The junction of the resister and cap would then be bypassed solidly to
the 0v reference point to minimise distortion and hum loops. Since we
now have two caps, it would be simpler to just wire them in series back
to back without the bias circuit at all.


There is _already_ a bias circuit. We aren't _adding_ anything here.

hint: http://www.anasoft.co.uk/EE/index.html


Sorry, I tried to look at the "very low distortion amp" circuits, but
the resolution was very poor and they were pretty much unreadable,


Strange, it aint that good, but its certainly readable on my system.


My problem is that I couldn't read the numbers on the parts, either on
the screen or printing it out. So I can't say things like "what is the
base on Q1" set to, because I can't tell if that is Q1 or Q7.

so
I can't judge anything either way.


Well, if you download SuperSpice, I can send you the proper schematic so
that you can simulate it.


I'll pass, although we have Spice on the HP-UX boxes here.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #48   Report Post  
Scott Dorsey
 
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Arny Krueger wrote:

I can give you two amps with similarly low high-level distortion
figures, which sound audibly different in a very obvious way, and
which have
very different looking outputs on a scope given a 1 KC square wave
input.


Well yes, but at last one of them is a bad amp. Most modern amps have
good nonlinear distortion performance at both low and high levels.


Just one word: Stewart.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #49   Report Post  
Frank Stearns
 
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"Arny Krueger" writes:

Thank you for your observations, but please -- could you describe

your
room where you're making these peceptual observations -- LEDE? RFZ?
Hybrid? Other? Any acoustical treatment at all?


Let's make it easy and do our listening tests with some really-pretty
good headphones - say HD 580s.


I was waiting for someone to mention headphones. And while in theory this
would be great, in practice (for me, anyway) using headphones just never
seems to cut it other than for a few limited applications. Mixing with
phones, for example, can result in mixes that are a little odd and don't
translate well. With phones monitoring some things are overemphasized,
others are lost.

It would seem that many mixing and mastering engineers feel the same,
otherwise why bother with buiding the really good rooms one finds at
reputable and well-known studios around the world? Be cheaper by orders of
magnitude to just hand everybody a pair of phones. But we don't do that --
I wonder why. (There's probably a doctoral thesis in there somewhere.)

Phones for these evals *might* work, but I'd prefer to use a good room, if
available.

Frank Stearns
Mobile Audio
--
  #52   Report Post  
Arny Krueger
 
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Frank Stearns wrote:
"Arny Krueger" writes:

Thank you for your observations, but please -- could you describe

your
room where you're making these peceptual observations -- LEDE?

RFZ?
Hybrid? Other? Any acoustical treatment at all?


Let's make it easy and do our listening tests with some

really-pretty
good headphones - say HD 580s.


I was waiting for someone to mention headphones. And while in theory
this would be great, in practice (for me, anyway) using headphones
just never seems to cut it other than for a few limited

applications.

Silly me. I use them for all sorts of things.

Mixing with phones, for example, can result in mixes that are a
little odd and don't translate well.


So can mixing with the wrong speakers or the wrong person mixing.

With phones monitoring some
things are overemphasized, others are lost.


You never mix on the playback system that everybody uses. Therefore,
mixing is lots about translation. Learning to make mixes on one set of
monitors, and have them translate well on a goodly selection of other
listening systems is a matter of learning.

It would seem that many mixing and mastering engineers feel the

same,
otherwise why bother with buiding the really good rooms one finds at
reputable and well-known studios around the world?


It's kind of hard to fit two people in one set of headphones.

Be cheaper by
orders of magnitude to just hand everybody a pair of phones. But we
don't do that -- I wonder why. (There's probably a doctoral thesis

in
there somewhere.)

Phones for these evals *might* work, but I'd prefer to use a good
room, if available.


One nice things about being able to track, monitor and mix on
headphones is that they are easier to carry around than a good
sounding room.


  #53   Report Post  
Arny Krueger
 
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Scott Dorsey wrote:
Arny Krueger wrote:

I can give you two amps with similarly low high-level distortion
figures, which sound audibly different in a very obvious way, and
which have
very different looking outputs on a scope given a 1 KC square wave
input.


Well yes, but at last one of them is a bad amp. Most modern amps

have
good nonlinear distortion performance at both low and high levels.


Just one word: Stewart.


I said *good* amps, right? ;-)


  #54   Report Post  
Lorin David Schultz
 
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"Kevin Aylward" wrote:

Why this sort of nonsense is still persisting today is pretty much
incredible.





I used to think any decent amp was pretty much as good as another, until
I one day I noticed a difference when my usual amp was unavailable and I
went out on a remote with a different one. The difference was obvious.

That made me think my usual amp had a problem, so I tried another amp.
It sounded different too.

I offer no explanations as to why, but I can say with certainty that
there ARE audible differences between supposedly well designed amps.

FWIW, the three I went through that day were a BGW, a Bryston and an
NAD.

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

(Remove spamblock to reply)


  #55   Report Post  
Lorin David Schultz
 
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"Arny Krueger" wrote:

Silly me. I use them for all sorts of things.

Mixing with phones, for example, can result in mixes that are a
little odd and don't translate well.


So can mixing with the wrong speakers or the wrong person mixing.





I understand your point, but clarify something for me: are you actually
*endorsing* the notion of mixing with headphones?

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

(Remove spamblock to reply)




  #56   Report Post  
Lorin David Schultz
 
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wrote in message
ups.com...
Sounds like someone has blown a gasket. If you react so negativly to
freely offered information, I suspect you may have a heart attack if
anyone dared charge you for anything. I don't think you own a Delta
console so I wonder why you are even here...

BTW, I don't need to advertise for work, I have enough already, feel
free to not ever ask me for anything.

Go take a walk in the garden, find a girlfriend, go kill a cat and
switch to de-caf! One of these should work for you.

Jim Williams
Audio Upgrades




FWIW Jim, I smacked lips with delight over your post.

First, because I own a couple Deltas and may actually put that info to
use someday. Knowing your track record with Deltas, I know better than
to second-guess your suggestions about that particular device! g

Second, and more importantly, because it made me feel good to see that
kind of expertise sharing going on here. Gabe would be proud!

Don't let someone who sees things differently discourage you. You done
good.

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

(Remove spamblock to reply)


  #58   Report Post  
Chris Hornbeck
 
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On Tue, 26 Apr 2005 03:15:25 GMT, "Lorin David Schultz"
wrote:

Please please please adjust the universe to
make this true.


And sadly, the map is not, and cannot be, the world.
Our innate drive to model the unknowable external
world often overwhelms us with the perfection of our
models, however 1930's they may be.

"But the morals of models is not!" -Flanders and Swann


Chris Hornbeck
"This has been an account for those who don't keep them"
J-LG, _Tout Va Bien_ 1972
  #59   Report Post  
Bob Cain
 
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Arny Krueger wrote:

One nice things about being able to track, monitor and mix on
headphones is that they are easier to carry around than a good
sounding room.


And if someone here has such a room that has been well
proven and will agree to gather some simple measurements for
me with their favorite 'phones and their favorite monitors
I'll give them a good semblance of that "portable room"
capability with any DAW that supports stereo convolution
natively or via a VST plugin.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
  #62   Report Post  
Kevin Aylward
 
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Paul Stamler wrote:
"Kevin Aylward" wrote in message
...

The problem with specs is that often the spec are wrong or
misleading. The specs tell the story if they are correct and fully
understood.


Trouble is, they never are. Never. Proper specs would include full
harmonic spectra at high *and* low levels, into various loads, and
various two- and three-tone intermodulation spectra. For example,
I've measured some sound-cards that tested wonderfully on every
harmonic-distortion test I tried, no problem. Then I tried three-tone
high-frequency IM tests and, whoa, some tested really well and some
didn't. Manufacturers don't publish those specs.


If a basic spec isn't quoted, its invariable bad.


Selling a two channel mic amp for $1500 is snake oil. There is zero
chance that its value for money.


Excuse me, but that's tommyrot. I suggest you spend some time with a
Great River preamp and a cheaper preamp with as close a frequency
response as you can find. Do some listening tests, making sure you
match levels carefully. You will almost certainly hear the
difference.


No chance. Hey, what did your horoscope tell you to do today? How about
the tea leaves?

Then use both for ten years, and see which one is broken.
More expensive preamps usually do sound better, and they're also
better built, which is part of what professional gear is about.


Excuse me, this is complete nonsense. Again, if the amp has say, 0.01%
thd and imd, frequency response flat to say, 0.2db and all te usual
stuff like reasonable headroom, drives a load correctly and stable etc,
then the all sound identical. End of story. Its been proven in too many
controlled ab tests. Its just not worth debating, and I'm not going to
any more.



But then, if it tests so well that you know you won't hear a
difference, you probably won't hear a difference. You will, however,
notice the scratchy pots and busted switches ten years down the road.

There is a sensible limit. Anything better is worthless. You cant get
any better then the weakest link in the chain. This is the speakers.
To get distortion lower then 1% costs you an arm and a leg. To get
speakers flat to 1db, costs the other arm and leg.


The latter points are quite correct. The former is not. The facts of
information theory are that the total chain is always *worse* than its
weakest link.


In what way does the statement:

"You cant get any better then the weakest link in the chain"

logically contradict your statement?


If there is degradation of the signal in the early
stages of the chain, generating harmonic and intermodulation
distortion products, these products will generate further distortions
downstream in addition to the distortions generated by the original
program material. Cleanliness is a virtue even with imperfect devices
at the end of the chain. And cleanliness means keeping the
distortions that are most annoying to the ear out of the chain. Which
is why that amp with .001% THD may still be a stinker,


Very, very unlikely, all things being equal.

if the
distortion harmonic is 9th or 11th, and it produces IM at low levels.


The simplest approximation is a taylor series

V = avi + bVi^2 + cVi^3 ++...

This can be used to calculate both imd and thd. Sure, in detail imd and
thd are not an isomorphism. However, in a competently designed amp, they
do go hand in hand. Its would be hard to actually design an amp that had
say 0.001% thd at 20khz and have 0.1% imd.


Specs are useful things, but until we've found specs that correlate
perfectly with human hearing, and use them, they're at best an
imperfect map of the behavior of electronic devices.


If the specs are "good enough", we can indeed remove that spec from
consideration.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.


  #63   Report Post  
Kevin Aylward
 
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Lorin David Schultz wrote:
"Kevin Aylward" wrote:

Why this sort of nonsense is still persisting today is pretty much
incredible.





I used to think any decent amp was pretty much as good as another,
until I one day I noticed a difference when my usual amp was
unavailable and I went out on a remote with a different one. The
difference was obvious.
That made me think my usual amp had a problem, so I tried another amp.
It sounded different too.

I offer no explanations as to why, but I can say with certainty that
there ARE audible differences between supposedly well designed amps.


I doubt very much you were comparing apples with apples. There are a lot
of poor spec amps out there. Specifically, Crown has dreadful specs for
a modern amp.


FWIW, the three I went through that day were a BGW, a Bryston and an
NAD.


What were the actual specs of all amps? However were they all connected
up etc. Are these straight amps, or ones with tone controls? What was
the output level?

Briefly, I know of actual tests when this sort of thing was belived to
be occurring, and at first astounded the investigators. On further
examination, they discovered a problem with the A/B switching circuit
contacts (I think). After the correction, all differences disappeared.

There are simply too many unknown variables in you description here to
make further comment. It simply wasn't a controlled test.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.


  #64   Report Post  
Kevin Aylward
 
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Frank Stearns wrote:
"Kevin Aylward" writes:

but please -- could you describe your
room where you're making these peceptual observations -- LEDE? RFZ?
Hybrid? Other? Any acoustical treatment at all?


Name any room you like. It matters squat. Its a dead issue.


Oh my. Kevin, you're expressing perhaps unintentional gross ignorance
here.


On the contrary, I am displaying actual knowledge of controlled tests
performed by many, as to the audibility of distortion at the 0.01%
level.

I would have to go and do a search of all the classics.

I'm speaking of rooms that properly control early reflections,
balance decay times, and mitigate LF problems as a way to help make
otherwise subtle elements and changes audible and unambiguous. Such
rooms are tools, just like a stone chisel -- or a laser milling
machine.

You might try mixing or mastering a project in your untreated spare
bedroom v. Capital Records, Abbey Road, the old A&M Mastering studios
or Masterfonics, The Mastering Lab, or any other 1000s of studios
world-wide that have recognized the importance of this and built their
rooms accordingly.

Sure be nice if we didn't have to bother with this stuff (it can get
expensive and exasperating at times), but you can't change the laws of
physics.

And yes, transducers do distort more than any other component but that
does *not* mean that lesser problems are always obscured by this. As
one exmple, to some degree humans can readily hear a signal that is
enveloped in noise. (It's evolution, as you say -- the cave guy, with
the waterfall nearby, still manages to hear something and looks up
and gets out of the way of a charging sabertooth.)


Sure, room acoustics effect the sound. It may well make 1% distortion
sound different in different rooms. I don't personally think it will,
but it might. However, for 0.01%, no chance.


- snip -

Such rooms also help solidly eliminate imagined differences.


High end audio is a scam to make money. Its that simple.


High-end consumer audio mostly is, agreed. But higher end pro audio,
when implemented properly, can make large differences in how our
clients and their listeners can more fully enjoy the art that has
been captured and reproduced. The general public doesn't give a damn
whether there was a 741 in the signal path or a 2134, but one will
most likely sound a little more pleasant than the other.


Actually, a 741 can easily measure bad enough such that the level of
distortion it produces has already been experimentally proven to be
detectable. It only has a GBW of 1Mhz, so if its set to a gain of 50,
its running open loop at 20Khz. IMD will be somewhat large:-)

I don't claim that low order effects are not audible, I am claiming that
there is a point where effects are indeed so low as to be inaudible. For
me, if its below 0.01% across the board, its a straight piece of wire
with gain.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.


  #65   Report Post  
Kevin Aylward
 
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Scott Dorsey wrote:
Kevin Aylward wrote:
Scott Dorsey wrote:
input transistors. That's, dare I say, just plain daft, and don't
work.

Its like nails scratching nails down a blackboard to us analogue
designers. There are so many reasons not to try this. Indeed, in my
current designs, there arnt any, its all current sources.

(Note that by input I was referring
to the negative-going input on the differential pair that is used
for feedback, but of course if you offset one side of the
differential pair, you offset both of them)


You also offset the output, which don't do very nice things to the
speaker.


No. There is a capacitor in the way. That's the point. You want
that offset on the capacitor.


One doesn't use output capacitors for power amps nowadays. Amps are DC
coupled. Don't know the last time I saw a single supply amp. Probable in
Dr. Who's TARDIS.



To further clarify, if you offset the + input, the negative input
will follow. If you offset the - input, you have to force the +
input to follow. By itself, it will stay just where you set it.

To do what you suggest requires having the + input as usual, that is
connected to Ov in order to ensure that the output is also zero.


No, the + input is also floating above ground.


Not if one is using anyone of the 100's millions of DC coupled power
amps one doesn't.

There is a DC blocking
cap between the input jack and the + input. If you raise the voltage
of one input, you raise the voltage of the other.

The
bypass capacitor is then offset with a voltage and fed via a
resister. The junction of the resister and cap would then be
bypassed solidly to the 0v reference point to minimise distortion
and hum loops. Since we now have two caps, it would be simpler to
just wire them in series back to back without the bias circuit at
all.


There is _already_ a bias circuit.


Not when we are first designing the circuit there isn't. When we do, we
need to make sure that bias voltages are very clean. This requires
capacitors.

We aren't _adding_ anything here.


See above.


hint: http://www.anasoft.co.uk/EE/index.html

Sorry, I tried to look at the "very low distortion amp" circuits,
but the resolution was very poor and they were pretty much
unreadable,


Strange, it aint that good, but its certainly readable on my system.


My problem is that I couldn't read the numbers on the parts, either on
the screen or printing it out. So I can't say things like "what is
the base on Q1" set to, because I can't tell if that is Q1 or Q7.


Oh...point taken.

However, the design is easily understood from inspection by anyone that
understands circuit design. There is no rocket science here. All the
blocks are standard stuff. The only bit that might need explaining is
the somewhat novel second feedback loop on the output transistors on one
of the circuits. Oh..and that some of the diodes are zenors for
simulation purposes.


Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.




  #66   Report Post  
Arny Krueger
 
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Lorin David Schultz wrote:
"Arny Krueger" wrote:

Silly me. I use them for all sorts of things.

Mixing with phones, for example, can result in mixes that are a
little odd and don't translate well.


So can mixing with the wrong speakers or the wrong person mixing.


I understand your point, but clarify something for me: are you
actually *endorsing* the notion of mixing with headphones?


Hey, if you are good enough at managing translation, you can even
master with headphones.


  #67   Report Post  
Arny Krueger
 
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Bob Cain wrote:
Arny Krueger wrote:

One nice things about being able to track, monitor and mix on
headphones is that they are easier to carry around than a good
sounding room.


And if someone here has such a room that has been well
proven and will agree to gather some simple measurements for
me with their favorite 'phones and their favorite monitors
I'll give them a good semblance of that "portable room"
capability with any DAW that supports stereo convolution
natively or via a VST plugin.


Don't you need two convolutions - one of the target room and one of
the room at hand?


  #68   Report Post  
Arny Krueger
 
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Paul Stamler wrote:

Excuse me, but that's tommyrot. I suggest you spend some time with a
Great River preamp and a cheaper preamp with as close a frequency
response as you can find. Do some listening tests, making sure you
match levels carefully. You will almost certainly hear the
difference. Then use both for ten years, and see which one is

broken.
More expensive preamps usually do sound better, and they're also
better built, which is part of what professional gear is about.


I would consider that to be an unproven hypothesis. AFAIK nobody has
done any revealtory technical tests that show what say, a Great River
does that is extra wonderful. Nobody has done the controlled listening
tests that would be required to conclusively show that its the
preamp's performance, and not the hype that people *hear*.

Neither Great River nor their competition whether priced high or low
deliver the goods when it comes to complete technical information.


  #69   Report Post  
Scott Dorsey
 
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Kevin Aylward wrote:

Hey, I have a few oxygen free cables that I can sell you, only $500 for
a pair, but make sure you connect them the correct way from the speaker
to the amp. They are colour coded to make this easier for you.


So you have decided that, since much of the high end world is completely
bunk, that therefore there are no audible differences between amplifiers
with low THD numbers?

There is quite a jump between these two statements.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #70   Report Post  
Scott Dorsey
 
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Kevin Aylward wrote:
Scott Dorsey wrote:
Kevin Aylward wrote:
Scott Dorsey wrote:
input transistors. That's, dare I say, just plain daft, and don't
work.

Its like nails scratching nails down a blackboard to us analogue
designers. There are so many reasons not to try this. Indeed, in my
current designs, there arnt any, its all current sources.

(Note that by input I was referring
to the negative-going input on the differential pair that is used
for feedback, but of course if you offset one side of the
differential pair, you offset both of them)

You also offset the output, which don't do very nice things to the
speaker.


No. There is a capacitor in the way. That's the point. You want
that offset on the capacitor.


One doesn't use output capacitors for power amps nowadays. Amps are DC
coupled. Don't know the last time I saw a single supply amp. Probable in
Dr. Who's TARDIS.


Are you listening to anything I am saying? I am not talking about an
output capacitor, I am talking about a capacitor in the feedback loop
between the output and the inverting side of the differential input
pair.

Let's go through this again:

1. If there is no offset, you don't need a capacitor

2. If the offset is larger than the signal, you use a capacitor.

3. If the offset is smaller than the signal, make it larger.

This is not anything particularly difficult here. Read the Sanyo
capacitor handbook for a description of the whole thing. Read Doug
Self's series on amp design.

However, the design is easily understood from inspection by anyone that
understands circuit design. There is no rocket science here. All the
blocks are standard stuff. The only bit that might need explaining is
the somewhat novel second feedback loop on the output transistors on one
of the circuits. Oh..and that some of the diodes are zenors for
simulation purposes.


Yes, but not being able to read the numbers makes it problematic for
use as an example circuit to point out DC setpoints.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."


  #71   Report Post  
Lorin David Schultz
 
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"Arny Krueger" wrote:

Hey, if you are good enough at managing translation, you can even
master with headphones.




If you say so... I sure wouldn't want to, and it's not something I'd
recommend to most people.

You must be either extremely well-versed in compensation techniques or
highly skilled in the art of self-delusion! g

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

(Remove spamblock to reply)


  #72   Report Post  
Scott Dorsey
 
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In article ,
Arny Krueger wrote:
Bob Cain wrote:
Arny Krueger wrote:

One nice things about being able to track, monitor and mix on
headphones is that they are easier to carry around than a good
sounding room.


And if someone here has such a room that has been well
proven and will agree to gather some simple measurements for
me with their favorite 'phones and their favorite monitors
I'll give them a good semblance of that "portable room"
capability with any DAW that supports stereo convolution
natively or via a VST plugin.


Don't you need two convolutions - one of the target room and one of
the room at hand?


In the case of headphones, the room at hand is the inside of your head.
And I will say that ear shapes do vary enough that this might be an
issue if your model is good enough.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #73   Report Post  
Lorin David Schultz
 
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"Kevin Aylward" wrote:

Oh lord, please deliver us from the ignorant.

Hey, I have a few oxygen free cables that I can sell you, only $500
for a pair, but make sure you connect them the correct way from the
speaker to the amp. They are colour coded to make this easier for
you.




Kev, baby, relax -- I'm on your side on the snake-oil issue. It's just
an ENORMOUS leap from "many esoteric audio products are a rip-off" to
"all properly-designed amps sound the same." I couldn't believe you
really meant that, so I figured you must be probing for reaction.

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

(Remove spamblock to reply)


  #74   Report Post  
Lorin David Schultz
 
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"Kevin Aylward" wrote:

There are simply too many unknown variables in you description here
to make further comment. It simply wasn't a controlled test.




I know, and I tend to be suspect of drawing any kind of conclusions
under such circumstances too. In this case, though, the variables were
controlled enough for the point I'm making.

I'm NOT saying one amp was better than the others, but I AM saying that
they all sounded different under identical circumstances. All that
changed was the amps, nothing else. Same place, same input, same
monitors.

Maybe that's attributable to different input stages, or one being
happier with the load those particular speakers presented, or maybe it
was just the phase of the moon. The point is that WHY they sounded
different is irrelevant. My point was (and is) that three supposedly
"well-designed" amplifiers (NAD, BGW and Bryston, all of similar power
ratings, straight power amps with no controls other than level) all
sounded different in that setting. I say this to refute the argument
that all well-designed amps sound alike.

Like I said, I used to believe that too. I don't anymore.

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

(Remove spamblock to reply)


  #75   Report Post  
Arny Krueger
 
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Lorin David Schultz wrote:
"Kevin Aylward" wrote:

There are simply too many unknown variables in you description here
to make further comment. It simply wasn't a controlled test.




I know, and I tend to be suspect of drawing any kind of conclusions
under such circumstances too. In this case, though, the variables
were controlled enough for the point I'm making.

I'm NOT saying one amp was better than the others, but I AM saying
that they all sounded different under identical circumstances. All
that changed was the amps, nothing else. Same place, same input,

same
monitors.


Given that no two amps of different makes and models have overall gain
matched within 0.1 dB, the simple act of swapping the amps introduced
a potentially audible difference.

There are other issues - when we were doing lots of ABX tests of power
amps way back when, we'd run into what might be called interfacing
problems. Some amps wanted one kind of grounding to be hum-free while
others would want something else. Amps would turn out to have non-flat
frequency response, but only in certain test setups, etc.




  #76   Report Post  
Mark
 
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this is really a ying and yang type of argument.
one is of no value without the other

The state of the art of signal analysis is advanced to the point where
I do not believe it is possible for a difference in amplifiers to be
audible but not measurable. It may not be obvious at first what
measurement is needed, but once that is unraveled, some measurement
should always be able to explain any audible difference (talking about
amplifiers here, mics and loudspeakers are another matter)

If a critical listening test should uncover an audible difference
between two amps, the next step should be to make whatever measurements
are needed to identify the cause of the difference. Then the designers
can use that information to make design changes. Something like, amp A
has a more solid sound compared to amp B and we discovered that the
reason is the difference in damping factor (a trivial example).

Mark

  #78   Report Post  
 
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Perhaps a career in video would suit your talents better. If you can't
hear any of this stuff, maybe you can see some of these things.

I use the Audio Precision analyzer in the design and testing of the
High Speed Mic Preamp as well as mods done to other manufacturers
equipment. Yes, it does show subtle test variations. It also will show
measurements that may be nearly identical, but sound different. It,
like any test rig has severe limitations due to the fact it uses steady
state stimulus rather than the violent waveforms of actual music.

Folks that design gear based on test results will miss the boat every
time. Test gear will tell you if something is wrong, only your ears
will tell you when something is right. Yes, once the bugs are worked
out on a design, there comes a point when you turn off the analyzer and
turn on the ears.

Jim Williams
Audio Upgrades

BTW, replace the 220 uf or 47 uf power supply filters on each Delta
module with a Panasonic 470 uf 25v FM series. Replace the 10 ohm 1/4
watt fusing resistors wth 10 ohm 1/2 watt. Better low end punch.

  #80   Report Post  
Mark
 
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this is really a ying and yang type of argument.
one is of no value without the other


The state of the art of signal analysis is advanced to the point where
I do not believe it is possible for a difference in __amplifiers__ to
be
audible but not measurable. It may not be obvious at first what
measurement is needed, but once that is unraveled, some measurement
should always be able to explain any audible difference (talking about

amplifiers here, mics and loudspeakers are another matter)


If a critical listening test should uncover an audible difference
between two amps, the next step should be to make whatever measurements

are needed to identify the cause of the difference. Then the designers

can use that information to make design changes. Something like, amp A

has a more solid sound compared to amp B and we discovered that the
reason is the difference in damping factor (a trivial example).

Not all tests are steady state. Square waves are not steady state.
Tone bursts are not steady state. Impulse response testing is not
steady state.

Please provide an example of an amplifier performance characteristic
that can produce an audible difference that cannot be measured.


thanks
Mark

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