[Kevin Aylward[_3_]]

Eeyore wrote:
Don Pearce wrote:

Actually the "right" place to connect the feedback sensing resistor
is right out at the speaker itself, via a third sensing wire.

You don't realise just how true that is. I've tuned pcb layouts for
THD just by moving that node. PCB layout guys look perplexed but
thankfully usually do it. In fact there's loads of layout tricks the
PCB guys are hopeless at, loops in particular.

Yes indeed. This is exactly what happened on the 1st PCB prototype of the
MOSFET 1000. Ian did the layout. When it came back, I was only getting 0.02%
thd. Now..this is *exactly* how it happened. I looked at the routing,
immediately noticed that the feedback point was picked up along a high
current trace, took a piece of wire and jumpered across the offending trace,
and thd dropped down to 0.002%. Like, simple putting a wire in || with
another one (that had a tee in it) worked magic!


Kevin Aylward
www.blonddee.co.uk
www.kevinaylward.co.uk

[Eeyore]

Jan Panteltje wrote:

On a sunny day it happened Don Pearce wrote

Actually the "right" place to connect the feedback sensing resistor is
right out at the speaker itself, via a third sensing wire.

Ha, why did I never think of that...
This will eliminate my massive gold feed rods to the woofer.

You will need 2 sensing wires, and a diff amp.

LOL ! See one of my other posts.

Graham

[Don Pearce]

Eeyore wrote:

Don Pearce wrote:

Kevin Aylward wrote:
Don Pearce wrote:
Kevin Aylward wrote:
Eeyore wrote:
John Larkin wrote:
Eeyore wrote:
John Larkin wrote:
Eeyore wrote:
Learn something about LATERAL mosfets that were designed for
audio. I've already given part number and links to data sheets.
That doesn't really matter. The transfer function only needs to
be continuous so that you can close a loop around it, and the fet
needs to be able to stand the peak power dissipation. That can
easily be done with vertical "switching" type fets. A modern
FLOOD architecture [1] works great with most any kind of fet.
Lots of things have changed in the last few decades.

John

[1] Of course you've never heard the term before. I just invented
it.
Fine. Can you elaborate some more on it ? Laterals have some truly
lovely features for audio. The only downside being a slightly
highish Ron. Not really a problem when (as I have) used as many as
6 in parallel (12 mosfets per channel / 24 per amp). They also
match beautifully with no need for source balance resistors (so
some of the Ron loss 'goes away').
An opamp per fet, closing a local loop, feedback from the fet
source, makes each fet look like a perfect unity-gain, fast,
zero-offset device.
Interesting idea. I'll have to chew that one over. I can see
possible problems fron op-amp output overshoot.
I have a simple embodiment of that concept here, done a while ago, in
virtual land;-)

http://www.kevinaylward.co.uk/ee/cir...ortionAmp2.jpg

Its a push/pull gain loop around the output devices, forcing them to
be unity gain followers.

You can get lower distortion, at the expense of speed, because you
have to compensate earlier.

Common mode feedback at the second stage, allows for enormous dc/lf
gain. cascodes to allow the use of fast small transistors to do all
the main work. Emitter follower buffer to reduce the current swing
in the input pair, as per doug self. Spice says it should be in the
0.0001% , 20Khz range, maybe...

Kevin Aylward


Kevin - an interesting circuit, and I appreciate what you have done
with the output stage, but I'm still wondering why you didn't include
it within the global feedback loop - that could only have made it
better, lower output impedance, more load insensitive etc etc etc.
It is.!!!

I think the schematic is not as clear as it should be.. I have a zero volt
source near the output devices in the feedback circuit to calculate LG. The
overall loop feedback passes through this source!!!
Ah, is that what it was? I thought you were putting actual voltage
sources in there that would be replaced by some small circuit in an
actual design. I hope you are connecting the sensing point of the
feedback resistor to the final summed speaker connection, not some
random point in amongst the bunch of fets (teaching granny to suck
eggs?) ;-)

Actually the "right" place to connect the feedback sensing resistor is
right out at the speaker itself, via a third sensing wire.

Better still, have differential sensing, to compensate for the volt drop in the
groundy side wire too !

Graham


I wrote an article for one of the Hi Fi mags a few years ago with
exactly that idea - suggested easy ways to do it too. Only problem is
when you accidentally connect the sense wires in wrong polarity - smoke
ensues.

d

[MooseFET]

On Sep 19, 8:01*pm, "Michael A. Terrell"
wrote:
MooseFET wrote:

On Sep 19, 7:37 am, Eeyore
wrote:
MooseFET wrote:
Bewa *Mosfets like the STW55NM60 have a decreasing threshold
voltage for increasing temperature. *This means that biasing them to a
low idle current isn't so easy.

Indeed. You'll need lossy ballast resistors. Laterals are different that
way.

Yes, but once the STW55NM60 or equiv. is biased up, it makes a nice
200V at about 100KHz. Its not exactly audio but is sure isn't really
RF either.

* *Tell that to WWVB, who transmits at 60 kHz.

Good point. I wasn't radiating, at least not on purpose.

A lot of echo sounders work up at 500KHz so 100KHz wasn't really too
high to be called sound too.

[isw]

In article ,
Jan Panteltje wrote:

On a sunny day (Sat, 20 Sep 2008 10:22:09 +0100) it happened Don Pearce
wrote in
:

Actually the "right" place to connect the feedback sensing resistor is
right out at the speaker itself, via a third sensing wire.

Ha, why did I never think of that...
This will eliminate my massive gold feed rods to the woofer.

You will need 2 sensing wires, and a diff amp.

If you really think that's important (and I don't), why not just put the
amplifiers near the speakers? That way, there won't be any nasty
stability problems to deal with.

Isaac

[Eeyore]

isw wrote:

Jan Panteltje wrote:
it happened Don Pearce wrote

Actually the "right" place to connect the feedback sensing resistor is
right out at the speaker itself, via a third sensing wire.

Ha, why did I never think of that...
This will eliminate my massive gold feed rods to the woofer.

You will need 2 sensing wires, and a diff amp.

If you really think that's important (and I don't), why not just put the
amplifiers near the speakers? That way, there won't be any nasty
stability problems to deal with.

They're called active speakers and are widely used by many professionals.

Graham

[Kevin Aylward[_3_]]

Eeyore wrote:
isw wrote:

Jan Panteltje wrote:
it happened Don Pearce wrote

Actually the "right" place to connect the feedback sensing
resistor is right out at the speaker itself, via a third sensing
wire.

Ha, why did I never think of that...
This will eliminate my massive gold feed rods to the woofer.

You will need 2 sensing wires, and a diff amp.

If you really think that's important (and I don't), why not just put
the amplifiers near the speakers? That way, there won't be any nasty
stability problems to deal with.

They're called active speakers and are widely used by many
professionals.

Indeed.

I don't actually like powered speakers though. They need *two* leads. Just
more hassle in setting up for the gig.


Kevin Aylward
www.blonddee.co.uk
www.anasoft.co.uk

[Don Pearce]

Kevin Aylward wrote:
Eeyore wrote:
isw wrote:

Jan Panteltje wrote:
it happened Don Pearce wrote

Actually the "right" place to connect the feedback sensing
resistor is right out at the speaker itself, via a third sensing
wire.
Ha, why did I never think of that...
This will eliminate my massive gold feed rods to the woofer.

You will need 2 sensing wires, and a diff amp.
If you really think that's important (and I don't), why not just put
the amplifiers near the speakers? That way, there won't be any nasty
stability problems to deal with.
They're called active speakers and are widely used by many
professionals.

Indeed.

I don't actually like powered speakers though. They need *two* leads. Just
more hassle in setting up for the gig.


Wouldn't want them on a gig - very good for studio monitoring though.

d

[Eeyore]

Kevin Aylward wrote:

Eeyore wrote:
isw wrote:
Jan Panteltje wrote:
it happened Don Pearce wrote

Actually the "right" place to connect the feedback sensing
resistor is right out at the speaker itself, via a third sensing
wire.

Ha, why did I never think of that...
This will eliminate my massive gold feed rods to the woofer.

You will need 2 sensing wires, and a diff amp.

If you really think that's important (and I don't), why not just put
the amplifiers near the speakers? That way, there won't be any nasty
stability problems to deal with.

They're called active speakers and are widely used by many
professionals.

Indeed.

I don't actually like powered speakers though. They need *two* leads. Just
more hassle in setting up for the gig.

I know exactly what you mean. Far too much hassle and just more leads getting
in the way for live.

When The Horn had an upgrade last year, all the PA amps, crossover (controller
now actually) went into a back room in a dedicated amp rack with ventilation
and speaker lines (in 4mm2) were run in trunking to the appropriate points.
The monitors sit on a raised surface at the front of the stage and the runs to
them terminate in connectors mounted in purpose made pressed metal panels
mounted in the performer's side of the upright. This means you need only 1 or
2 m leads to wire them up. It's lovely.

Graham

[MooseFET]

On Sep 21, 12:02 pm, isw wrote:
In article ,
Jan Panteltje wrote:

On a sunny day (Sat, 20 Sep 2008 10:22:09 +0100) it happened Don Pearce
wrote in
:

Actually the "right" place to connect the feedback sensing resistor is
right out at the speaker itself, via a third sensing wire.

Ha, why did I never think of that...
This will eliminate my massive gold feed rods to the woofer.

You will need 2 sensing wires, and a diff amp.

If you really think that's important (and I don't), why not just put the
amplifiers near the speakers? That way, there won't be any nasty
stability problems to deal with.

You can do about as well if you characterize what a linear system does
and then correct for it. If a system is nonlinear it is harder to do.

If you want to go all the way to having feedback from the speaker, it
seems to me that moving the feedback detection as close to the sound
output as practical is the way to go. Sensing actual cone movement is
better than sensing the driven voice coil's voltage. Some years back I
saw a really nice design for a subwoofer that did this. Here is
basically what the design did:

There was no voice coil at all. The cone was moved by a fast servo
motor with a metal belt drive that drove a rod on the cone center..
This allowed motions of several inches but didn't have a very flat
frequency response.

A position sensor on the rod on the cone center and a pressure
transducer where combined to form the feedback signal. The position
sensor couldn't know about the cone flex and the pressure sensor
couldn't know the very low frequency components. The combined signal
covered the entire range of interest.

There was a really massive servo amplifier driving the motor giving
the system the ability to work up to several Hz.

It seems to me that this sort of thing could be done today and make it
up into the 10s of Hz.

[Vladimir Vassilevsky]

MooseFET wrote:

If you want to go all the way to having feedback from the speaker, it
seems to me that moving the feedback detection as close to the sound
output as practical is the way to go. Sensing actual cone movement is
better than sensing the driven voice coil's voltage.

The idea of the feedback directly from the cone is no new. The main
problem is economical: it is easier to make a reasonable conventional
speaker rather then trying to make a good speaker from the bad one by
the means of feedback and feedforward compensation.


Some years back I
saw a really nice design for a subwoofer that did this. Here is
basically what the design did:

There was no voice coil at all. The cone was moved by a fast servo
motor with a metal belt drive that drove a rod on the cone center..
This allowed motions of several inches but didn't have a very flat
frequency response.

A position sensor on the rod on the cone center and a pressure
transducer where combined to form the feedback signal. The position
sensor couldn't know about the cone flex and the pressure sensor
couldn't know the very low frequency components. The combined signal
covered the entire range of interest.

There was a really massive servo amplifier driving the motor giving
the system the ability to work up to several Hz.

It seems to me that this sort of thing could be done today and make it
up into the 10s of Hz.

In geophysics, they use the powerful hydraulic vibrators which operate
at the frequencies up to 100Hz. It is interesting that the flat response
and the linearity are important for geophysical application; so some
sort of compensation is applied. This technology can be used for the
woofers if we are after the power levels of 10kW or higher.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

[Eeyore]

Don Pearce wrote:

Kevin Aylward wrote:
Eeyore wrote:
isw wrote:
Jan Panteltje wrote:
it happened Don Pearce wrote

Actually the "right" place to connect the feedback sensing
resistor is right out at the speaker itself, via a third sensing
wire.
Ha, why did I never think of that...
This will eliminate my massive gold feed rods to the woofer.

You will need 2 sensing wires, and a diff amp.
If you really think that's important (and I don't), why not just put
the amplifiers near the speakers? That way, there won't be any nasty
stability problems to deal with.
They're called active speakers and are widely used by many
professionals.

Indeed.

I don't actually like powered speakers though. They need *two* leads. Just
more hassle in setting up for the gig.

Wouldn't want them on a gig - very good for studio monitoring though.

Exactly. KRK have a very good name in that respect at the moment and I think
they do actives.

Graham

[Eeyore]

MooseFET wrote:

isw wrote:
Jan Panteltje wrote:
it happened Don Pearce wrote

Actually the "right" place to connect the feedback sensing resistor is
right out at the speaker itself, via a third sensing wire.

Ha, why did I never think of that...
This will eliminate my massive gold feed rods to the woofer.

You will need 2 sensing wires, and a diff amp.

If you really think that's important (and I don't), why not just put the
amplifiers near the speakers? That way, there won't be any nasty
stability problems to deal with.

You can do about as well if you characterize what a linear system does
and then correct for it. If a system is nonlinear it is harder to do.

If you want to go all the way to having feedback from the speaker, it
seems to me that moving the feedback detection as close to the sound
output as practical is the way to go. Sensing actual cone movement is
better than sensing the driven voice coil's voltage.

Philips did that decades ago with a piezo transducer IIRC. No idea why it
didn't take off other than Philips aren't exactly reknowned for hi-fi.

Graham

[Eeyore]

Vladimir Vassilevsky wrote:

MooseFET wrote:

If you want to go all the way to having feedback from the speaker, it
seems to me that moving the feedback detection as close to the sound
output as practical is the way to go. Sensing actual cone movement is
better than sensing the driven voice coil's voltage.

The idea of the feedback directly from the cone is no new. The main
problem is economical: it is easier to make a reasonable conventional
speaker rather then trying to make a good speaker from the bad one by
the means of feedback and feedforward compensation.

The other problem is which part of the speaker cone do you sense ? They
'bend' and resonate etc etc in use.

Graham

[Jan Panteltje]

On a sunny day (Sun, 21 Sep 2008 18:43:24 +0100) it happened Eeyore
wrote in
:

I don't actually like powered speakers though. They need *two* leads. Just
more hassle in setting up for the gig.

Wouldn't want them on a gig - very good for studio monitoring though.

Exactly. KRK have a very good name in that respect at the moment and I think
they do actives.

Graham

I think it should be possible [I could] design powered speakers with a WiFi interface.
Each speaker would have its own IP address, or perhaps its own port on one IP,
and from the [new] mixer only digital Ethernet to a wireless access point.
No bandwidth problem I think.
56 Mbits / second, should be enough for a few channels.
You will have power cables to the speaker, but not a lot of audio wiring.

mmm maybe do the mikes too ;-)

[Vladimir Vassilevsky]

Jan Panteltje wrote:

I think it should be possible [I could] design powered speakers with a WiFi interface.

How would you synchronize the different channels?

Each speaker would have its own IP address, or perhaps its own port on one IP,
and from the [new] mixer only digital Ethernet to a wireless access point.
No bandwidth problem I think.
56 Mbits / second, should be enough for a few channels.

The real 802.11G throughput is 2.8MB/s at the best. An uncompressed
audio channel takes roughly 100KB/s.

You will have power cables to the speaker, but not a lot of audio wiring.
mmm maybe do the mikes too ;-)

The big problem with WiFi for audio is the synchronization between the
different WiFi units while maintaining the reasonable delay. This is
hard (if possible at all) to attain with the WiFi equipment.

AFAIK the solutions for audio via Ethernet (CobraNet and such) used the
special protocol stacks and were not fully compatible with the standard
networking stuff. In the general, Ethernet is not good as the network
for the multimedia; it was not designed for that purpose.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

[Jan Panteltje]

On a sunny day (Sun, 21 Sep 2008 13:41:43 -0500) it happened Vladimir
Vassilevsky wrote in
:



Jan Panteltje wrote:

I think it should be possible [I could] design powered speakers with a WiFi interface.

How would you synchronize the different channels?

Yes, good point, timestamp would be one way, but that does not solve the delay.
the delay would be fatal in a live application.


Each speaker would have its own IP address, or perhaps its own port on one IP,
and from the [new] mixer only digital Ethernet to a wireless access point.
No bandwidth problem I think.
56 Mbits / second, should be enough for a few channels.

The real 802.11G throughput is 2.8MB/s at the best. An uncompressed
audio channel takes roughly 100KB/s.

There is no reason not to use a compressed format, mp2 or AC3 would be cool.


You will have power cables to the speaker, but not a lot of audio wiring.
mmm maybe do the mikes too ;-)

The big problem with WiFi for audio is the synchronization between the
different WiFi units while maintaining the reasonable delay. This is
hard (if possible at all) to attain with the WiFi equipment.

See above.


AFAIK the solutions for audio via Ethernet (CobraNet and such) used the
special protocol stacks and were not fully compatible with the standard
networking stuff. In the general, Ethernet is not good as the network
for the multimedia; it was not designed for that purpose.

OK, it looks like we have to scrap this idea, in its current form, but
the basic principle could work.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Good observation!

[krw[_3_]]

In article ,
says...


Jan Panteltje wrote:

I think it should be possible [I could] design powered speakers with a WiFi interface.

How would you synchronize the different channels?

Don't. One WiFi channel.

Each speaker would have its own IP address, or perhaps its own port on one IP,
and from the [new] mixer only digital Ethernet to a wireless access point.
No bandwidth problem I think.
56 Mbits / second, should be enough for a few channels.

The real 802.11G throughput is 2.8MB/s at the best. An uncompressed
audio channel takes roughly 100KB/s.

You're going to have to justify that number. 100MB/s? I can see
20KB, *maybe*. Five channels at perhaps three times this...

You will have power cables to the speaker, but not a lot of audio wiring.
mmm maybe do the mikes too ;-)

The big problem with WiFi for audio is the synchronization between the
different WiFi units while maintaining the reasonable delay. This is
hard (if possible at all) to attain with the WiFi equipment.

Why is that so hard? All of the recievers get the same stream.
Each takes what it needs and throws the rest in the bit bucket.

AFAIK the solutions for audio via Ethernet (CobraNet and such) used the
special protocol stacks and were not fully compatible with the standard
networking stuff. In the general, Ethernet is not good as the network
for the multimedia; it was not designed for that purpose.

It may not be good, but easily could be good enough.

--
Keith

[Eeyore]

Vladimir Vassilevsky wrote:

Jan Panteltje wrote:

I think it should be possible [I could] design powered speakers with a WiFi interface.

How would you synchronize the different channels?

Each speaker would have its own IP address, or perhaps its own port on one IP,
and from the [new] mixer only digital Ethernet to a wireless access point.
No bandwidth problem I think.
56 Mbits / second, should be enough for a few channels.

The real 802.11G throughput is 2.8MB/s at the best. An uncompressed
audio channel takes roughly 100KB/s.

You will have power cables to the speaker, but not a lot of audio wiring.
mmm maybe do the mikes too ;-)

The big problem with WiFi for audio is the synchronization between the
different WiFi units while maintaining the reasonable delay. This is
hard (if possible at all) to attain with the WiFi equipment.

i.e. latency. All the specialist solutions to this issue have addressed this problem
specifically.


AFAIK the solutions for audio via Ethernet (CobraNet and such) used the
special protocol stacks and were not fully compatible with the standard
networking stuff. In the general, Ethernet is not good as the network
for the multimedia; it was not designed for that purpose.

Cobranet causes trouble does it ? I know they have some kind of 'sync' signal.

Graham

[Eeyore]

Jan Panteltje wrote:

There is no reason not to use a compressed format, mp2 or AC3 would be cool.

You vile vermin !

Graham

[Eeyore]

krw wrote:

You're going to have to justify that number. 100MB/s?

He said kBps.

I can see 20KB, *maybe*.

44.1k samples / sec x 2 bytes each = 88.2kBps. Allow overhead for collisions etc. Actually if
you transmit the full AES/EBU SPDIF data it's THREE bytes.

100kBps sounds about right for one mono channel. Or 150 kBps with flags etc.

Graham

[Jan Panteltje]

On a sunny day (Sun, 21 Sep 2008 20:18:50 +0100) it happened Eeyore
wrote in
:



Jan Panteltje wrote:

There is no reason not to use a compressed format, mp2 or AC3 would be cool.

You vile vermin !

Graham

mm actually, I had the intention to use separate amps in the speakers
for woofer, midrange, and tweeter, and do the filtering _in the mixer_,
so then you could compensate per speaker so to speak :-)
Anyways, for people with supernatural hearing, like some animals, that
would perhaps not give full satisfaction.
Most people are satisfied with AC3 though.

[Jorden Verwer]

Kevin Aylward wrote:
Don't you at least agree there are many similarities between 1/f
noise and offset?


Actually, I do. By and large, they amount to the same thing. Its all low
frequency variations. For example, if one designs a chopper amp to get low
offset, it also kills/corrects for 1/f noise as well. If one has 1/f
problems in an system, one immediately thinks about using a chopper..well
I
do any way...
Yes, that's exactly what I meant.

[Jorden Verwer]

MooseFET wrote:
If you look for an op-amp with an extremely low offset voltage, you
will find that it uses MOSFETs to obtain that extreme low offset.
Quite right. In hindsight, I could've been more clear about this not being
relevant here, I just didn't want any "You're wrong because MOSFETs have
lower offset"-type responses, so that's why I mentioned it...

[Jorden Verwer]

MooseFET wrote:
Radiation hardness
Boundary condition.

Safe operating area
Boundary condition.

Bandwidth
AFAIK, BJTs still hold the world record for cutoff frequency.

[John Larkin]

On Thu, 18 Sep 2008 09:25:39 -0000, "Jorden Verwer"
wrote:

RichD wrote:
Who do MOSFET sound better than bipolar, as an audio amp output
driver?

The device properties of BJTs are superior to those of MOSFETs in all
respects, except for offset - there MOSFETs have the advantage. Whether you
will actually hear this depends on many more factors.


Offset? Two BJTs of the same part number will have delta-Vbe well
below a tenth of a volt. A similar pair of mosfets will have Vgs-th
and transfer curves that can differ by a volt or more. And the mosfet
thresholds will change with time a lot more then the bjt's.

Mosfets have zero storage/desaturation time, far better SOAR specs,
and are easier to drive.

John

[Jorden Verwer]

Jan Panteltje wrote:
I think it should be possible [I could] design powered speakers with a
WiFi
interface.
Yuck, wireless...

[Don Pearce]

Jorden Verwer wrote:
Jan Panteltje wrote:
I think it should be possible [I could] design powered speakers with a
WiFi
interface.
Yuck, wireless...



Around the house these days Homeplug is far better than WiFi.

d

[Jan Panteltje]

On a sunny day (Sun, 21 Sep 2008 20:24:20 -0000) it happened "Jorden Verwer"
wrote in
et:

Jan Panteltje wrote:
I think it should be possible [I could] design powered speakers with a
WiFi
interface.
Yuck, wireless...

You mean you do not watch TV and listen to radio?
And have no cellphone too?

[Jorden Verwer]

Jan Panteltje write:
You mean you do not watch TV and listen to radio?
And have no cellphone too?
I mean I try to avoid wireless whenever possible. So when I'm at home, I
watch cable TV and listen cable radio and use my landline phone...

[Jan Panteltje]

On a sunny day (Sun, 21 Sep 2008 21:25:33 +0100) it happened Don Pearce
wrote in
:

Jorden Verwer wrote:
Jan Panteltje wrote:
I think it should be possible [I could] design powered speakers with a
WiFi
interface.
Yuck, wireless...



Around the house these days Homeplug is far better than WiFi.

d

I have looked a bit at homeplug, because the new TVs seem to support it,
but really, I am a step ahead, I use the laptop as portable TV monitor to
watch satellite TV, and any file on the server I like.
Using WiFi ! so wireless.
This is an old blog entry, have added much cool stuff since:
http://panteltje.com/panteltje/blog/index.html
Playing nice slide shows now too.
http://panteltje.com/panteltje/jpg_to_mjpegtools_yuv/

It is in this that it shows, and is proof of,
that WiFi is not in any way a real bandwidth problem
This is all Linux soft of course, so highly efficient.

The worlds is just spitting out one marketing term after the other, now
it is 'home plug'.
Really, as far as network is concerned, ssh, netcat, scp, transport stream,
etc... rules it all.

They (Philips, others), want to sell you an 'internet radio', a 'digital picture frame',
a this, a that, while any laptop running Linux with a 5 line script does it all.
With more possibilities and more flexible, and future proof, and wireless too.
Often for less money.

[Jan Panteltje]

On a sunny day (Sun, 21 Sep 2008 20:44:55 -0000) it happened "Jorden Verwer"
wrote in
et:

Jan Panteltje write:
You mean you do not watch TV and listen to radio?
And have no cellphone too?
I mean I try to avoid wireless whenever possible. So when I'm at home, I
watch cable TV and listen cable radio and use my landline phone...

OK, whatever you like best.
See also my other posting.

[Chronic Philharmonic]

"RichD" wrote in message
...
Who do MOSFET sound better than bipolar, as an audio amp output
driver?

A lot of bits have been spilled on this thread so far, but I think it is the
same question as "Why do tubes sound better than transistors?" or "How many
angels can dance on the head of a pin?"

First of all, it implies a truth that may not objectively be the case. But
tubes, BJTs and MOSFETs all have very different characteristics and
engineering trade-offs. I think it has been reasonably well established that
it is possible to make excellent sounding amplifiers with any of those
technologies.

In the end, I think it boils down to the experience and skill of the
engineer in working with a given technology, and how that impacts the
economics of producing the end product using said technology.

For example, I think we no longer use vacuum tubes for mainstream audio
power amplifiers because they:

1. Require an additional power supply and heat to operate.
2. Are bulky compared to their solid-state alternatives.
3. Are not available in complimentary pairs (e.g., P-channel/N-channel)
4. Have output impedance that usually requires an output transformer.

None of these are insurmountable obstacles, but they do increase the size,
cost, power consumption and heat load for a given output power.

Similar, but less obvious considerations affect the choice of BJTs and
MOSFETs. They have different characteristics, and the skilled engineer will
exploit them for optimal effect -- sonic quality, economy, reliability and
so on. The marketing department will define the requirements for the product
based on the target market, and the engineer will attempt to design a
product that fits within those constraints. In all that I have read here, I
have not seen anything that would consistently make me select MOSFETs over
BJTs. But I might have a preference based on a *given set* of product
requirements.

[Vladimir Vassilevsky]

Jan Panteltje wrote:
On a sunny day (Sun, 21 Sep 2008 13:41:43 -0500) it happened Vladimir
Vassilevsky wrote in
:



Jan Panteltje wrote:


I think it should be possible [I could] design powered speakers with a WiFi interface.

How would you synchronize the different channels?

Yes, good point, timestamp would be one way, but that does not solve the delay.
the delay would be fatal in a live application.

Here is the idea: using the power frequency as the common timing
reference. In the local WiFi network, the ping time would be at the
order of 1ms, so all channels could be PLLed to the same half period of
the AC power without an ambiguity. With the sufficient amount of
buffering, that should allow streaming multiple synchronized channels.
Sooo simple... I bet somebody already got a patent on that.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

[Jan Panteltje]

On a sunny day (Sun, 21 Sep 2008 16:46:27 -0500) it happened Vladimir
Vassilevsky wrote in
:



Jan Panteltje wrote:
On a sunny day (Sun, 21 Sep 2008 13:41:43 -0500) it happened Vladimir
Vassilevsky wrote in
:



Jan Panteltje wrote:


I think it should be possible [I could] design powered speakers with a WiFi interface.

How would you synchronize the different channels?

Yes, good point, timestamp would be one way, but that does not solve the delay.
the delay would be fatal in a live application.

Here is the idea: using the power frequency as the common timing
reference. In the local WiFi network, the ping time would be at the
order of 1ms, so all channels could be PLLed to the same half period of
the AC power without an ambiguity. With the sufficient amount of
buffering, that should allow streaming multiple synchronized channels.
Sooo simple... I bet somebody already got a patent on that.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Clever!
How about this: we give each speaker a GPS.
It will also send back its position, and the 'mixer' will
then calculate the optimum sound pattern for 5.1.
GPS also has a very precise clock.

[Eeyore]

Jan Panteltje wrote:

Most people are satisfied with AC3 though.

Dumbing down wins again.

Graham

[Eeyore]

Jorden Verwer wrote:

Kevin Aylward wrote:
Don't you at least agree there are many similarities between 1/f
noise and offset?

Actually, I do. By and large, they amount to the same thing. Its all low
frequency variations. For example, if one designs a chopper amp to get low
offset, it also kills/corrects for 1/f noise as well. If one has 1/f
problems in an system, one immediately thinks about using a chopper..well
I do any way...
Yes, that's exactly what I meant.

And a chopper amp has exactly WHAT to do with ultra high quality audio ?

Graham

[Eeyore]

Jorden Verwer wrote:

MooseFET wrote:
Radiation hardness
Boundary condition.

Safe operating area
Boundary condition.

Bandwidth
AFAIK, BJTs still hold the world record for cutoff frequency.

In devices suitable for audio amps ?

You are totally incapable of staying on-topic.

Graham

[Eeyore]

John Larkin wrote:

"Jorden Verwer" wrote:
RichD wrote:
Who do MOSFET sound better than bipolar, as an audio amp output
driver?

The device properties of BJTs are superior to those of MOSFETs in all
respects, except for offset - there MOSFETs have the advantage. Whether you
will actually hear this depends on many more factors.

Offset? Two BJTs of the same part number will have delta-Vbe well
below a tenth of a volt.

IME typically within a 10mV range. That saved a trimpot and the line time to
adjust it on more than one occasion.


A similar pair of mosfets will have Vgs-th
and transfer curves that can differ by a volt or more.

For vertical types, yes. Not for laterals.


And the mosfet thresholds will change with time a lot more then the bjt's.

No comment. Never known it be a problem with laterals.


Mosfets have zero storage/desaturation time,

Well, 60ns on the data sheet was good enough for me.


far better SOAR specs, and are easier to drive.

True.

Graham

[Eeyore]

Chronic Philharmonic wrote:

"RichD" wrote

Who do MOSFET sound better than bipolar, as an audio amp output
driver?

A lot of bits have been spilled on this thread so far, but I think it is the
same question as "Why do tubes sound better than transistors?" or "How many
angels can dance on the head of a pin?"

First of all, it implies a truth that may not objectively be the case. But
tubes, BJTs and MOSFETs all have very different characteristics and
engineering trade-offs.

Actually, certain mosfets are not at all unlike triodes.

More to the point is whether you are anti-science and despise negative feedback.
And / or LIKE your music deliberately distorted as some seem to do.

Graham