MOSFET output stage

[JosephKK]

The copper thingy is flexible, about 15' long,
attaches to the box with the magnets at one end.

It would indeed be unusual to use that
as heatsink, but perhaps novel and efficient.


So the output driver feeds the output stage?
Is that the standard jargon?

Yes. And not only in audio power amplifiers, it occurs in RF power
amplifiers as well.

 

[JosephKK]

I know that, and I never claimed otherwise. Offset is a form of noise, in a
sense. And like noise, it is caused almost completely by the input
transistors. I'm well aware of all that.

Yes.

Offset is a form of noise???? This is the first time i have ever
heard that. There is no engineering reason to look at it that way. It
is fundamentally a different property with different physics.

 

[JosephKK]

Let me put it this way...

Noise-like phenomena, in increasing order of bandwith:
Offset ==> 1/f noise ==> white noise

OK alligator, where does shot noise fall in the spectrum?

 

[JosephKK]

it.


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...


Kevin Aylward
www.anasoft.co.uk
SuperSpice

I am less sure about it killing 1/f (flicker) noise rather than band
shifting it to a place where is can be filtered out. It is not
offset, though the chopper amplifiers can mask it out. Ah, yes, noise
shaping; making some undesired near band interfering signal content
terms go where they are easier to separate from the desired signal.

 

[Phil Allison]

"Don Pearce Pommy Liar Extrordaire"

Just had a look at a few QSC schematics, and it is apparent that the
output transistors are biased - not quite to zero current, but certainly a
very low current.

** Wot absolute fucking drivel.

Only seeing a REAL example of a QSC amp allows one to tell what the bias
current setting is.

As it depends critically on the adjustment of a trim pot.

This is held in position a by a long time constant RC pair,

** There is no such RC pair involved - you congenital, criminal dim wit.




...... Phil

 

[Jan Panteltje]

48KHz is the DAT tape rate.

It is also what is normally used in digital TV.
That means digital recordings from TV use 48KHz.

Maybe when CDs die, then 44.1 is dead?

 

[MooseFET]

It is also what is normally used in digital TV.
That means digital recordings from TV use 48KHz.

Maybe when CDs die, then 44.1 is dead?

Many computers sound cards are made to produce 44.1K exactly and many
digital recordings are already made at 44.1. It will likely stay
around as a standard.

 

[Phil Allison]

"Jan Panteltje"

It is also what is normally used in digital TV.
That means digital recordings from TV use 48KHz.

** Nonsense - DTV is all MP3 encoded.

There is no defined sampling rate.



...... Phil

 

[Phil Allison]

"Don Pearce Pommy Liar Extraordinaire

There are no trim pots on the three schematics I've looked at.

** Then you have NOT looked at any USA or MX or even the PL series amps.


AS IS 100% REQUIRED BY THE CONTEXT !!!



YOU VILE, LYING ASININE ASD FUCKED PILE OF POMMY EXCREMENT !!!






...... Phil

 

[Jan Panteltje]

"Jan Panteltje"




** Nonsense - DTV is all MP3 encoded.

There is no defined sampling rate.



..... Phil

First it is mp2 encoded, and second most is 48KHz sampled.
Here is an example:

mplayer -ao oss:/dev/dsp1 goldfinger.ts
MPlayer 1.0pre7try2-3.3.6 (C) 2000-2005 MPlayer Team
CPU: Advanced Micro Devices Duron Spitfire (Family: 6, Stepping: 1)
Detected cache-line size is 64 bytes
CPUflags: MMX: 1 MMX2: 1 3DNow: 1 3DNow2: 1 SSE: 0 SSE2: 0
Compiled for x86 CPU with extensions: MMX MMX2 3DNow 3DNowEx


Linux RTC init error in ioctl (rtc_irqp_set 1024): Inappropriate ioctl for device
Try adding "echo 1024 > /proc/sys/dev/rtc/max-user-freq" to your system startup scripts.
Playing goldfinger.ts.
TS file format detected.
DEMUX OPEN, AUDIO_ID: -1, VIDEO_ID: -1, SUBTITLE_ID: -1,
PROBING UP TO 2000000, PROG: 0
VIDEO MPEG2(pid=2342)AUDIO MPA(pid=2343) NO SUBS (yet)! PROGRAM N. 0
Opened TS demuxer, audio: 50(pid 2343), video: 10000002(pid 2342)...POS=10340
VIDEO: MPEG2 544x576 (aspect 3) 25.000 fps 10000.0 kbps (1250.0 kbyte/s)
==========================================================================
Opening audio decoder: [mp3lib] MPEG layer-2, layer-3
AUDIO: 48000 Hz, 2 ch, s16le, 192.0 kbit/12.50% (ratio: 24000->192000)
Selected audio codec: [mp3] afm:mp3lib (mp3lib MPEG layer-2, layer-3)
==========================================================================
vo: X11 running at 1440x900 with depth 24 and 32 bpp (":0.0" => local display)
==========================================================================
Opening video decoder: [mpegpes] MPEG 1/2 Video passthrough
VDec: vo config request - 544 x 576 (preferred csp: Mpeg PES)
Could not find matching colorspace - retrying with -vf scale...
Opening video filter: [scale]
The selected video_out device is incompatible with this codec.
VDecoder init failed
Opening video decoder: [libmpeg2] MPEG 1/2 Video decoder libmpeg2-v0.4.0b
Selected video codec: [mpeg12] vfm:libmpeg2 (MPEG-1 or 2 (libmpeg2))
==========================================================================
Checking audio filter chain for 48000Hz/2ch/s16le -> 48000Hz/2ch/s16le...
AF_pre: 48000Hz/2ch/s16le
AO: [oss] 48000Hz 2ch s16le (2 bps)
Building audio filter chain for 48000Hz/2ch/s16le -> 48000Hz/2ch/s16le...
Starting playback...
VDec: vo config request - 544 x 576 (preferred csp: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1.78:1 - prescaling to correct movie aspect.
VO: [xv] 544x576 => 1024x576 Planar YV12

 

[Phil Allison]

"Jan Panteltje"

First it is mp2 encoded, and second most is 48KHz sampled.

** ROTFLMFAO !!

WOT COMPLETE BOLLOCKS !!!!!!!!!!


MP2 is a fucking VIDEO format - you MORON !!!!!!!!!!!

Wot a pathetic, ridiculous ASD fucked, wog IMBECILE !!!


Go DROP FUCKING DEAD

- NOW !!!!!!!!!!!!!!!!!!!!!!!!!!!



..... Phil

 

[Eeyore]

OK alligator, where does shot noise fall in the spectrum?

LOL ! I'd toyed with suggesting that one myself but I'd got tired of his
idiocy.

Graham

 

[Eeyore]

Just had a look at a few QSC schematics, and it is apparent that the
output transistors are biased - not quite to zero current, but certainly
a very low current. Certainly a long way below what I would consider a
normal bias level. This is held in position a by a long time constant RC
pair, which I suspect doesn't track LF-induced temperature variations
too well.

How did you establish that ? I don't recall the schematics giving any clues like that
away. The typical quiescent Vbe of the ultimate output devices is in the 0.5V region
from memory.

As you say though, it's certainly not 'conventional' biasing.

Their higher end models have reverted to emitter followers btw. Incidentally you can
do the same trick with these too.

Graham

 

[Eeyore]

"Don Pearce Pommy Liar Extrordaire"

** Wot absolute fucking drivel.

Only seeing a REAL example of a QSC amp allows one to tell what the bias
current setting is.

AFTER you've erroneously fiddled with the trimpot ?

Graham

 

[Eeyore]

Short answer - Graham has no immediate practical experience with measuring
QSC amps, just like I said.

What's 'immediate' got to do with it ? I've measured plenty of QSCs and the
MX1500 I had was shocking. The RMXs are a bit better but still nothing to write
home about. I refined the RMX design for a semi-cloner of the output stage btw
and knocked the THD down significantly with some of my little tricks like
pole-zero compensation and also made the input to the amp 'module' quasi balanced
to reduce 50/100 etc hum pickup..

I've also measured the Powerlights but I don't exactly recall their THD now
mainly because my enduring memory of them is that the short circuit protection
doesn't work if you short out a 'live signal'. Thankfully it was under guarantee.
It probably works if powered up with a short on the output. It's easy to see why.
Their protection method is shit. Read the patent. There's too much stored charged
in those 2 electrolytic caps.

Graham

 

[Eeyore]

If you had a group of 30 well-chosen, well-trained listeners, then there
would be no such thing as "...30 listeners and 3 were consistently about to
determine A from B and the other 27 couldn't..."

And how exactly do you determine that ?

You just proved that ABX testing ignores those with the most sensitive or highly
trained hearing and is therefore merely a lowest common denominator test.
Suitable say for determining the quality of TV sound.

Graham

 

[Eeyore]

All the audiophool golden ears say *exactly* the same thing.

And as I said it was chalk and cheese.

Not stupid liquid nitrogen dipped speaker cables or that kind of garbage.

Graham

 

[Eeyore]

I have more highly sensitive audio test gear by accident then most people
have on purpose. I probably shouldn't admit this because it shows a certain
kind of carelessness.

Not more sensitive than Audio Precision or Prism Sound.

Graham

 

[Phil Allison]

"Don Pearce Congenital ASD fucked LIAR "



** WRONG ONES - you FUCKING IDIOT !!

In a conventionally biased amp there is a biasing transistor between the
two op bases which is thermally linked as closely as possible to the
output devices - this (to some extent) tracks the Vbe changes through a
slow bass cycle and maintains the bias point. In the QSC design,

** WRONG ONES - you FUCKING IDIOT !!





...... Phil

 

[Eeyore]

"Jan Panteltje"


** Nonsense - DTV is all MP3 encoded.

There is no defined sampling rate.

First it is mp2 encoded, and second most is 48KHz sampled.
Here is an example:

mplayer -ao oss:/dev/dsp1 goldfinger.ts
MPlayer 1.0pre7try2-3.3.6 (C) 2000-2005 MPlayer Team
CPU: Advanced Micro Devices Duron Spitfire (Family: 6, Stepping: 1)
Detected cache-line size is 64 bytes
CPUflags: MMX: 1 MMX2: 1 3DNow: 1 3DNow2: 1 SSE: 0 SSE2: 0
Compiled for x86 CPU with extensions: MMX MMX2 3DNow 3DNowEx

Linux RTC init error in ioctl (rtc_irqp_set 1024): Inappropriate ioctl for device
Try adding "echo 1024 > /proc/sys/dev/rtc/max-user-freq" to your system startup scripts.
Playing goldfinger.ts.
TS file format detected.
DEMUX OPEN, AUDIO_ID: -1, VIDEO_ID: -1, SUBTITLE_ID: -1,
PROBING UP TO 2000000, PROG: 0
VIDEO MPEG2(pid=2342)AUDIO MPA(pid=2343) NO SUBS (yet)! PROGRAM N. 0
Opened TS demuxer, audio: 50(pid 2343), video: 10000002(pid 2342)...POS=10340
VIDEO: MPEG2 544x576 (aspect 3) 25.000 fps 10000.0 kbps (1250.0 kbyte/s)
==========================================================================
Opening audio decoder: [mp3lib] MPEG layer-2, layer-3
AUDIO: 48000 Hz, 2 ch, s16le, 192.0 kbit/12.50% (ratio: 24000->192000)
Selected audio codec: [mp3] afm:mp3lib (mp3lib MPEG layer-2, layer-3)
==========================================================================
vo: X11 running at 1440x900 with depth 24 and 32 bpp (":0.0" => local display)
==========================================================================
Opening video decoder: [mpegpes] MPEG 1/2 Video passthrough
VDec: vo config request - 544 x 576 (preferred csp: Mpeg PES)
Could not find matching colorspace - retrying with -vf scale...
Opening video filter: [scale]
The selected video_out device is incompatible with this codec.
VDecoder init failed
Opening video decoder: [libmpeg2] MPEG 1/2 Video decoder libmpeg2-v0.4.0b
Selected video codec: [mpeg12] vfm:libmpeg2 (MPEG-1 or 2 (libmpeg2))
==========================================================================
Checking audio filter chain for 48000Hz/2ch/s16le -> 48000Hz/2ch/s16le...
AF_pre: 48000Hz/2ch/s16le
AO: [oss] 48000Hz 2ch s16le (2 bps)
Building audio filter chain for 48000Hz/2ch/s16le -> 48000Hz/2ch/s16le...
Starting playback...
VDec: vo config request - 544 x 576 (preferred csp: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1.78:1 - prescaling to correct movie aspect.
VO: [xv] 544x576 => 1024x576 Planar YV12

-------------------------------------------------

You make too much noise, make yourself look ridiculous.
It sort of invalidates the rest of your remarks, as when you are so wrong
about this, how should I pay attention to the other stuff you scream?

True. Once he gets into rage mode, it all goes to pot.

In the meantime it seems he's been mis-biasing QSC amplifiers for years.

Graham