Dynamic Headroom: Where is the limit? - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st July 2002, 04:04 AM   #21
Account Disabled
 
Join Date: Jul 2002
Location: North
Send a message via ICQ to gromanswe Send a message via AIM to gromanswe Send a message via Yahoo to gromanswe
Right

You are a good listener
Serves you well

gro
  Reply With Quote
Old 21st July 2002, 04:21 AM   #22
Warp Engineer
On Holiday
 
AudioFreak's Avatar
 
Join Date: Oct 2001
Location: Queensland, Australia
I must agree with all that has been said since my last reply and yes Helix there is a huge difference between good engineering practices and a well engineered product... primarily in that the well engineered product should best fit all the design criteria whereas a product that follows good engineering practices does not necessarily meet the design criteria.... indeed i could be asked to design an amp that costs $250 to manufacture and finish up with an amp that costs 5 times that to produce. It's not well engineered but it may well adopt good engineering practice in the design. Now personally i believe that it should be the job of the engineer to best produce a well engineered product while not sacrificing good engineering practice. I realise this is not the case because profits have become of all consuming importance but alot of things could be corrected for a matter of 5 or 10 dollars. It isnt going to send the big guys broke and the funds could easily be diverted from the almost useless features that PR make a song and dance about... but that would require PR to start advertising the truth and not a sack of whimsical garbage.. Anyway, that's just my 2 cents.
  Reply With Quote
Old 21st July 2002, 04:51 AM   #23
diyAudio Moderator Emeritus
 
roddyama's Avatar
 
Join Date: Jan 2002
Location: Michigan
Default Please forgive me Mr. Pass

Quote:
NAD, Apt, Hitachi, Technics, Soundcraftsmen, and others have all used various amplifier designs, with various levels of success, to provide more power at a reasonable price.
I must appologize to Mr. Pass for relegating him to "others". The Threshold 800a was one of Mr. Pass' first amps and one of the first amps to use the "dynamically biased" class A configuration back in the 70's. This is a method of getting more power from a class A amp with smaller (cheaper?) parts.
Attached Images
File Type: jpg threshold-800a.jpg (21.2 KB, 525 views)
  Reply With Quote
Old 21st July 2002, 05:16 AM   #24
Account Disabled
 
Join Date: Jul 2002
Location: North
Send a message via ICQ to gromanswe Send a message via AIM to gromanswe Send a message via Yahoo to gromanswe
Default Re: Please forgive me Mr. Pass

Quote:
Originally posted by roddyama


I must appologize to Mr. Pass for relegating him to "others". The Threshold 800a was one of Mr. Pass' first amps and one of the first amps to use the "dynamically biased" class A configuration back in the 70's. This is a method of getting more power from a class A amp with smaller (cheaper?) parts.
There are suitable methods of storing energy.
In caps or coils.

how effective they store energy
and the Quality of that energy
are matters

no fault in going your own way
that what you must do
anyway
he went his way
like a slaughtered lamb

We all must
"carry that weight" John Paul 1969 Abbey Road
what is an abbey - we do not sell tem in Land of Vikings

gro
  Reply With Quote
Old 21st July 2002, 05:47 AM   #25
Account Disabled
 
Join Date: Jul 2002
Location: North
Send a message via ICQ to gromanswe Send a message via AIM to gromanswe Send a message via Yahoo to gromanswe
Default HERE comes THE SON, same LP, get it

g
  Reply With Quote
Old 21st July 2002, 01:28 PM   #26
diyAudio Moderator Emeritus
 
roddyama's Avatar
 
Join Date: Jan 2002
Location: Michigan
Default Two Questions for Gro

Hey Gro,

What are you smoking?

Where did you get it?

Rodd Yamashita
  Reply With Quote
Old 21st July 2002, 01:46 PM   #27
Account Disabled
 
Join Date: Jul 2002
Location: North
Send a message via ICQ to gromanswe Send a message via AIM to gromanswe Send a message via Yahoo to gromanswe
Default Caravelle - local food store

g
  Reply With Quote
Old 21st July 2002, 06:12 PM   #28
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
"The NAD spec of having a 6 dB headroom is the marketing and sales department's way of saying that the amp has a lousy power transformer that sags badly, and low power rated output transistors."
Nothing could be further from the truth than the above statement. For people with an open mind I will try and explain some of the NAD design. But load the Nelson Pass patent first, I will refer to it later.
http://patft.uspto.gov/netacgi/nph-P...number=5343166
How does the NAD power envelope amplifier work? What trade-offs did they make?
The schematic for the 100W NAD power envelope amplifier looks almost like a Bryston 3B or an Accuphase P300, but with a tiered power supply. Cross coupled dual differential inputs, fully complimentary from input to output. But with a high voltage tier.
I have bench tested the 100W NAD with both channels driven at 8R with a 1Khz sine wave and got 360W/ch RMS. After a couple of seconds at this level the RayChem PolySwitch opens up and shuts down the high voltage tier. With the high voltage tier shut down the amp will do 100W/ch RMS.
As long as the peak to average ratio in the program material is better than about 6dB the high voltage tier will be available. Even highly compressed rock music meets this requirement.
Money is saved compared to a 400W amp in that the transformer and heatsink is sized for a 100W amp.
The downside is some noise where it switches to the high voltage tier.
There are ways to eliminate the switching. See the Pass patent. While the NAD used a hard switch for the high voltage tier, the Pass works like a normal amplifier up to the tier, and then cascodes itself for the rest of the swing! The higher voltage tier operates in a linear, rather than a switched mode.
Let's do some bench racing. You own some inefficient speakers like the B&W 801s that need 300W/4R to make them get up and go. Well class A is OK if you have $1,000 for heatsink. What about AB biased 10W into class A? OK, our supply voltage is +/- 57V to do 300W/4R, a brute force unregulated supply with lots of filter caps and a big low voltage transformer. Say 40-0-40 at 1KVA with 120,000F filter capacitance (one 30,000F per rail, per channel. To put this in perspective, an Adcom GFA555 puts out 325W/4R with a much higher +/- 75V and half the filter capacitance with only a 700VA transformer). 10W/8R is 1.58A peak, or 360W at idle for a stereo amp. This is a LOT of heat. A normal 300W stereo class AB amp would only have to get rid of about 240W of heat (60% efficency) at full power.
Now let's add a +/- 12V tier. With our same 1.58A bias we now only have 76W of heat for the stereo amp at idle! At full power the efficency would be about 70%, so we could either reduce the size of the heatsink, or choose to increase the class A power point a little higher.
I think one IRF 640/9640 pair in the TO247 package would do for the 12V tier (no matching dozens of transistors), and I would use two pair MJ21193/21194 for the cascode. The Apex jr 37-37-37-37 at 1KVA would be just right for the main rails, and for a stereo amp the low voltage tier need only be 3A or so.
  Reply With Quote
Old 21st July 2002, 08:12 PM   #29
Account Disabled
 
Join Date: Jul 2002
Location: North
Send a message via ICQ to gromanswe Send a message via AIM to gromanswe Send a message via Yahoo to gromanswe
Default MJE 15030/31

Best TO220 bipolar power device
Inform Me

I use it a lot!

gro
  Reply With Quote
Old 22nd July 2002, 12:01 AM   #30
diyAudio Member
 
promitheus's Avatar
 
Join Date: Jan 2001
Location: Germany
Talking about power supplies in amplifiers...

I see audio amps as big power supplies controlled by small audio circuits to give power to loudspeakers. The better the power supply is, the better the thing works.

Headroom, as I understand it, means you have a bigger power supply then you will be using, so you have some extra power for the peaks.
That means, according to the above, that if you need 10 watts of power to listen to music, you will want some extra "space" over that. I think 10 times more is a good choice. 100 watts for the peaks. Thats + 10 dB of headroom.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Calculating PT headroom in PP class AB Salas Tubes / Valves 12 14th March 2007 10:56 PM
HeadRoom AirBag, black DLJunkie Swap Meet 0 14th January 2007 11:04 PM
Driver stage headroom Klimon Tubes / Valves 6 14th July 2006 04:44 PM
IP headroom with LTP splitter ray_moth Tubes / Valves 8 27th April 2005 03:04 PM
What is Dynamic Headroom? keyser Solid State 3 17th February 2005 07:41 PM


New To Site? Need Help?

All times are GMT. The time now is 02:24 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2