Yet another Aleph3 question - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 18th July 2005, 08:59 AM   #1
Kanawat is offline Kanawat  Thailand
diyAudio Member
Join Date: Mar 2005
Location: Bangkok, Thailand
Default Yet another Aleph3 question

Hi, I'm a newbie in this forum. In fact I just finished building a pair of Aleph 3 mono block, thanks to you all .. I really get a lot of insight in building an amplifier from this forum. The amp sounds really great ... until ... I decided to stack my DIY A3 up against my uncle original Aleph 3 from Pass Labs. Overall sound quality is almost identical except that my A3 has a little more pronouced high/ more treble. It can get to the point when I feel uncomfortable after listening to it for a while.

I used IRFP244s as the active current source and the output stage. I reduced the source resistor of the active current source to get about 2.4 amps bias. A little higher than then spec which helps reduce the problem a little bit. But I don't think this is the right way to go.

Does anybody experience the same problem as I am?
  Reply With Quote
Old 18th July 2005, 09:51 PM   #2
The one and only
Nelson Pass's Avatar
Join Date: Mar 2001
If the AC current gain ratio of the current is much higher than
50%, then this will result in sonic degradation. Also, as the
open loop gain is increased, you again get degradation. Lowering
the value of the Source resistances will get you both, and you
may need to check the ratio of current supplied by the current
source against the output current, and perhaps take a look at
the square wave with a scope. While you're at it, look for

  Reply With Quote
Old 20th July 2005, 01:29 AM   #3
Kanawat is offline Kanawat  Thailand
diyAudio Member
Join Date: Mar 2005
Location: Bangkok, Thailand
Thank you Mr.Pass!! I was under the impression that pumping more bias will make the device more linear without knowing the downside of it.

Could you please describe more about the sonic degradation you've mentioned? Will I be able to observe it in the output waveform? either in time/frequency domain?
  Reply With Quote
Old 20th July 2005, 01:53 AM   #4
The one and only
Nelson Pass's Avatar
Join Date: Mar 2001
Pumping more DC bias will make the devices more linear, but
the Aleph current source has a constant DC component upon
which is overlayed an AC component which is an arbitrary
percentage of the output current, anywhere from 0% (CCS)
to close to 100%. As a practical matter, greatest efficiency is
seen at about 50% if you want to always remain in Class A
up to voltage clipping. As you increase this percentage, the
performance measures better at the lower levels and less well
somewhere below clipping, where the current source starts
shutting down. There is also a character that creeps in at high
gain settings which is not preferred, so the general
recommendation is around 50% or less.

In actual testing, I have listeners tending to prefer figures of
40% over 50%, and 40% over 30%, so it looks like the sweet
spot is maybe the 40% range. This does vary from version to
version and depends a lot on the taste of the listener, so I
don't spend a lot of time worrying about the absolutes.

  Reply With Quote


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
Aleph3:one more question sherwood Pass Labs 1 2nd November 2004 12:17 PM
aleph3, 30 and 5 kslim Pass Labs 1 9th September 2004 01:58 AM
Question - Heatsink for Aleph3 vsr123 Pass Labs 1 26th March 2003 10:07 AM
Aleph3 biasing question victor Pass Labs 6 28th March 2002 04:46 PM
Aleph3 PSU victor Pass Labs 3 20th August 2001 11:42 AM

New To Site? Need Help?

All times are GMT. The time now is 11:33 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2