aleph 30 project - 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 2nd April 2011, 11:06 AM   #21
diyAudio Member
 
Join Date: Dec 2010
Location: Melbourne
Zen Mod, Bill, thanks for taking time to help with this!

Cheers,

Boris
  Reply With Quote
Old 20th April 2011, 10:23 AM   #22
fulvio is offline fulvio  Italy
diyAudio Member
 
Join Date: Jun 2006
Location: Trieste, Italy
Hi, I’ve finished to build an Aleph 30 some days ago; the main differences respect the original Pass schematic are the power devices I used (IRFP350 instead of IRFP240) and the source resistance of the power devices (0.6 ohm instead 0.47).
The power supply is 24.0 volts, and the biasing is 1.5 A (0.5 per mosfet); AC current gain is near 50%.
I experienced the same behavior of dslsa666 Aleph, that is a clean clipping at about 16 Vrms at 1 KHz, but a bad waveform distortion at higher frequency, beginning over 13.5 Vrms at 10 KHz.
The distorted waveform is exactly the same as the ones in the dslsa666 post (a notch just before the top of the positive peak), so I don’t attach any picture.
I used a 8 ohm load but the I noticed that the distortion remains the same also without load (output open circuit), so I don’t believe it is a current problem; in any case I tried to increase the bias and modify the AC current gain, but without a real improving in the waveform.
The only change that seems “positive” is to increase the capacitor across the feedback resistor (C104 in the 1994 Nelson Pass drawing of Aleph 30, initial value 10 pF) but this produces a roll-off in the frequency response; more over this roll-off can reduce CMRR when the amp is used with balanced input.
Maybe the notch in the waveform is the beginning of a high frequency parassitic oscillation?
With a 43 pF (10 + 33) capacitance value, the loss at 20 KHz is about 1 dB; I measured the following THD values:

C104= 10 pF

1 KHz 15Vrms THD = -48 dB
14Vrms THD = -54 dB
13Vrms THD = -56 dB

10 KHz 15Vrms THD = too high
14Vrms THD = -36 dB
13Vrms THD = - 44 dB

C104= 43 pF

1 KHz 15Vrms THD = - 47 dB
14Vrms THD = - 52 dB
13Vrms THD = - 55 dB

10 KHz 15Vrms THD = too high
14Vrms THD = - 41 dB
13Vrms THD = - 47 dB

Please note that THD is measured in the band 0 – 600 KHZ so it could be higher than THD in audible range 20Hz - 20 KHz, especially for 10 KHz fundamental.
In the next days I’ll do more measurements, picking up the single harmonic level.
A funny thing: making distortion measurement, I noticed that THD value sometimes showed fluctuations of 3 or more dB; at the end I realized that it was a consequence of the mains voltage fluctuations that, in turn, caused fluctuations of the DC power supply voltage: when you work near clipping, also little variations of supply voltage are significant.
  Reply With Quote
Old 13th June 2012, 02:50 AM   #23
nrg2009 is offline nrg2009  United States
diyAudio Member
 
Join Date: Apr 2009
Location: Detroit, born and raised in the netherlands.
Any more information on this? I am about to start my build with the same boards..
Does anyone have a stuffing guide or other documentation?
  Reply With Quote
Old 15th June 2012, 02:40 AM   #24
diyAudio Member
 
Join Date: Feb 2012
Location: Stad Gemeente Batavia
hi everyone,
i need to add a passive volume pots for my aleph 30 in balanced way.
i am planning to use 10k 24step attenuator pots like this one :

Click the image to open in full size.

my question is:
how to use this attenuator in dual channel balanced
using only one attenuator like the picture.

thanks.
visit my blog here

Last edited by wengtech; 15th June 2012 at 02:46 AM.
  Reply With Quote
Old 15th June 2012, 05:47 AM   #25
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
you have an answer in your thread
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  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
X Aleph Project Down Under macka Pass Labs 111 30th June 2008 01:55 PM
Aleph 2 project Thago Pass Labs 2 21st April 2007 07:44 AM
need enclosures for your aleph project ? jrsun Pass Labs 2 19th February 2004 01:34 PM
My aleph 2 project Jean Pass Labs 13 21st January 2004 07:14 AM
Aleph 2 (& others) as a project GRollins Pass Labs 41 11th February 2002 12:05 AM


New To Site? Need Help?

All times are GMT. The time now is 08:02 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