Aleph-X builder's thread. - Page 128 - 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 30th January 2007, 07:44 PM   #1271
Paper mache horn fabricator
diyAudio Member
 
carpenter's Avatar
 
Join Date: Mar 2002
Location: Oregon City, Oregon
Gaborbela, go to ebay and purchase a cheap variac. They're under a hundred dollars and worth every penny you spend for the peace of mind they give you!!!

You're writing makes you sound like you're in panic mode. If that's the case, then STOP. Rest your mind. Take a couple days off and gently mull over the schematics and the concepts that make the AX work. Go back to square one if you have to. Read as many post as you can in the AX threads.

Check your pcb for stray wire filaments, blobs of solder, etc. Do an unpowered check of the resistance of one side of the pcb against the other to see how well they match. Check one pcbs resistance readings against the other channel as well. Record these readings and then ponder.

John
__________________
I enjoy audio so much that I constructed a web site. I share my ideas at: www.inlowsound.com
  Reply With Quote
Old 30th January 2007, 07:49 PM   #1272
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Quote:
Originally posted by gaborbela
HI
I tested the offset between the ground and + it is over 5V .
Between the ground and the -2.7V .All these when the after a couple minutes when the amp is still cold .
No no longer possible to leave the power on to warm up the amp because the transformer start buzz very loud .
Now I'm going to remove the pc boards and look for possibility of mistakes .
If I find that good news , if not unfortunately that will be the end of the AX .
Regards

have you McMilan resistors in place?
__________________
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
Old 31st January 2007, 12:51 AM   #1273
diyAudio Member
 
Join Date: Dec 2003
Location: Victoria - Aus
Hi all,

I've been building a pair of aleph-x's over the past few weeks and have got a problem.

First off, I'm aiming for 40-50W into 8ohm, i got ~16V rails, 4A bias, 4 fets per amp, 2*12VAC transformer secondaries on a 300VA transformer for each amp with 100,000uF caps per rail which is all working very well. I've designed my own circuit board and chassis consisting of 2 large heatsinks that run both lengths of the case sides, see quick picture of it here

Powering up I can adjust the bias just fine and have 4.4v over the 0.22ohm source resistors, but then the problem I'm having is that I cannot fix the absolute DC offset with the 3rd pot, both sides measure ~ -15.5V for the entire travel of the pot. I've replaced the differential input and current source fets thinking it is probably them, which didn't help. All parts were hand matched very well

Is there anything I can measure to see what it could be?

Thanks,
Dan
  Reply With Quote
Old 31st January 2007, 03:59 AM   #1274
diyAudio Member
 
Join Date: May 2005
Location: austria, kottingbrunn
Hi Dan!

I got the same, and I found the Zener Diode of the input current source was installed in wrong direction.
But I hope you mean 0.44V over the 0.22ohm!

Robert
  Reply With Quote
Old 31st January 2007, 05:04 AM   #1275
diyAudio Member
 
Join Date: Dec 2003
Location: Victoria - Aus
Quote:
Originally posted by james watt
Hi Dan!

I got the same, and I found the Zener Diode of the input current source was installed in wrong direction.
But I hope you mean 0.44V over the 0.22ohm!

Robert
Yes, 0.44v

The zener is in the right way and has 8.8v across it while running
  Reply With Quote
Old 31st January 2007, 10:02 AM   #1276
diyAudio Member
 
wuffwaff's Avatar
 
Join Date: Aug 2001
Location: Ingolstadt Germany
Hi Dan,

-15.5 volt means the output fets are completely open. This means that the current through the current source is too high.
You can measure it by looking at the voltage over the drain resistors from the input fets.

Try to raise the value of the resistor parallel to the 3th pot and turn the pot to max resistance.
This should do the job.

William
__________________
een ooievaar is geen konijn want zijn oren zijn te klein!
  Reply With Quote
Old 31st January 2007, 06:31 PM   #1277
diyAudio Member
 
hifimaker's Avatar
 
Join Date: Oct 2003
Location: San Jose
I'm llloking for help understanding what the McMilan resistors are and how they are used. The search feature has been frustrating in this regard.

Could someone kindly point me to a link that explains what McMilan resistors are and how they improve DC offset?

Thank you!

-David
  Reply With Quote
Old 31st January 2007, 06:42 PM   #1278
gl is offline gl  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Sierra Foothills - California
Hi David,

It's all in the wiki. Look for R46 and R47 in hifizen's schematic. Also look in the "Other stuff from the big thread" section in the wiki.

Graeme
  Reply With Quote
Old 31st January 2007, 06:42 PM   #1279
diyAudio Member
 
wuffwaff's Avatar
 
Join Date: Aug 2001
Location: Ingolstadt Germany
Hi David,

the McMillan´s:

they are connected between the outputs (+ and -) and the sources of the input diff pair (R46 R47)
they are between 2k2 and about 10k
they form a feedback loop

suppose the outputs absolute output becomes positive. Now the current through the diff pair will become higher and the voltage over the drain resistors (R23 / R25) becomes higher.

Now the output fets will open up a bit (Rds gets lower) and the dc voltage at the output becomes lower.

It works the same way the other way round.

I tried different R´s starting from 2k7 and ending up with 10k. The higher the value is the better the sound quality will be and the higher the absolute dc startup value.

hope this simplistic explanation helps,

William
__________________
een ooievaar is geen konijn want zijn oren zijn te klein!
  Reply With Quote
Old 1st February 2007, 11:11 PM   #1280
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default toroidal

It seems everyone uses a toroidal power transformer for the Aleph x
My intention is not to start a debate between EI and toroidal but simply what are the advantages besides low EMI.
Also it seems I am having a difficult time finding a suitable toroidal
I need 300va @ 12-0-12. I know of victoria Magnetics, are there any other good suppliers ?


J
__________________
"If every one is making wheels , why make wheels ? " Steve Jobs
  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



New To Site? Need Help?

All times are GMT. The time now is 01:11 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