Aleph 5 bias diferential - 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 January 2010, 03:02 PM   #1
john65b is offline john65b  United States
diyAudio Member
 
john65b's Avatar
 
Join Date: Jan 2005
Location: Chicago
Default Aleph 5 bias diferential

Hey all,

I had quite a bit of "room" in my heat sinks, so I decided to remove R19. All biased up from .618 to .650 on the same emitter resistor (.91ohm 3 watt emitter resistors)...all good.

For S&G, I decided to check the other bias voltages on the same OP PCB (Brian's boards). I noticed the middle MOSFET on all OP PCBs had much higher bias than the top/bottom.

655/850mv/650mv

other channel,

649mv/880mv/650mv

Now I used a bar (securing the MOSFETs to heatsink) across all three MOSFETs and can see a slight bow over the center MOSFET...I am using pads too.

Could this be the reason for center bias imbalance across the output PCB?

I plan on replacing the bar with a thicker bar ASAP - I just hate drilling taps into heatsinks as I always break the taps off (I know Peter Daniels has a tried and true method of using a clutched drill to tap into sinks)

This problem most likely was there before I removed R19, but never realized it until I checked it...

Seems an obvious solution, but wanted to ask the pros. I have searched and found nothing much as far as a similar problem with heatsink mounting...
__________________
All right, but apart from the sanitation, medicine, education, wine, public order, irrigation, roads, the fresh water system and public health, what have the Romans ever done for us? Life of Brian
  Reply With Quote
Old 2nd January 2010, 03:47 PM   #2
john65b is offline john65b  United States
diyAudio Member
 
john65b's Avatar
 
Join Date: Jan 2005
Location: Chicago
Oh, and all output devises were matched from Tech-DIY...

And I am using T-Pli 240 Insulators:

http://lairdtech.thomasnet.com/item/...=10&assetid=g2
__________________
All right, but apart from the sanitation, medicine, education, wine, public order, irrigation, roads, the fresh water system and public health, what have the Romans ever done for us? Life of Brian

Last edited by john65b; 2nd January 2010 at 04:00 PM.
  Reply With Quote
Old 2nd January 2010, 07:34 PM   #3
john65b is offline john65b  United States
diyAudio Member
 
john65b's Avatar
 
Join Date: Jan 2005
Location: Chicago
Well I changed the bar to a thicker one and all tracks cleanly at 750mv (+/-2mv) across the emitter resistors on one side and 730mv (+/-3mv) across the emitter resistors on the other side...all good.

Heat sinks still nice and toasty and 111F. I will allow the amp to warm up an hour or so.

I had put a 75C switch too close to one MOSFET and was wondering why the amp was shutting down. Sure enough the temp at the center MOSFET was 78C when not fully attached to the sink...
__________________
All right, but apart from the sanitation, medicine, education, wine, public order, irrigation, roads, the fresh water system and public health, what have the Romans ever done for us? Life of Brian
  Reply With Quote
Old 3rd January 2010, 01:44 AM   #4
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Even when the pressure is the same, the one in the middle
tends to be warmer.

  Reply With Quote
Old 3rd January 2010, 02:23 AM   #5
john65b is offline john65b  United States
diyAudio Member
 
john65b's Avatar
 
Join Date: Jan 2005
Location: Chicago
Thanks for your reply Nelson...

When the middle MOSFET is a bit warmer (in my case - carrying more of the current load), is the sound quality compromised?
__________________
All right, but apart from the sanitation, medicine, education, wine, public order, irrigation, roads, the fresh water system and public health, what have the Romans ever done for us? Life of Brian
  Reply With Quote
Old 3rd January 2010, 04:26 PM   #6
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
I don't think so.

  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
aleph x CCS curent for diferential input elviukai Pass Labs 14 10th November 2006 09:05 PM
input output diferential in LM317 Pablo Analogue Source 4 15th June 2004 05:26 AM
double vs diferential Praise! Solid State 11 7th November 2003 02:31 PM
Aleph 5 bias billy Pass Labs 8 11th April 2003 02:35 PM
aleph bias, ... janey Pass Labs 3 10th June 2002 01:40 PM


New To Site? Need Help?

All times are GMT. The time now is 01:32 PM.


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