Aleph 3, option to get less current temporarely - 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 18th September 2005, 08:39 AM   #1
rmgvs is offline rmgvs  Netherlands
diyAudio Member
 
Join Date: Apr 2001
Location: Netherlands
Default Aleph 3, option to get less current temporarely

I plan to build an Aleph 3. There has been a lot of discussion about the temperatures of heatsinks/reliability and total dissipation versus sound quality. Suppose that I do not need 30 Watts at all times. I have the same voltage rails (25 Volts) but wish that I can turn the amp to an idle current that corresponds with a decent output (soundwise) of 10-15 Watts. I guess an idle current of around 700 mA (instead of 1 A) per transistor should do the job? What resistor(s) value(s) should I change to do the job? Maybe some small switch can be built in the amp so that you can change the amp at will to a current of 1 A (normal 30 Watt operation) and 0.7 A. I guess the life expectancy of the amp will increase considerably?
  Reply With Quote
Old 18th September 2005, 11:05 AM   #2
diyAudio Member
 
wuffwaff's Avatar
 
Join Date: Aug 2001
Location: Ingolstadt Germany
Hi,

you can change R114 for different bias points. Just put a pot in here and set the two or more bias points you want. Measure the resistor values and put in a switch to change between values.
You must measure both channels cause the resistor values tend to be different in each channel because of transistor tollerances.

As long as dissipation per fet is below 30-35watts and cooling is sufficient the amp will life longer as is needed anyway so no use changing this from 20 to 40 or 60 years

William
__________________
een ooievaar is geen konijn want zijn oren zijn te klein!
  Reply With Quote
Old 18th September 2005, 08:45 PM   #3
diyAudio Member
 
Join Date: Feb 2001
Location: Columbia, SC
If you build a stock Aleph 3, the device dissipation is around 25W/device. With decent heatsinking, your output devices should last quite a long time. I've not heard of any consistent reliability problems with the Aleph 3--most problems arise because people do not use sufficient heatsink. When in doubt, buy more. MOSFETs will not die from being too cool, but they will surely perish from excess heat.

Grey
  Reply With Quote
Old 19th September 2005, 06:28 AM   #4
rmgvs is offline rmgvs  Netherlands
diyAudio Member
 
Join Date: Apr 2001
Location: Netherlands
Default R113 and pot

Thanks for reactions. So it is R113 in the circuit diagram of Aleph 3 that has to be changed. What would be the problem of using a pot permantly anyway? I guess in this place it will not degrade sound quality?

I understand that there is no problem when ample cooling is used. But as it often goes, I have a enclosure in mind that is nice and seems apt, with a temperature coefficient of 0,31 per side/channel. But I had not counted with the correction factor (around 1.33 I guess), so for 55 degrees I can only put away 70 Watts of heat.

Besides that, what is wrong with using some less idle current when you are not using it most of the time? Anybody has experimened with 700 or 800 mA per mosfet and want to tell about the sound differences with 1 Amp?

I do not understand the circuit in its single-ended class A nature. The amp can put 60 Watts into 4 Ohms. Normally a single-ended amp works only in class-A and cannot put more power into low impedances. Of course it has something to do with the special Pass-arrangement of the upper mosfets.

What would be the output capabilities into 8 and 4 Ohms using 700 mA per mosfet (1.4 Amps total) using +/- 25 V of DC?
  Reply With Quote
Old 19th September 2005, 02:03 PM   #5
diyAudio Member
 
wuffwaff's Avatar
 
Join Date: Aug 2001
Location: Ingolstadt Germany
Hi,

at 50% ac-current gain peak current would be 2.8A. So max power into 8Ohms is 30watts (voltage limited) and 16 watts into 4 Ohms.

You can use a pot all of the time

Even a single ended class A amp has a maximum output power defined by supply voltage and bias. This can be at 16 Ohms but also at 2 Ohms depending how you set them.

Lowering the bias will change the sound character. I would suggest to listen for yourself but in my case upping the bias gave a more relaxed sound with better ambient retrieval capabilities.

William
__________________
een ooievaar is geen konijn want zijn oren zijn te klein!
  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
Current mirror for the aleph? 3nity Pass Labs 11 8th August 2013 07:23 AM
bias current: Zen vs. Aleph Peter Huang Pass Labs 6 4th August 2003 05:39 AM
Aleph X option question CH2 Pass Labs 3 25th June 2003 01:51 PM
Aleph X bias current SteveG Pass Labs 7 25th July 2002 12:12 AM
Aleph Current Source Vince Maida Pass Labs 2 2nd April 2002 12:56 AM


New To Site? Need Help?

All times are GMT. The time now is 05:21 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