Adjusting Aleph 3 Gain Level - 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 29th January 2005, 10:22 PM   #1
diyAudio Member
 
Join Date: Sep 2001
Location: Salt Lake City
Default Adjusting Aleph 3 Gain Level

What is the formula for calculating the gain of the Aleph 3? I built a 3 for a friend and he complains that just cracking his attenuator open on his grounded grid is too much. His Ascend Acoustics speakers are 91db sensitivity and the Grounded Grid has 12 db of gain. It would be easiest for us to lower the gain of the Aleph 3 for now. He will be replacing the Asccends with Proac 2.5 clones and we will probably restore the 3 to normal.

Thanks!

Mark
  Reply With Quote
Old 29th January 2005, 11:16 PM   #2
diyAudio Member
 
Join Date: Feb 2001
Location: Columbia, SC
Honestly...I think I would check the volume pot on his preamp. Did he use a linear pot? If so, that will give you all your gain in the first quarter-turn. The solution might be as simple as a law-faking resistor across the volume pot.
The Alephs are, if anything, less sensitive than other amps. An average amp has about 26dB gain. The Alephs have 20dB, so you're starting off with a 6dB deficit. Any system that gets too loud, too quickly with a regular Aleph should be examined further upstream.

Grey
  Reply With Quote
Old 30th January 2005, 01:33 AM   #3
cowanrg is offline cowanrg  United States
diyAudio Member
 
cowanrg's Avatar
 
Join Date: Apr 2002
Location: Lafayette, CO
Send a message via AIM to cowanrg
yeah, my alephs had a gain issue, but even with only 20dB gain, they worked "ok" on my 84dB sensitive speakers, just a BIT quieter than normal.... so there is a problem elsewhere.
  Reply With Quote
Old 30th January 2005, 04:03 PM   #4
MikeW is offline MikeW  United States
diyAudio Member
 
MikeW's Avatar
 
Join Date: Sep 2002
Location: North of Boston
Default 20 Log( feedback res/ground res)

This should give you a good idea of the voltage gain. If most Alephs unbalanced 20log(100k/10k)= 20 db gain. If the unbalanced input is grouned it is 20log(100k/5k)= 26db gain. If you want more gain, increase the feedback res or decrease the ground res. These amps are very stable, but if you have the gain to high you may run into some oscillations. I blew up a speaker yesterday working on my Aleph 3.
__________________
MikeW
  Reply With Quote
Old 30th January 2005, 04:34 PM   #5
Account Disabled
 
Join Date: Aug 2002
Location: Near to the Pacific Ocean
Do you mean 10K/1k in case of Aleph 3?
  Reply With Quote
Old 30th January 2005, 05:22 PM   #6
diyAudio Member
 
Join Date: Sep 2001
Location: Salt Lake City
His attenuator is a log type unit as built from the specs page at Goldpoint. The only difference is that his is built out of a blank Daven attenuator switch. Its a 50k series type and pretty standard stuff. I agree with him and have been to his place.... the gain does seem to be a bit too much. The 12 db gain afforded by the GG is not very much either and pretty standard.

Just a thought but perhaps he should skip using the GG tiill the Proac 2.5 Clones are done and with their much lower sensitivity he will probably need the GG back in there.....

Thanks Mike W. for that formula!

Mark
  Reply With Quote
Old 31st January 2005, 12:01 AM   #7
diyAudio Member
 
Join Date: Sep 2001
Location: Salt Lake City
One thing I've noticed is that most of the Alephs... the 2, 4 and 5 use a 100K and 10K resistor in the feedback loop whilst the 3 uses a 10K and 1K in the feedback loop to set gain. Why is this?

Mark
  Reply With Quote
Old 31st January 2005, 03:22 AM   #8
diyAudio Member
 
Join Date: Sep 2001
Location: Salt Lake City
My friend brought his Aleph 3 amp over tonight and we compared it to(listening) my pair of Aleph 2s, the gain is definately ALOT higher. Will actually measure it tommrrow and see what the actual difference is..... I've got to wonder what the heck is goung on here.....

Mark
  Reply With Quote
Old 31st January 2005, 03:25 AM   #9
Account Disabled
 
Join Date: Aug 2002
Location: Near to the Pacific Ocean
Quote:
Originally posted by Mark A. Gulbrandsen
Why is this?
The sizes of resistors seems to be arranged to get maximum effect for the following items:

1. Size of input resistor
2. Amp gain control
3. CMRR

I don't like to say, "must be," but "most probably."
  Reply With Quote
Old 31st January 2005, 04:27 AM   #10
diyAudio Member
 
Join Date: Feb 2001
Location: Columbia, SC
Check the feedback resistor values. This story has Something Is Wrong written all over it.

Grey
  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
Adjusting Discrete Class A buffer for gain? TheSeekerr Solid State 8 28th February 2008 07:53 PM
Line Level BSC Again, adjusting dB. kvk Multi-Way 2 27th February 2008 07:14 PM
adjusting current gain for Aleph30 necessary? h_a Pass Labs 15 17th February 2007 08:30 AM
adjusting gain? ThSpeakerDude88 Tubes / Valves 12 21st May 2006 11:20 PM
Potentiometer VS variable resistor for level adjusting Bricolo Everything Else 5 1st March 2003 01:31 AM


New To Site? Need Help?

All times are GMT. The time now is 01:42 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