How to set AC current gain in Aleph-X ? - 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 22nd August 2004, 10:00 AM   #1
yoke is offline yoke  Croatia
diyAudio Member
 
yoke's Avatar
 
Join Date: Jan 2004
Location: Split
Default How to set AC current gain in Aleph-X ?

Nead help how to set AC current gain in Aleph-X ?

I have put together one channel of Aleph-X…but have some question…I try to find answer by searching, but no luck…to many posts…

Any way…

I have connect PC in input and play some sine wave of 100Hz and this is what I measure

R5=0,5 Ohm V=0,0064
R2,R3=0,22 Ohm V=0,008

So this gives me by this formula ;

0.05V / ( 0.22 / 2 ) = 0.45A
0.05V / 0.22 = 0.227A
(1 - (0.227 / 0.45)) * 100 = 50%

0,008 / ( 0,22 / 2 ) = 0,0727
0,0064 / ( 0,5 / 2 ) = 0,0256
( 1 – ( 0,0256 / 0,0727 )) = 64.8%

Now, I have solder already R12=1,2 Kohm...But If I replace it with 1,5K pot , will it give me enough room to trim this to 50% ?

Or is there some thing else I can do ???
What if I add some other resistors, other value, in parallel with R2,R3, how do you calculate it then ???


Thanks
Josip
  Reply With Quote
Old 22nd August 2004, 08:33 PM   #2
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
There's a ton of postings on this issue, many by me. It's the
same as an Aleph. Rather than me trying to recapitulate them,
try a search.
  Reply With Quote
Old 23rd August 2004, 07:09 AM   #3
D3 is offline D3  England
diyAudio Member
 
D3's Avatar
 
Join Date: Nov 2003
Location: bolton
Default AC Current gain

Hi Yoke spotted your question..............please could you post any usefull links on this thread to help others..................

Cheers
  Reply With Quote
Old 23rd August 2004, 07:21 AM   #4
yoke is offline yoke  Croatia
diyAudio Member
 
yoke's Avatar
 
Join Date: Jan 2004
Location: Split
Thanks Mr. Pass for the answer, last night I spend some time reading and trying to find something, at the and I get sleepy and give up...
So I have tried again today


O.K.
I have found this but it's different method then describe on Wiki Aleph-X tread...

Wrote by Mr. Nelson Pass

You will note in the Aleph schematics that the Base of the NPN
transistor which controls the current source attaches to the
output of the amplifier through an RC network. The value for
C is set arbitrarily high so that it does not interfere with audio
frequencies, and it is the value of R which is the most convenient
spot to adjust the gain of the current source. For the purpose
of this discussion, I'll call it R0.

If you set the amplifier driving a sine wave into a load (let's say
16 Vrms into 8 ohms at 100 Hz), you can measure the current
variation of the gain N channel Mosfets (whose Sources attach
through power resistors to the - supply rail) with a cheap AC
voltmeter placed across one of these Source resistors. With
R0 taken out of the circuit, you will get one AC value across the
Source resistor (say 470 mV, for example). As you put a value
for R0 in the circuit, this will decline, and when it measures 1/2
the value without R0, you have reached 50%. If it measures
1/4 the value, the current gain of the Aleph source is 75%, and
this figure is too high for a standard Aleph. Most listeners like
the Alephs at 50% or lower, so I recommend between 50% and
100% of the AC voltage value compared with no R0.


So in Aleph-X revision V1 ;

R0 would be R12...so I pull out ( disolder ) R12 and measure voltage on R5 ( source resistor )...then place pot in a place of R12 and trim it until I get 50% of the value, I get without pot in place of R12, again on R5 ( lets say voltage on R5 was 0.5V I trim R12 ( R0 ) until I get 0.25V on R5 ) ...replace pot with resistor...

Is this correct ???
Will I damage amplifier if I don’t have R12 in place ???
  Reply With Quote
Old 23rd August 2004, 11:25 AM   #5
ljozsef is offline ljozsef  Hungary
diyAudio Member
 
Join Date: Apr 2003
Location: Budapest
Default Yes, Yoke,

Basically, for 50% it were correctly described.
However, be careful: Nelson's explanation was I think for measuring the R6 voltage. At 50% the values are identical on the R5, too, only for different tuning have care.

But another question:
Nelson mentions sine waves - would it be with square waves possible, too (scope calibrating signal), supposing that measurements are made with a true-RMS meter? I did it in that manner, and the A-X sounds marvellous (despite of the failing NFB 5-10 pFcapacitors and grounding output resistors). I don't know if there were paras. oscillations, but the absolut offset w/o resistors remains under 0.5 V, hot 0.15 V. Diff. offset 8 mV.
May I ignore them?

Have success, Yoke!
Laci
  Reply With Quote
Old 24th August 2004, 04:38 PM   #6
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Default Re: Yes, Yoke,

Quote:
Originally posted by ljozsef
Nelson mentions sine waves - would it be with square waves possible, too (scope calibrating signal), supposing that measurements are made with a true-RMS meter?

I don't know if there were paras. oscillations, but the absolut offset w/o resistors remains under 0.5 V, hot 0.15 V. Diff. offset 8 mV.
Any wave you like is fine with me.

Your DC offset figures are just fine, better than average.

  Reply With Quote
Old 25th August 2004, 11:24 AM   #7
yoke is offline yoke  Croatia
diyAudio Member
 
yoke's Avatar
 
Join Date: Jan 2004
Location: Split
Here I’ am again...
First I would like to say thanks to everyone who help me with their answers, not only here but on AX builders tread to...

Now…I have replace R12 with 2,5Kohm trim pot. But I was not able to set current gain to 50%...
I have disolder R12 and play 100Hz sine wave…voltage on R6 was 20.9mV…I try to trim R12 to get 10.5mV but only could get to something like 16.4mV…Resistance on trim pot was around 2K…If I rise or drop resistance, voltage on R6 starts to rise…

So, what else I can do ???

  Reply With Quote
Old 25th August 2004, 11:36 AM   #8
D3 is offline D3  England
diyAudio Member
 
D3's Avatar
 
Join Date: Nov 2003
Location: bolton
Default Sine Wave

Hi Yoke............what...are you using to generate sine wave????
  Reply With Quote
Old 25th August 2004, 11:42 AM   #9
yoke is offline yoke  Croatia
diyAudio Member
 
yoke's Avatar
 
Join Date: Jan 2004
Location: Split
Now when you mention it...I am wondering am I doing it right ?!?...but I think this is correct...
I am using signal generator from WinISD...I play it on PC and connect it to preamp then to amp...
  Reply With Quote
Old 25th August 2004, 12:19 PM   #10
yoke is offline yoke  Croatia
diyAudio Member
 
yoke's Avatar
 
Join Date: Jan 2004
Location: Split
Can I replace R2,3 which are 0,22Ohm with 0,44 ( 0,22+0,22 )...would that help ???
  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 AC current gain made easy darian Pass Labs 8 13th September 2007 05:52 PM
The effect of the ac current gain in Aleph Peter Daniel Pass Labs 20 8th February 2003 03:16 PM
Aleph current gain and transconductance Mad_K Pass Labs 5 30th January 2003 04:28 PM
R21? and Current Source AC Current Gain macka Pass Labs 9 20th May 2002 08:58 PM


New To Site? Need Help?

All times are GMT. The time now is 11:28 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