How to ruin a perfectly good alephX - 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 August 2003, 03:24 PM   #1
grataku is offline grataku  United States
diyAudio Member
 
Join Date: Dec 2000
Location: -
Default How to ruin a perfectly good alephX

In short:
add input capacitors.

The long story:
after getting the differential probe I readjusted the AC current gain which was kind of off and I got an additional 3 volts RMS out of the amp.
This was all dandy until I pugged the amp into the speakers at which point the DC offset at the speaker was no longer 15mV like I measured it before, but 200 mV. I always use a cap in the input when testing the amp since I never bothered measuring the DC offset of the oscillator. I wasn't worried because earlier in the system with preamp and speakers only a modest 10mV increased was produced. So I figured input caps don't matter.

So a couple of days ago I got a batch of 4.7 N type BG and I put them in. While DC is back under control, the whole tonal balance of the amp is changed for the worse, and it now sounds flat, ie the harmonic content of the instruments is gone (well, gone enough).

I am now reevaluating the whole need for AC current gain...
  Reply With Quote
Old 2nd August 2003, 06:53 PM   #2
diyAudio Member
 
Join Date: Dec 2002
Location: Poland
Hi,
Did you read this?
http://www.diyaudio.com/forums/showt...519#post105519
__________________
Jarek
  Reply With Quote
Old 2nd August 2003, 07:11 PM   #3
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Send a message via AIM to Peter Daniel
Default How to ruin a perfectly good alephX

I still can't figure out if you complaining about caps or active current gain?
__________________
www.audiosector.com
“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
  Reply With Quote
Old 2nd August 2003, 08:32 PM   #4
grataku is offline grataku  United States
diyAudio Member
 
Join Date: Dec 2000
Location: -
Default Re: How to ruin a perfectly good alephX

Quote:
Originally posted by Peter Daniel
I still can't figure out if you complaining about caps or active current gain?
As a result of my "adjusting" the current gain I run into this DC offset problem, but the caps screwed up the sound so I guess it's a little bit of both.

Jarek,
I don't think manifacturers are smart enough to be able to do what Jcarr claims they are doing (artificially coloring the sound of audiophile parts)
  Reply With Quote
Old 2nd August 2003, 08:41 PM   #5
Netlist is offline Netlist  Belgium
diyAudio Moderator Emeritus
 
Netlist's Avatar
 
Join Date: Jan 2003
Default Re: How to ruin a perfectly good alephX

Quote:
Originally posted by grataku

after getting the differential probe I readjusted the AC current gain which was kind of off and I got an additional 3 volts RMS out of the amp.
Do you mean R12/R34 in Grey's schematic?
I took out the input caps in my 'final' version, readjusted DC and all is fine now and sounds good to me.

/Hugo
  Reply With Quote
Old 2nd August 2003, 09:52 PM   #6
diyAudio Member
 
Join Date: Dec 2002
Location: Poland
Grataku,
About two weeks ago I changed one of the filtering caps on my PSU from 10 000uF to 20 000uF. It was a shock for my AX and the sound went worse, no musicality etc. After one week, things started going better and after another week I observed first signs of the musicality . Sound is still changing.
You did two significant things with your AX. Changing the current gain, you changed needs of the current in your amp and the PSU must adapt to that. New caps at the input also have big influence on whole amplifier performance. I think, you must be patient and verify your observations after running amp some time.
I know, that what I say is very controversial, but my experiences are just like that.
__________________
Jarek
  Reply With Quote
Old 2nd August 2003, 10:28 PM   #7
diyAudio Member
 
dshortt9's Avatar
 
Join Date: Apr 2001
Location: Milwaukee, Wisconsin
Be patient, caps take time to break in. I have replaced caps in electronic equipment and they do sound flat for a while. BG in particular can take 10's of hours to break in.
  Reply With Quote
Old 3rd August 2003, 02:30 AM   #8
grataku is offline grataku  United States
diyAudio Member
 
Join Date: Dec 2000
Location: -
Default Re: Re: How to ruin a perfectly good alephX

Quote:
Originally posted by Netlist

Do you mean R12/R34 in Grey's schematic?
I took out the input caps in my 'final' version, readjusted DC and all is fine now and sounds good to me.

/Hugo

Yep, things are ok in terms of DC on the bench as soon as the pre amp and speakers are put in the offset jumps up to 200mV and over. This is with absolute and relative DC offset adjusted to 0 after the amp is at steady state temperature.

Let's hope this flatness comes from BG break in.
  Reply With Quote
Old 3rd August 2003, 05:37 AM   #9
diyAudio Member
 
macka's Avatar
 
Join Date: Dec 2001
Location: Australia
Grataku,

I think I understand what you are saying, but something else could be wrong or out of wack here.

Previously you ran the pre amp direct (without capacitors) to your X Aleph with only 10mv offset?

You have only tweeked the AC current gain, so both sides of the amp have the same AC current right (ie same value for R 20 & R9 or R12 & R34 depending on the schematic).

If this is the case then only VR1 for the CCS of the input pair needs to be tweeked for near zero DC offset. There should be sufficient range if the actual DC bias is also balanced on each side, you may need to reset this also after tweeking the AC current gain and then check the ac current gain for close to 50%.

However, it depends on the conditions under which you calibrate the amp for 50/50 AC current gain and DC offset.

When I set up my AC current gain I fed the ocsillator via the pre amp to get a true balanced input to the X Aleph. The BOSOZ with active ccs is capacitor coupled with BG's, so there is no dc bleed to the X Aleph.

I tweek the AC current gain in this condition and the DC offest to simulate actual operatiing conditions (ie with a 8 ohm load).

So I cannot see why the BG's are necessary when they were not there previously for 10 mv offset?

It is also possible that if the BG's are not a perfect match then the balance of each side of the amp will be uneven. I think Peter Daniel raised this in another thread.

Perhaps try without the caps (bypass them) to realign the current gain and offset and see what happens. Besides 200mv although a little high is not too bad for the price of good sound, anything inder 100mv is for this type of amp is very good.

Hope this helps,

Macka
  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
Will it ruin the great sound I have? Marsh Subwoofers 27 27th June 2007 07:04 PM
not audio- why do sportscasters ruin the suspense? lgreen The Lounge 6 13th October 2005 06:47 AM
A perfectly nice budget high-end hi-fi... mjarve Everything Else 4 16th August 2004 03:21 PM


New To Site? Need Help?

All times are GMT. The time now is 08:09 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