High Distortion on Aleph 5 - 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 9th March 2007, 04:16 PM   #1
Jaac is offline Jaac  Netherlands
diyAudio Member
 
Jaac's Avatar
 
Join Date: Oct 2002
Location: Laren NH
Default High Distortion on Aleph 5

Hello,

i have a question about the distortion of mine aleph 5. I've been working on the amp for a couple of years now slow but i finely am in the final stage,....i hope.
Last night i was at the lab of a colleague of mine and we've tested one of my mono aleph 5. And came to the conclusion that there is a nasty distortion when we are putting more like 21,1 Watt (13 V in 8 Ohm ) and that looks like this:

Click the image to open in full size.

It's about 0,025 % THD at 400Hz (nakamichi t-100)

At this point the distortion is building up to te point that the output is visable clipping at around 78 Watt ( 25 V in 8 Ohm ) then it looks like this:

Click the image to open in full size.

And another picture at 15 volts into 8 ohm where you can see the sharp edge of the distortion and that flank is at almost the bottom of the sine.
Click the image to open in full size.
We tried finding out the problem here and i've searched the forum for a solution. i find that there is maybe a problem with R17 the 4,75K resistor in a thread for the aleph 30

aleph 30 thread

because i'm using a 2x30 volt tranny that gives about 38 40 Volt DC. is that maybe the problem that i have to change the R17 to a higer resistance ???

Here are some more pictures about my amp

Click the image to open in full size.

Click the image to open in full size.
__________________
The right tool for the right job, a very nice Solarboat || Ready for a groupbuy ? CLick
  Reply With Quote
Old 9th March 2007, 04:39 PM   #2
Netlist is offline Netlist  Belgium
diyAudio Moderator Emeritus
 
Netlist's Avatar
 
Join Date: Jan 2003
Very nice amps.
If I understand you correctly, you have about 0.025% distortion at 21.1Watt and the amp clips grossly at 78Watt.
Looking at the specs of the stock unit, the amp is only capable of giving 60 Watt and a distortion of 0.025% is about the lowest I've seen in the Pass Labs forum.
If this is correct, your amps are fine.
What's the distortion at say 55Watt?

/Hugo
  Reply With Quote
Old 9th March 2007, 04:54 PM   #3
Jaac is offline Jaac  Netherlands
diyAudio Member
 
Jaac's Avatar
 
Join Date: Oct 2002
Location: Laren NH
hhhmm oke butt the kind of distortion is not normal i think the sharp edges on it are in my eyes some what hard. for THD at 55 Watt i most make a visit to my friend whit the right measure equipment.

or maybe i wrote the wrong numbers down while my friend was calling them ?? I was late last night so that could happen but the nasty distortion remains
__________________
The right tool for the right job, a very nice Solarboat || Ready for a groupbuy ? CLick
  Reply With Quote
Old 9th March 2007, 05:34 PM   #4
steenoe is offline steenoe  Denmark
diyAudio Member
 
steenoe's Avatar
 
Join Date: Mar 2004
Sorry to tell, but I made an Aleph5 with stock components. The amp just played sweet music!! I think you made a mistake, some where?? Please, check out all your components!

Steen
  Reply With Quote
Old 9th March 2007, 07:11 PM   #5
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
I would say that your bias is running low and/or the current gain
of the current source is too high. The distortion you see is the
current source shutting off on negative current swing.

For optimal performance you want to confirm that the positive
current source doesn't contribute more than 50% of the
current (this need not be an exact figure) and then that the
bias current is greater than 1/2 the current expected into the
load with any particular waveform. For a 50 watt amp, I expect
this to be about 1.8 amps.

  Reply With Quote
Old 9th March 2007, 08:16 PM   #6
Jaac is offline Jaac  Netherlands
diyAudio Member
 
Jaac's Avatar
 
Join Date: Oct 2002
Location: Laren NH
Oke so i think that R21 the 453 ohm comes quite precieze ? i think i put an other value for that becuase i hadden't had the correct one around

i'll try it and for now thank u !!!
__________________
The right tool for the right job, a very nice Solarboat || Ready for a groupbuy ? CLick
  Reply With Quote
Old 12th March 2007, 08:34 PM   #7
diyAudio Member
 
wuffwaff's Avatar
 
Join Date: Aug 2001
Location: Ingolstadt Germany
Hi,

the 453R are quite precise but only for one special amp.

The best way to get it right is to measure ac-current-gain with a pot replacing R21. If you have set it to 50% you can measure the pot and replace it with a resistor (or leave it in).

In my Aleph5 klone the following Rs where measured (at 2,1A bias):

left channel:

66,2% 390R
55,6% 470R
47,0% 560R

right channel:

67,1% 390R
56,3% 470R
47,6% 560R

I drew a graph with excel and found 525R / 540R for the left and right channel.
Eventually I put in 500R in the left and right channel......

William
__________________
een ooievaar is geen konijn want zijn oren zijn te klein!
  Reply With Quote
Old 12th March 2007, 09:35 PM   #8
Jaac is offline Jaac  Netherlands
diyAudio Member
 
Jaac's Avatar
 
Join Date: Oct 2002
Location: Laren NH
Ok

yesterday i tried a 453R resistor at R21. It liked that the level at witch the distortion began is raised to 16V into 8 ohm. So we can say its a AC Current Gain issue.

But to avoid any confusion about AC current gain you must explain me how i can measure that. maybe just explain in clear words where AC current gain stands for.
Most i measure/calculate the input current and measure/calculate the output current ??
In my eye's gain is a number not a percentage ???? because of the English I'm a bit confused.
When i know how to get the ac current gain then I can do the same as you William and calculate the exact value for R21 and place a nice dale resistor there and enjoy a bit of music..... or start building me another Pass amp !!
__________________
The right tool for the right job, a very nice Solarboat || Ready for a groupbuy ? CLick
  Reply With Quote
Old 12th March 2007, 11:33 PM   #9
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Somewhere on this forum I have posted a detailed procedure
for measuring and setting the ratios, maybe some good
Samaritan will point you to it.

But you have a distortion analyzer! I suggest you put a pot
there and trim the value until you're happy.

  Reply With Quote
Old 13th March 2007, 08:24 AM   #10
Jaac is offline Jaac  Netherlands
diyAudio Member
 
Jaac's Avatar
 
Join Date: Oct 2002
Location: Laren NH
Oke i was bad on the searching part.

Now i know it and here is a link to the correct thread

Proper Current Source Adjustment

and as attachment the qoute of mr Pass.

i will do the measurement later this week maybe after i complete the other channel
Attached Files
File Type: pdf adjusting accg.pdf (3.6 KB, 105 views)
__________________
The right tool for the right job, a very nice Solarboat || Ready for a groupbuy ? CLick
  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 (Single Ended) + Larvadin (no Memory Distortion) = Ultimate Aleph? tiefbassuebertr Pass Labs 19 25th January 2014 02:15 AM
high frequency distortion paul_peraic Parts 2 7th May 2008 03:48 PM
Turntable High Frequency Distortion Sibilance Signal Analogue Source 1 8th January 2008 06:09 PM
Low Distortion High Dynamic Range Pre-amp Nico Ras Pass Labs 64 18th May 2007 05:26 AM
Is there a no/gain preamplifier schematic using high-distortion EC90? Layberinthius Tubes / Valves 6 10th May 2004 06:13 AM


New To Site? Need Help?

All times are GMT. The time now is 12:34 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