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 6th March 2005, 08:40 PM   #41
diyAudio Member
 
wuffwaff's Avatar
 
Join Date: Aug 2001
Location: Ingolstadt Germany
Hi Sippo,

it is important to know that there are two sorts of DC-offset in an X.
1. relative offset between + and - out
2. absolute offset between the outputs and ground.

The first is the offset seen by the speaker. Like I said this is below 20mV in both amps from startup and changes only marginal during warmup.

The second offset is not seen by the speaker, starts at 6V or so and slowly goes to zero. Having a high absolute offset reduces headroom but I wouldnīt know any other disadvantages.

I donīt use a relais, thereīs no thump whatsoever an turnon (there is in my Aleph5) or turn off.

William
__________________
een ooievaar is geen konijn want zijn oren zijn te klein!
  Reply With Quote
Old 6th March 2005, 08:51 PM   #42
diyAudio Member
 
wuffwaff's Avatar
 
Join Date: Aug 2001
Location: Ingolstadt Germany
Default more impressions

Hi,

after a lot more records and cdīs I can only repeat that it does sound very different.
Bass is very well defined and punchy, mids and highs are a lot better defined and have a somewhat cooler character. The amp is a bit less forgiving than my Aleph5 but on most records does sound a lot better (so it seems I donīt have to buy some new trannies after all)

William
__________________
een ooievaar is geen konijn want zijn oren zijn te klein!
  Reply With Quote
Old 6th March 2005, 09:38 PM   #43
diyAudio Member
 
macka's Avatar
 
Join Date: Dec 2001
Location: Australia
William ,

Nice to see your amp going.

I recenlty changed back to my Aleph 60 and as you comment above it tends to be more forgiving and romantic in presentation.

I suppose there's nothing wrong with having both styles ready and waiting.

Ian
  Reply With Quote
Old 7th March 2005, 02:02 AM   #44
DaveM is offline DaveM  United States
diyAudio Member
 
DaveM's Avatar
 
Join Date: Feb 2003
Location: Vermont
Very Nice work. I love the cases. They look truly professional.

I was wondering what you used for output transistors, IRFP044s or IRFP240s. I am trying to do my homework before buying the parts to populate my boards from the recent group buy.

Thanks

Dave
  Reply With Quote
Old 7th March 2005, 07:26 AM   #45
diyAudio Member
 
wuffwaff's Avatar
 
Join Date: Aug 2001
Location: Ingolstadt Germany
Dave,

Iīve used IRFP240īs. 12 per channel at aprox. 25watts each.

I will post the excel file with all the parts and resistor/cap values sometime this week.

William
__________________
een ooievaar is geen konijn want zijn oren zijn te klein!
  Reply With Quote
Old 7th March 2005, 04:31 PM   #46
sippo is offline sippo  Germany
diyAudio Member
 
Join Date: Mar 2004
Location: Northern Germany
Send a message via AIM to sippo Send a message via MSN to sippo Send a message via Yahoo to sippo
Thank you William for make this clear to me.

I was afraid to get in to trouble starting the X-Project (beside the normal troubles )


Frank
  Reply With Quote
Old 25th March 2005, 05:47 PM   #47
diyAudio Member
 
wuffwaff's Avatar
 
Join Date: Aug 2001
Location: Ingolstadt Germany
Hi,

Xīs are still working. They even had a duration test after my wife left them on for two days

After listening to many many records and cdīs the difference between this and my aleph5 getīs bigger and bigger and I donīt want to go back anymore.

There are some problems though:

1. Mechanical hum during warmup wich is probably causes by the assymetrical loading of the transformer because of the absolute dc-offset. I will try some lower values for R46/47 like 2k7 or 2k2.

2. Mechanical hum when the neighbours use some nice electrical devices like a hairdryer. This is caused by connecting the amps directly to the mains instead of my balanced ac power transformer (wich getīs a bit too hot at 900 watts). I will order a second transformer and experiment a bit with some chokes in the primaries to get everything silent again.

Iīve attached a short excel file with the parts used in the amp and power supply. It is the original file with the values changed and some more comments. Part designators are unchanged.

William
Attached Files
File Type: zip a-x parts.zip (6.6 KB, 317 views)
__________________
een ooievaar is geen konijn want zijn oren zijn te klein!
  Reply With Quote
Old 19th April 2005, 02:28 PM   #48
Eric is offline Eric  United States
diyAudio Member
 
Eric's Avatar
 
Join Date: Nov 2000
Location: Central PA, USA
Default Lowering Bias

William,

Nice job on your amps! They look great! At some point in the future, I'll be building a set of these for my new theater and was thinking that I need to be able to deliver approx 100wpc into the speakers I'll be using. So my goal is to build something very close to what you have but with a lower bias point.

I was figuring on 22v rails and about 6A of bias per channel - using the AXE spreadsheet, this would provide about 100wpc into both 8 ohms and 4 ohms.

So, my question: To set the bias lower, it looks like I would just need to adjust V1 and V3, and maybe increase R6/R41 slightly. Is this correct?

Also, where did you find those great heatsinks?

Thanks!
Eric
  Reply With Quote
Old 19th April 2005, 03:17 PM   #49
diyAudio Member
 
wuffwaff's Avatar
 
Join Date: Aug 2001
Location: Ingolstadt Germany
Hi Eric,

thanks for the compliments!
It will suffice to adjust V1 and 3 to get to 6A. But youīll have to change the ac-current gain resistors too.

The heatsinks are Fisher SK-157 300x200x85mm and around 0,2°K/W

William
__________________
een ooievaar is geen konijn want zijn oren zijn te klein!
  Reply With Quote
Old 19th April 2005, 03:41 PM   #50
Eric is offline Eric  United States
diyAudio Member
 
Eric's Avatar
 
Join Date: Nov 2000
Location: Central PA, USA
Thanks for the quick reply!

There is a lot of great info in the Aleph-X wiki, but nothing about how to adjust the circuit to different voltage & bias levels. I noticed you changed many of the resistor values from Grey's original circuit, and I really have no idea how to determine what to change...

Unfortunately, I don't have any test equipment (beyond an LCR meter), so I am not sure how to adjust the ac-current gain and determine its effect on the output and bias level.

Are there any rough formulas that can be used, or is this strictly a "try it an measure" kind of thing?

For my purposes, I think I'll need about 100wpc into a 4 ohm load, possibly a little more. I'm not sure whether I should follow your schematic and just reduce the bias a little, or try to build a version that runs on 20v rails at 6 or 7 amps of bias. The PS caps I have are 25v 220,000uF and I was planning on building a choke input power supply using Hammond 156B chokes (1.5mH, 0.07 ohms, 5A).
  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 ONO working - belated thanks to pquadrat GaryB Pass Labs 96 14th October 2009 06:44 PM
Aleph mini one channel not working yoke Pass Labs 7 9th March 2008 11:15 AM
My Aleph-p isn't working PatPet Pass Labs 11 24th August 2004 11:04 AM
Aleph 2 Working!! Mark A. Gulbrandsen Pass Labs 14 17th December 2002 01:56 PM
My Aleph 5 isn't working DJG Pass Labs 26 7th December 2002 10:49 PM


New To Site? Need Help?

All times are GMT. The time now is 03:22 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2