First Pass project, need Aleph-M PSU advice please - 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 3rd May 2007, 11:52 AM   #1
ssmith is offline ssmith  France
diyAudio Member
 
Join Date: Aug 2005
Location: Paris
Default First Pass project, need Aleph-M PSU advice please

Hi all

Having dabbled in T-amp, cobbled together a gainclone, built frugel horns and a dac... the diy addiction has deepened. I strayed into the Pass Labs forum (I always used to avoid it because you're all so damn clever), where I stumbled across a Grey's highly entertaining Mini-A thread. Literally hundreds of hours of reading and searching later I'm putting together a Mini-A build.

My plan is to make two stereo amps to biamp two-way speakers. The Mini-A PCBs are on order, I have the transformers, huge heatsinks (just in case), and P-A's softstart/DC filter/rectifier PCBs.

I've almost got it all figured out (as best as a non-techie can hope to), except the PSU. The CRC/CLC business had me stumped for a while, but afte some searching I decided to go for CCRCCCCc (inductors are heavy to get posted to me and expensive).
My draft PSU schematic (WARNING: Microsoft Paint) is attached.

There will be 2 PSU's, each in their own chassis and each supplying two channels -- one high freqs (active xover point of 2,500hz) and one for lows. I assumed that going full dual mono would be a bit of a waste.

If anyone could comment on the schematic I'd be most grateful -- main question is the value and power rating of the resistor (I don;t want to have to heatsink it), and bypassing (I have some 2.2uf teflon speaker xover caps handy so just stuck those on). For the 10,000uf/35v caps I was planning on Nichicon KG.

thanks in advance!
Attached Images
File Type: jpg aleph-m psu draft.jpg (19.8 KB, 1437 views)
  Reply With Quote
Old 3rd May 2007, 12:49 PM   #2
diyAudio Member
 
MEGA_amp's Avatar
 
Join Date: Oct 2003
Location: CT
I would parallel another 0.50R 20W to be supersafe, that should be fine, and if you want to increase bias you wont have to change your PS capability. With 15V secondaries you dont need to drop much voltage. I'm currently running my Mini-A at +/-17.5Volts at 2.7amps with a trafo at 19volts. I have two paralleled 0.47R 25W per rail, and they get HOT, they're holding up fine and heatsinking isnt necessary. The rest of the PS looks fine.



-john
  Reply With Quote
Old 3rd May 2007, 01:28 PM   #3
ssmith is offline ssmith  France
diyAudio Member
 
Join Date: Aug 2005
Location: Paris
John,
Many thanks.
I found on Mouser some Vishay Dale 25w aluminium housed resistors so will go for those paralleled or one 50w.
As you said, the option to increase bias is nice to have. Hadn't thought of that. Would prefer for them not to get HOT, so can always add some extra little heatsinking to them anyway.
regards and thanks again,
stefan
  Reply With Quote
Old 3rd May 2007, 01:50 PM   #4
diyAudio Member
 
Join Date: Jan 2002
Location: Tyrone Ga. U.S.A.
Why not just use an inductor instead of the power resistor. A
.5mh air core inductor from Madisound using 16 gage wire is
priced at $7 and has a dc resistance of .22 ohm. You would get
a little high frequency filtering thrown in for free.
  Reply With Quote
Old 3rd May 2007, 03:49 PM   #5
ssmith is offline ssmith  France
diyAudio Member
 
Join Date: Aug 2005
Location: Paris
Hello Woody and thanks.
To be honest I was wary of using an air core inductor having read about saturation and it throwing off interference.

I also read this in the Aleph X wiki :

Quote:
Aleph-X wiki
L vs. R... Some general notes: Large enough L values are difficult to achieve at typical Aleph-X power currents. Large and expensive coils are needed, and they have high series resistance. Due to the high R and low L values of such inductors, my simulations show little difference in performance between realistic CLC and CRC filters. Magnetic fields from inductors may also be a concern, especially for air-core inductors, so give due consideration to mounting and shielding. Many iron core coils used for speaker crossovers will not be suitable for power supply use, as they will saturate and lose their inductance due to the DC currents.
Although much higher currents are involved in the Aleph-X (4.5A) and this does not apply the the Mini Aleph (1.5A to 2.5A or so I guess), I do not have the knowledge to determine DC current handling on aircore coils and this is something you don;t see on published specs. But if you say a 16 or so gauge air core inductor would be fine, I guess that would be a preferable option.... as the resistors I mentioned are about the same price anyway....




  Reply With Quote
Old 3rd May 2007, 03:49 PM   #6
diyAudio Member
 
MEGA_amp's Avatar
 
Join Date: Oct 2003
Location: CT
sure no prob, I used the cement types, resistors can be run closer to their stated ratings without failure. I dont know why I said I ended up with +/-17.5 volt rails, its more like 21.5V, I shouldn't post as soon as I wake up.

-john
  Reply With Quote
Old 3rd May 2007, 05:56 PM   #7
juma is offline juma  Germany
diyAudio Member
 
juma's Avatar
 
Join Date: Nov 2005
Location: Berlin
This is how I did it:
(Iq=1.8A per channel, ripple=70mV peak-to-peak)
Attached Images
File Type: gif sem-psu.gif (10.8 KB, 1269 views)
  Reply With Quote
Old 3rd May 2007, 07:14 PM   #8
diyAudio Member
 
Join Date: Feb 2001
Location: Columbia, SC
Default Re: First Pass project, need Aleph-M PSU advice please

Quote:
Originally posted by ssmith


main question is the value and power rating of the resistor (I don;t want to have to heatsink it)

Hundreds of hours reading the Mini-A thread? Goodness, that thread must have grown considerably since the last time I looked at it.
If I understood correctly, you're planning on running two channels of Mini-A (what's an Aleph-M?) off of each power supply. Assuming that the bias current is anywhere near the stock value, you'll see 1A per channel, 2A total per power supply. Unless I'm even shorter on sleep than I think I am, that's around 2W dissipation. Given a 20W resistor, I'd say you're pretty much good to go.

Grey
  Reply With Quote
Old 3rd May 2007, 07:58 PM   #9
ssmith is offline ssmith  France
diyAudio Member
 
Join Date: Aug 2005
Location: Paris
Default Re: Re: First Pass project, need Aleph-M PSU advice please

Quote:
Originally posted by GRollins

Hundreds of hours reading the Mini-A thread? Goodness, that thread must have grown considerably since the last time I looked at it.
No. As I said, hundreds of hours reading and searching. Starting with that (your) Mini-A thread, the GB threads, the other (related) aleph threads, zen threads for good measure, then headed off at tangents -- crc, clc, biasing, mosfet matching, capacitance, heatsinking, Nelson's articles, electronics for dummies (I'm one of them)... and so on. Out of what I read, I probably vaguely grasp about a quarter of it at best, and truly understand far less than that. Still, I have a plan on paper and some parts.


Quote:
Originally posted by GRollins
what's an Aleph-M?
Blasphemy, apparently? Sorry.


Quote:
Originally posted by GRollins
Assuming that the bias current is anywhere near the stock value, you'll see 1A per channel, 2A total per power supply. Unless I'm even shorter on sleep than I think I am, that's around 2W dissipation. Given a 20W resistor, I'd say you're pretty much good to go.
thanks.


Quote:
Originally posted by juma
This is how I did it:
(Iq=1.8A per channel, ripple=70mV peak-to-peak)
Thanks.

Quote:
Originally posted by MEGA-amp
I'm currently running my Mini-A... at 2.7amps
Is that per channel? And what kind of power output does that give you into 8ohms?
  Reply With Quote
Old 4th May 2007, 12:24 AM   #10
diyAudio Member
 
Join Date: Feb 2001
Location: Columbia, SC
Given the numbers quoted above--roughly 22W into 8 Ohms.

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
Pass Aleph 4 Project out !!! promitheus Pass Labs 28 8th August 2010 07:40 PM
Pass Labs BZLS and Aleph 2 Clone project for sale qwertyl Swap Meet 0 9th September 2008 03:11 PM
Pass Tharagard A75 vs Pass Aleph 1.2's daly41k Pass Labs 7 18th February 2007 03:10 PM
pass aleph P VS pass X2 first version perusicchio Pass Labs 10 5th March 2004 10:06 AM
Pass aleph 3 project promitheus Pass Labs 90 9th August 2001 07:58 AM


New To Site? Need Help?

All times are GMT. The time now is 11:14 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