Beginner to build an Aleph30 needs some help - Page 2 - 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 20th January 2014, 01:41 PM   #11
cowneko is offline cowneko  France
diyAudio Member
 
Join Date: Apr 2013
Location: Valenciennes
I'll probably use those capa Invalid Request
I think i'll bypass the electrolytic with some mks film (like 2.2uf wima) as to speed them up a bit: good, bad?

As for the resistance, I'll be using 4 parallel 0.47ohm resistors per channels (0.12ohm/channel)

Anyway, what about the capacitor arrangement suggested by Zen mod?

thanks again for all your advices
  Reply With Quote
Old 20th January 2014, 01:45 PM   #12
6L6 is offline 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
The electrolytic caps look very good.

Bypass caps are to your taste, the MKS are fine.

The PCB can't be adjusted to place single cap first, so just use it as designed - it's a great PCB, I've used it in two different projects. I really like it.
  Reply With Quote
Old 20th January 2014, 02:03 PM   #13
diyAudio Member
 
BobEllis's Avatar
 
Join Date: Sep 2003
Location: Upstate NY
Those capacitors will be fine. A bit big to mount to the bottom of the board if you want to add after the R. How about mounting them on a small piece of perf board right up at the end of the main PSU board to hold another pair of caps? Either CCRCC or C-RCC

Your net R is in the normal Pass range, should work well.

IMHO, the bypass caps would be better on the amp boards if used at all. On the PSU board it may oscillate with the main caps' self inductance and the power supply lead inductance. There are strong opinions on both sides of the issue, some claiming that it adds life to their amp, others saying it causes oscillation and ringing. At my skill level and limited measurement equipment, I tend to leave it off it it could cause harm if not properly sized, like snubbers. As always, YMMV and it probably wouldn't hurt to try and see if you think it makes a difference.

I agree with Jim (6L6) that is a nice PSU board, It's in a couple projects of mine with more on the way.
  Reply With Quote
Old 20th January 2014, 02:50 PM   #14
cowneko is offline cowneko  France
diyAudio Member
 
Join Date: Apr 2013
Location: Valenciennes
Quote:
Originally Posted by BobEllis View Post
Those capacitors will be fine. A bit big to mount to the bottom of the board if you want to add after the R. How about mounting them on a small piece of perf board right up at the end of the main PSU board to hold another pair of caps? Either CCRCC or C-RCC
That was precisely what I had in mind , 2 additionnal 22000uf capa on a perf board wired to the underside of the PCB, I'll try the CCRCC approach.

Quote:
Originally Posted by BobEllis View Post
Your net R is in the normal Pass range, should work well.
Ok so i'll stick with 4x0.47ohm resistor network on each channel.

I think I can place the order for the PSU parts now


I still have to be sure what Bias resistor I should buy; the spreadsheet (on page 1 of this thread) leads me to 1ohm 3W resistors (X12 for two channels) instead of the 0.47ohm ones listed in the BrianGT BOM, is it right?
  Reply With Quote
Old 20th January 2014, 03:35 PM   #15
diyAudio Member
 
BobEllis's Avatar
 
Join Date: Sep 2003
Location: Upstate NY
An Aleph biases up to roughly 0.5V across the Source resistors. So if you choose 1R resistors you will have roughly .5A per fet, 1.5A total bias since you are going with three devices per current source. Assuming that you have the heat sink to handle it, you probably will want to go more towards the original 0R47 so that your amp isn't current limited at lower impedances.

You have enough voltage swing with 30V rails to drive ~100W peaks into 8R. At 1.5A total bias, and 50% AC gain you'll be current limited to 27W. At 3A bias (0R47 source resistors) you will be voltage limited.

If you need to limit dissipation but want a little more bias choose 0R68.

Last edited by BobEllis; 20th January 2014 at 03:38 PM.
  Reply With Quote
Old 20th January 2014, 06:03 PM   #16
cowneko is offline cowneko  France
diyAudio Member
 
Join Date: Apr 2013
Location: Valenciennes
I made another calculation with a goal of 0R68 as a target for resistor to Bias fet (gives me 2.6A total bias)
Seems like my heatsinks are just enough for this setting (heatsink= 0.2C/W for one channel)

Click the image to open in full size.
Click the image to open in full size.

Witch value should I choose for source resistor (now 0R82) ?

On the schematic Fet source resistors are R35 to R41 and bias resistors are R18 to R21 right?

What are the purpose of R23 to R26? How to choose their value and number (since you can install a total of 6 resistor here)

I realize that my questions are quite trivial and i'm really grateful that you're taking the time to explain things to me.
  Reply With Quote
Old 20th January 2014, 06:09 PM   #17
6L6 is offline 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
If you have 3 pair of Mosfet per channel and 32V rails, you are basically building an Aleph 5.

For source resistors, don't worry too much about changing anything. What Bob says is spot on.

Not knowing what schematic you are looking at I assume that R23-R26 are the (4) 0.47ohm resistors near the output. Those are the Aleph CCS sense resistors. Use (4) 0.47ohm
  Reply With Quote
Old 20th January 2014, 06:34 PM   #18
diyAudio Member
 
BobEllis's Avatar
 
Join Date: Sep 2003
Location: Upstate NY
I'd go with 0R68 Source resistors if your heat sinks can't handle the current with 0R47.

Not sure which are which - I don't have that board's schematics handy. The ones whose source resistors connect to the negative rail are the output devices and the ones whose source resistors connect to the output through a bunch of other resistors are the current source's and set bias. Generally use the same values in both places.

Guessing again, but R23-26 are for setting the AC current gain. Are they the ones that connect the junction of the upper and lower transistors to the output? The easiest way to do it is use the same value as your source resistors and as many. In your case 6. (Seeing Jim's note, the goal is to have 1/2 the net resistance of the ACS 3 parallelled source resistors. Using 4 will result in higher AC current gain)

You're welcome of course. hopefully This will help someone else, too.

Last edited by BobEllis; 20th January 2014 at 06:44 PM.
  Reply With Quote
Old 20th January 2014, 06:45 PM   #19
cowneko is offline cowneko  France
diyAudio Member
 
Join Date: Apr 2013
Location: Valenciennes
Here the schematic of the board

Click the image to open in full size.

Click the image to open in full size.

For the heatsinks, here the big babies

Click the image to open in full size.

Click the image to open in full size.

Last edited by cowneko; 20th January 2014 at 06:57 PM.
  Reply With Quote
Old 20th January 2014, 07:02 PM   #20
6L6 is offline 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
I think R12 is going to set the AC gain of the ACCS... Not the value of R23-26. I need to read Zen V2 again... (It has the Aleph CCS explanation)
  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
Beginner's Build Guide: Pearl II jhsjhs99 Pass Labs 96 17th June 2013 05:20 PM
Beginner wanting to build a subwoofer amp mk2singh Class D 8 28th October 2012 04:19 AM
First Amp Build, (But not complete beginner to electronics) agreco1489 Tubes / Valves 12 2nd July 2012 06:26 AM
Planning an F5 build - some beginner questions njepitt Pass Labs 144 15th March 2009 11:55 PM
Beginner looking to build Bloody_Sorcerer Subwoofers 5 27th October 2007 08:56 PM


New To Site? Need Help?

All times are GMT. The time now is 11:07 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