F5 power amplifier - Page 729 - 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 8th March 2010, 08:10 PM   #7281
diyAudio Member
 
Join Date: Mar 2008
Hello,

sorry if it has been covered before but I've read about half of this thread and this took me two weeks worth of my spare time

I wonder if any of the semiconductors in standard F5 have to be matched? I think there's no need to match output devices cause I can adjust their bias with P1-P2.
How about input jfets?
Can I substitute transistors from protection circuit(Q5-Q6) with something more available like BC550-560? If not what makes zetex devices so special for our application?

looking forward for your help/explanation,

thanks
Michał
  Reply With Quote
Old 8th March 2010, 08:29 PM   #7282
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
BC...
Yes, but reversed
Cvillers guide would be good to read
http://viller.eu/audio/2009jan_gbf5/gbf5_guide.pdf

Yes, I think its best to use mayched Jfets, to make easier dc adjustment
__________________
sometimes we know very little, and sometimes we know too much
  Reply With Quote
Old 8th March 2010, 08:34 PM   #7283
cviller is offline cviller  Denmark
diyAudio Member
 
cviller's Avatar
 
Join Date: Dec 2005
Location: Copenhagen
Blog Entries: 2
You don't need to match the jfets, but I seem to remember to have read somewhere that jackinnj made some tests where he got better thd with matched jfets.
  Reply With Quote
Old 8th March 2010, 08:43 PM   #7284
diyAudio Member
 
Join Date: Mar 2008
Quote:
Originally Posted by cviller View Post
You don't need to match the jfets, but I seem to remember to have read somewhere that jackinnj made some tests where he got better thd with matched jfets.
Thank you for your fast replies. I think I'm gonna make first version with cheapo components and then, if I like the overal sound put some more money into fancier, matched devices/resistors.

One more thing: In your guide, Cviller, there's written in the PSU section:
"1-2 thermistors for soft starting the toroid"
If I'm not plannig to use any thermistors at all should I use slo-blo fuse or just bigger one?
  Reply With Quote
Old 8th March 2010, 08:48 PM   #7285
cviller is offline cviller  Denmark
diyAudio Member
 
cviller's Avatar
 
Join Date: Dec 2005
Location: Copenhagen
Blog Entries: 2
Quote:
Originally Posted by kalinowski View Post
One more thing: In your guide, Cviller, there's written in the PSU section:
"1-2 thermistors for soft starting the toroid"
If I'm not plannig to use any thermistors at all should I use slo-blo fuse or just bigger one?
It depends on the toroid you use. Way back, I tried without soft start thermistors running at 230V and the 4A slow blow fuses literally exploded.
  Reply With Quote
Old 9th March 2010, 03:03 AM   #7286
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
Originally Posted by cviller View Post
You don't need to match the jfets, but I seem to remember to have read somewhere that jackinnj made some tests where he got better thd with matched jfets.
I think the results were only a gnat's hair better -- and there was certainly no rigorous scientific method involved. You can use a BL as one JFET and a GR on the other and the amplifier will still work.

The Zetex's can be substituted, but be mindful of orientation (which Cviller has attended to.)

The output devices are of their own mind and don't have to be matched.

If you're building the amp just to measure THD% the 10K/22K resistors on the limiter can be swapped around, the source resistors on the JFETs, etc.

The most important factors to consider are an adequate heat sink and patience in setting up the bias and offset voltages.
  Reply With Quote
Old 9th March 2010, 03:49 AM   #7287
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
I think that accurately covers the subject.

  Reply With Quote
Old 9th March 2010, 03:52 AM   #7288
Blues is offline Blues  United States
Lightning In A Bottle
diyAudio Member
 
Blues's Avatar
 
Join Date: Sep 2003
Location: The Milky Way
Quote:
Originally Posted by jackinnj View Post
I think the results were only a gnat's hair better -- ...
Thanks!
__________________
Life simplified! Leap into the Warpspeed wormhole... http://www.6moons.com/audioreviews/warpspeed/1.html
  Reply With Quote
Old 9th March 2010, 09:51 AM   #7289
diyAudio Member
 
Join Date: Mar 2008
Quote:
Originally Posted by jackinnj View Post
I think the results were only a gnat's hair better -- and there was certainly no rigorous scientific method involved. You can use a BL as one JFET and a GR on the other and the amplifier will still work.

The Zetex's can be substituted, but be mindful of orientation (which Cviller has attended to.)

The output devices are of their own mind and don't have to be matched.

If you're building the amp just to measure THD% the 10K/22K resistors on the limiter can be swapped around, the source resistors on the JFETs, etc.

The most important factors to consider are an adequate heat sink and patience in setting up the bias and offset voltages.
thank you for detailed explenation. I can start my iron now, can't wait to listen to it.

M.
  Reply With Quote
Old 9th March 2010, 04:25 PM   #7290
Renron is offline Renron  United States
diyAudio Member
 
Renron's Avatar
 
Join Date: Jan 2007
Location: Sacramento
Quote:
Originally Posted by jackinnj View Post
The most important factors to consider are an adequate heat sink and patience in setting up the bias and offset voltages.
Amen to that brother Jack!


Question for the masses:

Do anyone else's heatsinks just barely get warm?
I haven't scanned them with the laser temp gun, but when I put my hand on them after hours of playing they are barely warm. Is this nOrmaL?
R11 / R12 .59V with DC offset at ~+/- .05V that fluctuates a little as it warms up.

Silent as a snowflake.

Ron
__________________
"If it doesn't work properly, hope it catches on fire"- Nelson Pass @ BA3
"I fired up the prototype. Literally." The Prophet Pass.
  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
Rockford Fosgate Power 20001 bd amplifier power rating?? pachoorion Car Audio 8 8th May 2011 10:49 PM
Power transformers versus amplifier output power..what is your option? destroyer X Solid State 38 9th May 2009 05:23 PM
McIntosh Power Amplifier Power Guard johnnyrt Solid State 2 23rd August 2007 10:22 PM
Output power for a power amplifier Progg70 Solid State 33 10th September 2006 08:44 AM
Amplifier 3000 Wats Rms Power + Smps Higcht Power Bestiality MARAVILLASAUDIO Class D 1 5th November 2004 04:06 PM


New To Site? Need Help?

All times are GMT. The time now is 12:17 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