F5 power amplifier - Page 263 - 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 1st February 2009, 02:24 PM   #2621
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Quote:
Originally posted by woodturner-fran
OK, so I done some more testing. First up was to check out Q1/Q2. I made up the circuit that someone posted a little back up here (Idss) - and I got 10mA for SJ74 and 9mA for SK170. So it would seem that they were alive still.


Next I decided to look at the current limiting circuit. I removed all the components from the circuit as detailed earlier in the thread. Now I found I could get the bias set ok across R11 and 12. Its set as 0.6V on both but my offset at the speaker terminals is high. The mosfets are heating up nicely, but they aren't that hot. I've left it on for a little while and will go back and check it again. The offset I'm seeing is "floating" ie moving around a good bit while the bias values seem pretty stable. I get 4.4-4.6V G-S on Q3 and 4 and I meaure 16V D to S on Q1 and 2.


Does this sound OK?

Fran
that's OK
now re-read Papa's procedure in F5 pdf and set it .

once finally set - offset is rock stable
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 1st February 2009, 02:25 PM   #2622
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
Yes.

And if you are using Fairchilds and not using thermistors, both the bias (up to 1A) and the offset (2 digit mAs) will move all over the place, even with adequate heat sinking. See my remarks on the Fairchilds umteen pages ago.


Patrick
  Reply With Quote
Old 1st February 2009, 05:25 PM   #2623
diyAudio Member
 
Join Date: Jan 2006
Location: Ireland
Nope, this ain't right.

OK, so I start with P1/2 at 0R. Turn on amp and make sure I have +/-24V rails. Then I alternately adjust P1/2 in small increments (1/2 turn each). I have 2 DMMs hooked up, one each across R11 and R12. Both of these read 0mV.

Nothing happens for the first few turns, then I see <10mV across R11 and R12. adjust a bit more and I get up to 100mV quickly enough.

But heres what I see then - after a certain point, if I adjust P1, the mV across R11 and R12 both increase. Its like as if P1 or P2 each controls the mV across both R11 and R12. All this time, if I stop and take a measurement across the speaker outputs, its floating anywhere from 100mV to 3,4,5 V.

I must be wrong in how I'm doing this... it can't be this difficult can it?

I double checked all the resistors and they all are the correct value (nice of dale to print the R on each one). The mosfets are IR ones that I bought from jackinnj (tech-diy). If I get a chance I'll take a few photos later. Obviously I've made a boo-boo somewhere, just can't see it.

Fran
  Reply With Quote
Old 1st February 2009, 05:33 PM   #2624
Tea-Bag is offline Tea-Bag  United States
not politcally affiliated
diyAudio Member
 
Tea-Bag's Avatar
 
Join Date: Feb 2006
Location: Kennebunk
Blog Entries: 7
Quote:
Originally posted by woodturner-fran
Nope, this ain't right.


Nothing happens for the first few turns, then I see <10mV across R11 and R12. adjust a bit more and I get up to 100mV quickly enough.

But heres what I see then - after a certain point, if I adjust P1, the mV across R11 and R12 both increase. Its like as if P1 or P2 each controls the mV across both R11 and R12. All this time, if I stop and take a measurement across the speaker outputs, its floating anywhere from 100mV to 3,4,5 V.
Fran

R11 and R12 should go up in tandem. P1 is Bias voltage, P2 is DC offset (DC on speakers). You should be able to slowly ramp up Bias and then get the DC offset down along the way. You dont need you speaker hooked up to do this. Just measure out to ground.

My advice --- I would have one DMM on R11 and one reading offset.
~.5v and <.02v offset, you should hook up your speaker and test.

Make sure you speaker didn't get shorted. Measure with ohm meter, and make sure that it reads something <10ohms.....

Good luck
  Reply With Quote
Old 1st February 2009, 06:34 PM   #2625
diyAudio Member
 
Join Date: Jan 2006
Location: Ireland
aaah, ok. I'll try again so.


More later, thanks for the help.

Fran
  Reply With Quote
Old 1st February 2009, 06:41 PM   #2626
RIP
 
Join Date: Oct 2005
Location: Central Florida
Fran,
Both P1 and P2 are bias pots. Put one meter on R11 and one meter on speaker outputs. Bring up P1 until you have 50mv or so on R11 then turn P2 until the offset goes back down around zero. Then back to P1, turn up some more then bring offset back down. Keep repeating until you have R11 up around .600V and zero offset, then let it cook awhile and recheck.
Bill
  Reply With Quote
Old 1st February 2009, 09:22 PM   #2627
diyAudio Member
 
Join Date: Jan 2006
Location: Ireland
ok, I concentrated on one channel. I have it sitting at around 0.5V and 40mV offset. I ran out of time then, so thats as far as I got, but I had it on for about 25mins or so and brought it up slowly. The plan is to do the same now with the other channel. If I can get both to around those figures then I'll try see does it play music.

Thanks to everyone so far for the help. The question still now remains over the current limiting part - maybe I might be able to reinstall those now (once I know its all working ok).

Fran
  Reply With Quote
Old 1st February 2009, 09:49 PM   #2628
diyAudio Member
 
MEGA_amp's Avatar
 
Join Date: Oct 2003
Location: CT
Quote:
Originally posted by woodturner-fran
The question still now remains over the current limiting part - maybe I might be able to reinstall those now (once I know its all working ok).

The current limiting parts (or lack thereof if I understand you correctly) shouldn't have any effect on setting bias and adjusting for low DC offset. I left it out as well as the thermistors. Without the thermistors, it takes a while for the bias to stabilize, so you might be adjusting for awhile. I might put them in to make things easier on power up.


edit: Choky....we're always posting at the same time, you got some kind of sixth sense?
  Reply With Quote
Old 1st February 2009, 09:49 PM   #2629
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Quote:
Originally posted by woodturner-fran
ok, I concentrated on one channel. I have it sitting at around 0.5V and 40mV offset. I ran out of time then, so thats as far as I got, but I had it on for about 25mins or so and brought it up slowly. The plan is to do the same now with the other channel. If I can get both to around those figures then I'll try see does it play music.

Thanks to everyone so far for the help. The question still now remains over the current limiting part - maybe I might be able to reinstall those now (once I know its all working ok).

Fran

current limiting parts - hardly that they're schorched , but in any case - test little bjts with Hfe tester on your DMM ;

what's playing with you now is lack of thermistors ;

even if you certainly didn't fried them ( no way with that PSU voltage ) - check them in cold ( for your piece of mind ) and solder them back ;

then biasing da thing will be piece of cake
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 1st February 2009, 10:07 PM   #2630
diyAudio Member
 
Join Date: Jan 2006
Location: Ireland
Nah, I measured them and cold (ie about 8deg C) they were 7K. If I held the tip in my fingers that went down to 5K... which would be correct wouldn't it?

So I could just add back in the thermistors without the other current limiting parts?


Fran
  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 02:18 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