Signs your Firstwatt DIY is unstable? - 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 11th April 2011, 02:35 PM   #1
diyAudio Member
 
Join Date: Mar 2003
Location: midwest
Default Signs your Firstwatt DIY is unstable?

I dont have a o-scope or this would quickly diposed of, so here goes: I have noticed recently that my DIY F-5 is running quite a bit warmer than it usually does. Typically, I wonder if it is hot enough, the large M&M sinks just getting good and warm, allowing you to touch as long as one would care to leave them on, but never really hot.

Recently, it has run considerably hotter, still can be touched for over 5 seconds, at around 9 seconds I start to wonder, then I can still leave hand on, albeit beginning to get uncomfortable.

The bias is sitting fine, only a few mV of offset. I know the ambient temp is a little warmer now than it was a month or so ago, but this amp went through last summer not nearly this hot.

I havent had any other indications of instability (the amp that is ), but dont really know what they are, other than overheating and bizarre sounds.
Only the heat issue concerns. Any comments would be welcome, I suppose getting the amp to someone with an o-scope would help.

Thanks in advance for any comment, searching didnt bring up what I was looking for, although I know I have read a few threads about this here.

Russellc
  Reply With Quote
Old 11th April 2011, 03:10 PM   #2
RIP
 
Join Date: Oct 2005
Location: Central Florida
Hi Russel,

I remember reading about using a small cap on the inputs to kill any RF signals from getting into the amp. The F5 has an outragously wide bandwidth and will happily amplify RF, causing overheating.

Best, Bill
  Reply With Quote
Old 11th April 2011, 06:06 PM   #3
flg is offline flg  United States
diyAudio Member
 
flg's Avatar
 
Join Date: Jul 2005
Location: North East
Do You have a DMM? Put it on AC and look for a signal level at the output FETs Gate or Drain... If it's only DC your good the reading will be 0...
__________________
"It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.
  Reply With Quote
Old 11th April 2011, 07:11 PM   #4
diyAudio Member
 
Join Date: Mar 2003
Location: midwest
Quote:
Originally Posted by flg View Post
Do You have a DMM? Put it on AC and look for a signal level at the output FETs Gate or Drain... If it's only DC your good the reading will be 0...
I do have a DMM. will try that tonight.

Russellc
  Reply With Quote
Old 11th April 2011, 10:03 PM   #5
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
If you are looking for oscillation, most DMM's will not read frequencies that
high at all.

Disconnect the speakers. If it stays at the same temp, then it's probably
fine. Remember that line voltage also comes into play with this.

  Reply With Quote
Old 11th April 2011, 10:11 PM   #6
diyAudio Member
 
Join Date: Mar 2003
Location: midwest
Quote:
Originally Posted by Nelson Pass View Post
If you are looking for oscillation, most DMM's will not read frequencies that
high at all.

Disconnect the speakers. If it stays at the same temp, then it's probably
fine. Remember that line voltage also comes into play with this.

Thank you for your response. Does the amp stabilize when the speaker load is disconnected? How does line voltage affect this? Thanks for the info, I'm trying to understand this. ( I'm sure a scope would help) If the amp runs considerably cooler with speakers disconnected, what would my next step be?

Russellc
  Reply With Quote
Old 12th April 2011, 12:39 AM   #7
Itsmee is offline Itsmee  England
diyAudio Member
 
Itsmee's Avatar
 
Join Date: Feb 2009
If the line voltage increases, so will the supply rail voltages to the amp, more voltage = more watts = more heat


The following test is crude and will not show anything below 1V.

To check if the amp is unstable, power off the amp, disconnect the speaker, connect one end of signal diode (1N4148 etc) to the speaker output, and the other end to a small polyester/polyprop cap, connect a DMM across the cap, power up the amp, connect the free end of the cap to speaker ground, If the DMM reads anything significant, you have instability. If you get a zero reading, try the test again with the diode reversed, then test again with the speaker connected.
  Reply With Quote
Old 12th April 2011, 01:02 PM   #8
diyAudio Member
 
Join Date: Mar 2003
Location: midwest
Thanks for the input guys, I'm certain others have wondered about this as well.
I think my amp is fine, there was an almost 20 degree difference in ambient temp when the amp was getting hotter. Today was a little cooler and normal temps were experienced...this amp went through last summer and I just didnt remember it getting that hot. Just the nature of the beast, maybe I will build one of ZenMod's babysitter devices for this summer.

Russellc
  Reply With Quote
Old 12th April 2011, 02:58 PM   #9
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
in that case - we must discuss royalty issue ;

waste one beer for me , and we are even

__________________
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 12th April 2011, 06:23 PM   #10
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
anyway

there is a search I'm doing in last 24 hours , and just now I catch exact phrase - oscillation detector

good trick for greenhorns : NAP-140 Clone Amp Kit on Ebay
__________________
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

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
signs of a dead lm3886 Ted205 Chip Amps 11 23rd August 2014 07:24 PM
Tell-tale signs of good feedback usage? kegger Tubes / Valves 22 21st January 2007 08:06 PM
where can i get good ht signs? slicemaster101 Multi-Way 8 11th June 2002 07:49 PM
where can i get signs? slicemaster101 Everything Else 0 11th June 2002 04:04 AM


New To Site? Need Help?

All times are GMT. The time now is 09:44 AM.


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