leach amp inductor smoking - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 19th April 2004, 11:39 AM   #1
Bosium is offline Bosium  South Africa
diyAudio Member
 
Bosium's Avatar
 
Join Date: Oct 2002
Location: Essex, UK
Default leach amp inductor smoking

hi there

I've just completed a dual mono leach amp, 750VA trans with separate bridge and 10000uf caps per channel. It sounds fantastic. I've been building it for ages and it seems tip top, BUT...

I was testing one channel with a 1khz sine wave input on a 8ohm dummy load and the resistor with the inductor wound around it started to smoke.

I removed power immediately, amp still 'works' and no fuses blew. What's up with that? I'm certain that I've assembled it correctly, both channels are biased at about 110ma and play audio perfectly into both 4 or 8 ohm loads.

Any help would be appreciated.
Gareth
  Reply With Quote
Old 19th April 2004, 12:15 PM   #2
diyAudio Member
 
Join Date: Jan 2002
Location: Livermore, CA
It could be indicative of oscillation, as little current should flow through the resistor except at very high frequency. OTOH, what gauge wire did you use for the inductor- it should be pretty healthy, like AWG14. or better.
  Reply With Quote
Old 20th April 2004, 12:41 AM   #3
diyAudio Member
 
slowhands's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
The resistor is what value (ohms, watts)? You need a 1 ohm 5-10 watter here. A more likely candidate to smoke is the Zobel net resistor, but at higher frequencies than 1 kHz. I suspect this inductor is not needed anyway, but people always seem to put them in.
  Reply With Quote
Old 20th April 2004, 03:47 AM   #4
diyAudio Member
 
Join Date: Jan 2002
Location: Livermore, CA
Quote:
I suspect this inductor is not needed anyway, but people always seem to put them in.
For many/most bipolar output stages, even the classic EF triple T circuit (much less a CFP output stage!) both an RC zobel and a series parallel RL network are necessary to assure stability with reactive loads, inductive and capacitive.

There are ways around it, but I'm not telling....


The inductor does introduce frequency dependent load sensitivity, unfortunately- it often does have some kind of impact on HF sonics, depending on the speaker load. I wouldn't recommend removing the RL network from a standard Leach amp, unless you're just using it for subwoofer duties, for example.

The resistor in parllel is for damping the network; the inductor value will typically be in the range of 2-4 uH.

If you have a scope, you can determine the real problem pretty quickly.

It's brave souls who build and test amplifiers without a scope..

Best regards,

Jon
  Reply With Quote
Old 20th April 2004, 04:42 AM   #5
diyAudio Member
 
slowhands's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
Quote:
Originally posted by JonMarsh


For many/most bipolar output stages, even the classic EF triple T circuit (much less a CFP output stage!) both an RC zobel and a series parallel RL network are necessary to assure stability with reactive loads, inductive and capacitive.

Jon
I am familiar with all the arguements for using the damped inductor to buffer capacitive loads. Most of the expert opinion says it is de riguer, with one notable exception (Pass). I realize suggesting it it not necessary is heretical.

The Leach amp uses feedforward compensation, from driver to inverting input. Furthermore, it has a low-pass filter on the output feedback, which makes it even more immune to hf instability with capacitive loads. In my experience with similar amps, if properly applied those two techniques keep an amp stable into capacitive loads.

Nelson Pass pointed out that the inductor degrades the damping factor at higher frequencies, and so in fact can impact tweeter damping. In light of that, I'd at least experiment with leaving it out.
  Reply With Quote
Old 20th April 2004, 05:32 AM   #6
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
One thing you might want to consider - if the Zobel inductor is the standard type with wire wound around a resistor, make sure it's sonnected well at both ends. Otherwise, you are pumping all the power through the resistor and it will smoke....
  Reply With Quote
Old 20th April 2004, 07:37 AM   #7
Bosium is offline Bosium  South Africa
diyAudio Member
 
Bosium's Avatar
 
Join Date: Oct 2002
Location: Essex, UK
thanks for the replies, wrenchone i think you have the answer, my inductor isn't well attached, i'll try that.

G
  Reply With Quote
Old 20th April 2004, 08:41 AM   #8
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
The inductor you have wound, what wire area did it have? Could it take the current?
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 20th April 2004, 07:21 PM   #9
lucpes is offline lucpes  Europe
diyAudio Member
 
Join Date: Dec 2003
Location: Iasi
Send a message via Yahoo to lucpes
The thing here is that all the power should go through the inductor which should be quite large to avoid troubles. You may even solder the resistor underneath the PCB, it only provides oscillation dampening for the coil.

Bullet-proof sized inductor compared to the white 5W resistors:
Attached Images
File Type: jpg inductor.jpg (28.4 KB, 314 views)
  Reply With Quote
Old 20th April 2004, 09:14 PM   #10
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
I have made an inductor of 1.5 mm Cu wire, 5 mohms = much current before it glows.
Picture here
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  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
Copper coil inductor vs. round core inductor tomchaoda Pass Labs 7 21st September 2011 04:42 AM
High Current Leach/leach super amp bowdown Solid State 41 2nd March 2011 02:15 PM
Zen V4 Smoking Q5 Diomedian Pass Labs 6 15th November 2005 02:46 PM
Resistor/Inductor at Leach Output BrianDonegan Solid State 10 22nd January 2005 06:22 AM
Smoking Amp jkramer Solid State 15 28th August 2004 04:17 PM


New To Site? Need Help?

All times are GMT. The time now is 09:26 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