Output transformer and FB - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 May 2008, 11:26 AM   #1
diyAudio Member
 
Ragnwald's Avatar
 
Join Date: Feb 2008
Location: Gotland
Default Output transformer and FB

Have some thoughts of feedback loop use and whant to know your opinion about it.

Most output transformers (poweramp) have two or three +terminals 4, 8, 16 ohms.

My state; the FB schould bee taken from the speakerterminal of the active winding of the speaker in use.
Itīs a bad way to let the feedback lapping through not used windings in the outputtransformer (16ohm taps if 8 ohm taps are in use).
And every outputwinding call for its own spec FB, of course one at a time when used.

Anyone done some measuring and comparing ?

Even an SS amp nead some corrections for doing its absolute best with different speakerloads, i recently lernt.
  Reply With Quote
Old 8th May 2008, 05:40 PM   #2
diyAudio Member
 
TubeHead Johnny's Avatar
 
Join Date: Jan 2005
Location: The emerald city, Seattle, WA.
Hi Ragnwald,

There's a great overview and other goodies right here:

http://www.aikenamps.com

Then go to: "Tech Info" then "Advanced" then "Designing for Global Negative Feedback"
__________________
"No man really becomes a fool until he stops asking questions" - Charles Proteus Steinmetz
  Reply With Quote
Old 8th May 2008, 08:16 PM   #3
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Default Re: Output transformer and FB

Quote:
Originally posted by Ragnwald
Have some thoughts of feedback loop use and whant to know your opinion about it.

Most output transformers (poweramp) have two or three +terminals 4, 8, 16 ohms.

My state; the FB schould bee taken from the speakerterminal of the active winding of the speaker in use.
Definitely. That's how I do it.


Quote:
Itīs a bad way to let the feedback lapping through not used windings in the outputtransformer (16ohm taps if 8 ohm taps are in use).
And every outputwinding call for its own spec FB, of course one at a time when used.
Take care of it by including variable gNFB. That way, you can tailor the feedback to the speeks, music, and preference.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 8th May 2008, 09:24 PM   #4
diyAudio Member
 
Ragnwald's Avatar
 
Join Date: Feb 2008
Location: Gotland
Thanks Johnny

Massive reading, but the best iīve seen on the subject.

After a fast reading i snapt that, the amount of voltage being fed back get half, when the feedback is changed from the 16ohm tap to the 4ohm tap. And the serie- and groundrecistor have to be recalculated to get the same amount of feedback.

That was not new to me, but now i have some nice reading of how to calculate the loop.

David Manley says in his book that the loop shall go from the winding where the speaker is connected, to optimize the interface, and 16ohms windings just "flapping in the breeze" and wasting valuable current (Amperes) that could and should be channeld into the loudspeakers.
  Reply With Quote
Old 8th May 2008, 09:45 PM   #5
diyAudio Member
 
Ragnwald's Avatar
 
Join Date: Feb 2008
Location: Gotland
Default Re: Re: Output transformer and FB

Quote:
Originally posted by Miles Prower


Definitely. That's how I do it.

Take care of it by including variable gNFB. That way, you can tailor the feedback to the speeks, music, and preference.
Yes Miles i use a switch to alter terminal and feedback, when i listen to 4ohm speakers.
To get the most accuracy hifi feedback, take some listening.
  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
Difference between SE output transformer and push-pull output transformers hilbert_mostert Tubes / Valves 12 8th March 2009 05:10 PM
3C24 in a SE output stage - output transformer impedance recommendation !!! aldovan Tubes / Valves 15 6th September 2008 10:18 AM
Adding secondary of output transformer into cathodes of output stage ? Eico ST-70 freddymac406 Tubes / Valves 3 21st April 2007 06:15 PM
Can An Output Transformer Change A Voltage Amp's Output Impedance From 0.1 To 47 Ohms kelticwizard Everything Else 11 25th March 2007 05:17 AM
toroid Transformer as output Transformer for tube preamp? tone Tubes / Valves 15 2nd February 2003 04:36 AM


New To Site? Need Help?

All times are GMT. The time now is 11:16 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2