Output transformer and FB

[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.
It´s 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.

[TubeHead Johnny]

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"

[Miles Prower]

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.

It´s 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.

[Ragnwald]

Thanks Johnny

Massive reading, but the best i´ve 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.

[Ragnwald]

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.