diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Solid State (http://www.diyaudio.com/forums/solid-state/)
-   -   Butler input pair (http://www.diyaudio.com/forums/solid-state/68156-butler-input-pair.html)

rtarbell 19th November 2005 07:14 AM

Butler input pair
 
I know that some audio-grade opamps use Butler front ends (a pair of BJT and FET transistors in parallel as the input transistors, to try and achieve the best of both worlds), but has anyone tried this for a discrete power amp? What where your results?

amplifierguru 19th November 2005 07:26 AM

Hi rtarbel,

What problem to solve? This is probably the question to ask. BJT stages have 'bias cancellation' and FET chips have adequate monolithic matching to suit audio. Could simply be introducing the weaknesses of both.

I don't see a need so wouldn't be looking for this.

Cheers,
greg

djk 19th November 2005 12:51 PM

Just what I always wanted.

High input bias (BJT) and output phase reversal on overdrive (FET).

http://patft.uspto.gov/netacgi/nph-P...&RS=PN/5101126

mikeks 20th November 2005 01:26 AM

Quote:

Originally posted by djk
...............output phase reversal on overdrive.....
Vanishingly unlikely in an audio amp....

djk 20th November 2005 02:48 AM

Right.

Do you have any real experience?

I didn't think so.

Having built an amp with this (and other FET opamps) with this problem is why I bring it up.

The data sheet from Analog Devices (OP275) even talks ways to minimize the problem.

Of course, what do they know? They just designed it, built it, and got a patent on it.

Maybe to be of help you should write us an application note, AD may even pay you for it.

mikeks 20th November 2005 03:33 AM

Quote:

Originally posted by djk
.....got a patent on it.....
...patents can be obtained for virtually anything....

...usefull...or otherwise...

...phase reversal due to overdrive in an audio power amp specifically is a non-issue....

mikeks 20th November 2005 03:42 AM

Quote:

Originally posted by djk
Right.

Do you have any real experience?

I didn't think so.




http://www.diyaudio.com/forums/showt...393#post198393


All times are GMT. The time now is 08:17 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