optical bias, how does it work? - 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 9th September 2004, 05:17 PM   #1
Hardi is offline Hardi  Germany
diyAudio Member
 
Join Date: Feb 2004
Location: Germany
Default optical bias, how does it work?

Hi there,

what are the advantages (or disadvantages) of an optical Bias amplifier and how does it work ? (must not be a 100% description)

Is it an (opto coupler) controlled, dynamic bias regulation, that depends on the value of the input (output) Signal ??

thanks
Hardi
  Reply With Quote
Old 9th September 2004, 08:29 PM   #2
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
In the case of my patent #4,752,745, an optocoupler is used
to transmit the value of the bias current to an earlier stage
which contains the bias circuit. It works very conveniently
to keep the bias at a constant value while isolating the
front end VAS from the output.
  Reply With Quote
Old 10th September 2004, 04:16 AM   #3
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
The way Denon and others use this is to switch to a higher bias state depending on mode. This may be automatic on signal level or by a switch on the front panel. Normally the switch is marked "class A", should be marked "runs too hot". What it does is to put another resistor in parallel with one in the bias circuit. The optocoupler acts as a switch. That's all it does.

Nelson,
I'd like to read how your circuit works, but have no patience for finding patent articals. Is it on your site, or can you email it to me?
Thanks,
-Chris
  Reply With Quote
Old 10th September 2004, 09:42 PM   #4
diyAudio Member
 
Join Date: Aug 2004
Location: florida
Default Patent your looking for

Here you go on that patent

http://patft.uspto.gov/netacgi/nph-P...&RS=4,752,745,

Heres the tool for searching patents next time
http://patft.uspto.gov/netahtml/search-bool.html
  Reply With Quote
Old 10th September 2004, 11:28 PM   #5
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Thanks John,
Turns out the site does not like Netscape. I had to use IE.
I have some reading to do.
-Chris
  Reply With Quote
Old 11th September 2004, 11:10 AM   #6
Steven is offline Steven  Netherlands
diyAudio Member
 
Steven's Avatar
 
Join Date: Oct 2003
Location: The Netherlands
Or use the European alternative:
http://l2.espacenet.com/espacenet/vi...b&LG=en&DB=EPD
For US patents the number (without commas) should use a US-prefix, e.g. US4752745 instead of 4,752,745. No Alternatiff viewer is required, only Acrobat Reader. Note: this site is not too fast.

Home page: http://gb.espacenet.com/espacenet/gb/en/e_net.htm

Steven
__________________
The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
  Reply With Quote
Old 11th September 2004, 02:08 PM   #7
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Thanks Steven, I'll try that one too.
-Chris
  Reply With Quote
Old 14th September 2012, 08:36 PM   #8
diyAudio Member
 
Join Date: Sep 2012
Quote:
Originally Posted by Nelson Pass View Post
In the case of my patent #4,752,745, an optocoupler is used
to transmit the value of the bias current to an earlier stage
which contains the bias circuit. It works very conveniently
to keep the bias at a constant value while isolating the
front end VAS from the output.
Hello Mister Pass,

I used a Threshold S 500 first series without optikal bias.
Bias is adjusted.
If the amp is hot 50-55Grad Celsius and the sound level is in living room level ...bass and sound is O.K..
If I get a higher level the bass is going out and the sound would be bad.

What can I do?

Best Regards, Norman
  Reply With Quote
Old 4th July 2013, 02:47 AM   #9
GregH2 is offline GregH2  Australia
diyAudio Member
 
GregH2's Avatar
 
Join Date: Oct 2009
Hi All,

I'm trying to understand this optical bias thingy and would appreciate some help.

I can see how it neatly maintains the bias current through the output driver transistors and hence the bias voltage seen at the bases/gates of the output devices. I can also understand that this neatly thermally compensates the output driver transistors.

However, is this circuit sufficient to thermally compensate the output transistors or is additional thermal compensation needed?

Just curious!

Thanks,

Greg.
  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
Using Batteries to Bias crossovers into Class A, how does it work? pjpoes Multi-Way 33 2nd April 2014 02:12 PM
Changing grid leak bias preamp to cathode bias bereanbill Tubes / Valves 8 28th March 2009 05:26 PM
Stray hum pickup *preamp* cathode R-bias vs. battery bias & 12AU7vs.5687 awedio Tubes / Valves 2 19th April 2008 01:30 AM
Tech help needed Threshold S/300 MkII optical bias georgehifi Pass Labs 4 18th January 2005 06:49 PM
Tech help needed Threshold S/300 MkII optical bias georgehifi Solid State 15 17th January 2005 01:30 AM


New To Site? Need Help?

All times are GMT. The time now is 12:39 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