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-   -   optical bias, how does it work? (http://www.diyaudio.com/forums/solid-state/40689-optical-bias-how-does-work.html)

Hardi 9th September 2004 05:17 PM

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

Nelson Pass 9th September 2004 08:29 PM

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.

anatech 10th September 2004 04:16 AM

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

johnsciolino 10th September 2004 09:42 PM

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

anatech 10th September 2004 11:28 PM

Thanks John,
Turns out the site does not like Netscape. I had to use IE.
I have some reading to do.
-Chris

Steven 11th September 2004 11:10 AM

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

anatech 11th September 2004 02:08 PM

Thanks Steven, I'll try that one too.
-Chris

lautsprecherklinik 14th September 2012 08:36 PM

Quote:

Originally Posted by Nelson Pass (Post 471291)
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

GregH2 4th July 2013 02:47 AM

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.


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