optical bias, how does it work?

[Hardi]

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]

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]

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

 

[deafbykhorns]

Patent your looking for

Here you go on that patent

http://patft.uspto.gov/netacgi/nph-...txt&s1=4,752,745,&OS=4,752,745,&RS=4,752,745,

Heres the tool for searching patents next time
http://patft.uspto.gov/netahtml/search-bool.html

 

[anatech]

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

 

[Steven]

Or use the European alternative:
http://l2.espacenet.com/espacenet/viewer?PN=US4752745&CY=gb&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]

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

 

[lautsprecherklinik]

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]

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.