AD797 guts

aparatusonitus · 21st March 2008, 01:23 AM

Hi,

Could one of you guys (Scott Wurcer

) explain the purpose of Q50/Q64 in AD797 simplified schematic, thank you?

darkfenriz · 21st March 2008, 08:46 AM

soft clipping, anti-saturation

aparatusonitus · 21st March 2008, 01:52 PM

Thanks darkfenriz, I thought it is some kind of protection, but I can't figure out the mechanism of it, could you elaborate it a bit further?

darkfenriz · 21st March 2008, 06:02 PM

As far as I understand the circuit:
-at normal operation, both Q50 and Q64 are kept below threshold Vbe
-Q19 and I3 form the main, final VAS
-collector of Q17 drives the Q18 buffer and this drives Q19 VAS
- at positive overload Q17 collector to I3 upper node voltage gets high, here Q64 starts to conduct
- at negative overload Q50 conducts

I understand it as two anti-parallel diodes at current mirror.

Regards
Adam

21st March 2008, 01:52 PM	#3
aparatusonitus diyAudio Member Join Date: Jan 2004 Location: Split, Croatia	Thanks darkfenriz, I thought it is some kind of protection, but I can't figure out the mechanism of it, could you elaborate it a bit further? __________________ Non é mai abbastanza...

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21st March 2008, 08:46 AM	#2
darkfenriz diyAudio Member Join Date: Jun 2004 Location: back to civilization	soft clipping, anti-saturation

21st March 2008, 06:02 PM	#4
darkfenriz diyAudio Member Join Date: Jun 2004 Location: back to civilization	As far as I understand the circuit: -at normal operation, both Q50 and Q64 are kept below threshold Vbe -Q19 and I3 form the main, final VAS -collector of Q17 drives the Q18 buffer and this drives Q19 VAS - at positive overload Q17 collector to I3 upper node voltage gets high, here Q64 starts to conduct - at negative overload Q50 conducts I understand it as two anti-parallel diodes at current mirror. Regards Adam

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