The purpose of R0 in Aleph 30 circuit

Peter Daniel · 28th March 2005, 06:07 AM

I have a question with regards to the actual purpose of R0 in Aleph 30 circuit. It's been said that this resistor breaks ground loops, but I can't quite figure out how it does that. I mean, would it make any difference if R4/R5 were connected directly to signal ground, as it seems like signal ground connects to those resistors through R0?
http://www.passlabs.com/downloads/ol...t/a30manr0.pdf

jh6you · 28th March 2005, 08:19 AM

It seems to be for the zeners not directly to see the ground.

Netlist · 28th March 2005, 08:53 AM

R0 is not strictly necessary, but I think of it as a resistor in the ground loop, reducing the amount of hum-current. Call it some sort of ground lift.

/Hugo

jarek · 28th March 2005, 10:02 AM

I think, that it is here to prevent zener diodes from blowing when they get the voltage more than expected.

jarek · 28th March 2005, 10:30 AM

Or better, to keep a low voltage at gates of the differential pair when diodes had blown.

Peter Daniel · 28th March 2005, 12:57 PM

I thought initially that this is a resistor separating signal ground from output ground, but it does not seem to be a case (you can notice such resistor on National's LM4780 evaluation board). So in most cases it's probably not needed anyway ( as I'm also not using the input diodes).

I'm still considering improving the ground scheme on the A30 board. I recall Zigybait commenting that running separate ground paths from current source circuit and the signal ground to main star ground point improved performance.

jarek · 28th March 2005, 03:25 PM

Quote:

I recall Zigybait commenting that running separate ground paths from current source circuit and the signal ground to main star ground point improved performance.

You can try to put an about 24V Zener diode between R13 and supply (-). Than you don’t need a connection R13 to the ground.

Nelson Pass · 28th March 2005, 08:54 PM

As I recall, R0 simply helped to break the RCA connection
loop going back to the source equipment. There was a
little less noise this way, and both the input and feedback
referenced to it, so it didn't compromise performance. If you
don't need it, there's no requirement to use it.

Peter Daniel · 28th March 2005, 09:47 PM

Now I understand it, thanks for that info.

28th March 2005, 06:07 AM	#1
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	The purpose of R0 in Aleph 30 circuit I have a question with regards to the actual purpose of R0 in Aleph 30 circuit. It's been said that this resistor breaks ground loops, but I can't quite figure out how it does that. I mean, would it make any difference if R4/R5 were connected directly to signal ground, as it seems like signal ground connects to those resistors through R0? http://www.passlabs.com/downloads/ol...t/a30manr0.pdf __________________ www.audiosector.com “Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC

28th March 2005, 10:02 AM	#4
jarek diyAudio Member Join Date: Dec 2002 Location: Poland	I think, that it is here to prevent zener diodes from blowing when they get the voltage more than expected. __________________ Jarek

28th March 2005, 10:30 AM	#5
jarek diyAudio Member Join Date: Dec 2002 Location: Poland	Or better, to keep a low voltage at gates of the differential pair when diodes had blown. __________________ Jarek

28th March 2005, 12:57 PM	#6
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	I thought initially that this is a resistor separating signal ground from output ground, but it does not seem to be a case (you can notice such resistor on National's LM4780 evaluation board). So in most cases it's probably not needed anyway ( as I'm also not using the input diodes). I'm still considering improving the ground scheme on the A30 board. I recall Zigybait commenting that running separate ground paths from current source circuit and the signal ground to main star ground point improved performance. __________________ www.audiosector.com “Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC

28th March 2005, 09:47 PM	#9
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	Now I understand it, thanks for that info. __________________ www.audiosector.com “Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC


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28th March 2005, 08:19 AM	#2
jh6you Account Disabled Join Date: Aug 2002 Location: Near to the Pacific Ocean	It seems to be for the zeners not directly to see the ground.

28th March 2005, 08:53 AM	#3
Netlist diyAudio Moderator Join Date: Jan 2003	R0 is not strictly necessary, but I think of it as a resistor in the ground loop, reducing the amount of hum-current. Call it some sort of ground lift. /Hugo

28th March 2005, 08:54 PM	#8
Nelson Pass The one and only Join Date: Mar 2001	As I recall, R0 simply helped to break the RCA connection loop going back to the source equipment. There was a little less noise this way, and both the input and feedback referenced to it, so it didn't compromise performance. If you don't need it, there's no requirement to use it.

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