Gainclone zobel question.

zebra100 · 18th September 2009, 08:39 PM

Hi,

Just a quick question on GC's and zobel networks.

I have an Audiosector LM3875 GC, running in dual mono configuration, driving 8 ohm speakers. I would like to try out a Zobel network, mainly for peace of mind.

I was wondering what the stock values are (or should be) for R and C, and what type of capacitor is the best to use?

Chris.

mjf · 18th September 2009, 09:43 PM

hello.
often used r=2,7 ohm , c=100 nf /100v or more
greetings

zebra100 · 18th September 2009, 10:00 PM

0.1uF/2.7ohm? What effect will these values have on the sound, and will a ceramic capacitor (I have some 0.1uF Kemet's in my spares box) be Ok in this application?

Regards,

Chris.

Peter Daniel · 18th September 2009, 10:04 PM

Yes, those are correct values, and they also have been specified here: http://audiosector.com/lm4780%20amp.pdf

Use metalized film cap, similar to this: http://search.digikey.com/scripts/Dk...name=BC2054-ND

zebra100 · 18th September 2009, 10:08 PM

Thanks Peter.

Chris.

Peter Daniel · 18th September 2009, 10:17 PM

Quote:

Originally Posted by zebra100

What effect will these values have on the sound, and will a ceramic capacitor (I have some 0.1uF Kemet's in my spares box) be Ok in this application?

Those parts will add coloration to the sound, I never tried ceramic in this application, so can't comment, but generally film would be better.

madqwerty · 18th September 2009, 10:42 PM

Quote:

Originally Posted by mjf

c=100 nf /100v or more

to all..
sorry 4 my silly question..
why using 100v or more cap, when outputs won't reach 30v max?
probably less than 20..
thanx

zebra100 · 18th September 2009, 11:32 PM

As well as giving me peace of mind, I am hoping the zobel network will solve a minor issue I have. Occasionally I get interference (using FM receiver) which causes a humming noise at the speakers. This noise remains present even after the source attenuator (50k Alps blue, dual log with a 47k metal film shunt) is turned down to minimum, i.e. input shorted to earth.

Chris.

Peter Daniel · 18th September 2009, 11:35 PM

It could be Zobel, or maybe you need this mod: http://www.diyaudio.com/forums/showp...2&postcount=51

Peter Daniel · 18th September 2009, 11:36 PM

Quote:

Originally Posted by madqwerty

to all..
sorry 4 my silly question..
why using 100v or more cap, when outputs won't reach 30v max?
probably less than 20..
thanx

It does not need to be 100V, 63V will work fine too

18th September 2009, 08:39 PM	#1
zebra100 diyAudio Member Join Date: May 2008	Gainclone zobel question. Hi, Just a quick question on GC's and zobel networks. I have an Audiosector LM3875 GC, running in dual mono configuration, driving 8 ohm speakers. I would like to try out a Zobel network, mainly for peace of mind. I was wondering what the stock values are (or should be) for R and C, and what type of capacitor is the best to use? Chris.

18th September 2009, 10:04 PM	#4
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	Yes, those are correct values, and they also have been specified here: http://audiosector.com/lm4780%20amp.pdf Use metalized film cap, similar to this: http://search.digikey.com/scripts/Dk...name=BC2054-ND __________________ 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

18th September 2009, 11:35 PM	#9
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	It could be Zobel, or maybe you need this mod: http://www.diyaudio.com/forums/showp...2&postcount=51 __________________ 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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18th September 2009, 09:43 PM	#2
mjf diyAudio Member Join Date: Jan 2009 Location: upper austria/near linz	hello. often used r=2,7 ohm , c=100 nf /100v or more greetings

18th September 2009, 10:00 PM	#3
zebra100 diyAudio Member Join Date: May 2008	0.1uF/2.7ohm? What effect will these values have on the sound, and will a ceramic capacitor (I have some 0.1uF Kemet's in my spares box) be Ok in this application? Regards, Chris.

18th September 2009, 10:08 PM	#5
zebra100 diyAudio Member Join Date: May 2008	Thanks Peter. Chris.

18th September 2009, 11:32 PM	#8
zebra100 diyAudio Member Join Date: May 2008	As well as giving me peace of mind, I am hoping the zobel network will solve a minor issue I have. Occasionally I get interference (using FM receiver) which causes a humming noise at the speakers. This noise remains present even after the source attenuator (50k Alps blue, dual log with a 47k metal film shunt) is turned down to minimum, i.e. input shorted to earth. Chris.

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