Bridge+Parallel LM3886, Doable?

Tim__x · 23rd June 2004, 03:42 AM

I want to build a bridged LM3886 based amp for use with 8/4 and yes even 2 ohm loads. I already have a suitable 20-0-20 transformer.

What I'm thinking is a standard configuration with four IC's, two in parallel per a side. Would this be sufficient? Maximum peak current would be slightly under 10 amps an IC, I'm thinking I would use a rather large heatsink with a temp controlled fan.
Would this work? Or should I use three IC's a side?

cdoggy81 · 23rd June 2004, 05:34 AM

Tim,
4 chips will work out fine.

Tim__x · 23rd June 2004, 06:49 AM

Thanks, I had seen that example from the datasheet before, but thank-you anyway.

Really what I'm asking is would it be safe with two ohm loads?
I guess I didn't really make that clear before, sorry 'bout that.

peranders · 23rd June 2004, 08:56 AM

Have you checked Thomas madsen's pcb?
200 watts Gäjnklon (Gainclone) - BPA200
http://www.pbase.com/tlmadsen/das_modul

Have you seen this spreadsheat?

http://www.national.com/appinfo/audi...gn_Guide13.xls
http://www.national.com/appinfo/audi...sign_Guide.pdf

tlmadsen · 23rd June 2004, 10:17 AM

Hi Tim

I think that you are "pushing it" with a 2 ohm load for a bridge/parellel config. Remember that each arm only see ½-load, this means 1 ohm. Since each arm are two chips in parallel they see 2x load, this means that each chip sees 2 ohm !!!!!!!!!!
It does help with the "lower" voltage you have, but I still think it is "pushing it".
Either you can put more chips in each arm OR make a parallel config with your 4 chips (this will "limit" your power in 8 ohm), but make it fly for 2 ohm load.

Have fun

Thomas

peranders · 23rd June 2004, 10:35 AM

I wonder, do you have two 4 ohms speaker in parallel or four 8 ohms in parallel? Maybe it's better to build two amps

Tim__x · 23rd June 2004, 06:32 PM

Thank you all for your help. I knew it would be pushing it, but I wanted to know exactly how much it would be pushing it.
I think I will go for 6 IC's, 3 a side with very hefty heat-sinking.

23rd June 2004, 03:42 AM	#1
Tim__x diyAudio Member Join Date: Jun 2004 Location: Edmonton area, Alberta	Bridge+Parallel LM3886, Doable? I want to build a bridged LM3886 based amp for use with 8/4 and yes even 2 ohm loads. I already have a suitable 20-0-20 transformer. What I'm thinking is a standard configuration with four IC's, two in parallel per a side. Would this be sufficient? Maximum peak current would be slightly under 10 amps an IC, I'm thinking I would use a rather large heatsink with a temp controlled fan. Would this work? Or should I use three IC's a side?

23rd June 2004, 08:56 AM	#4
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Have you checked Thomas madsen's pcb? 200 watts Gäjnklon (Gainclone) - BPA200 http://www.pbase.com/tlmadsen/das_modul Have you seen this spreadsheat? http://www.national.com/appinfo/audi...gn_Guide13.xls http://www.national.com/appinfo/audi...sign_Guide.pdf __________________ /Per-Anders (my first name) or P-A as my friends call me

23rd June 2004, 10:35 AM	#6
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	I wonder, do you have two 4 ohms speaker in parallel or four 8 ohms in parallel? Maybe it's better to build two amps __________________ /Per-Anders (my first name) or P-A as my friends call me

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23rd June 2004, 06:49 AM	#3
Tim__x diyAudio Member Join Date: Jun 2004 Location: Edmonton area, Alberta	Thanks, I had seen that example from the datasheet before, but thank-you anyway. Really what I'm asking is would it be safe with two ohm loads? I guess I didn't really make that clear before, sorry 'bout that.

23rd June 2004, 10:17 AM	#5
tlmadsen diyAudio Member Join Date: Aug 2003 Location: Roskilde - The vikingships	Hi Tim I think that you are "pushing it" with a 2 ohm load for a bridge/parellel config. Remember that each arm only see ½-load, this means 1 ohm. Since each arm are two chips in parallel they see 2x load, this means that each chip sees 2 ohm !!!!!!!!!! It does help with the "lower" voltage you have, but I still think it is "pushing it". Either you can put more chips in each arm OR make a parallel config with your 4 chips (this will "limit" your power in 8 ohm), but make it fly for 2 ohm load. Have fun Thomas

23rd June 2004, 06:32 PM	#7
Tim__x diyAudio Member Join Date: Jun 2004 Location: Edmonton area, Alberta	Thank you all for your help. I knew it would be pushing it, but I wanted to know exactly how much it would be pushing it. I think I will go for 6 IC's, 3 a side with very hefty heat-sinking.

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