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Old 15th November 2005, 10:06 PM   #1
diyAudio Member
 
Join Date: Jan 2005
Location: Argentina
Default lm3886 project

hi!!!! I'm new in the forum, my name is Jorge, I'm from Argentina. I'm really happy of having found this forum.

Last week I bought 2 lm3886. I need some power for my brand-new Yamaha NS-c444 central speaker. I was using two lm1875 with a smaller speaker.

So I used an experimental board to build a single LM3886 to try it up and look how it sounds. AMAZING!!!!

The speaker is 6ohm 60W. I have a 18+18 300VA transformer from another project, so I think the best is use this transformer with 2 mono amps and bridge them with 2 opamps like this circuit:

Click the image to open in full size.

I know you have build lot of amps and have more experience than me, so ... what do you think?

Any advice is welcome!!

thanks a lot!!! and sorry for my english
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Old 15th November 2005, 11:01 PM   #2
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Join Date: Oct 2004
Why not try a simpler bridge amp with less parts?.

http://www.national.com/an/AN/AN-1192.pdf#page=1
5.2.1 bridged amp schematic

Figure 3
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Old 16th November 2005, 01:55 PM   #3
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Location: Argentina
good idea!!

I'm not sure how to connect the other pins of the LM, it's correct to connect the other pins like in the normal schematic? (not bridged) ?
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Old 16th November 2005, 10:42 PM   #4
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Yes it the same as normal schematics but output ground is not connected and the inverted input is used with one chip.
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Old 17th November 2005, 02:20 AM   #5
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Join Date: Jan 2005
Location: Argentina
well I built the amp. Sounds nice, but i think there is some problem with the bass. Maybe small camps in my PSU



some pics:
[img=http://img262.imageshack.us/img262/5121/amp15om.th.jpg]
[img=http://img262.imageshack.us/img262/4594/amp24sr.th.jpg]
[img=http://img262.imageshack.us/img262/8541/amp36hc.th.jpg]

my PSU is not good. 18+18 360VA transformer with 1 bridge rectifier and 2 5000uFx55v caps.

[img=http://img163.imageshack.us/img163/9355/psu17ce.th.jpg]
[img=http://img444.imageshack.us/img444/6466/psu26ob.th.jpg]

i will make a better PSU like the ones i've found on this page. looking in my depot, i found these babys:

[img=http://img483.imageshack.us/img483/7733/caps5ss.th.jpg]


i hope the caps improve the bass of the amp.


And the speakers i use to try the amp:
my yamaha center speaker:
[img=http://img483.imageshack.us/img483/5779/yamaha4gy.th.jpg]

and another bigger made by me
(Bass reflex, DAS B-20 12" + 1.5" driver DAS ND-10)
[img=http://img55.imageshack.us/img55/3915/das5uk.th.jpg]

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Old 17th November 2005, 05:16 AM   #6
gamma is offline gamma  Sweden
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Join Date: Jun 2005
Location: Jönköping
zafira1981: I have no experince of building power amps ...but I think its a problem to use LM3886 in bridge-configuration for a 6 ohm load.

Maybe better to use parallell configuration instead then...but in that case you have to have higher power supply voltage...+/-30 Volt
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Old 17th November 2005, 10:47 AM   #7
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Join Date: Oct 2004
With 18-0-18 transformer driving 6ohms is not a problem. I use 15000uf caps per rail and the bass is fine. So if everything is wired corecting you should get better bass with the change of caps.

Have you tried to use speakers with large woofers,to test the amps bass response?

What are the trimmers for?
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Old 17th November 2005, 01:18 PM   #8
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Join Date: Jan 2005
Location: Argentina
Quote:
Originally posted by jaudio
With 18-0-18 transformer driving 6ohms is not a problem. I use 15000uf caps per rail and the bass is fine. So if everything is wired corecting you should get better bass with the change of caps.

Have you tried to use speakers with large woofers,to test the amps bass response?

What are the trimmers for?
I've not tried YET.

Yesterday night, I was changin the rectifier bridge with 2 bridges to improve the PSU, but I did something wrong and fried both bridges. I was lucky to test them alone BEFORE conecting the caps, .......

so now im going to buy new bridges and some resistors&MKT caps for filtering.

they're not trimmers, they're variable resistors. i used them to make the 51.1K & 3.32K of the bridged schematic.


when i have the new PSU working, i will test it with my sub. (18" RCF)


thankssssssss



And i have another question: why to use MKT capacitors in the PSU?
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Old 18th November 2005, 12:51 PM   #9
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Different capacitor material handles frequecies differently. If I remember corecting MKT caps ,cleans up high frequecies better than elec. cap. It will change impedance of the power supply. For a better explaination read this and do a search.

http://www.tnt-audio.com/clinica/ssps2_e.html
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Old 23rd February 2007, 10:06 AM   #10
SUBHANI is offline SUBHANI  Pakistan
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PLZ TELL ME ABOUT THE POWER MODULE SVI 3102D
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