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Old 15th December 2012, 11:59 AM   #1
Joseph1 is offline Joseph1  Sri Lanka
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Question Subwoofer Chip Recomendation

Guys I need to make a DIY subwoofer amp.

I have seen original active subwoofers like Kenwood SW-900, SW-40 etc…They produced 70W RMS & 100W somewhat near sound. With that wattage you can shake your house. Also they don’t use bigger woofers, maximum they use 8” inch woofers to their designs.

I need to make a subwoofer amp like that.

My choices are LM3876, LM3886 & TDA7294.

After a forum search I found that LM3876 sound quality is excellent. Is it enough for a subwoofer amp?

I need advice from you what chip do you recommend?
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Old 15th December 2012, 12:20 PM   #2
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Sound quality is not that much of an issue for a subwoofer. That is why you can buy plate amps and even complete active subs that are cheaper than a DIY chip amp.

How much power is enough depends on the woofer and your listening habits. Especially how low and loud it has to go. All three ICs you mentioned will be sufficient in more than 80 % of all cases. So if your case does not belong to the remaining 20 %, go for the one you like best of the three.
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Old 15th December 2012, 12:37 PM   #3
Joseph1 is offline Joseph1  Sri Lanka
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Hi thanks for your response.I can understand what you say.

Recently I made a subwoofer amp by using LM1875.No one worked with LM1875 as a sub amp & I noticed its output power is not enough for a subwoofer system.

I hope I can hear a noticable change if I make a LM3876 based sub amp
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Old 15th December 2012, 01:10 PM   #4
AndrewT is offline AndrewT  Scotland
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if your bass only speaker has a sensitivity in the >90dB/W @ 1m then 50W to 100W should be plenty for home use.

That puts the 1875 pretty close to being a good usable chipamp for bass only duty.

However if you try to drive a 80dB/W @ 1m bass only speaker with 30 to 40W of maximum output power then you will be very disappointed.
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Old 15th December 2012, 01:31 PM   #5
Joseph1 is offline Joseph1  Sri Lanka
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Hi Andrew

Here is my woofer specifications its a Roadmaster RSW80

* 8" Pressed Aluminum Cone
* 30 oz. Magnet
* Rubber Surrounds
* 200 Watts Total Instantaneous Peak Power
* 40 watts Total RMS

* 45 to 3500 Hz Frequency Response
* Dual Voice Coil
* fits a .75 to 1.5 CF sealed box
* Push On Terminals
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Old 15th December 2012, 01:32 PM   #6
AndrewT is offline AndrewT  Scotland
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Does not help me.
Do they help you?
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Old 15th December 2012, 01:35 PM   #7
Joseph1 is offline Joseph1  Sri Lanka
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Quote:
Originally Posted by AndrewT View Post
Does not help me.
Do they help you?
No it does not helped me either

It doesn't mentioned the sensitivity in the datasheet
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Old 15th December 2012, 02:17 PM   #8
Einric is offline Einric  United States
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You could use a parallel set of LM4780's to drive a dual voice coil subwoofer.
Each parallel LM4780 could deliver 120W per voice coil @ 4Ω and you could feed them from a single RCA input.
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Old 15th December 2012, 02:23 PM   #9
Joseph1 is offline Joseph1  Sri Lanka
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Sorry LM4780 is not available here.

All other ICs available here except LM4780

My goal is to drive a 8ohms subwoofer.For LM1875 also I series the two 4ohms voice coils & made 8 ohms
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Old 15th December 2012, 02:29 PM   #10
Einric is offline Einric  United States
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Look up a design here on the forums for an LM3886 parallel design.
The LM4780 has 2 LM3886's onboard.
2 LM3886's actually are better at dissipating the heat since they have a greater surface area.

If you will be running the sub in series 8Ω then you could bridge two 3886's and run them from an 18v secondary transformer.
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