Subwoofer Chip Recomendation

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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?
 
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.
 
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 :)
 
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.
 
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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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.
 
Hi Joseph1,

My goal is to drive a 8ohms subwoofer

@PB already posted for subwoofer, quantity first then quality.

Assume, tda7294 is available to you. Look at tda7294 datasheet. page # 13, Fig.25, AND Esp-P48

tda7294-bridge may be plenty of power should drive with 25VDC(+/-) for 8R Load

Subwoofer may needs separate power supply having good capacitance It may be complete stand-alone project.

One ore thing, keep moderate gain. Don't put like 70-times etc., Fit Volume POT at input.
 
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.

Hi this is good.Can you tell what is the output wattage I can get by using a 8 Ohms load by paralleling two chips?

I read the PA100 app note,but it has no output wattage or formula mentioned :(
 
Hi Joseph1,



@PB already posted for subwoofer, quantity first then quality.

Assume, tda7294 is available to you. Look at tda7294 datasheet. page # 13, Fig.25, AND Esp-P48

tda7294-bridge may be plenty of power should drive with 25VDC(+/-) for 8R Load

Subwoofer may needs separate power supply having good capacitance It may be complete stand-alone project.

One ore thing, keep moderate gain. Don't put like 70-times etc., Fit Volume POT at input.

Hi pra nice you are back.

I have that chip as well.

Pricing is
TDA7294 = 1$ (US)
LM3886 = 4.5$ (US)

That is a huge gap.Hopefully from price wise I can tell LM is much sound qualitier than TDAs :)

But logitech Z5000 series has that TDA series chip.That has volume much but not the heavy bass :(
 
You won't gain much by paralleling into 8ohm.

+/- 35VDC is pretty good for 8 ohm speakers with the LM3886. The datasheet curves say about 64W, but I would be more conservative at about 50W output.

The speaker "specs" say 40W RMS. 50W would hopefully be plenty. Instantaneous peak power is often an entirely fictional number.
 
The maximum output power of the 3886 running on +-39Vdc is about 65W (+-5W) into 8r0.

If you parallel a pair of 3886 on the same PSU you might get an extra 5W.

If you bridge 4 off 3886 as in bpa200 you should get double the power into double the impedance. i.e 130W +-10W into 16r. There may be a possible increase of a further 10W for the paralleled 3886 in the bPa200.

But you want to drive 8ohms speakers.
So determine the maximum rating for a 4r0 load.
Expect about 65W +-5W into 4r0 on +-30Vdc
If you parallel for increased current then expect 70W +-5W into 4r0 when on +-30Vdc.

Now if you bridge the paralleled 3886, you will get 140W +-10W into 8r0 when on +-30Vdc
Notice that the same 4 chips end up with very similar output power of around 130W to 140W in the two situations.

However, you can increase the supply voltage for these BPA200 from +-30Vdc to closer to +-35Vdc and still not blow up the chips. This will get a big increase in output power (into resistive test loads) but will be incapable of driving real speakers to the currents they will demand when aiming for the highest output powers.

If instead you built a PA200 (4 off 3886 in parallel) then there will be sufficient current capability when you then bridge them into BPA400 to drive 8ohms speakers from +-39Vdc supply rails.

Silly project, just use an LME49810+ 2 BJTs instead of 8 chips.
 
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The maximum output power of the 3886 running on +-39Vdc is about 65W (+-5W) into 8r0.

If you parallel a pair of 3886 on the same PSU you might get an extra 5W.

If you bridge 4 off 3886 as in bpa200 you should get double the power into double the impedance. i.e 130W +-10W into 16r. There may be a possible increase of a further 10W for the paralleled 3886 in the bPa200.

But you want to drive 8ohms speakers.
So determine the maximum rating for a 4r0 load.
Expect about 65W +-5W into 4r0 on +-30Vdc
If you parallel for increased current then expect 70W +-5W into 4r0 when on +-30Vdc.

Now if you bridge the paralleled 3886, you will get 140W +-10W into 8r0 when on +-30Vdc
Notice that the same 4 chips end up with very similar output power of around 130W to 140W in the two situations.

However, you can increase the supply voltage for these BPA200 from +-30Vdc to closer to +-35Vdc and still not blow up the chips. This will get a big increase in output power (into resistive test loads) but will be incapable of driving real speakers to the currents they will demand when aiming for the highest output powers.

If instead you built a PA200 (4 off 3886 in parallel) then there will be sufficient current capability when you then bridge them into BPA400 to drive 8ohms speakers from +-39Vdc supply rails.

Silly project, just use an LME49810+ 2 BJTs instead of 8 chips.

Nice information. Very easy to understand :) thanks for that.

Now I slightly opened my eyes & can see the real situation.

I just postponed my subwoofer project because my wooden subwoofer boxes will arrive somewhat two weeks ahead.And also my my mind is moving to stereo listening after reading many passed threads.Many people here didn't make subwoofer amps using these chips they all stereo lovers :)

For the time being I'm going to build a hi-fi stereo system using two LM3886.

By using a 28-0-28 AC transformer it will deliver 39.5V DC per chip. According to the graph in the datasheet it will output 80W of power.

By using two of these chips as stereo system it will sound a lot. I’ll also add an active preamp with tone control to adjust bass & trebles.

Can I be able to make a high quality amplifier using this chip?
80W + 80W = 160W

What you think of this design?
 

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