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-   -   DIY AMP Three parallel LM3886 power amplifier board 150W Current fever #868 (http://www.diyaudio.com/forums/chip-amps/213390-diy-amp-three-parallel-lm3886-power-amplifier-board-150w-current-fever-868-a.html)

nelnar 27th May 2012 04:28 AM

DIY AMP Three parallel LM3886 power amplifier board 150W Current fever #868
 
3 Attachment(s)
Please help me:
I am researching to buy AliExpress - Buy directly from China, two plates 3XLM3886 amplifier and 150W power supply with speaker protection:

-->> Wholesale DIY AMP Three parallel LM3886 power amplifier board 150W Current fever #868

1 - 3XLM3886 on the board, has optional capacitor blue and red. Is there a difference in quality of these capacitors?
2 - As the source, this speaker protection, capacitors have 10.000uf of 50v. Can be used only one source to supply the two plates of the amplifier?

-->> Wholesale F6 universal power supply board integrated speaker protection circuit power amplifier boards #878

3 - The transformer, Transformer required: Two 20-28V 200W power more than enough power. Say that use 28V-0-28V, but how many amps?
Please help me!

pacificblue 27th May 2012 07:26 AM

1 - The red one is supposed to be of better quality. With products from China you never know however. There are just too many suppliers to maintain an overview which one is good and which one is bad and what is really inside of a component.
2 - You can use one supply for several amps.
3 - Depends on the application.

You should calculate how much output power can be expected and buy a transformer accordingly. Reasonable transformer sizes are 70-300 % of the expected output power, where the region from 100-200 % does probably make most sense. For home audio you can go to the low side, for PA you should choose the high side. If the case in which the transformer resides is small, badly ventilated or cramped with many other heat sources you should also rather choose a bigger power rating.

Expect 120-130 W into 4 Ohm or 70-80 W into 8 Ohm from a 28 V transformer. With a 20 V transformer you will probably get 70-80 W into 4 Ohm and 35-40 W into 8 Ohm.

With 50 V capacitors in the power supply, I would limit myself to 25-0-25 V. That should give 110-120 W into 4 Ohm and ~60 W into 8 Ohm. In that case a 200 VA transformer would be the low limit for two 4 Ohm speakers, but absolutely OK for a single 4 Ohm or two 8 Ohm speakers.

For 8 Ohm speakers that means you can achieve the same performance with a single LM3886. Three in parallel only make sense, if the transformer has more than 25-0-25 V or if the load is less than 8 Ohm.

bcmbob 27th May 2012 12:08 PM

Here is another option. I bought two of these and sourced my own parts. PCB quality is excellent.

LM3886 x3 150W amplifier PCB Reliable Design ! | eBay

http://www.ebay.com/itm/Heavy-duty-p...item4aa9746804

Vendor provides BOM and docs after sale via email.

nelnar 27th May 2012 03:09 PM

Many thanks for your feedback!

Considering 3Cis, which the ideal voltage transformer to extract the full power of this amplifier?

AndrewT 27th May 2012 04:10 PM

about 26+26Vac to 27+27Vac.

pacificblue 28th May 2012 06:39 AM

Depends on the load impedance, your listening habits and how much you want to invest into heatsinking. What is the average ambient temperature where you live?

With three LM3886s in parallel you can use the max supply voltage from 6 Ohm upwards, i.e. 2x30 VAC, although it is a good idea to leave some voltage headroom and not go above 2x28 VAC, which is also the limit for 4 Ohm.
For 2 Ohm loads, e.g. certain subwoofers, the limit is most probably 2x20 VAC, but at such a low impedance the ambient temperature and how the amp is used can make a big difference.

syklab 28th May 2012 07:48 AM

I like to understand why parallel 3 LM3886? Is 3 a magic number ? Why not 2 or 4?

AndrewT 28th May 2012 11:07 AM

I thought 7 was the magic number.

Sorry off topic.

Look at the specification for the 3886. the min value for maximum peak output current when Tc = 25C is 7Apk. Clever of National to omit the pk from the 7A value so that they don't draw too much attention to the limitation of their chipamp.

A single 3886 can just about drive a severe reactance speaker to ~60W with only a little intervention from Spike and other protections such that it sounds OK.
But, spend some time examining the peak transient current that can be demanded by a real speaker and you will find that the 3886 and all chipamps are severely current crippled.
That is why we see "band-aid" solutions to help out the chipamps.

Any number of parallel implementations can be used (2, or 3, or 4, or ??), I just accept those single 3886 limitations and adopt a more suited amplifier for the duty I need.

bcmbob 28th May 2012 11:24 AM

They are available though I don't remember seeing any post from builders.

LM3886 X 4+NE5532 BTL Audio power amplifier board 200W | eBay

pacificblue 28th May 2012 06:07 PM

Quote:

Originally Posted by syklab (Post 3039400)
I like to understand why parallel 3 LM3886? Is 3 a magic number ? Why not 2 or 4?

If you use two with a typical 4 Ohm speaker while at the same time making use of the upper limit of the supply voltage, you may still run into the current and/or thermal limits. Three are sufficient to get around those limitations. Four do usually not give any further advantage.


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