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

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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!
 

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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.
 
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.
 
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 = 25°C 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.
 
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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.
 
Please correct me if wrong.

You will need 2 of the amp module for each channel plus a phase splitter to drive them in bridge mode in order to deliver 100W for nominal 8R load? If we need to go down to 4R then each amp module will require 2 3886...2R will need 3 3886...etc ?

If it works in this fashion then I can use 4 (3 3886 parallel) modules connected in bridge mode (for both channel) to drive a power hunger Maggie?
 
Sorry about going off-topic, but...

GOD, how I love my Magnepan speakers!

You would be better off buying something like a used Adcom GFA-545 II, or a GFA-555 II, for your Maggies. They can be found in basically perfect condition for relatively low prices, and give truly-exquisite reproduction (designed by Nelson Pass, or closely adapted from his non-II model designs), and are built like tanks! They are a superb value, these days, on the used market (ebay, audiogon, et al)! It's just hard to believe that something so good can be so cheap!

The GFA-545 II will do 150 W/ch (average, continuous) into 4 Ohms. With it, I couldn't quite get my MG-12s to self-distort (mid/bass modulating tweeter due to shaking the panel too hard) before the 545 II's clipping LED lit up. But they were way too loud to listen to, at that point, anyway. Even my GFA-535 II was plenty loud-enough (i.e. way too loud at max usable volume setting), with the MG-12s. It's rated at 60 W/ch into 8 Ohms (and probably 100 W/ch into the 4 Ohm MG-12s). I got the GFA-535 II for less than $100, from ebay! You could get two or three Adcoms and bi-amp or tri-amp your Maggies, depending on which Magnepan model you have, and have more power than you could use.

I eventually went from a GFA-545 II to a GFA-585, which is rated to do 400 W/ch average, continuously, into 4 Ohms or 1000 W/ch average, continuously, into 1 Ohm (and 250 W/ch into 8 Ohms).

But the GFA-585, which also has much better distortion and intermod specs, cost me about $600 on ebay, whereas two GFA-545 II models cost me less than $200 each, on ebay.

Still, I couldn't resist. And it's somehow comforting klnowing that neither my Maggies nor my Vandersteen 2Ces (or at least their fuses) would survive if I wanted to see the clipping indicator on the amp light up.

On the other hand, with that amp I did quickly discover, to my surprise, that the Vandersteens have two red over-temp warning lights behind the sock, that start flashing if they are driven too hard. Somebody on another forum mentioned using that amp with some identical Vandersteens, and told a story about how he had them turned up really loud and went into another room for a few minutes and when he came back one of the speakers was engulfed in flames! (And the amp was still playing away happily...)

Later I went ahead and also got an Adcom GTP-500 II preamp, which has a remote control and a motorized volume knob. Wow how I dearly love having a remote control for the volume.

(Just for the sake of completeness: Note that the GFA-585 (and the similar GFA-565 monoblocks) had a bad batch of expensive 220 uF electrolytic caps on their input boards (in the servo circuits), which should be replaced ASAP (or, if they've already leaked, carefully follow the board-cleaning instruction posted at diyaudio, but sorry about your speakers because it usually caused the DC output offset to go to the power supply rails. Luckily, mine did not do that.) The other models I mentioned do not have that problem.)
 
Please correct me if wrong.

You will need 2 of the amp module for each channel plus a phase splitter to drive them in bridge mode in order to deliver 100W for nominal 8R load? If we need to go down to 4R then each amp module will require 2 3886...2R will need 3 3886...etc ?

If it works in this fashion then I can use 4 (3 3886 parallel) modules connected in bridge mode (for both channel) to drive a power hunger Maggie?
No.

If you want 100W into 8r0 from a bridged arrangement, then the amplifier in each half of the bridged arrangement must be designed to deliver 50W into 4r0 and also be designed to properly drive a 4ohms speaker.

That is not an easy achievement using current crippled chipamps. I see the smoke and 'am waiting for the flames.

I would recommend you don't even contemplate examining what you need to do to get adequate performance into a 2ohms speaker.
 
Hi AndrewT,
Thanks for your reply, I am still getting somewhat confused. By looking at post #1,
the link was claiming a 3 chip parallel can produce 150W, then I figure this 150W claim was referring to a 2R load. Can I assume that for a 8R load the chip can deliver say 50-60W? And even if 3 chips were in parallel it will still deliver 50-60W on a 8R load? Now if I bridge 2 of these 3 chip parallel modules I can expect a 100W output at 8R? It might be complicate to build but is this technically possible/reasonable? Isn't parallel will give more current and bridging will give you more output power?
 
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