DIY AMP Three parallel LM3886 power amplifier board 150W Current fever #868 - Page 2 - diyAudio
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Old 29th May 2012, 02:29 AM   #11
syklab is offline syklab  Hong Kong
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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?
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Old 29th May 2012, 04:17 AM   #12
gootee is offline gootee  United States
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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.)
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Old 29th May 2012, 09:10 AM   #13
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by syklab View Post
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.
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Old 29th May 2012, 09:38 AM   #14
syklab is offline syklab  Hong Kong
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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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Old 29th May 2012, 09:57 AM   #15
AndrewT is offline AndrewT  Scotland
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No.
A bridged amplifier delivers double the power into twice the load impedance.

I told you that if you want a bridged output of 100W into 8r0 then you need to design each half of the bridge to deliver 50W into 4r0.

Do you understand that?
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Old 29th May 2012, 10:08 AM   #16
bcmbob is offline bcmbob  United States
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Here is a reference page that may give some insight. DIY BPA300 6x LM3886 300W audio Amplifier
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Old 29th May 2012, 10:13 AM   #17
syklab is offline syklab  Hong Kong
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If I want to use 2 of the module from post #1 to create a bridge, how much would I get for a 8R load and 4R load?
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Old 29th May 2012, 10:15 AM   #18
syklab is offline syklab  Hong Kong
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Quote:
Originally Posted by bcmbob View Post
Here is a reference page that may give some insight. DIY BPA300 6x LM3886 300W audio Amplifier
Hi,
I read that and I am still not clear due to different feedback from different person.

Thanks
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Old 29th May 2012, 10:18 AM   #19
bcmbob is offline bcmbob  United States
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Please explain.
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Old 29th May 2012, 10:57 AM   #20
AndrewT is offline AndrewT  Scotland
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Syk,
there are three links in post1.
Which are you referring to?
Quote:
create a bridge, how much would I get for a 8R load and 4R load?
Quote:
A bridged amplifier delivers double the power into twice the load impedance.
Quote:
you want a bridged output of 100W into 8r0 then you need to design each half of the bridge to deliver 50W into 4r0.
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