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Chip Amps Amplifiers based on integrated circuits

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Old 12th July 2018, 10:23 AM   #1
bauderline is offline bauderline
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Hi Folks,

I recently bought four of these fellas...

Assembled LM3886 X3 in Parallel 150W Pure DC Mono Power Amplifier Board HIFI | eBay


... and I am interested in building something very similar to the BPA300 by Alex.

I'll hold my hands up an admit here that I am a complete novice to the DIY audio stuff and don't really understand what I am doing. I have dabbling with electronics for the last few years and working with things like RPi and Moteino to build some home automation stuff, so whilst I have a decent basic understanding of electronics at this stage this is quite a radical departure and I will need a lot of hand holding if people are willing to help. I do learn quickly as long as small words and visual aids are used. lol.

Looking at the build information on shine7 the design and construction of this setup appears to be fairly straightforward and I assume the board I have bought from ebay is a close derivative of the PA150 design, it certainly appears to be.

What I am curious about is the power amp setup used in the BPA300 seems quite different from what is used in other gainclone builds, where exactly is the rectification taking place in his setup. I am probably missing something obvious but would like to understand it better.

Best regards, Peter.
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Old 12th July 2018, 10:40 AM   #2
Mooly is offline Mooly  United Kingdom
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Welcome to diyAudio

The boards in your link require an external power supply. This would consist of a transformer with a either dual winding or a split winding, a bridge rectifier and two reservoir caps.

The board say up to -/+36 volts DC and so that places an upper limit of using a 25-0-25 volt AC transformer, however for safety and to allow for voltage rise at light loading a 20-0-20 would be more suitable. The caps should be around 6800uF to 10,000uF and the rectifier should be a 35A 400 volt type.

The transformer will need to be substantial if you are going to run four of these off one power supply, so something like a 500VA toroid in practice.
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Old 12th July 2018, 05:09 PM   #3
bauderline is offline bauderline
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Thanks for the welcome, much appreciated !!

The following rectifier/cap setup seems to be in line with the spec you have mentioned, the caps are apparently of good quality also..

Douk Audio LM3886TF Amplifier Board + Rectifier Filter Power PSU DIY Kit / 1Set 8589944621790 | eBay

I know there are amp boards bundled with that but I can put those to other uses later.

Thanks!
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Old 12th July 2018, 05:21 PM   #4
Mooly is offline Mooly  United Kingdom
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Yes, something like that is what you want. The other alternative would be a chassis mounted bridge rectifier and chassis mounted caps using suitable fixing clamps.
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Old 12th July 2018, 06:44 PM   #5
bauderline is offline bauderline
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Yes, I had a closer look at the images on Shine7 and can see he has couple of them fixed to the front of the case, his setup makes more sense now.

Thanks !!
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Old 13th July 2018, 12:28 AM   #6
asuslover is offline asuslover  Romania
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Can you plz post a decent picture of the power chips ?
The biggest concern is the fake components.
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Old 13th July 2018, 12:53 AM   #7
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by asuslover View Post
The biggest concern is the fake components.
I think it's a given that some of the components came from the flea market. I'd be more concerned about the engineering that went into that amp.

For example their claim of 150 W is flat-out wrong. It is true that a single LM3886 will provide 50 W into 8 Ω on a 35 V supply, but that doesn't mean you'll get 150 W if you put three in parallel. You'll still only get 50 W as the amp will be limited by the supply voltage.
You'll get about 100 W into 4 Ω, which is an improvement over the 68 W provided by the LM3886 by itself.

Tom
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MOD686: Up to 240W/8Ω, <0.00025% THD. MOD86: 40W/8Ω, 0.000054% THD. HP-1: 3W/20Ω, -130dBc THD, 128dB DNR.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 13th July 2018, 11:31 AM   #8
bauderline is offline bauderline
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Quote:
Originally Posted by tomchr View Post
I think it's a given that some of the components came from the flea market. I'd be more concerned about the engineering that went into that amp.

For example their claim of 150 W is flat-out wrong. It is true that a single LM3886 will provide 50 W into 8 Ω on a 35 V supply, but that doesn't mean you'll get 150 W if you put three in parallel. You'll still only get 50 W as the amp will be limited by the supply voltage.
You'll get about 100 W into 4 Ω, which is an improvement over the 68 W provided by the LM3886 by itself.

Tom
Tom,

Is this board/amp not basically a clone of the PA150 by Shine7, it also has the chips wired in parallel, if not what do you believe the differences are ?

BR Peter.
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Old 14th July 2018, 05:43 PM   #9
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by bauderline View Post
Is this board/amp not basically a clone of the PA150 by Shine7, it also has the chips wired in parallel, if not what do you believe the differences are ?
Note the spec by Shine7: 150 W into 2.7 Ω. Amplifiers are normally specified at 4 Ω or 8 Ω. Not 2.7 Ω. 150 W into 2.7 Ω is 20.1 V RMS, which will dissipate 101.25 W into 4 Ω. Physics.

I'm not interested in evaluating the various copycat eBay products. I am very familiar with the time, effort, skill, and money it takes to develop a good circuit and a good PCB layout. I see no point in helping the copycats in their mission to drive honest businesses, such as mine, out of business. I hope you understand.

If you're interested in Shine7's circuit, how about contacting him/her directly? It looks like they respond to comments via their Facebook page. Shine7 Audio DIY Page

Tom
__________________
MOD686: Up to 240W/8Ω, <0.00025% THD. MOD86: 40W/8Ω, 0.000054% THD. HP-1: 3W/20Ω, -130dBc THD, 128dB DNR.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 16th July 2018, 01:08 AM   #10
bauderline is offline bauderline
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Quote:
Originally Posted by tomchr View Post
Note the spec by Shine7: 150 W into 2.7 Ω. Amplifiers are normally specified at 4 Ω or 8 Ω. Not 2.7 Ω. 150 W into 2.7 Ω is 20.1 V RMS, which will dissipate 101.25 W into 4 Ω. Physics.

Tom
Yes, you are correct at that point, I had a good read again through the information on his site.

Quote:
Originally Posted by tomchr View Post
Note the spec by Shine7: 150 W into 2.7 Ω. Amplifiers are normally specified at 4 Ω or 8 Ω. Not 2.7 Ω. 150 W into 2.7 Ω is 20.1 V RMS, which will dissipate 101.25 W into 4 Ω. Physics.

I'm not interested in evaluating the various copycat eBay products. I am very familiar with the time, effort, skill, and money it takes to develop a good circuit and a good PCB layout. I see no point in helping the copycats in their mission to drive honest businesses, such as mine, out of business. I hope you understand.

If you're interested in Shine7's circuit, how about contacting him/her directly? It looks like they respond to comments via their Facebook page. Shine7 Audio DIY Page

Tom
I kind of see where you are coming from, at the same time I don't how providing me some high level detail on what you believe makes their product inferior is helping them. I would say quite the opposite is true, I would be more likely inclined to buy from a reputable source once I had some understanding of the differences.

Having said that I am going to get some of the original PCBs made up and will source the components myself and hopefully learn a bit more along the way.

BTW - I had a look at your products, some very nice kit there, fair play!
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