3886 based power amp kit, how to find the best AND the less expensive PCB board? - diyAudio
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Old 15th February 2011, 11:36 AM   #1
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Default 3886 based power amp kit, how to find the best AND the less expensive PCB board?

Hi,

Newbee in power amp design and construction.
I recently got interested in constructing myself a power amplifier.

My plan is to build an 8-way power amplifier based on the LM3886 chip, to actively drive a pair of speakers, not as a professional, merely as a hobby, for fun, for the beauty of building it myself.

I have absolutely no idea about the different power amp designs and their merits. There are many different PCB kits sold on the internet, including on ebay. Some are very cheap, some are way more expensive.
How to choose wisely for this plethora of kits, and simultaneously only spend the necessary money?
I do have plans of an obviously well designed power amp, but do not have the necessary skill to create a PCB myself, nor the necessary knowledge to pin point the exact replicate of it on a catalogue.

I have some basic skills in soldering and am not afraid to tackle a power amp project, but am reluctant to pay overpriced products, especially if it may result in some waste (due to my bad skills).

This may seem as a bottle in the sea, I just do not know where to search.

Regards,
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Old 15th February 2011, 03:00 PM   #2
jerryo is offline jerryo  Isle of Man
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Hi bidibidi,
I do not know if it is the best or cheapest but it is certainly one of the smallest pcb's for a 3886 chip amp and if you want to build an 8 channel amp then it will be worth a look.
Go to "search" and look for a member called "Digi01"; he has detailed information about the pcb and psu for his 3886 design.
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Old 15th February 2011, 03:06 PM   #3
jerryo is offline jerryo  Isle of Man
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Actually the thread is called "my 3886IGC pcb" (the IGC stands for inverted gainclone) The pcb's are only about 50mm square!
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Old 15th February 2011, 06:21 PM   #4
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Quote:
Originally Posted by jerryo View Post
Actually the thread is called "my 3886IGC pcb" (the IGC stands for inverted gainclone) The pcb's are only about 50mm square!
Many thanks for your reply.

A question of a newbie:
IGC stands for Inverted GainClone.
Why is the inverting necessary, and what would it be if there were no inverting?

Regards,

Last edited by bidibidi; 15th February 2011 at 06:39 PM.
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Old 15th February 2011, 06:32 PM   #5
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I have used several of these LM3886 chip amp "modules". They are available on Ebay from several sellers. I would avoid the versions that have other things on the PCB, like power supply or protection circuits. This one keeps it pretty simple, so there is not much to mess up!

Dual Mano LM3886 Mini Amplifier Finished PCB 68W X 2 - eBay (item 300525755209 end time Mar-14-11 18:52:51 PDT)

In case someone is reading this in the future, when the auction has been removed, just look for one like this:
Click the image to open in full size.

-Charlie
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Old 15th February 2011, 07:19 PM   #6
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Quote:
Originally Posted by CharlieLaub View Post
I have used several of these LM3886 chip amp "modules". They are available on Ebay from several sellers.
...
Dual Mano LM3886 Mini Amplifier Finished PCB 68W X 2 - eBay (item 300525755209 end time Mar-14-11 18:52:51 PDT)

-Charlie
Ok, thank you. Would you have any opinion on how it compares to other power amps?

The title says dual mano (mono?), but there is only one power amp chip on the picture, I guess two boards are supplied. Not sure about the tolerance of components used, it is not mentioned.
By the way, this particular PCB seems very popular as many sellers on ebay propose it, sometimes under a specific brand name.


Again, question of a newbie: using the same power amp chip, what makes one power amp design better than the other?
One may reply that I should do my homework, but have no idea where to start.

Regards,
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Old 15th February 2011, 07:36 PM   #7
AndrewT is offline AndrewT  Scotland
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The ebay link does not say you get two assembled amplifiers for the price.
I would not buy the kit. I do not know which components are genuine and which are fake.
The PCB is common between different resellers.
Buy a bunch of PCBs and source your own components.
__________________
regards Andrew T.
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Old 16th February 2011, 05:58 AM   #8
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Quote:
Originally Posted by AndrewT View Post
The ebay link does not say you get two assembled amplifiers for the price.
I would not buy the kit. I do not know which components are genuine and which are fake.
The PCB is common between different resellers.
Buy a bunch of PCBs and source your own components.
There's no need to be so doom and gloom. The guy is just getting going.

These are fine, yes you get TWO of them. I have bought lots of them from various sellers. All were fine. Sure, sure you can't verify the components, etc. They come assembled, so the newbie can cut to the chase and get something working. Then he can take it to the next level.

How many posts on these forums are something like "I can't get my chip amp project working... waaaaah!". Get the assembled one and don't worry.

Here's another tip - there are sellers who sell two of these chip amp boards plus a separate power supply board. These are also good if you are starting out. For instance: LM3886 High End Power Amp Refer Gaincard New - eBay (item 120474005627 end time Feb-18-11 10:20:35 PST) Notice it says "fully assembled and tested"...

-Charlie
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Old 16th February 2011, 07:43 AM   #9
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Ok, all comments are well understood.


Again, I will have to apologize for my ignorance: for an 8-channel amp, how many power supply regulators do I need? Is there any obstacle to feed all channels with one power supply regulator?
Please correct me if I am wrong: I guess that the number of power supply regulator depends on the number of power transformers.
So, the same question for the power transformer: ideally, how many is best? One power transformer for 2 channels? Or for 3 channels? Or for 4 channels?

I am here not only considering budget, but also the stability, noise, balance, and any other parameter which may affect sound in an active 2-speaker configuration (4 channels per speaker).
I realize it is many questions, I am again kindly soliciting your comments.

Regards,
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Old 17th February 2011, 09:27 PM   #10
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Quote:
Originally Posted by bidibidi View Post
for an 8-channel amp, how many power supply regulators do I need? Is there any obstacle to feed all channels with one power supply regulator?
Please correct me if I am wrong: I guess that the number of power supply regulator depends on the number of power transformers.
So, the same question for the power transformer: ideally, how many is best? One power transformer for 2 channels? Or for 3 channels? Or for 4 channels?

I am here not only considering budget, but also the stability, noise, balance, and any other parameter which may affect sound in an active 2-speaker configuration (4 channels per speaker).
It is possible to have:
a single power supply for all 8 channels
two or more power supplies, each supplying some subset of the channels

For each power supply, you need as a minimum:
1. a transformer of appropriate secondary AC voltage and current/power rating
2. a bridge rectifier or set of diodes to convert the transformer's secondary AC waveform to "pulsed DC"
3. Smoothing caps (large electrolytic capacitors) to smooth out the ripple in the "pulsed DC"

How many of these power supplies is a choice, and it depends on what you have available and how complicated you want to get with the design. You may find that you cannot purchase a single transformer in your area that is sufficient for all 8 channels, so you may need to think about how to proceed from there.

There are several things to think about when designing your power supply/supplies. There is a good overview for beginners here:
Elliott Sound Products - Linear Power Supply Design

Some additional higher complexity design tips can be found here:
Solid State Power Amplifier Supply Part 1

You will need to correctly size the voltage rating, capacitance, and ripple current rating of your capacitors. The transformer must have the correct secondary voltage and current capability. The rectifier must be able to handle the current demand of the amp at peak load with some headroom.

If you go for the power supply board from Ebay that I linked to, you should not expect the highest possible quality components, but they will likely be fine for two or even four of the LM3886 chip amps.

-Charlie
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