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Chip Amps Amplifiers based on integrated circuits

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Old 29th March 2014, 12:32 PM   #1
mattaus is offline mattaus  Australia
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Default First project with audio EVER

Hi all,

Straight off the bat I want to apologize if I am treading a well worn path here and repeating questions that people are sick to death of hearing. I have recently picked up the hobby of PCB design (while learning to build my own LED drivers) and I seem to like doing it so much that I am looking for larger projects to tackle. I read about Gain Clone amplifiers a few months back and decided I wanted to build my own. I found this instructable and figured that seen as it's more or less laid out for me, it would be a great one to start with.

However! I want to apply my PCB design hobby (Eagle for those following at home) to this amp. I want to lay everything out on one PCB - both amps and the power supply - and stick it all in one big housing. I'll insulate each section from one another as best I can but at the same time I want to reduce cable count as much as possible by using as many PCB traces as I can.

Now the reason I'm posting here is because prior to this project I've never had any experience with audio electronics at alll. I don't even own good headphones!

Because I know nothing I would like to know what parts, if any, can be swapped for surface mount equivalents. I have a re-flow station and solder paste and actually find this much easier and cleaner than through holes components. Now I understand that cutting down on noise etc in these devices can come down to the type of component used (electrolytic versus ceramic and so on) and as such would just like to know what parts in the linked project could be swapped? Or will it be so few it just won't be worth it? Come to think of it the component count is pretty low...

One other question - the toroid transformer. I live in Australia and our mains power is at 230V. The instructable above uses a 230V 2x18V toroid. The article states it's overkill; what would be more appropriate for the amp in question?

I clearly have more reading to do but I thought I'd ask these questions to help give me a boost.

Any advice would be appreciated. I have a few stickies to stumble way through

- Matt
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Old 29th March 2014, 12:43 PM   #2
AndrewT is offline AndrewT  Scotland
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educate yourself on Mains Electricity SAFETY !!!!!!!
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Old 29th March 2014, 12:46 PM   #3
mattaus is offline mattaus  Australia
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Thanks for the concern but I am aware of issues surrounding mains power and have worked with it before, albeit not in a professional environment
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Old 29th March 2014, 09:58 PM   #4
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Hi Matt,
I suggest reading the ESP website for general information.

The transformer you suggested is fine. I use a 25-0-25V 160VA tx from Jaycar for a tri-amped speaker. The choice of SMD over th comes down to two things; power rating, and the distance that musr be spanned. If yoh do not have to worry about spanning tracks, then you only concern is power rating. Do you have the data sheet?

Abs
I am in Port Melbourne.
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Old 29th March 2014, 10:14 PM   #5
mattaus is offline mattaus  Australia
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Thanks for the reply Absconditus. I don't have any parts yet - I'm busy researching before I place an order for all the parts. With rating in mind I'll pick parts that match the suggested parts ratings. Typically higher power SMD parts are larger footprints, but if the footprint is not large enough to span any potential tracks, then I will stick with what has been recommended.
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Old 29th March 2014, 10:36 PM   #6
Apogee is offline Apogee  United States
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Smile Wecome!

Hey Matt,

Welcome to the DIY hobby and the addiction that it will become!!!!

Regarding your proposed build, the reason that the power supply is usually on a separate board is due to noise. Sure, you can layout and build one big board, but as a practice it's usually better to divorce the power supply and keep it as far away from the signal components as you can.

Keep in mind that the pc boards all (maybe except teflon) have capacitance between the tracks. Hence, even though the tracks may not be connected, they still have the ability to interact with one another. This is where the art of design comes in. There are folks here that are well schooled in the art of proper board layout who will be happy to guide you if you're open to it and allow them to do so.

You might also take a look at how many high-end preamps are designed for ideas. Usually much attention has been paid to keeping the signal paths as short as possible as well as minimizing noise. You will also see the power supplies often located in their own internal compartment with metal shielding separating them from the signal circuitry also to minimize noise interaction.

Finally, once you graduate to digital layout, it becomes an entirely different can of worms dealing with high frequencies, proper ground planes and everything becomes even more critical.

The bottom line is, WELCOME TO THE HOBBY! Even when it gets frustrating, remember this is all about fun, enjoyment, and making the stuff the best that it can be. Each of us has the same ultimate goal... To learn from each other and have fun!

Kind regards,

Steve
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Old 29th March 2014, 10:52 PM   #7
mattaus is offline mattaus  Australia
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Thanks Steve I have a feeling I'm heading down another dark road lol.

I'm starting to think I need to take a step back and re-stock on exactly what I want to do here. That and the speakers I've chosen are only rated to 20W, so a 68W amp (30W at 8ohm) might not be the best idea! For what it's worth the drivers in question are Mark Audio CHR-70A's. The input will be from a Raspberry Pi device running the XBMC media application.

I want to build an amp (and matching power supply) that will produce good, reasonably high quality sound. It needs to be as compact as possible though from what I've seen so far nothing has popped out as being too big. I don't know much about amplifiers but I believe Gain Clone style devices are a good compromise between complexity, cost and fidelity.

Are you (or anyone else reading this) aware of a good project to look at? Or what sort of solution would be best for this set up?

- Matt
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Old 29th March 2014, 11:04 PM   #8
scott17 is offline scott17  United States
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This is an LM3886 project using SMD if I'm not mistaken:

My_Ref Fremen Edition - Build thread and tutorial
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Old 29th March 2014, 11:57 PM   #9
warrjon is offline warrjon  Australia
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Quote:
Originally Posted by mattaus View Post
That and the speakers I've chosen are only rated to 20W, so a 68W amp (30W at 8ohm) might not be the best idea!
I used to work on the bench for Marantz and most Monday/Tuesday mornings we would get the obligatory dead amplifier and toasted speaker/s for repair. Amplifier rated at 40W (approx) and speakers 100W.

The the thing that mostly blows speakers is clipping of the amplifier. This effectively puts DC on the speaker voice coil, heats it up and POOF.

Moral of the story is use the volume control wisely.

Quote:
Originally Posted by mattaus View Post
I want to build an amp (and matching power supply) that will produce good, reasonably high quality sound. It needs to be as compact as possible though from what I've seen so far nothing has popped out as being too big. I don't know much about amplifiers but I believe Gain Clone style devices are a good compromise between complexity, cost and fidelity.

Are you (or anyone else reading this) aware of a good project to look at? Or what sort of solution would be best for this set up?
If I were you I would start with the Gainclone LM3875/3886, you can use 2 eBay 36V 9.7A SMPS to power it these are cheap, this is what I am building ATM.

I would not make your own PCB for this unless you have a good amount of experience. These chips are very wide band amplifiers and if you get it wrong (ie too much capacitance in the PCB) it will oscillate.

SMD components can take a fair amount of power. A couple of weeks ago I replaced a 12V 1A SMD MAX635 that was so small I had to use the microscope and tweezers (no heatsink)
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Old 30th March 2014, 12:50 AM   #10
mattaus is offline mattaus  Australia
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OK, so you're suggesting I build the amplifier I originally linked to, but use one of these to power it for the time being?

I do think I will start small and just build an amp on it's own to learn and experiment with, and then move on from there.
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