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Chip Amps Amplifiers based on integrated circuits

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Old 30th May 2011, 07:35 PM   #1
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Default Beginning DIY Audio

Hi All

With the conclusion of my last big project, I've found myself becoming very interested in building some sort of amplifier. This is where the ignorance begins...

Initially I thought some sort of subwoofer set up would complement my existing Hi-Fi, then I thought about the larger power involved in any sub, and I think a low cost low power system would be a much better starter project.
Am I right in assuming a subwoofer amp and crossover would be harder to build than a small component set-up?

I've read a little about gaincards and the simplicity of the circuits involved, but I still manage to become lost in all the options involved! I was hoping someone with some experience might be able to point me towards a suitable schematic, or even better a how-to or build log? I'm not too bothered by working with mains electricity, and ideally I suppose I would love to be pushing at the thick side of 100W through the amp (split into 2 channels if possible)

What sort of expenditure (minus enclosures) is involved with constructing one of these? as I'm on a student budget :P

Sorry for the essay, I got carried away
Cheers

Ben
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Old 30th May 2011, 08:26 PM   #2
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Hi,

No, I'm sorry to say that, but a Subwoofer with a Plateamp is about as easy to build as it gets.
Just do yourself a favor and don't start with something too complicated...

Define your goals and then think about it. What do you want/need? How big is your room? Music or HT? How loud do you listen?

And, what do you want to build? The loudspeaker? Or are you more interested in electronics?

I'd say start simple, things will get complicated anyway ;-)

Michael
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Old 30th May 2011, 08:57 PM   #3
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Thanks for the reply
I'm pretty happy to hear that a subwoofer amp would be an easy build. I would love to make an acrylic enclosure for the sub. I suppose I would buy the actual woofer and focus more on the amp and enclosure.
Music and tone wise, I'm looking for bass that is fairly window shaking, but not at the expense of being flabby. I listen to a lot of drum and bass and breakbeat, so tight, deep kicks and fast punchy sub notes are what I'm looking for.
I may be aiming high here, but working on what I have experienced, 250W would be more than enough.
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Old 30th May 2011, 11:16 PM   #4
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"Biumph", aka- "Triumph V2"... - Techtalk Speaker Building, Audio, Video, and Electronics Customer Discussion Forum From Parts-Express.com

This may be louder than you think.
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Old 31st May 2011, 01:26 PM   #5
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I think being over ambitious and trying to build the amp and enclosure would be my ideal way forward. A plate amp isn't related to a common plate tube amp is it?
Hypothetically, if I paralleled 3 LM3875 or 3 LM3886 that would give me nearly 200W into 4ohm (or do these chips not appreciate being paralleled) ?

Would the schematic for a sub IC amp look any different from a normal amp, excluding the low pass filter? What would be the most efficient way of sending the signal from source into 2 separate amplifiers if I used my existing amp for high frequency?

Cheers
Ben
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Old 31st May 2011, 02:10 PM   #6
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Get a board or kit off eBay and make your life easier. Perhaps a board with 4x parallel chips. But youre going to need a big power supply and heatsinks.
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Old 1st June 2011, 02:47 AM   #7
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Unhappy more info than you wanted

Hi Ben,

I think you misunderstood Michaelís statement ďa Subwoofer with a Plateamp is about as easy to build as it gets.Ē I think he meant building the subwoofer and purchasing a ready-made plateamp is about as easy as it gets.

Iíve been looking into subwoofer amplifiers too, and have come to the conclusion that no such thing exists, meaning there is no such thing as an amplifier designed specifically for driving subwoofers Ė at least not in kit form. If anyone reading this knows of one, please post a link to it.

That being said, it sounds like you may want to build an amplifier. I agree with TheLaw117 when he recommends buying a board, but I would go further and recommend buying a kit with all the components and detailed instructions. I recently built this kit DIY Chip Amplifier Kits, PCB's, Components and Information. and found the instructions easy to follow, and I like the final product, but I fear it may not have enough power for your application. For my subwoofer Iím considering one of these three: Mosfet Subwoofer Amplifier Kit - 330Watts/RMS by AmpsLab , Connexelectronic or Connexelectronic . When shopping for a kit, keep in mind that the power supply is usually sold separately from the amplifier boards. However, most kit vendors sell both power supplies and amp modules, and they can help you match one of their power supplies to your amp board(s).

A note on costs: I think you will be surprised at how quickly things add up. I recommend before committing to a DIY amplifier project that you price the following:
  • Amplifier modules
  • Power supply
  • Transformer
  • Metal chassis (metal acts as an rf shield)
  • Heatsinks, if they are not included in the chassis
  • Mains connector and power cord
  • Mains fuse(s) and holder(s)
  • More fuses & holders for your amp board, if theyíre not already included in the kit
  • Power switch
  • RCA jacks & speaker terminals
  • PCB standoffs
  • A variety of wire, for mains power, line level, and output level. Color-coded wire is nice too.
  • Tools tools tools:
    • Good quality soldering station. A 30W non-adjustable iron will not do.
    • Solder sucker or other desoldering tool for all the mistakes youíll make.
    • Wire cutters, strippers & crimpers
    • Good quality multimeter
    • Something to cut holes in your metal chassis. I recommend a unibit.
    • Helping hands are nice but not necessary
If you donít want to build an amplifier, here are two reputable dealers for ready-made plate amps: https://www.madisound.com/store/index.php?cPath=360 Subwoofer Amplifiers, Plate Amplifiers, Home Audio/Video Subwoofer Amplifiers, Powered Subwoofer Amplifiers Perfect for Building Your Own Powered Subwoofer. .

I keep meticulous records of project costs, and my 70W X 70W chipamp cost $240.88 in parts. I also spent $96.14 on new tools, and $22.75 on mistakes. Of course cost goes up as power goes up.
Oh, donít forget your electronic crossover.

So, I think the answer to your question: ďAm I right in assuming a subwoofer amp and crossover would be harder to build than a small component set-up?Ē is YES, and it will be more expensive too.

Now, if Iíve scared you out of building an amplifier, you may prefer to build a subwoofer with ready-make plateamp (with build-in crossover). Again, kits abound. Here are some more kits from reputable dealers: https://www.madisound.com/kits/subwoofer-kits.php SUBWOOFER KITS from Parts Express ship same day and come with 45 day money back guarantee. Free Shipping Available. Order free 10,000 product catalog. with more plans here: Parts-Express.com - Project Showcase Index: Browse Through Speaker Building Projects From The Last Four Years . Of course, there will be plans in the subwoofer forum of this web site, but be warned! Many people on this web site like to build some rather unconventional designs. 5 way project - tapped, bass, mids and tweeter, big boy system

FYI: acrylic is not a good enclosure for a subwoofer. There just so happens to be a long thread on speaker cabinet materials here: What are the characteristics of a better material for enclosure?

Tell us whatever you decide to do, and have fun!
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Old 1st June 2011, 06:53 PM   #8
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Hi Byron

Cheers for the reply

I did a little further research, and came up with an alternate option. Hypothetically, if I were to be using a dual 4 ohm voice coil subwoofer, would I be able to drive each coil from a separate amplifier using an LM4780 in each (either bridging both chip, or paralleling them, I'm unsure which would be more appropriate for driving a 4ohm load), based on this schematic:
http://www.audiosector.com/lm4780%20amp.pdf

If that wouldn't work, would it be possible to link the 2 voice coils to form one 8ohm load and drive them from one chip? I guess I'm just a fan of homebrewed ideas :P

Looking ahead a little, would this kit work as a preamp / electronic crossover?
Subwoofer (12HZ-48HZ)+(28HZ-112HZ) preamplifier board | eBay UK

Thanks again

Ben
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Old 1st June 2011, 07:40 PM   #9
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Quote:
Originally Posted by Ben B View Post
Hi Byron

Cheers for the reply

I did a little further research, and came up with an alternate option. Hypothetically, if I were to be using a dual 4 ohm voice coil subwoofer, would I be able to drive each coil from a separate amplifier using an LM4780 in each (either bridging both chip, or paralleling them, I'm unsure which would be more appropriate for driving a 4ohm load), based on this schematic:
http://www.audiosector.com/lm4780%20amp.pdf

If that wouldn't work, would it be possible to link the 2 voice coils to form one 8ohm load and drive them from one chip? I guess I'm just a fan of homebrewed ideas :P

Looking ahead a little, would this kit work as a preamp / electronic crossover?
Subwoofer (12HZ-48HZ)+(28HZ-112HZ) preamplifier board | eBay UK

Thanks again

Ben
Hey Ben, I have that preamp/crossover board. I actually haven't used it yet. I'm still in the middle of the build. I'll be completely done by the end of the month, and I can tell you how it works. I know that I can't tell you much about it for about a month, but YOU will have to do a lot of planning before you actually start putting stuff together,

I am also using an LM4780 as a subwoofer amp in my own setup. Since my sub can only handle nominally 40W and 80W max, I'm only going to be using one channel. However, if I upgrade in the future, I do have the option of running the 4780 is parallel, which gives me 100W-150W, depending on the sub.

Again I have not tested the 4780 either. I have tested my 2x LM3886 segment which will be driving the satellites. The LM3886s do have quite a big of power behind them as well.

It seems that we are a long the same lines of interest. I'm pretty much packed with work, but I can probably have this all done fairly quickly...if you're interested in the results.

I'm using this LM4780 board: LM4780 stereo/parallel power amplifier PCB ! | eBay

But be warned, as noted above. You will probably look at all of these things and think that it would be pretty cheap. While in fact, it CAN BE far from it. Depending on the components you use, you can slim down the price a bit, but you will surprised how quickly a few resistors can add up. My LM3886 x2 Amp + LM4780 sub amp, which is driving Hivi M4Ns + TN25s, and a Tang Band 5.25inch sub...has added up to over $400. I used very good quality components, yes, but you'll probably only save $50 if you cheap out on components. So your sub might wind up being $150-200.

Not the worst, not the best. It definitley is rewarding though. Good Luck.
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Old 1st June 2011, 09:14 PM   #10
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well, 200 watts area lotta powa.
but actualy power is not what you need in the first place, even if it will be a subwoofer.
supposedly the correct way to achieve statisfaction may be as following:
-> seek out drivers that are available for You (location, bidget)
->model the drivers to find one that suits Your demand
-> predict the maximum power it could handle
seek possible amplidfier solutions for the required power output

if this is Your first amplifer, i would very strongly advice You to first build the most simplest and most fool proof amplifier.
Actualy my advice is usualy to pick up TDA1557q chip.
the reason behind it is very simple, as the chip is quite user friendly.
minimum external component count, fixed gain, good availability, even if it gets killed it is a cheap thingy. So are the few external components it requires. It can run -with limitations in both output power and quality- using a very freindly supply voltage -in other words for the sake of testing 99% sure to find some wallplug adapter or a battery, or a cheapo pack of battery cells that manage to run the amp-.
other than that the chip is excelent to practice proper grounding, and allso will enable the user to see real life form of RF interference, and how to deal with it.
Notice, that the chip can be turned into a subwoofer amp -a normal amp with a lowpass filter- with very little efforth. In fact, for that role in a smaller scale hi-fi i do consider this chip to be a proper low cost choice.

If i was to give a shot at DIY amps surely it would be the first one to build.
with a little thinkering this chip, and 6 capacitors can yield an active 2 way mono amplifier with 1st order active filter. (well.. bit improper but close enough to be considered loosely identical in function) and giving a decent output power.
There are other chips with less pin count, more power and more quality, but actualy requiring more external components. And split power supply.

I think this chip is a good bang for the buck.
Allso, it has more expensive "realitves" giving better quality/performance, naturaly for a price.

Since it has so low count of external components it is reasonable to not demand a PCB at all.
Heatsinks is allso not an issue, as it can be salvaged from a wide range of sources.

And the best part is, that it can be tuned for ever with minimal efforth, and good results.
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