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Old 2nd February 2007, 06:16 AM   #1
yusuf is offline yusuf  India
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Default LM4780 kit vs ready car amplifier

ALl,

Please help me decide. I need amp for my DIY sub. I shortlisted two:
1) get DIY 4780 kit from audiosector which looks very good and costs around $73.
2) Sony xplod car amplifier for almost same cost. Advantgae is that this is available locally (I am in India) while kit needs to be ordered Internationally.

My question, is that major difference in quality in either approach? Is it worth the trouble ordering, building rather than buying off the shelf car amplifier. I am in India.

Many thanks
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Old 2nd February 2007, 02:13 PM   #2
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You're probably better off just buying an off the shelf amp. I feel if you're going to build an amp and you don't already have a lot of experience at it, it's going to be a while before it's completed and able to be used in the car. You may also run into problems while building it.

I'm looking into building one and can already see the kits are a fair price but I can order high end components from mouser and save a good amount of money.
Looks like the PCB's are the best way to go, granted you can pickup the components locally.

Check out Brian's site though, his kits are the cheapest and he seems to be the number one source on the net.
http://www.chipamp.com/orders.shtml

I just bought a cheapo Kingwood 4 channel, bridgeable car amplifier with low pass crossover, bass frequency range and bass gain control.
It's about 1,000 watts RMS and I can bridge it into 4 ohms to match my woofers' impedance.
Car amplifiers are almost always 2 ohms unless you're able to bridge them or it of course says otherwise. The point is, I got it for $60 with shipping and it actually looks really nice.
The top is made to look like a chrome op amp.

You're better off dumping the money into an off the shelf amp and build the gainclone for a special project. I've seen guys build the gain clones with as little as 9 parts which really makes them tempting since your build cost would probably max out at 30 USD once you added the power supply, housing and connectors...possibly less.
You could run it straight off the car battery but you wouldn't get much wattage out of it compared to with a transformer.

This is the main page:
http://www.geocities.com/rjm003.geo/...io/diy_gc.html
Check out the 9 part count version:
http://www.geocities.com/rjm003.geo/...ges/gc_brd.gif
Here is the classic version:
http://www.geocities.com/rjm003.geo/...gc_lm3875a.gif

If you do decide to build a gainclone, be sure to use at least 10,000 uf caps instead of the 1,000 uf. Everyone says it's horrible with the 1,000. The bass just won't be there. Some people go 15,000 or even 20,000.
You can get away with wiring it point to point which makes it very appealing to the newly budding diy artist.

I just may go low tech and point to point wire mine. I intend to use it in a guitar amp and want to have the lowest part count possible.

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Old 3rd February 2007, 03:45 AM   #3
yusuf is offline yusuf  India
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@DrFrankenstein, Thank you for your inputs.

I forgot to mention that I am building Sub for home theater use. Since there is no so moderate price plate amplifier available in India, I am opting for car amplifier or kit.

Although I do not have much audio experience, I have enough electronics experience and hence I may not have problem building kit if I get better quality. But if all remain same, I can opt for off the shelf car amplifier since it is available locally.

Btw, car amplifier I am opting is Sony XPLOD XR-552 in bridge mode (available for approx $70 in india).

Sub is build using sealed enclosure.

Look forward for suggestions.

Thanks
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Old 3rd February 2007, 04:58 AM   #4
dfdye is offline dfdye  United States
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Just to get the story straight, are you planning on using this amplifier in your home or in your car? If you care going to use it in a car, then you should NOT try and build a chipamp without having a fairly good knowledge of the PSU needed for it to run off of 12V DC. Here is a pretty good run down of the required PSU which is NOT simple. If you need this for car audio, I suggest the Sony amp as the best choice. If you are using this for home use and can use a standard transformer, I would use the audiosector kit.
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Old 3rd February 2007, 04:17 PM   #5
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OK knowing the purpose of the amp helps a lot.

Now I would say just build the gainclone amp and with your experience, you shouldn't need a kit. The 9 part count gainclone I linked you to sounds good from what I've been told.

If you use the LM3886, you'll be able to get about 70 watts RMS out of it and the only part that will cost you much will be the power transformer. The entire project probably wouldn't cost you more than $40-$50 USD.

The Sony amp will end up being in the $100 USD price range because of the cost of a decent power transformer.

Those are the approximate costs for us in the USA. I will be building the 9 part count gainclone and have a lot of scrap parts floating around. I might be able to get away with building it at little or no cost. Not sure if you have parts floating around but I'm suspecting so since you have a lot of electronics experience. I truly am still in the amateur stages but am fairy knowledgeable. My building experience is still minimal.
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Old 3rd February 2007, 04:54 PM   #6
dfdye is offline dfdye  United States
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An additional comment:

The gainclone circuit is NOT the chipamp you should be using for a sub amplifier. The bass response is less than ideal due to the relatively anemic rail capacitors used. I would instead use much beefier rail caps and use a modified version of the BPA200 found in the National data sheets. This will give you plenty of smack and tight low end response that is lacking in the gainclones.

If you would rather not use a 4X chip setup, I personally use Linkwitz's take on the LM3886 set up with the 110uf N.P. cap for Ci. This circuit does a great job of effectively targeting the chips for bass reproduction and definitely gives great impact that I do not get with the standard gainclone circuit. Though it is not sold in kit form, it is very simple to wire using protoboard (I have not tried P2P). I use about 5k uF per rail per chip using an unregulated PSU, which is in line with Linkwitz's recommendation. One of these chips is NOT enough to effectively drive a sub at "Home Theater" listening levels, but it is a good start and should be enough to favorably compare to the Sony.
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Old 3rd February 2007, 05:29 PM   #7
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Im not sure a chipamp is the best way to go for powering a sub? And also its going to end up costing a bit more then $75. You still need to ship it to inda and buy a transformer and any connectors. So figure a minimum of $125. Im not sure whats availabel in India, but you may want to look on ebay or second hand shops for something like an old NAD amp like the 2150 which uses nice 150w Sanken output transistors and can be bridged for 150w
Nad 2155

There are alot of other powerful well built amps from the 80's that can work very well for powering subs and can be had very cheap. Nad, Rotel, Adcom, Hafler.....etc Since your expereinced with electronics you may even find a real bargain on something that needs a repair.
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Old 3rd February 2007, 05:58 PM   #8
dfdye is offline dfdye  United States
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Quote:
Originally posted by imperfectcircle
Im not sure a chipamp is the best way to go for powering a sub?
You do make a very good point, especially considering that a rather nice sub amp can be had for about the cost of a chipamp after housing and PSU components are considered (I have that Bash amp in my HT sub and it works just fine for me). The rub here, if I am correct, is availability. If this is indeed the case, many of the options you mentioned (while indeed nice) will not be possible for yusuf to fine.

I have seen a number of chip-based sub amps here and have built one myself. Though they do not have the raw power often found in many other sub specific amps, they do indeed serve the purpose and do it well at moderate volume levels. It not be the "best" way, but it is a way, and it works well for a moderate price.
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Old 3rd February 2007, 06:21 PM   #9
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I have to DITTO that. I have the same sub (BASH 300S). Superb performer. And more power than I need! I've also made an LM3886 based sub amp and was very happy with it. But, realistically, money and hassle, it doesn't come close to the Bash.

But, I DID enjoy the challange. So it's up to you again.
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Old 4th February 2007, 08:02 AM   #10
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Quote:
Originally posted by dfdye
An additional comment:

The gainclone circuit is NOT the chipamp you should be using for a sub amplifier. The bass response is less than ideal due to the relatively anemic rail capacitors used. I would instead use much beefier rail caps and use a modified version of the BPA200 found in the National data sheets. This will give you plenty of smack and tight low end response that is lacking in the gainclones.

If you would rather not use a 4X chip setup, I personally use Linkwitz's take on the LM3886 set up with the 110uf N.P. cap for Ci. This circuit does a great job of effectively targeting the chips for bass reproduction and definitely gives great impact that I do not get with the standard gainclone circuit. Though it is not sold in kit form, it is very simple to wire using protoboard (I have not tried P2P). I use about 5k uF per rail per chip using an unregulated PSU, which is in line with Linkwitz's recommendation. One of these chips is NOT enough to effectively drive a sub at "Home Theater" listening levels, but it is a good start and should be enough to favorably compare to the Sony.
Swapping the 1,000 UF caps with 10,000 or higher takes care of the bass punch issue, basically a pretty off the shelf mod I mentioned early on. All the guys I've talked to swear by this swap up and the results.

I also recommended simply going with the 9 part count build and point to point wiring. Even in India, that's going to be a really cheap build granted you can get the power transformer for a decent price. You can cram it into a pretty small case and it's it's metal, it will also serve as the heat sink.

He's going for cost effective, I suspect most of you are going high budget in your heads. Going with the point to point, 9 part count build and a cap and coil 12 dB crossover, he'll have one heck of a sub system for about $50 USD, not this $125 most of you speak of. As it is you can get the chips pretty cheap. Order them as samples from National Semi Conductors and the only thing you'll pay for is shipping. There's also a handful of companies that will send out caps and coils as samples and they'll send you any value and voltage you want, I've got a bunch of them.
..$125 + ?
Not if you're moderately resourceful.
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