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Old 13th September 2006, 03:25 AM   #1
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Default Newbie needs suggestions

Okay, so I finally got a little bit of soldering experience under my belt. This coupled with the circuits course I took this spring has me feeling confident that could finally put one of these things together, here is where I need you guys:

1. It seems like the three main chips used here are the LM4780, LM3886 and LM3875. What are the differences between these chips in terms of power, distortion, etc. Why would I choose one over another?

2. I have been planning on purchasing a kit from chipamp.com for quite some time, unfortunately last time I checked they were out of stock of almost everything. Any other recommended vendors?

3. Lastly, what exactly is a "snubberized" power supply and should I purchase a kit for one of these additionally if the kit already includes a basic power supply?

Thanks
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Old 13th September 2006, 04:33 AM   #2
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The LM3886 is a 68W amp the LM3875 is a 56W otherwise there the same. The distortion is around 0.03%

The LM4780 is a 60W x2 (stereo instead of mono like the other two). The distortion is around 0.07%

There all the same speed in response time so thats no big deal.

As for getting a kit, I don't know of any places off the top of my head.

And a "snubberized" power supply is one that has extra filtering to keep unwanted noise out. Though noticing a difference in sound is concerned, it's up to your ears.

And here is a web site that you can get datasheets for those chips if you want to do more reaserch
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Old 13th September 2006, 05:21 AM   #3
preiter is offline preiter  United States
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http://www.audiosector.com/

is another good site with 3785 and 4780 kits
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Old 13th September 2006, 01:41 PM   #4
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So the LM4780 is a stereo chip? Meaning if I got the audio sector kit which included 2 amplifier/rectifier boards I would be building a stereo amp with 120 wpc? That extra power might be nice.

Currently i've got a very good Marantz 2215b reciever that kicked *** in my tiny dorm room at school. Now that I'm back at home, the 15wpc has a hard time driving my relatively insensitive Wharfedale diamond 8.2's (6 ohm's btw) at loud levels and I would like something with a bit more power. My first project will probably just include a passive preamp with a line straight from my sacd player. I've got some plans for more sophisticated amps/preamps etc. but want to get some more experience before I tackle anything too huge.

Thanks for the help, hopefully I'll make up my mind and order something soon.
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Old 13th September 2006, 02:14 PM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
the 8.2s might just be 4 to 8ohm speakers with an 8ohm treble and a 4ohm bass unit.

Chipamps do not like high current loads unless you take steps to help them.

Paralleling chipamps is another design exercise that would better suit lower impedance speakers, your 8.2s included.

If you do plan to drive either 6ohm or 4ohm speakers then pay particular attention to the voltage limits stated by the chip manufacturer.

A 60W into 8r chip will try to drive 120W into a 4r load so be carefull you do not ask the chip to do too much. Most will just shutdown without any damage.

A parallel pair of chipamps will drive 60W into an 8r load and drive 120W into a 4r load, but each chipamp thinks it is driving an 8r load and so the stresses in the output stage are as if an 8r load was connected.

BTW. 60W is only 6db more than 15W. You might not notice much difference.

Good luck. But, why competent designers should need to rely on luck is beyond me.
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Old 14th September 2006, 12:10 AM   #6
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Good point, I hadn't really understood the differences between bridged and parallel connections. So lets get this straight:

If you bridge two chips that normally drive 60w into 8ohms,
you end up supplying 120w, with each chip seeing a 4ohm load.

If you parallel the same two chips you end up supplying still 60w, but each chip sees a 16ohm load instead.

Now, the manual for my speakers says that "All models are suitable for use with 8 ohm amplifier outputs." However If I were to bridge the 4780's then each would be seeing a 3ohm load, which seems like it might be a bit of a stretch for these chips.

hmmmm.....

Maybe I should just go with the simpler LM3875. I still don't feel like I exactly understand the benefits of paralleling though, if there is anything i'm missing, feel free to explain.

Thanks
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Old 14th September 2006, 12:35 AM   #7
preiter is offline preiter  United States
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There is a big difference between 50W of solidly designed DiY lm3875 power and an equivalent amount of manufacturer's specified commercial amplifier power.

Most manufacturers skimp on the power supply and their wattage specifications are highly optimistic.

Forget bridge/parallel for now. Focus on a vanilla lm3875 implementation. I think you will be surpised by what it is capable of. I find my chipamp to be quite loud even through very inefficient Dayton BR-1 kit speakers in a relatively large room.
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Old 14th September 2006, 08:15 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
where did this come from?
Quote:
differences between bridged and parallel connections
No one on this thread said anything about bridging.
I suggest you build up a lot of experience and knowledge before you even consider bridging.

Parallel operation allows for double the output current.
Supply voltage and output current causing heating in the output stage.

If you ask a chipamp to send too much current it will get hot and it should shut down to protect itself.

If you parallel the chipamps then each chipamp sends only half the output current and the chips run cooler, as well as a number of other (but smaller) advantages.

If you run 8ohm speakers the data sheet specifies a maximum voltage for the supplies.
If you reduce the load impedance then you must follow the datasheet recommendations by reducing the supply voltages.

If you run your 6ohm speakers from low voltage supplies then you should not need to parallel.
The two channel chipamp then becomes a stereo amp in one chip.
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