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Old 3rd April 2010, 03:33 PM   #1
Buddie is offline Buddie  United States
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Default 5.1 Channel Chip Amp/Gainclone for Home Theater

Hey Guys,

I am looking to build a 5.1 channel chip amp to go with my decoder/DAC that I am also building. It is all for a surround system for my TV. I think that I will be using the LM3875, but am open to suggestions. I have a few question and hope that you guys can help me as I begin to design the amp. I hope to breadboard at least one channel before designing a PCB. Here are my questions:
1. What output power is appropriate for each channel of a surround system? I don't need to rattle the house, but I want sufficient power.
2. Does the sub need a different type of amp?
3. Should I power the whole amp with one transformer/psu?
4. How should I decide on a heat sink and where should I get it?
5. Is the sample circuit in the datasheet a good place to start for the circuit?
6. I would rather not have a preamp if I can. I the volume control on my DAC (CS4360) sufficient?
I want to build a nice amp, but I don't want to spend a fortune.

Thanks in advance for all your help!
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Old 3rd April 2010, 04:35 PM   #2
pra3718 is offline pra3718  India
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Quote:
What output power is appropriate for each channel of a surround system? I don't need to rattle the house, but I want sufficient power.
I would go for TDA2030A (Bi-Amp) OR TDA2050 OR LM1875.

Quote:
2. Does the sub need a different type of amp?
My choice is YES, LM3886 OR TDA7294 or similar

Quote:
3. Should I power the whole amp with one transformer/psu?
one transformer for surround amp & another for sub.
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Old 3rd April 2010, 05:06 PM   #3
AndrewT is offline AndrewT  Scotland
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the required output power of the amplifier is determined by the sensitivity of your speakers and what volume you require (hear and fill).

If you find 100mW (800mVac to 1000mVac into 8ohms) is sufficient for your average listening needs then an amp with a maximum power output between 50 and 100times your average will cover much of your use except loud.
If your speakers are too quiet with 100mW, then you have to turn up the volume until you have found your comfortable average level and then apply the 50 to 100times to find your amplifier power.

The cheapest way is one transformer and one PSU and one chassis to power all six channels.
The dearest way is one transformer and one PSU and one chassis to every channel.
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Last edited by AndrewT; 3rd April 2010 at 05:08 PM.
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Old 3rd April 2010, 10:47 PM   #4
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by Buddie View Post
..
1. What output power is appropriate for each channel of a surround system? I don't need to rattle the house, but I want sufficient power.
2. Does the sub need a different type of amp?
3. Should I power the whole amp with one transformer/psu?
4. How should I decide on a heat sink and where should I get it?
5. Is the sample circuit in the datasheet a good place to start for the circuit?
6. I would rather not have a preamp if I can. I the volume control on my DAC (CS4360) sufficient?
I want to build a nice amp, but I don't want to spend a fortune.

Thanks in advance for all your help!
1) Speaker efficiency matters a LOT. A small change in this number has the same effect on loudness as doubling or more the power. Adds watts is a poor way to make a system play louder. Speaker design matters a LOT more. For example I have a 5W guitar amp and a very efficient speaker (abot 100 db/W 1M) People across the street can hear it. But the same 5W amp driving a 4: diameter 84db speak is not loud at all

2) For pactical purposes yes.

6) Volume controls -- yes. Even if these are just trimmer pots inside the case. You will need a way to adjust the relative volue of each speaker. You will need to balance the system some how. Of cource your amp may have these controls But still I'd want to be able to adjust relative volume

7) heat sink info is on the spec sheets.
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Old 5th April 2010, 07:17 PM   #5
Buddie is offline Buddie  United States
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Thanks for the info guys ... keep it coming. I guess I will need to look at what speakers I will use to determine what kind of amplifier I need. Can someone tell me what kind of speakers are generally used for each channel on a 5.1 system? I am totally new to this. Also, what type of ceramic SMD caps do you guys use for bypassing? I have never done surface mount before and I could use some help. Thanks!
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Old 5th April 2010, 07:44 PM   #6
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by Buddie View Post
Thanks for the info guys ... keep it coming. I guess I will need to look at what speakers I will use to determine what kind of amplifier I need. Can someone tell me what kind of speakers are generally used for each channel on a 5.1 system? ...
It depends on the goal. If this is for action films and you are listening to car crashes and explosions then you can get by with small speakers and a huge sub-woofer. But if for music then you want at least the two front L and R speakers to look and sound a lot like conventional home stereo speakers and if a sub is used to cross it over "way low"

And then pratical conciderations, what's the budget and how large can the speakers be

The design of any sound system should begin with writing down the size of the room, a floor plan and then what it is you'll be listening to. The floor plan tell you things like how far th rear wall is from the listener's head Floor plan will also say if you can use little satilite speakers ot floor standing ones. In terms of sound you want the listener in the cente of the room and speakers all pull in off the walls. Practically people prefer everything to be alow the edges of the room
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Old 5th April 2010, 08:10 PM   #7
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Any kind of speakers are used. Your choice depends on the SPL you want and the sizes of your listening room and wallet. Some people are quite happy with five 3" full-rangers and a 6" subwoofer. Others have five 2- or 3-way speakers with 12" woofers and several even bigger subwoofers strategically placed around the room plus body-shakers below each seat. Usually you have two big main speakers accompanied by a center speaker that should be as similar to the mains as the space allows and smaller effect speakers. The sub should cover 20..80 Hz, mains and center 80..20.000 Hz and the effect speakers depending on the surround specification either 125..20.000 (ProLogic) or 80..20.000 Hz (Digital or DTS). If you additionally want to cover THX specs all speakers must reach 105 dB at the listening position with low distortion.

The types of bypass caps are often determined by their size. The most recommendable NP0 or C0G are only available in small values or at extreme prices, which limits your choice to X7R, because the remaining ceramics don't provide sufficient quality for that purpose.
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Old 7th April 2010, 01:50 PM   #8
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Id like to jump in here too because im thinking of doing this. My question is how do i get a 5.1 dac? It seems once you switch to surround sound your stuck using the receiver as a preamp and you cant diy any section other then the non integrated amp.
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Old 7th April 2010, 02:29 PM   #9
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I am currently building my own system which has been coming along over a long time.

MY current system:

5.1 DAC = rotel 985 rsp (bought from a guy who thought it was broken)

5 Main amplifiers (already built):
Powersupply: 500VA 25-0-25V transformer with 40000uf per voltage rail.
amplifier: 5 x lm3886 with 100uF per voltage rail close to each rail on chip, using standard national circuit

Fotos: Heinrich Spreeth's Photos - My eerste amplifier | Facebook




subwoofer currently building:
bpa300 with 500VA with 2 x 12" drivers
the linkwitz tranform circuit is done and speaker enclosure but still need to built the amplifier itself.

fotos:
Heinrich Spreeth's Photos - Home cinema .1 channel in the making | Facebook
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Old 7th April 2010, 02:35 PM   #10
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Hi nightanole

For a DAC you have 3 options in my opinion.

1) look for mainstream namebrand 5.1 decoder that has line level analogue output that support all the codecs you want (dts , dolby digital) with a few analogue inputs ,does it need phono input?

2) look for a kit on ebay , a quick search and I found something like this:
DTS AC3 5.1 DIGIT AUDIO DECODER dac mocha JY-M2 SKU39 - eBay (item 330347698128 end time Apr-22-10 18:01:54 PDT)

3) Use a pc based system with a decent sound card.
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