| Dxvideo |
Hi all,
I plan to make a new good chipamp for our DIY Audio club in Turkey. It will have to be exactly in audiophile quality.
I want to have 100W at least per channel and will a be stereo power amp. Also I want to drive both 4, 6 and 8 ohm loads with it.
I thought the parallel clone of LM3886 would suite for that project. However, as I calculated on Overture Design Guide; 6 and 8 ohm is not working with parallel configuration.
Does anybody has any idea about that? Can I work with 6 and 8 ohms with parallel configuration?
Best regards, |
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| ttan98 |
don't let others tell you otherwise, 1*LM3886 can drive 4 ohms resitor, I don't see any reason why parallel 3886 won't not drive 4 ohms.
The only reservation I give is is that some speakers are general capacitive in nature, sometimes 4 ohms speakers(eg MTM configuration) due to capacitive loading will drop below 4 ohms, at times 2 ohms, in this situation 3886 may not be able to handle with ease. If you have this problem, then you can connect a parallel resistors and inductor circuit inseries with the 3886's output, see website below and down LM4780(dual 3886) applications note for details of how to do this.
http://www.national.com/pf/LM/LM4780.html |
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| Dxvideo |
In fact, the problem is not driving lower values.
The problem is driving higher value loads. If I paralelled two LM3886 and drive a 8ohm load then the load looks 16ohm for each chip. I ask; is this a problem? |
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| dfdye |
Not in the slightest. It is only for hard loads (meaning lower impedance) that you should worry about the chip. In other words, if it can drive a 4 ohm load, it can drive a 6, 8 or 16 ohm load more easily. The reason for this is that during higher loading (lower impedance loads) the chip must drive more current, making the overall power required from the chip greater.
David |
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| Dxvideo |
Thats ok.
But I have another question. I plan to use regulated supplies. And have the maximum output value. So if I use LM338 for regulator, and apply 38 or 40v per chip (TA case) that causes any problem (for 6 ohm load).. |
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| eLarson |
| Is 6 ohms your minimum impedance or a nominal value? |
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| Dxvideo |
| No thats a general using project. Users may apply loads in 4 ohm to 8 ohm range. |
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| Minion |
A Paralell LM3886 into 8 Ohms means that each Chip is Driveing 4 Ohms which means you should have your PSU in the +/-24v range.....
When driveing 4 ohms each chip will see 2ohms which will probably heat the chip up a Bit because Lower impedances are harder to drive so make sure you have a Large Heatsink......
Cheers |
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| Dxvideo |
Wrong!
If you paralelled two LM3886 and put a 8ohm load to the outputs then every chip drives 16ohm load... |
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| dfdye |
| quote: | Originally posted by Minion
A Paralell LM3886 into 8 Ohms means that each Chip is Driveing 4 Ohms which means you should have your PSU in the +/-24v range.....
When driveing 4 ohms each chip will see 2ohms which will probably heat the chip up a Bit because Lower impedances are harder to drive so make sure you have a Large Heatsink......
Cheers |
I think you have your logic/math a little backwards. If you load an amplifier with a parallel speaker load, each of the speakers being an 8 ohm load, the apparent load to the amp is indeed 4 ohms. If, however, you drive ONE speaker that is an 8 ohm load with paralleled output stages, each of the power devices will only have to deliver half the effective current to produce the same power for the load, effectively "doubling" the apparent impedance of the speaker (of course this isn't technically correct, but it is convenient to think about it this way some times). The reason you parallel output devices is to lower the overall load on each device. Your argument would imply that by providing additional output devices, you would INCREASE the load on each device, which would be counterproductive to the goal of being able to drive a more difficult load. If I am somehow misinterpreting your comments, I sincerely apologize, but I do believe you are mistaken.
David |
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| Minion |
| It"s Just the Impression I got from the Datasheet.....I could very well be wrong.... |
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| AndrewT |
Hi,
in general all solid state amplifiers prefer to drive higher impedance loads.
Quite definately ALL solid state amplifiers do not like driving low impedance loads.
Chipamps, in particular, do not like 4ohm reactive loads.
But used gently, or with the correct supply rail voltages, they do seem to survive.
Using a pair of chipamps in parallel eases the drive problem considerably. 4ohm reactive loading becomes reliable, but in my opinion the pair will sound better driving a higher impedance load.
There is no reliability issue with chipamps driving higher impedances.
Design for 4r0 and take a chance with 4ohm reactive.
Design for 4r0 and it will cruise with 8ohm reactive (upto 45degrees) and 16ohm reactive (upto 60degrees). |
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