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Old 3rd June 2012, 03:15 PM   #1
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Default 2 ohm with 100W class AB or D amplifier

Hi every body
My name is Hadi
I am from iran
sorry for my bad english
i realy need to 2 ohm amp
I test Ax12 of apex but sound not good in +-30VDC , 2OHM
I have 4 speaker 2 ohm, 100W
made by kenwood company
when i use any amp from 2 ohm, my amp teransistor is very hot.
i can not use big heatsing becuse dont have enough spase for that.
please hellp me to make a cold amp in 2ohm with 100w power.
thanks
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Old 3rd June 2012, 03:18 PM   #2
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hi Hadighorbani
greetings try the ultra simple class d amp
warm regards
andrew lebon
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Old 4th June 2012, 04:15 AM   #3
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Quote:
Originally Posted by andrewlebon View Post
hi Hadighorbani
greetings try the ultra simple class d amp
warm regards
andrew lebon
thanks to your answer
is it 2 ohm?
i use some amp but they was warm when i conect my 2 ohm speakers.
please help me to creat my owne amp.
thanks
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Old 4th June 2012, 08:35 AM   #4
jaycee is offline jaycee  United Kingdom
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To drive 2 ohm in class AB you will need a lot of output transistors and a large heatsink. There is no way around that.

Class D would be better, but that is not really possible for DIY.

Why not connect the speakers in series so that together they are 4 ohm?
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Old 4th June 2012, 08:50 AM   #5
wahab is offline wahab  Algeria
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Well , given his requirements , about 20V peak on 2 ohms , that is 10A ,
quite possible with an AB amp using three pairs of output devices as
2SA1943/2SC5200 and simply BD139/BD140 as drivers since the supply
voltage is within their rating.

The preceding stage , the VAS , should have at least 6mA drive
capability , so 12mA standing current is minimal.

Last edited by wahab; 4th June 2012 at 08:52 AM.
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Old 4th June 2012, 11:54 AM   #6
jaycee is offline jaycee  United Kingdom
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in theory. in practice a 2 ohm speaker would go lower than 2 ohms, and of course its inductive. I'd recommend at least 4-6 pairs of TO-3 case devices to cope.
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Old 5th June 2012, 01:10 AM   #7
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For a newb, I don't think it's helpful to leave the matter at a designer's level. Perhaps taking a standard amp. of arouind 60 watts/ 4 ohms and doubling the PSU current. output transistors, sinks and driver capability would be a simple and easily understood approach? Since nobody designs medium domestic amps for 2 ohm loads, you won't see many genuine options out there.

Otherwise, since these are likely car audio speakers, why not DIY with a suitable old car amp. that may well be designed to drive 2 ohms anyway. A heavy duty 14V PSU may be all you need to construct.
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Old 5th June 2012, 08:18 AM   #8
wahab is offline wahab  Algeria
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Car amps can be specified for 2 ohms but they are not really
built according to that requirement.

I have a Pioneer wich is 2R but it has only one output pair...

Besides , it may be even worse according to the OP ,
hope he will clarify his actual setting since it could be even
a 1 ohm load , hence his amp overheating :

Quote:
Originally Posted by Hadighorbani View Post
I have 4 speaker 2 ohm, 100W
If it is 2 ohm speakers he can simply put them
in serial , as pointed above , it will do just fine with 4R total load.
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Old 5th June 2012, 09:08 AM   #9
CBS240 is offline CBS240  United States
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Is this 100Wrms or 100Wpeak?

100Wpeak @ 2R is only 10Vrms and 5Arms. That can be done with one pair of output transistors as far as SOA goes. However, at least 3 pair will be needed for the required current gain since you have to assume the worst case situation would be 14Vp into 1R reactive. (also Hfe decreases as frequency increases) I do not know what components are available in Iran, but try to choose lower Vceo higher conductance devices where DC Hfe holds up to at least 7A or so. Because Vce is low, secondary breakdown shouldn't be a problem. 100Wrms @ 2R would require more pairs of BJTs to be safe into reactive loads and have the current gain required. Or you can go with mosfets, but for that conductance range you would be limited to vertical type fets, or use multiple pairs of laterals.


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Last edited by CBS240; 5th June 2012 at 09:12 AM.
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Old 5th June 2012, 09:26 AM   #10
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Quote:
Originally Posted by jaycee View Post
To drive 2 ohm in class AB you will need a lot of output transistors and a large heatsink. There is no way around that.

Class D would be better, but that is not really possible for DIY.

Why not connect the speakers in series so that together they are 4 ohm?
thanks to your answre my friend
i have just one way
2 ohm, 100w
i cant use 4 ohm
whay?
i can make classD if diy guys help me.
sorry for my bad
thanks
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