2 ohm with 100W class AB or D amplifier

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Hadighorbani

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Joined 2010
#1
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🙂
 
#4
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?
 
#5
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.
 
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#7
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.
 
#8
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 :

Hadighorbani said:
I have 4 speaker 2 ohm, 100W
Click to expand...

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.
 
#9
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.


:2c:
 
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#10
jaycee said:
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?
Click to expand...
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🙂
 
#11
jaycee said:
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.
Click to expand...
my dear friend
i cant use TO3 case
i dont have spease for heatsinc for that.
just tip of TIP142 and similar.
sorry for my bad
i like class D amp
help me please.
sorry for my bad conditions.
sorry for my bad english
thanks to all🙂
 
#12
🙂
CBS240 said:
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.


:2c:
Click to expand...
hi dear friend
my country have bad poletice condition with usa
like jery and tom
my piopels love iran and our government
i can by any thing from out of iran but it is important to be cheap
bjt is expencive in iran and i dont like that
i have +-30 volt DC
help to creat class D please.
sorry for my bad english
thanks.🙂
 
#15
At those low rail voltages, slower switching speed isn't the end of the world. And low on-resistance high current TO-220 Hexfets should be easy enough to find if you need less than 100V Vds. It won't be 98% efficient, but 80% would do with a small heat sink. Still better than class AB, even if the design is not optimum.

Start with the data sheets for Hexfet drivers from IR, and the like. They have tutorials and app notes on class D. It's almost impossibe to get something like this custom designed for you over the internet unless a generous member steps in and works with you for a couple of weeks/months straight. The likelihood of that happeing is small. Learning to use resources like vendor data sheets, and getting ides from existing deisgns and modifying them is part of what you should be learning for your "university project".
 
#16
ttp://www.schematicsforfree.com/archive/dir/Audio/Circuits/POWER+AMPLIFIERS-CLASS-D
maybe this can help you Hadighorbani the easiest dclass amp with easy to get parts
is the ULTRA SIMPLE CLASS D AMP in the dclass thread comes on first time cant
get simpler than this
warm regards
andrew lebon
 
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