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Old 13th April 2011, 02:17 PM   #21
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We've all been there.
I've probably got half a dozen of the very same hats floating around, if only I can remember where i left one......
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Old 15th April 2011, 03:07 AM   #22
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Quote:
Originally Posted by toprepairman View Post
Taking another look at the circuit, the design parameters are quite wrong.
The 'mid point' output voltage should not be 12V. For maximum output into 8R it should be at 8 Volts. This would instantly quadruple the power output!
We'd get an earth shattering 4W rms. (with the original 15R resistor)
hi, i had also done this project but i put 8 ohm load resistor instead of 15r. what should be the right midpoint voltage in order to get maximum output swing out the ckt with an 8 ohm speaker? will it be 8volts too?

My current set up is at 12v midpoint voltage. Also planning to use automotive head lamp 12v 90w..will it be possible as load?
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Old 15th April 2011, 08:01 AM   #23
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Hi Junm.
You should be about right with 12V for 8R resistor. Best way to check is to feed a sine wave in and up the volume until you get clipping then adjust the volts set pot for equal clipping as seen on a 'scope.
Don't use a headlamp bulb as the resistance changes dramatically depending on temperature (intensity of illumination), and you may well blow the FET when switched on cold.
Regards
Henry

PS do let us know how it works out.
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Old 15th April 2011, 08:07 AM   #24
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I've thought about this a bit more and it could be that even with 8R the output should be at 8V, and with 15R possibly even lower.
I might even have to knock up this circuit quickly to test the guess.
Probably won't be able to do that until next week as I'm busy getting myself organised for the Big Audiojumble at Bracknell this Sunday (Stallholder)
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Old 15th April 2011, 08:08 AM   #25
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Quote:
Originally Posted by Junm View Post
hi, i had also done this project but i put 8 ohm load resistor instead of 15r. what should be the right midpoint voltage in order to get maximum output swing out the ckt with an 8 ohm speaker? will it be 8volts too?

My current set up is at 12v midpoint voltage. Also planning to use automotive head lamp 12v 90w..will it be possible as load?
Teoretical, and my SPICE simulation test shows, it should be +8V to +9V for a 8R resistor.
This means like 2A current. This gives maximal outputt.
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Old 15th April 2011, 08:11 AM   #26
Junm is offline Junm  Philippines
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Okay thanks henry for the info....one more thing how about 2 pcs // 20w 12 volts (40W total) bulb which i also have..will it suite the requirement?
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Old 15th April 2011, 08:14 AM   #27
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Quote:
Originally Posted by lineup View Post
Teoretical, and my SPICE simulation test shows, it should be +8V to +9V for a 8R resistor.
This means like 2A current. This gives maximal outputt.
thanks lineup, i try to play with this soon and even test it with other kind of load.
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Old 15th April 2011, 08:37 AM   #28
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Originally Posted by SSDIY View Post
Hi Andrew

May I ask what is the different between bridged and balanced if I make this amp a balanced (4 boards of this circuit one for + phase signal and one for - phase signal x 2 channel for a stereo 2 channel amp)? Please advice as my other thread in this forum I am going to change my entire stereo system from RCA to XLR.
If you make this amp balanced then you've also made it bridged. The major difference, other than power, is that the relatively high distortion of such a simple circuit is going to change in character quite a bit between single-ended and differential mode. Maybe someone running simulations of these circuits can post some FFTs of the same circuit in both modes.
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Old 15th April 2011, 08:41 AM   #29
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Hi Lineup, thanks there for the confirmation, around 8V will be correct for 8R resistor.
Junm, don't use light bulbs here, they are very non linear as are highly temperature dependent.
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Old 15th April 2011, 08:55 AM   #30
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Quote:
Originally Posted by toprepairman View Post
Hi Lineup, thanks there for the confirmation, around 8V will be correct for 8R resistor.
Junm, don't use light bulbs here, they are very non linear as are highly temperature dependent.
Advice taken......thanks... so I'll try to do 8v...
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