| jackinnj |
Finally got around to testing this amplifier -- THD + N averages 0.01% across the audio spectrum -- the 3dB down point is about 10Hz -- the longest sinewave test I did was 3 hours at 120 watts into an 8ohm resistive load -- and it didn't blow up! As I have said before, the device must be firmly affixed to the heat sink -- and I am using a 12V fan to cool it -- the fan runs at 7V which is quieter than the hard-drive on the TIVO:
it's a proto -- the big polypropylene caps have been moved for the boards that were sent out. |
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| jackinnj |
output graphs -- into a resistive load:
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| jleaman |
look's good i should try one of these now : O )
How do you like it .. ? What are you comparing it to or what could or would you compare it to ? |
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| diysmartdeep21 |
what are the ratings of your transformer?
Im planning to use toroidal transformer with the LM4780 ic and tell me what is the capacitor value that you are using per rail... |
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| diysmartdeep21 |
| hey hey can u tell me how to bridge it ive seen in the datasheet but i couldnt understand it well, if u have schematics then please send me some... and if u have pcb design then send it please.... |
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| jackinnj |
| quote: | Originally posted by diysmartdeep21
what are the ratings of your transformer?
Im planning to use toroidal transformer with the LM4780 ic and tell me what is the capacitor value that you are using per rail... |
in the bridged configuration one half of the LM4780 is inverting, the other is non-inverting -- the difficulty with the bridged configuration is that the power dissipation of the chip as heat
(not sound) is much greater than a "non-bridged" -- National Semi says it is 4 times as much, I actually measured it as being somewhat greater !
my transformer is 400VA -- I think that this is about right for two bridged devices (if you are using it to drive music through speakers), if you were using it as a laboratory amplifier I would probably go to 600VA.
Distortion is comparable to that outlined in the Nat Semi website for a single, non-inverting amplifier (edit) (note that I cut out of the graph the 78kHz and 100kHz distortion from the graph, it is 7.4% at 78kHz and I shut it down before going to 100kHz):
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