howdy
i r a total noob at building amps that aren't in kitset form (hell, anyone can build a kitset) and i've whacked together a 20W stereo amp using an LM1876TF stereo 20W IC
see pics here. also it's worth noting if you see a flaw in any of the pics, the amp has changed since they were taken and is now "complete"
the design is almost exactly based on the "Auxillary Amplifier" schematic contained within the
datasheet from National, the only difference being larger caps
it sounds beautiful - while it works, nice bass response, VERY good volume (especially considering the size of the thing). after about a minute however it shuts down. i initially thought it might be overheating but in theory the temperature protection should shut it down then turn it back on again once the chip cools. besides that, the chip isn't even remotely hot. the shutdown time is always the same regardless of volume, somewhere between 60 and 70 seconds.
anyways, after puzzling over it for quite some time and searching these forums as well as the web for an anwser, i thought to check the PSU voltages while the amp is running and noticed that the +VE rail was slowly increasing while the -VE rail was decreasing. once it gets below -10V the amp shuts down due to it's power supply rejection system as it would be expected really. the +VE rail eventually reaches the PSU total of ~44V (relative to ground) while the -VE rail sits at around zero (to ground). at startup the supply is +/-22V
i tried swapping my big caps on the amplifier (5600uF) with the 1000uF the design calls for the amp does the same only shuts down much sooner (makes sense really)
has anyone else had this problem? or failing that, does anyone know a: what would cause this problem, and more importantly b: how to fix it
cheers
i r a total noob at building amps that aren't in kitset form (hell, anyone can build a kitset) and i've whacked together a 20W stereo amp using an LM1876TF stereo 20W IC
see pics here. also it's worth noting if you see a flaw in any of the pics, the amp has changed since they were taken and is now "complete"
the design is almost exactly based on the "Auxillary Amplifier" schematic contained within the
datasheet from National, the only difference being larger caps
it sounds beautiful - while it works, nice bass response, VERY good volume (especially considering the size of the thing). after about a minute however it shuts down. i initially thought it might be overheating but in theory the temperature protection should shut it down then turn it back on again once the chip cools. besides that, the chip isn't even remotely hot. the shutdown time is always the same regardless of volume, somewhere between 60 and 70 seconds.
anyways, after puzzling over it for quite some time and searching these forums as well as the web for an anwser, i thought to check the PSU voltages while the amp is running and noticed that the +VE rail was slowly increasing while the -VE rail was decreasing. once it gets below -10V the amp shuts down due to it's power supply rejection system as it would be expected really. the +VE rail eventually reaches the PSU total of ~44V (relative to ground) while the -VE rail sits at around zero (to ground). at startup the supply is +/-22V
i tried swapping my big caps on the amplifier (5600uF) with the 1000uF the design calls for the amp does the same only shuts down much sooner (makes sense really)
has anyone else had this problem? or failing that, does anyone know a: what would cause this problem, and more importantly b: how to fix it
cheers
nope. no center tap. it's not ideal at all really. should it matter tho?. the whole set up had cost me absolutely nothing tho.
the tranny is not thermally protected as far as i know. also i'd expect the fuse to blow before any thermal protection kicks in considering how little power the amp actually draws.
i just tested the suppy minus the amp, it still does drift but very slowly. so now i'm happy, the amp works fine and damn well too
just need to find some cash for a "real" transformer i guess. ah well, if' i'm gonna do that it might as well swap the dual20W chip out for the dual50W that turned up today
then i'll switch to the BIG supply on my PSU board. (you'll see in the power supply pics, i'm using the bridge on the right with the appallingly small 470uF 50V caps)
the tranny is not thermally protected as far as i know. also i'd expect the fuse to blow before any thermal protection kicks in considering how little power the amp actually draws.
i just tested the suppy minus the amp, it still does drift but very slowly. so now i'm happy, the amp works fine and damn well too
just need to find some cash for a "real" transformer i guess. ah well, if' i'm gonna do that it might as well swap the dual20W chip out for the dual50W that turned up today
then i'll switch to the BIG supply on my PSU board. (you'll see in the power supply pics, i'm using the bridge on the right with the appallingly small 470uF 50V caps)
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