Hi All,
I will soon be building a circuit around this chip. I see that R2 and R3 are responsible for gain. I would like to replace one or the other with a variable pot. I also see that R1 should = R3 for pop optimization. So, should I replace then R2 with a variable for the gain control?
Thank you,
AP
I will soon be building a circuit around this chip. I see that R2 and R3 are responsible for gain. I would like to replace one or the other with a variable pot. I also see that R1 should = R3 for pop optimization. So, should I replace then R2 with a variable for the gain control?
Thank you,
AP
Very bad idea.
Using a pot in the feedback loop is a recipe for disaster on many counts, not least because the chip will become destructively unstable if you drop the closed loop gain to low.
Use a pot in the conventional way at the input to control gain and stick to recommended values for the other components.
Using a pot in the feedback loop is a recipe for disaster on many counts, not least because the chip will become destructively unstable if you drop the closed loop gain to low.
Use a pot in the conventional way at the input to control gain and stick to recommended values for the other components.
AP--if there's anything I can suggest, it's following the datasheet carefully and reading up on Tom Christiansen's (sp? Goes by Tomchr here) guides to best practices on the lm3886. Much/most of which is directly translatable, as it's largely a guide to good practices with power opamps wrt routing and supply decoupling. Mind that the voltage rails come up and down together, too, as this chip wants to short if they aren't playing nice. (ilimzn offers up some very good info, too)
Do you actually need variable gain? Also remember, minimum gain is 20. It's much better to know your upstream voltage output (DAC, phono pre, preamp) and what your voltage rails are and determine the appropriate gain to mesh those together (which, likely, is less than 20, so you're right back to where you started). I cannot recommend NOT using a potentiometer for gain setting enough.
You could do much worse than looking at the block from this thread: http://www.diyaudio.com/forums/chip-amps/3857-tda7293v.html#post873005
Do you actually need variable gain? Also remember, minimum gain is 20. It's much better to know your upstream voltage output (DAC, phono pre, preamp) and what your voltage rails are and determine the appropriate gain to mesh those together (which, likely, is less than 20, so you're right back to where you started). I cannot recommend NOT using a potentiometer for gain setting enough.
You could do much worse than looking at the block from this thread: http://www.diyaudio.com/forums/chip-amps/3857-tda7293v.html#post873005
Thank you all very much for your quick a good feedback. I've built only one other amp ever based on LM1875. I've noticed than when connected to a cellphone or MP3 player, when the volume is increased it does so in db chunks. So the amplified volume changes a lot when just clicking the MP3 volume once. Trying to remedy this I figured a variable pot would be the way to go. Guess I just had it in the wrong location.
So break the input + signal with it?
Thanks again,
AP
So break the input + signal with it?
Thanks again,
AP
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