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Beijing
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I build a audio player, using schematics from adafruit's wave sheild.
http://learn.adafruit.com/adafruit-wave-shield-audio-shield-for-arduino


The amp in schematics say is TL072, so I used the same one. But the actual sound quality is bad. You can see attachment below for details(green for amp input, yellow for output).
Then I accidently found that adafruit's wave shield isn't using TL072 but TS922. Then I changed the amp and got really nice sound quality, also the output of amp is exactly the same as input.

So I am wondering which is the difference between Tl072 and TS922.
PS TS922 I got is really expencesive.


* scope_0.png (41.78 KB, 800x503 - viewed 21 times.)

* scope_1.png (33.56 KB, 800x503 - viewed 25 times.)
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the ts922 is a rail-to-rail opamp, whereas the tl072 is not.  this means that the tl072 can not amplify signals that get too close to ground or the powersupply rail, either at the input or the output (which happens in this circuit).   the ts922 also has a higher max output current.
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Beijing
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the ts922 is a rail-to-rail opamp, whereas the tl072 is not.  this means that the tl072 can not amplify signals that get too close to ground or the powersupply rail, either at the input or the output (which happens in this circuit).   the ts922 also has a higher max output current.

Thanks for reply and reveal the truth. I finally understand the term "rail to rail". In both of the two picture, the output under 1.3V is terminal at 1.3V(because it can't go too close to ground).
Thanks again!
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I build a audio player, using schematics from adafruit's wave sheild.
...


Then I accidently found that adafruit's wave shield isn't using TL072 but TS922. Then I changed the amp and got really nice sound quality, also the output of amp is exactly the same as input.

So I am wondering which is the difference between Tl072 and TS922.
PS TS922 I got is really expencesive.

I can explain what happened I think.   When the circuit was designed in Eagle there
wasn't a part in the library for the TS922, so another opamp of the same pinout was
substituted (because the point of the Eagle design process is primarily to create a PCB)

So some of the information in the schematic was misleading.  This is unfortunate,
and in general it always pays to be a little circumspect in trusting infomation in the
schematic.  Its perfectly possible to define your own parts in Eagle, and this would
have been the correct approach, but it takes time, life is short, and people want to
get shiny new gadgets out the door.

Anyone with experience would automatically know that a TL072 doesn't work on
5V, those with less experience can go and double check information in datasheets
(again time-consuming but does increase confidence when creating one's own
designs).

And the other thing is that you've gained experience - maintain a healthy scepticism
and be thorough in checking (check twice, build once!).

Also look around for better/cheaper supplier - which part of the world are you in?
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Beijing
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Thanks Mark, learn many from you.
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