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View Poll Results: Was a good idea to use two lm1875 or a big stk chip
Use stk 8 27.59%
use lm1875 21 72.41%
Voters: 29. You may not vote on this poll

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Old 6th January 2013, 02:42 PM   #21
PetruV is offline PetruV  Romania
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Quote:
Originally Posted by bobodioulasso View Post
This one is now symmetrical supply.
From the start i had a dual 18v transformer but i thought it would matter which schematic i used,now i decide to use this,tomorow morning<now is 5:42pm> il go buy the components marked in blue
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Old 6th January 2013, 03:05 PM   #22
johnr66 is offline johnr66  United States
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Using 100k resistors in the voltage divider circuit plus the 100k for the input bias is too high. The input will pickup a lot of noise and you will pickup positive feedback from the output which causes oscillation. A RF filter on the input will help also.

Don't power this at more than 20 volts with 4 Ohm loads with that small heatsink.
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Old 6th January 2013, 03:16 PM   #23
PetruV is offline PetruV  Romania
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Quote:
Originally Posted by johnr66 View Post
Using 100k resistors in the voltage divider circuit plus the 100k for the input bias is too high. The input will pickup a lot of noise and you will pickup positive feedback from the output which causes oscillation. A RF filter on the input will help also.

Don't power this at more than 20 volts with 4 Ohm loads with that small heatsink.
Im not using the single rail schematic animore,and that hatsing was jut for a test,im gona have a bigger heatsinc for two chips,which is just a little bigger than a coke can
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Old 6th January 2013, 04:14 PM   #24
PetruV is offline PetruV  Romania
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One question:can i not use mica insulators when using 2 chips on one heatsink with the schematic above<the split supply one>
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Old 6th January 2013, 04:42 PM   #25
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No, the body is at -V.
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Old 7th January 2013, 10:09 AM   #26
PetruV is offline PetruV  Romania
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I bought all the parts and polisier caps and im building now the schematic from the datasheet
i also bought mica insulators
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Old 7th January 2013, 11:02 AM   #27
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From the datasheet:

"Proper layout of the printed circuit board is very important. While the LM1875 will be stable when installed in a board similar to the ones shown in this data sheet, it is sometimes necessary to modify the layout somewhat to suit the physical requirements of a particular application. When designing a different layout, it is important to return the load ground, the output compensation ground, and the low level (feedback and input) grounds to the circuit board ground point through separate paths. Otherwise, large currents flowing along a ground conductor will generate voltages on the conductor which can effectively act as signals at the input, resulting in high frequency oscillation or excessive distortion. It is advisable to keep the output compensation components and the 0.1 μF supply decoupling capacitors as close as possible to the LM1875 to reduce the effects of PCB trace resistance and inductance. For the same reason, the ground return paths for these components should be as short as possible."
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Old 7th January 2013, 09:08 PM   #28
PetruV is offline PetruV  Romania
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I put away the lm1875 since it was too much of a pain in the behind,and i started building an usb powered tda1517,which on power up makes a way too tiny pop and then when i touch the input wires the is no buzz,is this amp dead?,i aleardy have and usb powered tda 2003 but i wanted stereo
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Old 7th January 2013, 09:13 PM   #29
PetruV is offline PetruV  Romania
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Is it safe to plug it in my computer
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Old 7th January 2013, 09:39 PM   #30
johnr66 is offline johnr66  United States
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From now on, put a small light bulb in series with the power supply to limit current to your circuits in the testing phase. If the bulb goes bright, you know you have a problem with wiring, otherwise you may pop your chip. The bulb should be rated at the same voltage as the supply, so if you use 12 volts use a 12 volt, .5 amp bulb.

As for the TDA1517, if the signal ground pin is not connected to power ground, the chip will draw heavy current and could be damaged. Also be sure the mute pin is set up right or you get no sound.
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