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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 20th January 2013, 04:49 PM   #151
blu_glo is offline blu_glo  England
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There's a very interesting application on P. 28 of the PCM2706 datasheet - it seems you can configure the chip to demand 500mA for your power amplifier.......
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Old 20th January 2013, 05:49 PM   #152
PetruV is offline PetruV  Romania
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aLtough it dosent look more than a bunch of coloted spaghetti,its actualy coming along nicely
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Old 20th January 2013, 05:50 PM   #153
blu_glo is offline blu_glo  England
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- did the attenuator work ok?
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Old 20th January 2013, 06:07 PM   #154
PetruV is offline PetruV  Romania
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- did the attenuator work ok?
Made it and hooked it up but not tried it,since my mom was constantly using the other comp which has hooked up to the speakers an rca cable,when my mom is not usin it i caan steal the cable and play with it,the subwoofer on that computer is coincidentaly usin an lm1875t,but i had not built it it has bee bought like that,and the problem with it is that one of the chanel is full of his which temporaryly goes away when you hit it so i have nothing hooked up to that chanell,but im trying to fix it for years and u guys can help me now
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Old 20th January 2013, 06:11 PM   #155
PetruV is offline PetruV  Romania
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Finished !!! ,what should i do when powering it up the first time to make sure everithin is alright,also is it safe to have the center tap of the transformer as grounf for everithing and the case,btw the chips are isolatd from the heatsink
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Old 21st January 2013, 08:34 AM   #156
PetruV is offline PetruV  Romania
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Quote:
Originally Posted by blu_glo View Post
It is still a good idea, especially with "chip amps" to leave the specified Zobel network in. This is because like in the old days, the easiest way to get a power output stage in a chip is using NPN transistors only. You can see this if you look at P. 2 of the datasheet. The bottom transistor is working with it's collector going to the speaker. This is inherently problematic and can result in instability with open circuit or high impedance loads. The Zobel network helps keep things under control - so leave it out at your peril!!

BTW you are unlikely to *hear* the oscillation - it's clattering away at way beyond human hearing, - perhaps at a Mhz or so!! The normal giveaway (without resorting to an oscilloscope) is a very hot chip, even when it's doing nothing...

The chip ran 10 minutes at full power at 5v with 4ohm load and didnt even get warm
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Old 21st January 2013, 08:44 AM   #157
blu_glo is offline blu_glo  England
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Quote:
Originally Posted by PetruV View Post
aLtough it dosent look more than a bunch of coloted spaghetti,its actualy coming along nicely



SWITCH OFF AND UNPLUG IT FROM MAINS!!

TAKE the foil off the transformer - it is not needed and dangerous you are close to creating a shorted turn with the transformer top plate and base. Please remove ALL silver foil.......


Last edited by blu_glo; 21st January 2013 at 09:12 AM.
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Old 21st January 2013, 09:22 AM   #158
PetruV is offline PetruV  Romania
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Originally Posted by blu_glo View Post


SWITCH OFF AND UNPLUG IT FROM MAINS!!

TAKE the foil off the transformer - it is not needed and dangerous you are close to creating a shorted turn with the transformer top plate and base. Please remove ALL silver foil.......

Thanks for reminding me i didnt even plug it in i will alwais ask you before doing something the foil wasnt touching anithing.is it safe to have the center tap hooke up to the casing
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Old 21st January 2013, 11:50 AM   #159
blu_glo is offline blu_glo  England
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Forgive me for asking but are you * OLD ENOUGH * to be working on mains?

If not you must have a suitably qualified person supervising and check your work before plugging in!

I give out information on these boards on the assumption anyone following them is suitably qualified and competent in electronics.
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Old 21st January 2013, 12:02 PM   #160
blu_glo is offline blu_glo  England
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Quote:
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Thanks for reminding me i didnt even plug it in i will alwais ask you before doing something the foil wasnt touching anithing.is it safe to have the center tap hooke up to the casing
The fastest and easiest thing to do is put a 0.1uF capacitor in parallel with 22-100 ohm resistor between 0V RCA inputs and the metal chassis. The metal chassis should be earthed at all times, please see my above post about working with mains.
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