lm1875 fizzing away probelm - Page 11 - diyAudio
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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 11th January 2013, 11:59 AM   #101
blu_glo is offline blu_glo  England
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Quote:
Originally Posted by PetruV View Post
wil the lm need mica isulators even if the heatsink does not touch the casing and there are 2 chips on the heatsink
- Yes it is advisable to fully insulate both LM devices from the heatsink. Their tabs are at -25V and would potentially short this rail to anything the heatsink touches!
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Old 11th January 2013, 12:01 PM   #102
blu_glo is offline blu_glo  England
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make sure you use a very thin smear of heatsink compound ** both ** sides of the mica and don't bend the mica!
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Old 11th January 2013, 01:50 PM   #103
PetruV is offline PetruV  Romania
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Nicely coming along with 18v transformer and isolated from heatsink
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Old 11th January 2013, 05:56 PM   #104
PetruV is offline PetruV  Romania
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this amp alerardy has an rc4558p up amp preamplifier so it may me too loud,i need to change the preamp chips gain to 1 ,its also +- powered so this is why i needed the the two 15v regulators,also the board has input a and b and a preamplified output coming out of pins marked R and L,
AL and AR are from input a from the back,and BL BR is from input B
LOUT AND ROUT i guess are the output to amplifier,Please tell me what to modify to make that chips gain 1 so there is no amplification since the amp is loud enough at line level
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Last edited by PetruV; 11th January 2013 at 06:00 PM.
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Old 11th January 2013, 07:24 PM   #105
blu_glo is offline blu_glo  England
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If the amp is loud enough - don't bother with preamp! Make input switches (if necessary) and a volume control. Most modern equipment (CD players, Tuners, Computer sound outputs) have enough drive and a preamp is probably not needed!

If you want to change the preamp gain you'll need to supply the schematic for that preamp as I cannot guess from the pictures!!

Last edited by blu_glo; 11th January 2013 at 07:26 PM.
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Old 12th January 2013, 07:23 AM   #106
PetruV is offline PetruV  Romania
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Quote:
Originally Posted by blu_glo View Post
If the amp is loud enough - don't bother with preamp! Make input switches (if necessary) and a volume control. Most modern equipment (CD players, Tuners, Computer sound outputs) have enough drive and a preamp is probably not needed!

If you want to change the preamp gain you'll need to supply the schematic for that preamp as I cannot guess from the pictures!!
Nope cant find such thing,i searched for the schematic for 2 years
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Old 12th January 2013, 07:24 AM   #107
PetruV is offline PetruV  Romania
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Now im building and usb powered tda 8560q with current limit for usb and a jack for 12v power
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Old 12th January 2013, 08:39 AM   #108
PetruV is offline PetruV  Romania
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It didnt work ,it wont power on at 5v
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Old 12th January 2013, 08:55 AM   #109
blu_glo is offline blu_glo  England
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Quote:
Originally Posted by PetruV View Post
It didnt work ,it wont power on at 5v
no it won't its another car amplifier chip and needs at least 7V.
the only thing you'll be able to drive reliably off usb is a pair of lm386 for approx 0.5W per channel.... its enough if you have some very efficient speakers and don't want it too loud!!
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Old 12th January 2013, 09:31 AM   #110
PetruV is offline PetruV  Romania
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Quote:
Originally Posted by blu_glo View Post
no it won't its another car amplifier chip and needs at least 7V.
the only thing you'll be able to drive reliably off usb is a pair of lm386 for approx 0.5W per channel.... its enough if you have some very efficient speakers and don't want it too loud!!
I aleardy have an tda2003 for usb which im using right now but its mono and my friend also wants one so im going to buy 3 more chips
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