lm1875 fizzing away probelm

[blu_glo]

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!

 

[blu_glo]

make sure you use a very thin smear of heatsink compound ** both ** sides of the mica and don't bend the mica!

 

[PetruV]

Nicely coming along with 18v transformer and isolated from heatsink

 

[PetruV]

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

 

[blu_glo]

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!!

 

[PetruV]

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

 

[PetruV]

Now im building and usb powered tda 8560q with current limit for usb and a jack for 12v power

 

[PetruV]

It didnt work ,it wont power on at 5v

 

[blu_glo]

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!!

 

[PetruV]

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

 

[PetruV]

The project im building is a 2 tda 2003 with dc jaack for powering from usb,9v battery ,car batery for max power or power plug also for max power

 

[blu_glo]

if you can find an old laptop supply 12 to 18V they usually give out several amps and would be ideal!

 

[PetruV]

if you can find an old laptop supply 12 to 18V they usually give out several amps and would be ideal!

yep but i cant find not event a crt monitor thrown out these days

 

[PetruV]

Please help me with something,find me a chip that is high power when powered at higher voltage but still turn on and work at 5v

 

[johnr66]

Authentic TDA2050 ICs turn on at 3 volts. The LM1875 turns on at 9 volts. The TDA2050 has a slightly higher output swing at a given supply voltage than the 1875 and it has 5 amps of peak current vs 4 for when you really push it. It sounds just as good to my ears. The TDA2050 is all around a better chip in my book.

BTW, if you want people to help you, you need to focus on one chipamp and design. Stop bouncing all over the place. Most people have stopped replying to this thread. Too many questions and no focus.

 

[PetruV]

Authentic TDA2050 ICs turn on at 3 volts. The LM1875 turns on at 9 volts. The TDA2050 has a slightly higher output swing at a given supply voltage than the 1875 and it has 5 amps of peak current vs 4 for when you really push it. It sounds just as good to my ears. The TDA2050 is all around a better chip in my book.

BTW, if you want people to help you, you need to focus on one chipamp and design. Stop bouncing all over the place. Most people have stopped replying to this thread. Too many questions and no focus.

I really agree but I need to find the schematic for the preamp in that amp,im going to take a photo of the bottom of the board and someone coud figure out what schematic it is, or most better i wil do it.
But that tda 2050 turns on and works at 5 v in single supply?

 

[PetruV]

Even more pics of the sittuation on the lm1875

 

[blu_glo]

I'd say if you ever give up on finding the schematic for that board, google 3 band tone control and rebuild it salvaging (carefully) the pots from that board. There seems to be delay line circuits amongst others involved on that board but without schematic it's almost impossible to tell whats going on....

 

[PetruV]

I would remove the preamp crap but my mom would be pissed because she liked that amp and we paid a lot for it

 

[PetruV]

Id say ,i wll jut make a pot volume contol for now, i will be using an 1k pot,is it useefull for this. I also have 100r ,33k ,1m.Sadly thats all i have