lm1875 fizzing away probelm

[PetruV]

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

 

[johnr66]

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.

 

[PetruV]

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

 

[PetruV]

One question:can i not use mica insulators when using 2 chips on one heatsink with the schematic above<the split supply one>

 

[bobodioulasso]

No, the body is at -V.

 

[PetruV]

I bought all the parts and polisier caps and im building now the schematic from the datasheet
i also bought mica insulators

 

[bobodioulasso]

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."

 

[PetruV]

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

 

[PetruV]

Is it safe to plug it in my computer

 

[johnr66]

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.

 

[PetruV]

Signal ground is not conected to power ground and standby pin is conected to positive,while writing this,i realized!maybe 5v is not enough to get it out of standbyD:

 

[PetruV]

Yep just checked the datasheet and the switch on curent for standby is 8.5v
Now need a circuit that can get me 12v from 5v but not drawn too much current to damage a laptop

 

[PetruV]

would a 55w lightbulb work

 

[PetruV]

Just found an 21w lightbulb

 

[picowallspeaker]

Hey, I like the way you take possession of your thread!
I would say : keep the audio things separate from the computer thing!
Or you risk to break both! But the main matter is the power supply: it's much
better in having a linear supply - noiseless and powerful- such a transformer-bridge-reservoir/smoothing capacitors. For USB powered amplifiers, I would
stick to amplifiers based on chips housed in 8 pin-dual in line which may absorb
no more than 1 W. Also find some 4 Ω( or 3.2 Ω ) speakers that may enhance
sinergy between a low voltage supply amplifier and speakers.

OMG! Sinergy !!!

 

[superR]

Maybe this is a better option for a first project;
LM1875 GC Circuit Audio Amplifier Board Kit | eBay

 

[PetruV]

Now testing it with the sinal round hooked up to power ground,i only very distorted audio from just one chanell,why? please answer

 

[PetruV]

Hey, I like the way you take possession of your thread!
I would say : keep the audio things separate from the computer thing!
Or you risk to break both! But the main matter is the power supply: it's much
better in having a linear supply - noiseless and powerful- such a transformer-bridge-reservoir/smoothing capacitors. For USB powered amplifiers, I would
stick to amplifiers based on chips housed in 8 pin-dual in line which may absorb
no more than 1 W. Also find some 4 Ω( or 3.2 Ω ) speakers that may enhance
sinergy between a low voltage supply amplifier and speakers.

OMG! Sinergy !!!

This powesuplly is very good and sounds better than some linear supplies.The transformers are very expensive and big and offer not much benefit,Yes im realy afraid of breaking my gaming laptop so any of you can come up with a simple tone generator?
All my spekers are 4 ohms,3.2 ohms are those little crap speakers that i blow up from the moment i see

 

[PetruV]

I have aleardy used tda 2003 kit in my usb amp and tda 8560 or something like that in my main amp

 

[picowallspeaker]

55 and 21 W don't exist as values for 'old type' lightbulbs
I know 25 and 60 W ratings ! So, are you sure that you are referring to
the classic lightbulbs, and not the electronic ones ?
Same for the power supply

RE: I blew those crappy speakers from the moment I see