lm3886...i need help.

[Morbid]

Hi to you all, after your recommandation i have built the LM3886 amplifier with this schematic i found here.. ...
after i've build it and i had the old pre-amp i made...i connected them together as modules should be...
and first time i had a small burn going on the wires
after couple of times (using Variac) i realize that the metal plate on the chip is the -Vee. and it touched the ground (cause the heatsink is connected to the shield)....

so i isolated the heatsink and now its working
but i dont know whats wrong...the sound is pretty good
but the volume is toooooo low.....
im using power supply circuit that provides +/-~27V
and +/-15V for the pre-amp....

i'm also using 2x8ohm speakers (4ohm load)
and that's still low...like a 15w amp playing middle vol....

what can i do?!
thanks, Chen.

[Morbid]

forgot to mention...
im using this preamp

and also when i bought the chip i saw his size and i couldnt believe he supply 63W..maybe he can be very hot that thing....

the STK chips are bigger and u can expect them to getting that level....i dunno...

[lgreen]

Hey, that's my GC schematic, glad it works but sorry you are having trouble. Using that cicuit I can drive an 8 ohm speaker relatively loudly with just a cd player or walkman as the input, no preamp.

- Have you been turning the 50K potentiometer on the GC to see if the volume goes up?
- what is the peak to peak voltage coming out of your preamp?
- what is the peak to peak voltage at the input of the 4.7uF capacitor?

If you are using a preamp you might want to try the GC without the input "POT 50K" potentiometer, do this by removing the 50 K pot and connecting the preamp output directly to the 4.7 uF capacitor.

[carlosfm]

Originally posted by lgreen
Hey, that's my GC schematic...

Chen, are you using a pre?
What's the gain of your pre?
What you made there with the LM3886 is a typical power amp, if you use it as an integrated amp (I see a pot there) you need more gain, change R3 (220k) for 330k.

[janneman]

Originally posted by lgreen
Hey, that's my GC schematic, glad it works but sorry you are having trouble. Using that cicuit I can drive an 8 ohm speaker relatively loudly with just a cd player or walkman as the input, no preamp.

- Have you been turning the 50K potentiometer on the GC to see if the volume goes up?
- what is the peak to peak voltage coming out of your preamp?
- what is the peak to peak voltage at the input of the 4.7uF capacitor?

If you are using a preamp you might want to try the GC without the input "POT 50K" potentiometer, do this by removing the 50 K pot and connecting the preamp output directly to the 4.7 uF capacitor.

The gain is only 22x with the pot fully opened up. With the pot in mid position, the gain is only 10 or so, max. This circuit must have a funny volume control law.

Jan Didden

[lgreen]

The gain control is actually quite smooth with good resolution. However, I have to admit that I have put the controls on the inside of the amp because I'm using it as a power amp only. I also added to the circuit somewhat (by adding a differential buffer on the input), so its very similar to what Morbid has done with his chip preamp. Here is the final version.

As suggested, changing the feedback resistor R3 from 220K to 330K will increase the gain from 22 to 33.

[Morbid]

Hi! thanks for you reply's lgreen, yes i saw your schematic and i've use it...it looked the best (full detailed)...

hmmmm.....i didnt put the pot because of the preamp...
i connected the input directly to the cap...and also the input cap is nott 4.7 but 1uf...i will try to change those things...
i've checked the input before and after the preamp...
with the preamp the volume is stronger....
maybe i should put another opamp for the input (preamp)....
any suggestions? and i still need to isolate the heatsink from the ground...how can i do it? i will send you pictures later...my sister is in England with my cam...
thanks again, Chen.