LA4601 amp help

[exztinct01]

i removed the la4601 chip from my old yamaha psr keyboard and built a small amp based on its datasheet. (i can't attach datasheet since its in my laptop).
Anyway, the amp worked but it always produces this sound like when a message is coming to my phone near an amp. Of course, I tested the amp uncased so maybe shielding it will help. Or maybe you can recommend some mods to the datasheet schem to help remove those sounds. I will always be playing it with my phone.
Also, I think my phone's output level is too much for the amp coz most mp3's sound too distorted when my phone's volume is more than 10/30.
Does the LA4601 expect line/headphone level or not?
Sorry for posting this here. I know there are many forums where this topic is more suited but I'm at home in this forum. (more than any other)

[exztinct01]

here's the link to datasheet
http://www.promelec.ru/pdf/LA4601.pdf

[Enzo]

Let me get this straight, the amp you built makes sounds like from a cell phone, and you have your cell phone connected to the amp?

Does your amp make these sounds if you put your cell phone 10 feet away and plug some other signal source into it, like just a guitar or something?  You may plan to use it with your phone, but we need to determine if the amp on its own is clean.

Yes, it ought to be in a metal container for shielding.

How is it being powered?  Batteries?  Linear supply?  SMPS?  From your phone?

[exztinct01]

I play keyboard while my phone's in my pocket, phone receives message keyboard speaker produces this sound like its amp receives another signal, phone signal. That's what happens, is that radio interference or not?
Amp is powered with a linear regulator (LM317 at almost 12V), input signal is from phone.

[phatt]

Mobile phones are a nightmare on stage ,, should be banned around audio gear :trouble :grr

Yes shielding is the likely issue and the input should be well filtered above audio frequency.
With really high gain my strat  picks up my watch if it's within 6 inches of the magnets.
I'd be finding another way to play MP3 ,,, if that is what you are trying to do?
Phil.

[exztinct01]

oh I see.
I'll make a filter for it then.
What kind? low pass? high pass?

[phatt]

Please note what *Enzo* asked.
It will depend a bit on the circuit design you are using and also how well you have shielded the unit.
How well the supply is filtered,,
Maybe a schematic and a few close up pictures of what you have already made. 
Phil.

[exztinct01]

Here's the datasheet application schem

I changed the input caps to 1 uF each coz that's what was available

Here's the layout and the actual board



In its old board (Yamaha PSR), I saw some kind of circuit before the input pin of the chip amp which looks like this

What does that section do? Is it a filter?

[phatt]

Yep! That little RC circuit at the front is what is missing and will certainly help keep out excess hi frequency. 8|

Maybe go find the values on that input setup and wire that up to your new build and see if it helps,,, it maybe all you need to add.
Phil.

[exztinct01]

that's definitely a problem coz I don't know those values anymore. I removed those components some time ago and the board isn't labeled with values, only component type

[exztinct01]

ah the input also have polarized cap in series before the first resistor, Positive towards resistor

[phatt]

You really need a preamp / buffer stage with a level control to run this properly. Even the front end of TS9 circuit will work as long as you are working with 9~12Volts supply. Just add a 10~20k volume pot directly after the transistor buffer,, then into the main chip.

That will also help to control the level of distortion you mentioned. use the circuit topography you drew as the input and try a few resistors from 10k up 100k and that cap that goes to ground ,,try 100p ~ 500p.
use your ears to decide how well each value works,,, often faster than years learning to be an expert at the maths.  (and that's no disrespect to those who eat maths for morning tea. )

I'm busy now ,,but I'll post a circuit later that might help.
Phil.

[exztinct01]

I was looking forward to experiment and find the right values for that RC circuit but to many values to choose from. Thanks Phil for narrowing the range.
I still wish I know the math though, can't find it in Google
Even then, math won't know my ears' preferences

[phatt]

This might be all that is needed to kill off the phone noise.
Also gives you a level input control which might help tame the early distortion you mentioned.
Almost any small signal NPN transistor will work here. 

If you want more Bass, make C1 larger.
If you want more Treble,, make C3 smaller.

This is just One of many options that do same or similar.

Phil.