Building LM1875 GC

[JhonDoe]

Hello!..

Recently i'd decided to build a GC in a guide boad, following the schematic in the chip data sheet. I aded a pot(100k) in in-put for the volume but when i tested it with an 8 ohm 50 watts speaker i get a lauder hum and i tested it using VOM I got -2v in output.

How can i eliminate or reduce the hum?

Regarding in the schematic on data sheet, do i need to add the 1M ohm(R1) or replace it with Pot?

[elizard]

First step is to post the exact schematic you used.

[JhonDoe]

Originally posted by elizard
First step is to post the exact schematic you used.

as i mentioned, i used the schematic provided in the data sheet the split supply version. I did not included R1(1Meg) in my circuit, instead i used pot(100k)

Here is the schematic diagram

[GregGC]

And even more important is the actual way you've connected the parts. GND loops and stuff like that is mainly to blame for in cases like that. So show us the PCB or the ptp picture. PS included please.

/Greg

[JhonDoe]

Hi..

I re-assemled it again, pick-out all components and re-wiring it. with a new components(resistors and caps) with same chip.. When i tested it w/ VOM I got -30v dc intead of -2. For the time i did change the chip and test it.... and i dont get any reading.

I tink i got a faulty chip...

So now i'm ready to test it with my cd player and speaker..
I will post the rasuslt later.

Can anyone pls.. analyze my PCB layout in my attachment..
I used the schematic in data sheet of LM1875(split supply)

[JhonDoe]

I made it!!!..

It sounds good but got a little problem It picks-up RF. I guees it is a sielding problem coz i tested it as it is, w/out casing..

Now I'm planing to bridge to chip to gain some power.
How much is the output power if i bridge them?
My supply is 25-0-25

And I'm planing to experiment other chips like the LM3886 and LM3875 but i can't find them in local store here in the Philippines...