LM1875 non funziona

[csdcar]

LM1875

Hello everyone, I'm new to the forum and I wanted to ask you for a courtesy given your experience,
could you give me a correct schematic for an amplifier with lm1875,
I'm not very experienced, but I'm trying to make one.
I followed some pattern found on the net and they don't seem to work.
I tried to find some in the forum but I couldn't.
every time I assemble one I have a problem lately
the volume was faint, in another loud noise from the speakers.
I just can't understand where I'm wrong, but I would like to start at least from a fixed point, that is a working and well tested scheme.

thank you for your kindness.
See you soon

ps this is the last pattern I followed

Tales From the Chip: LM1875 Audio Amplifier : 8 Steps (with Pictures) - Instructables...
?

 

[Mooly]

That page says

1 - Negative Input (-IN)

2 - Positive Input (+IN)

which is the opposite of what they should be. The diagram looks to be correct though.

Are you using a split (dual rail) supply as shown ?

 

[csdcar]

ciao, hello, thanks for the answer, I feed it with alternately, to try, with a toroidal 17.0 17-30.0.30, and linear 24.0 24,
but the result is still the same atrocious noise

 

[Mooly]

If it is making a noise then it might be unstable or oscillating.

I assume all your power supplies are producing clean DC. For example the 17-0-17 toroidal needs a rectifier and reservoir capacitors to produce a clean -24, 0, +24 volt supply.

The layout and how you wire it all up is very very important. If you get this wrong then it will be unstable.

 

[csdcar]

but it is not only with that scheme that gives me problems, it is also with other schemes, I will have used about ten, and the result is always the same

 

[csdcar]

certo dc supply whit graetz bridge and capacitors filters

 

[csdcar]

I need a definitive and tested scheme, because I am going into confusion, many I have used

 

[Mooly]

Have you looked at the data sheet? There are designs within that document.

LM1875

 

[csdcar]

yes I know this is the national scheme I think? I should have used this too, you say it's the best model to follow?

 

[Mooly]

Its a model that should work correctly. I'm not sure there is any such thing as 'best' because that means different things to different people.

The data sheet diagram is correct and fully functional and should be used as a starting point.

 

[csdcar]

okay mooly I'll assemble one asap and let you know.
thank you for your kindness, you were very kind to answer me, see you soon, bye

 

[Mooly]

OK good luck

(and when you connect it all up make sure that you run the speaker return lead back to the power supply. That will prevent the high speaker currents causing possible feedback around the other parts of the circuit)

 

[csdcar]

which cable the gnd of the speaker?

 

[Sangram]

A few pictures of your build would be really helpful.

Anyway here's my schema and PCB, works pretty well. The relay is optional but avoids the very loud turn-off thump.

Edit:

I went through those links. You do not want to build this on a breadboard. At least a veroboard with tight component spacing and very short paths, as short as possible. I prefer using SMD as long as I can see them for this reason, it also simplifies layout. The 1875 is not the most stable chip at the best of times and needs babysitting. A breadboard is asking for disaster.

 

[csdcar]

thanks sangram, i will try both one on a millefori another with pcb

 

[csdcar]

sangram, but what are those elements detached from the context?

 

[Sangram]

Here's some views with the top copper and bottom copper. It might be helpful to visualise the effective current paths.

In hindsight I would have liked a different way of routing the signal ground, but even this works quite well.

 

[csdcar]

OK good luck

(and when you connect it all up make sure that you run the speaker return lead back to the power supply. That will prevent the high speaker currents causing possible feedback around the other parts of the circuit)

mooly, can you please explain that link better that I didn't understand?
thank you

 

[JMFahey]

Please post a picture of what you actually built.

The schematic can be correct, but layout, grounding, shielding all play a big part too.

 

[csdcar]

of course I will post some photos of what I did, but do you think I should reassemble according to the Texas or National scheme?