My Gainclone (by Carlos)

[Mooly]

Have you tried listening to it without that 220pF cap fitted ? That could possibly be making it unstable.

To roll off the high frequencies would need a simple R/C filter fitting at the input but you would be better doing that before the volume control.

Try taking that cap out first.

 

[franziscko]

And so...I've made all wrong with this amp!!
I've fitted the 220pf because I've read it will prevent oscillating!!!!
(Apexaudio, Elektor, Audiophonics, Neurochrome)
My question to roll off the hig frequencies was because I suffer of tinnitus
and some higs are annoying with my new Dynaudio.
I don't know if it is important, but I don't use the 4.7microf cap in input, because
I have no cd offset in cdp outpt, so I think it is useless.
Tomorrow I will try and post again!
Ciao!

 

[franziscko]

Ok, nothing happens with the caps removed.
Before putting everything away I want to build another pcb and take
some good capacitors for the supply. The 1000microf are almost unknown.
See you later...

 

[Mooly]

I think you are going to need to add the filter I mentioned earlier and experiment with values to suit your own preferences. That will allow a simple roll off of high frequencies.

 

[franziscko]

Yes but I need more space in the pcb so I will made another one and I will put 2 quality caps, Panasonic FM or FC I think

 

[Mooly]

Or just add the resistor and cap at the input sockets.

 

[franziscko]

Need space not for the imput but for caps psu and cap you told me to add.
Sorry for my bad english...I don't use google translator.

 

[Mooly]

no problem, I follow what you are saying.

 

[IDM]

And so...I've made all wrong with this amp!!
I've fitted the 220pf because I've read it will prevent oscillating!!!!
(Apexaudio, Elektor, Audiophonics, Neurochrome)

I am about to build an LM3886 gainclone and had read the same thing about stability. I agree it is very confusing to know which are the best and most reliable sources of information to build the amplifier.

I also read that the Thiele network and zobel network are highly advised, otherwise HF stability could damage or destroy a tweeter. Yet I see loads of designs without! I wonder what is really needed?

Ian

 

[Mooly]

Designs from data sheets can often omit details because they are not intended to be fully worked examples although generally if a design is accompanied by a PCB layout then it should be a fully worked example.

An output Zobel network is pretty much essential on most designs. Also using a good layout is everything when it comes to a successful design.

 

[mjf]

why not have a look at a commercial design , like cambridge azur340a?

 

[franziscko]

Absolutely NO!