guitar amplifier Behringer HA-40R

[hashwood]

hello,

can someone please help me with this guitar amp. It's making a strange noise, I included a recording, it's more obvious after 20 sec.
the amp also makes a 50hz noise, but I can live with it. the problem is that the sound seems like it has a buzzing worm attached to it.
maybe someone who has experience with guitar amps can please give me an advice. 

[CaptDon]

First, the hissing fizzing sound seems to be that the overdrive distortion setting is giving you the fuzz box sound which is completely normal if adjusted that way. Second as for the wah-wah-wah sound of the bass string, either your guitar needs tuned or your intonation adjustments are way out of whack!!! To a perfect pitch ear that rig sounds horrible! With even temper tuning it is hard to make any guitar sound good, some notes will always be disonant, but holy crap, you are plucking open strings and it isn't even in tune with itself.

[hashwood]

thanks for your reply, no it's not overdrive. the recording is on clean.
the guitar sounds good on the little roland micro cube.

[Audiorepair]

How does it sound with headphones?

[hashwood]

thanks for your reply. I tested on headphones, the sound is ok, there is the 50hz noise but that is ok (normal)
but the sound is not distorted, so it seems it's the amplifier circuit.
I also teste on another speaker and the sound is the same as the original speaker

[Audiorepair]

I was going to suggest it sounds like it may be the speaker.

Thing is, it looks like U2 is the power amplifier IC? 
And it also looks like as well as driving the speaker, it also drives the headphone via a couple of resistors.
And probably the headphone jack has a built in switch that disables the speaker in favour of the headphones.

So if the headphones are not distorted and the speakers is, that kind of narrows things down a lot.

Maybe a problem with the headphone sockets switch, which you could hard wire bypassed to check?

From the audio I would still suspect the speaker though.

[hashwood]

well, i tested the headphones connection, I shorted it, the problem remains.
I was at a shop that sells the same amplifier to test it. It sounds OK.

I guess the problem is the constant 50hz noise. the one from the shop didn't have it.

[Audiorepair]

Just listened to the recording gain.

I think we are hearing a constant noise, it is unrelated to the volume of the guitar.
Therefore the amplifier is not amplifing any incoming noise problem, the noise is somewhere between, and including, the amplifier IC itself and the speaker.

Maybe it is some kind of mechanical cabinet rattle, this may be a constant volume, but you say you tried it with another speaker and it is the same.

It is possible but rather unlikely the amp IC produces noise when supplying power to the speaker but not the reduced power to the headphones.

You could also try shorting the external speaker jack socket switch, this I suspect does exactly the same thing the headphone jack does, disabling the internal speaker in preference to the external one.

Maybe try again with an external speaker via this socket, it still sounds like a speaker problem to me.

[hashwood]

thanks

I tested the external speaker jack, it's ok there.

how can it be the speaker when the noise is constant without any jack inserted? As I said the one from the shop didn't make any noise without any cable connected.

[Audiorepair]

I don't understand what you are asking.

If the internal speaker is making a buzzing noise when there is sound going through it, then that is what you are hearing.