Please Help Identifying problem

[sonolink]

I have this Fender FM212 DSP that I haven't used for a long while. I switched it on yesterday and it makes a weird noise that I have linked here:
https://soundcloud.com/thesoundkitchen/amp

Any ideas? Of course it's an SS amp.
Thanks for the help

Cheers
Sono

[gbono]

What makes the noise change - controls on amp, pounding on cabinet?

[sonolink]

Hi gbono

Thanks for your reply. The noise change is partially due to the guitar itself (single coils) when its moved around and partially by the amp preset selector. The noise itself seems constant to me. What changes is the EQ depending on what amp model DSP preset is selected.

[phatt]

Hi Sono,
You might have a bad ground connection in the guitar.
Check the Bridge ground wire has not broken loose.
If you don't have a DMM to check continuity of guitar ground wires then Try another guitar and see if it has the same problem.
Phil.

[sonolink]

Hi phatt

With all due respect my guitar is not the problem. The noise comes from the amp. I'm not very acquainted with SS amps and can't locate the source of the problem.

Any ideas please?
Cheers
Sono

[Enzo]

OK, I assume your complaint is the sort of whirring background sound?  Pull the guitar cord out, nothing plugged into teh amp.  Does it still make that noise?  Do ANY of the controls affect that noise in ANY way?  Do they turn the volume of it up and down, do the tone controls change the tone of it?

Take the amp to the far end of the house and try it, or better, take it to a friends house.  That could easily be digital hash from some other equipment nearby.  And that equipment may not be musical stuff.   I have a cordless desk phone in my shop that sits on the corner of my bench.  It makes a VERY similar noise in high gain amps when the chassis sits a foot from it on my bench.  I once had a CD player that sent digital noise all over the room.  I finally noticed one day the digital noise I kept hearing in my sound system was going off and on at the same rate as the display on the player was blinking.  Cell phone and smart phones can make noises in your amaps when they sit on them.

SO getting the amp out of the area might reveal if there is a local electrical environmental noise.

For that matter, does moving the amp around the room make ANY change in the noise?  Turn the amp 90 degrees so it faces sideways, does that change anything?

It could be other things, but it sounds like digital hash to me.  SO computers or anything computerized (the display on my phone set is a small computer after all), but even switching power supplies could be doing this.  But if it is within the amp, you have a DSP circuit, that is digital.  There could be a problem with it, or even just a poor ground to its board inside.

I haven't been inside one of these in a while, I forget if the DSP is on its own little card, I suspect so, in which case, pull the chassis, and find the little board.   wiggle the board a little then press down to kinda reseat the multipin connector.  Does that change anything?

[sonolink]

Hello

Thanks for your reply Enzo. It's not a "complaint". As you can hear on the linked recording the noise makes the amp unusable. I'm trying to repair it. It IS the amp. I've tried it in different places before posting.

The controls do affect the noise as you can hear on the linked recording. Gain, Volume, Bass, Middle, and Treble, and each position of the amp simulation knob. This happens on BOTH channels with the FX return knob down to zero.

SO, my guess is the noise is produced somewhere else than the FX circuit OR if it is produced by the effect circuit it reaches elsewhere somehow.

You may be right and maybe it's digital hash but, just out of curiosity, COULD it be a PSU noise? I'm not sure but I think this amp works with a bipolar PSU and I'm not very acquainted with these. Could it be a source of noise if some component is dead?

Anyway I'll check the DSP card as you suggest
Also, I can't find a damn schem of this amp. Any one?
Cheers

[J M Fahey]

Hello

Thanks for your reply Enzo. It's not a "complaint". As you can hear on the linked recording the noise makes the amp unusable. I'm trying to repair it. It IS the amp. I've tried it in different places before posting.

Here everybody is suspect unless proven innocent, so pease run the tests suggested above and describe what happens, control by control.
*You*  have the amp, not us, so please do the tests we ask you, even if you find them useless.
And we ask *only*  what we would do ourselves if we had the amp on a service bench.
Suppose the amp does power up and you say: "it´s not the fuse, I put a new one there before leaving home"
Guess what we´ll do?
Yup, you are right, we will check the fuse anyway .And so on.

The controls do affect the noise as you can hear on the linked recording. Gain, Volume, Bass, Middle, and Treble, and each position of the amp simulation knob. This happens on BOTH channels with the FX return knob down to zero.

How would we know that?
It´s not a video so we have no clue whether you are touching any knob or not, nor you say "now I´m sweeping treble from 0 to 10" or"now I´m turning around" or "I´m putting the guitar horizontal"  or whatever.
FWIW buzz drops *a lot* from 0:12 to about 0:22, yet guitar volume stays about the same, so you did NOT touch the volume control, so *what* did you do at that moment?
There´s also a noise burst at around 0:31 , plus other unexplained changes, but again, why should we solve a riddle?

SO, my guess is the noise is produced somewhere else than the FX circuit OR if it is produced by the effect circuit it reaches elsewhere somehow.

Why?

You may be right and maybe it's digital hash but, just out of curiosity, COULD it be a PSU noise? I'm not sure but I think this amp works with a bipolar PSU and I'm not very acquainted with these. Could it be a source of noise if some component is dead?

Hum, maybe; but this kind of noise, very unlikely.

Anyway I'll check the DSP card as you suggest

The DSP crd and all other tests suggested in the same answer.

Also, I can't find a damn schem of this amp. Any one?

I don´t have it, but in similar amps I have seen that the main circuit is exactly the same, only instead of the spring reverb circuit you have a nice 6 or 8 pin flat cable connector labelled "To - From DSP card" or FX board , so main circuit can be btroubleshooted the normal way, and DSP card either works properly or not.
Absolute worst case, I guess you can unplug it and keep the effects less amp working.

[Enzo]

"Complaint" simply means problem specified.  it is not a description of mood or attitude or anything.  AMp makes enough noise to be unusable, that sounds like a valid complaint to me.


Even if the FX is turned down, the FX circuit is still in there running, and it is digital.  Digital hash can leak out into other sensitive circuits.  SO it COULD be the source of the noise without directly affecting the FX themselves.  or it could be totally innocent.

COntrols that affect the noise are after its source.  COntrols that have no effect are either before the source or not in line with it.  That can be tricky, if the digital circuit is noisung up the power supply, it might inject that noise into earlier circuits.

The main power supply is going to make hum, plain old 60Hz hum, if it has problems.  Unless it is an SMPS, it won't make that noise.

And missing ground connections internally can be possible causes.