Code 25, Ugly and Buzzing output after a strong feedback

[Fabio Fujita]

Hi, after turn on my CODE 25 at very high volume with a mic turned on I almost got deaf with the strong feedback. I turned off the Amp in 1 second... But after that all the low tones/frequencies are distorted/buzzing/ugly don't know how to explain (E string with or without Cab, Amp, Mod, Rev, Del). I tried to reset the amp and did a firmware update but I still have the issue.

I also tried several guitars, USB cables, guitar, and cables but I still have this distorted low tones. Could anyone give me any advice besides going to the maintenance?

High tones sound less distorted but everything sounds strange.

When I turn off the Distortion and the Pre-amp the sound gets a little bit better.

Could anyone send me the schematics for CODE 25? I’m electrical Engineer and I’ll try to find the issue before look for any Service Center in Brazil.

By the way, is there a Official Marshall Service Center in Brazil? São Paulo?

Thanks a lot guys!!

 

[fitz]

Musical Instruments | Brazil | CBORGES
Recommended Retailers - marshall.com

Here is a link from Marshall.com for service in Brazil.
I don't know if there is a schematic available on the Code25.
The inside of these amps are more like a computer than an amp.
Sorry I'm not more helpful.

 

[tschrama]

My first gues would be a defect in the power amp ouput stage. Maybe oart of the H bridge is fried, if its a classD , or one leg of the classB output stage is fried.

check if a alternative output still works: headphone output? Digital ouput? Try to narrow it down in what part of the amp something goes wrong...

 

[PelliX]

check if a alternative output still works: headphone output? Digital ouput? Try to narrow it down in what part of the amp something goes wrong...

This, indeed. Any chance this just simply blew the speaker and the solution is a bit simpler? The headphone output should confirm or reject that notion.

 

[Jethro Rocker]

This, indeed. Any chance this just simply blew the speaker and the solution is a bit simpler? The headphone output should confirm or reject that notion.

Yeah I wonder about a blown speaker. What was the mic doing, turned on where? What does the mic have to do with it?

 

[Maggot Brain]

I'm guessing a damaged speaker.

 

[paul-e-mann]

Probably cheaper and easier to just buy another one used than the trouble and expense to repair.

 

[PelliX]

Depends. Personally, I don't go in for 'smart' amps, I like them dumb as a box of rocks, but if the speaker is blown a replacement with a little Jensen or similar might not be bad. If it's the output transistor (well, voltage regulator, actually) then swapping that out shouldn't be hard. Anything else: indeed, get a new amp.

 

[Fabio Fujita]

Musical Instruments | Brazil | CBORGES
Recommended Retailers - marshall.com

Here is a link from Marshall.com for service in Brazil.
I don't know if there is a schematic available on the Code25.
The inside of these amps are more like a computer than an amp.
Sorry I'm not more helpful.

Thanks, I’ll try to contact them on Monday.

This, indeed. Any chance this just simply blew the speaker and the solution is a bit simpler? The headphone output should confirm or reject that notion.

My first gues would be a defect in the power amp ouput stage. Maybe oart of the H bridge is fried, if its a classD , or one leg of the classB output stage is fried.

check if a alternative output still works: headphone output? Digital ouput? Try to narrow it down in what part of the amp something goes wrong...

Same issue through the headphones.

My first gues would be a defect in the power amp ouput stage. Maybe oart of the H bridge is fried, if its a classD , or one leg of the classB output stage is fried.

check if a alternative output still works: headphone output? Digital ouput? Try to narrow it down in what part of the amp something goes wrong...

Same issue through the headphones.

This, indeed. Any chance this just simply blew the speaker and the solution is a bit simpler? The headphone output should confirm or reject that notion.

Same strange noise through headphones.

 

[Fabio Fujita]

I'm guessing a damaged speaker.

The speaker is good, external music from iPhone sounds normal.

 

[Fabio Fujita]

I think Tschrama is right, maybe a fried amp op, but I can’t find the schematics to confirm.

 

[PelliX]

If the AUX input (or BT, or however the iPhone was connected) works, it's not the output stage. Pre-amp for the guitar or something in the DSP circuitry which is pretty much a write-off, then. One could do some signal tracing with a needle on the SMD section, but chances are that you won't be able to source the fried/damaged component and desoldering the existing one would be a bit of a pain, too, unless you have the right gear for it.

My advice would be to get an amp that is 'only' an amp and have some kind of digital modeler (maybe with an integrated drum machine) in front.

 

[Fabio Fujita]

I found a post about MG50 and this small peace of MG's analysis sounds like my issue. Maybe that's why guitar input sounds strange even through headphone and music coming from AUX is ok.

 

[PelliX]

Yup, classic TL072 circuit there ^. Problem is that the MG's (as far as I know, but I'm not much of an expert on them) use through-hole components and a proper output transistor - the ones I've seen are much easier to deal with. The CODE circuitry is pretty much all SMD. Like I said, feel free to trace the signal, though I don't believe any schematics for the CODE are available. I would take a look (or probe) from the input jack up to the DSP area and maybe have a little look to see if there's an obvious OD circuit (back to back diodes, probably) - but the CODEs might do that in software.

Do you have SMD equipment for dealing with that kind of stuff?

 

[Fabio Fujita]

I have a PC Oscilloscope and a soldering station, sometimes I use to repair cellphones, video games and some simple electronics for my family and friends. It's a kind of Hobby - but really don't want to damage my precious Marshall Amp more than it is right now .
Worse case, do you think it's possible to ask for another DSP/Input Board direct from Marshall? Cause I have to import to Brazil and there is no spare parts option at Marshall home page.

 

[Fabio Fujita]

Yeah I wonder about a blown speaker. What was the mic doing, turned on where? What does the mic have to do with it?

Jethro, I have a sound table I use to mix voice. I now it's not recommended but... I juts have the Code today.

 

[PelliX]

I have a PC Oscilloscope and a soldering station, sometimes I use to repair cellphones, video games and some simple electronics for my family and friends. It's a kind of Hobby - but really don't want to damage my precious Marshall Amp more than it is right now .
Worse case, do you think it's possible to ask for another DSP/Input Board direct from Marshall? Cause I have to import to Brazil and there is no spare parts option at Marshall home page.

Cool, same here.

I don't mean to be the arsehole in the room here, but this amp is not that precious, really. It's a Marshall in name only (and they bought the company that writes the FX software/firmware). Due to them being relatively low-cost amplifiers and becoming obsolete over time (think interfaces, firmware, etc), I doubt they will supply you with a board. I believe they're manufactured in China. If you're outside warranty, then have a go at fixing it. Failing that, I really suggest using 'split' units. As a temp hack, you could put a modeler pedal type thing with a line out straight into the amp...

 

[Scumback Speakers]

Based on the original post, I'd probably have to guess the speaker is blown. It's one thing to blast high volume through the speaker, but if you couple that with feedback it could have overheated the voice coil and fried it. The sound described sounds like a blown speaker to me.

Easiest test, get another speaker or cab and try it with the amp.

 

[PelliX]

Based on the original post, I'd probably have to guess the speaker is blown.

That was my first hunch, too, but:

The speaker is good, external music from iPhone sounds normal.

I have no idea where the mic came into play, but I'm guessing the guitar input on the amp was in the feedback loop...

 

[Fabio Fujita]

You are right Pellix, Code is not that precious to anyone but considering the money my wife allows me to spend with musical instruments.... LOL...
I tried to use my multi effects pedal with Code setup Clean (No Pre FX, No Pre AMP, No Mod/Del/Rev) but the result is the same. When clean tones come from the pedals the sound is OK, but when I try medium to high distortion levels the noise and strange output is there again.