Ugly and Buzzing output low tones (E string)
0

votes

Hi, after turn on my CODE 25 at very high volume with a mic turned on I almost got deaf. I turned off the Amp in 1 second... BUT, after that all the low tones/frequencies are distorted/buzzing/ugly dont know how to explain (E string with or without Cab, Amp, Mod, Rev, Del), they are buzzing coming from any Guitar or even music coming from the Bluetooth ... High tones sound fine. I tried to reset the amp and did a firmware update but I still have the issue. Also i tried several guitars, usb cables, guitar cables and even my PC but I still have this distorted low tones. Could anyone give me any advice besides going to the maintenance?

Thanks!

asked 03 Jun 2021 at 06:26 PM

Fabio Fujita
Answers: 5
1

vote

Sorry, no idea. You should email Marshall support directly.

 

answered 06 Jun 2021 at 09:24 AM

Joliet Jake (30)
I will say that "Small Combo" patch you use on your youtube video sounds ghastly anyway so probably not the best sound to demonstrate anything.
Maybe show them something like the "American Clean" sound and play the low E string on its own or a chord and let the sound ring on and decay.
The cleaner sounds near the end of your video seem better to me. There did sound to me at the start of your video that there was significant fret buzz when you hit the guitar a little bit harder. This would be more noticeable on the low strings and sound horrible with distortion.
But if you feel there is a fault I still think you should email Marshall service.
- Joliet Jake 06 Jun 2021 at 09:30 AM
1

vote

Can you record it and put it on youtube or soundcloud so we can hear it?

 

answered 04 Jun 2021 at 07:45 AM

Joliet Jake (30)
Sure:
"youtube.com/shorts/eT7Gkaq4Tlk?feature=share"
"youtube.com/shorts/HSLVOVTolDk?feature=share"
"youtu.be/PjuqZ1SpAWE"
- Fabio Fujita 04 Jun 2021 at 04:32 PM
Does it sound the same through the headphones? - Joliet Jake 05 Jun 2021 at 01:41 PM
Yes, same strange output through the headphones. The Bluetooth sound coming from my cell phone is strange too. - Fabio Fujita 05 Jun 2021 at 01:51 PM
Bluetooth sound is a little bit distorted too. - Fabio Fujita 05 Jun 2021 at 01:51 PM
1

vote

If it sounds the same through the headphones its obviously not the speaker.

It sounds like you have tried everything. It could be a power amp or power supply problem, but unless you have some knowledge of electronics then you probably have no option other than to contact Marshall Service.

answered 05 Jun 2021 at 03:05 PM

Joliet Jake (30)
About the Bluetooth, the sound is ok from Bluetooth it was just an impression... I’ve muted the guitar and music from Bluetooth is ok. - Fabio Fujita 05 Jun 2021 at 03:07 PM
I actually have some knowledge of electronics but none in amps, Marshall amps nor musical equipment. Do you know any official assistance in Brazil? - Fabio Fujita 05 Jun 2021 at 03:09 PM
0

votes

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.

? sais:

"The input stage may be affected by transient-voltage/current spikes caused by faulty equipment or DC fluctuation. D1 and D2 (1N4148) back-to-back diodes connected between the supply rails and input are limiter clamping diodes, used to protect the circuit from input signals above 15V+VF (15.65V) or below -15V-VF (-15.65V) which can damage the circuitry."

Any comment on that?

Do you know if I can get the Schematics from Code25 through the support team considering we don't have an Marshall Service Centers in São Paulo/SP, Brazil?

answered 07 Jun 2021 at 02:35 PM

Fabio Fujita
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 07 Jun 2021 at 04:03 PM
0

votes

I received a idea from another Marshall Forum: "If it has a line out you could feed that into the line input (3.5mm jack, above the headphone socket). This will effectively remove all the cab simulation and onboard FX in the CODE".

So I craft a cable to plug my external multi effects modeler and another pedals direct to the AUX port... And it's working.

I've bypassed the DSP and Guitar Input and the sound coming from loudspeakers is nice again.

But I'll keep looking for the schematics and maybe I'll repair the input one day.

Maybe I could replace the Input PCB but I don't know if it's possible or if the cost will be fair.

answered 07 Jun 2021 at 05:46 PM

Fabio Fujita
Bear in mind it could still be a power supply issue as different voltages are derived from the PSU for different sections of the amp, so there will be a supply specifically for the preamp and digital electronics. If there is a problem with this supply it could cause all sorts of issues. Also note that there are 2 different power supplies used in these amps, some have switched mode supplies and some have discreet supplies.

I would be astounded if you manage to get a schematic diagram from Marshall for these amps, in particular the digital modelling section
- Joliet Jake 07 Jun 2021 at 07:12 PM
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