JCM800 2203 Buzz!

[Randy486]

Hi everybody,

About 7 months ago I bought a "2013 Marshall JCM800 2203 Reissue" and I bought it new (It was sitting in their storage), so that day I turned it on and it was working. Anyway I didn't used the amp until this week, and when I turned it on I noticed it was buzzing (I don't know if it was buzzing before) and I also don't know if this is normal or not, so I really appreciate it if you can help me.

I think the noise is coming from preamp section because when I pull PI tube and connect "FX Loop Send" to my audio Inteface I can still hear the buzz.

I also tried these methods:
1- Changed power cord, guitar cable and speaker cable = the buzz was still present.
2- Changed preamp tubes and the buzz was still present.
3- Pulled PI tube and connect "FX Loop Send" to my Laney "FX Loop Return" and the buzz was still present.
4- Connected the plate of V2b to my Laney FX Loop return, the buzz was still present.
5- Reflowed V1 and V2 solder joints, the buzz was still present.

Here are some sound clips of the noise:
1- No Input / gain and master volume on 10: https://instaud.io/1y7M
2- Low input / gain and master volume on 10: https://instaud.io/1y7O
3- High Input / gain on 10 and master volume on 2: https://instaud.io/1y7P
4- High input / guitar volume on zero / gain and master volume on 10: https://instaud.io/1y7R
5- High input / gain on 10 / PI tube pulled / FX Loop Send to audio interface: https://instaud.io/1y7T

Gut shots:
https://i.imgur.com/dkrhGAq.jpg
https://i.imgur.com/CyUWm0n.jpg
https://i.imgur.com/1peHgYC.jpg

[66Strat]

Sounds like rectified B+ voltage to me, about 100 hz. I don't think the noise level is necessarily too high. It's hard to tell without hearing the amp in person. I have heard noisier amps.

[92Volts]

How loud is it compared to the guitar signal? A 100W amp should be LOUD at maximum gain and volume settings. The signal-to-noise ratio may be no worse than a smaller/different amp yet the level is high due to the high power of the amp (especially with the volume all the way up).

Some noise is inherent to the design (due to limitations of the power supply's production of "clean" power, filament wiring, etc). Sometimes it could be from a fault or bad component. A common "preventable" cause is florescent lighting which produces more EM interference than other types of lights. External noise (from lighting for example) gets into your instrument and cable no matter how resistant the amp is to interference. This is why "humbucker" pickups were developed yet even they are not 100% immune from noise.

[Randy486]

Sounds like rectified B+ voltage to me, about 100 hz. I don't think the noise level is necessarily too high. It's hard to tell without hearing the amp in person. I have heard noisier amps.

So is it normal then? or it's a bad filter cap?

[Randy486]

How loud is it compared to the guitar signal? A 100W amp should be LOUD at maximum gain and volume settings. The signal-to-noise ratio may be no worse than a smaller/different amp yet the level is high due to the high power of the amp (especially with the volume all the way up).

Some noise is inherent to the design (due to limitations of the power supply's production of "clean" power, filament wiring, etc). Sometimes it could be from a fault or bad component. A common "preventable" cause is florescent lighting which produces more EM interference than other types of lights. External noise (from lighting for example) gets into your instrument and cable no matter how resistant the amp is to interference. This is why "humbucker" pickups were developed yet even they are not 100% immune from noise.

The guitar signal is louder than the buzz and also when I put my Les Paul pickup selector switch in the middle position (both pickups on) the buzzing almost fades away (it still buzzes a little bit), so I think it's the guitar and EM interference, right?

[mresistor]

I'm guessing your Les Paul is equipped with two P90 pickups.

[tubeswell]

... bad filter cap?

Most likely - Possibly a bad smoothing cap.

[Randy486]

I'm guessing your Les Paul is equipped with two P90 pickups.

Actually it's equipped with two humbuckers, SD Alnico II Pro (4 conductor wires).

[Randy486]

... bad filter cap?

Most likely - Possibly a bad smoothing cap.

The amp is made in 2013, do you think the caps could have gone bad?
And which ones are smoothing caps, cause I have 3 F&T 50+50uf caps laying around, I can change them.

[tubeswell]

... bad filter cap?

Most likely - Possibly a bad smoothing cap.

The amp is made in 2013, do you think the caps could have gone bad?
And which ones are smoothing caps, cause I have 3 F&T 50+50uf caps laying around, I can change them.

In a Pii filter, the smoothing cap is the 2nd filter cap in the power rail (the first cap being the reservoir cap), so named because it 'smoothes' out the power supply ripple. In a Marshall Plexi with 50-50 cap cans, the 'smoothing cap' is usually a stack of 2 sets of cap cans situated on the screen-supply node/end of the choke, with a resistive divider in parallel with the stack (to balance the voltage drop evenly across the stack). Only way to tell if the smoothing has failed is to stick a scope on the screen supply node. (I'd do that first rather than guessing and swapping needlessly).

[PRR]

> when I put my Les Paul pickup selector switch in the middle position (both pickups on) the buzzing almost fades away (it still buzzes a little bit), so I think it's the guitar and EM interference, right?

Walk around the room. Turn left and right. Rooms buzz all over in a way that guitar pickups will pick-up. But you can probably identify "more" when close to wall-wiring, "less" if get lucky and find a spot the fields cancel, even less if you send your friend out in the yard with the guitar while you listen (unless he stands over/under power wires).

If it "moves with the guitar", it isn't the amp.

[Randy486]

> when I put my Les Paul pickup selector switch in the middle position (both pickups on) the buzzing almost fades away (it still buzzes a little bit), so I think it's the guitar and EM interference, right?

Walk around the room. Turn left and right. Rooms buzz all over in a way that guitar pickups will pick-up. But you can probably identify "more" when close to wall-wiring, "less" if get lucky and find a spot the fields cancel, even less if you send your friend out in the yard with the guitar while you listen (unless he stands over/under power wires).

If it "moves with the guitar", it isn't the amp.

You're right, when I go to a particular side of the room with no lights or outlets, the buzzing almost fades a away (95% of the noise). So i guess the amp is fine.
The only thing that made me think the amp is faulty, was the fact that Marshall forgot to solder the ground lug of one of the filter caps, and they spilled some solder on FX Loop PCB board (It caused two components to be connected), and one of the filter caps positive wire was loose.

[shooter]

forgot to solder the ground lug

Check your input jack ground well, if there's a bad ground there your guitar becomes an even better antenna

[Randy486]

forgot to solder the ground lug

Check your input jack ground well, if there's a bad ground there your guitar becomes an even better antenna

I reflowed its solder joints along with all tube sockets, filter caps and pots, and checked the connections. I also moved some power cords around and it's pretty quiet now!