Amp Noise Help!!!

[Travis8]

Hi! I have one marshall 1987x with noise when I turn up high treble volume, some ideas about this problem?


Thanks

Here is the noise (it´s very anoying)

https://drive.google.com/file/d/1xf6d90 ... sp=sharing

[Travis8]

The noise still there with any cable connected

[Stevem]

Inside the amp the green wires going to each preamp tube are grid wires and the should get raised up above the other wires as much as possible.

There’s also a purple wire going to the presence control.
This should be moved away from the preamp section as much as possible also, in fact it’s a good idea to replace it with a shielded cable that’s ground at the front / pot side of the amp only.

[Travis8]

Inside the amp the green wires going to each preamp tube are grid wires and the should get raised up above the other wires as much as possible.

There’s also a purple wire going to the presence control.
This should be moved away from the preamp section as much as possible also, in fact it’s a good idea to replace it with a shielded cable that’s ground at the front / pot side of the amp only.

Thanks, also I read I can take out C5 and the noise dissapear.

It´s that´s true?

[Stevem]

C5 is a coupling cap and needs to be there to block DC voltage and pass just the audio signal on down stream just like C2 does for the other channel.

[johnnyreece]

Is this a new noise, or has it been this way since you got it? Have you tried swapping in known good tubes?

[Travis8]

C5 is a coupling cap and needs to be there to block DC voltage and pass just the audio signal on down stream just like C2 does for the other channel.

If I reduce this C5 the hiss could dissapear?

[Travis8]

Is this a new noise, or has it been this way since you got it? Have you tried swapping in known good tubes?

I try new tubes and the noise still there.

[Stevem]

If swapping the tubes did nothing then one of the two plate load resistors for that channels tube may be going bad.

These are 20 cent parts that take two minutes to unsolder and replace with a new one.

If you do so then up grade them from 1/2 watt up to 1 watt for even less noise and longer life!

[Travis8]

If swapping the tubes did nothing then one of the two plate load resistors for that channels tube may be going bad.

These are 20 cent parts that take two minutes to unsolder and replace with a new one.

If you do so then up grade them from 1/2 watt up to 1 watt for even less noise and longer life!

I will try! This resistor is on V2 (100k)

[Travis8]

I replace the resistor and it´s look like some noise go away but when I push presence and trebble to 10 and I turn up a little bright volume make noise

(I try it without any guitar plug in)

https://drive.google.com/file/d/1q69HTE ... sp=sharing

[Reeltarded]

Your grid wires are poorly routed and you need to fly the NFB above the board (like Steve said)
.

Also... YOUR AMP IS UNSHIELDED UNLESS IT IS MOUNTED IN THE CABINET

Put the amp back in the headbox. Problem nearly solved.

[Stevem]

If your just getting hiss and not a 120 hz grounding buzz then you can play around with this, just note that at some point you will start to roll off some top end sparkle ,

[Reeltarded]

or return the chassis to the shielded place where it lives..

These amp have ONE TREMENDOUS problem. The mixer bypass is 4700p. That needs to GO and can be replaced with a much smaller bright cap over the Vol I control. Do not heat the cap to remove it. Rock it about 14 times and pull it off the board.

[Stevem]

A high pass cap added across a volume pot will only be functional up until you get to 50% of the pots resistance range,
After that it’s out of the circuit and does not make a dam bit of difference should that matter to you in regards to how loud you normally play the amp.