MP-1 high pitch squeal

kfowler8 · September 06, 2014, 08:45:04 PM

I was doing the rear input jack conversion for my MP-1 and ran into an issue. I swapped the front and rear input jacks with a shorting jack and standard mono jack. When I have a guitar pluged into either jack everything works fine. However if no guitar is plugged in I het this high pitch squeal coming out and it changes when I turn the gain knob on the front. The higher I turn it the louder ang her pitch the squeal becomes. It's not the jacks because ice tried the original ones and have the same issue. I thought I may have a ground issue but it's weird that I don't have the same issue when a guitar is plugged in. Any ideas? Could the gain pot have gone bad?

GuitarBuilder · September 06, 2014, 09:18:06 PM

Can you share how you wired it all up?

kfowler8 · September 07, 2014, 04:53:26 AM

Yeah I'll try and load some pics later today. I used the instructions on here.

kfowler8 · September 07, 2014, 10:39:31 AM

Ok here some pics. I tried to match the pics with the instructions. Ignore the color scheme for the front jack. Red is going to ground. The front jacl is a shorting jack.

MarshallJMP · September 07, 2014, 01:39:34 PM

Can't see any pics?

Now the problem you have is that when no jack is connected the input should be grounded,so in your cas this is not the case.
Else email the pics to me so i can have a look?

kfowler8 · September 07, 2014, 03:24:08 PM

Quote from: MarshallJMP on September 07, 2014, 01:39:34 PM
Can't see any pics?

Now the problem you have is that when no jack is connected the input should be grounded,so in your cas this is not the case.
Else email the pics to me so i can have a look?

I think it's a bad ground somewhere as well but I can't find it.

Can you PM me your email address. When i try to send you an email through the site it won't let me attach anything.

kfowler8 · September 07, 2014, 06:38:39 PM

Couple of updates:

I checked what would happen if I plugged one guitar in the front and another in the back. It does work as it should where the front overrides the back. So that works at least.

I then ran a jumper cable from the hot of the rear jack to ground. Similar to what a shorting jack would do on the rear. It gets rid of the squeal but there's still a slight hum that gets louder as the front gain knob is turned. I would have thought it would have been dead silent.

Am I missing a jumper somewhere?

MarshallJMP · September 07, 2014, 08:15:12 PM

I send you a PM,sned the pics to my email.

kfowler8 · September 08, 2014, 06:03:06 AM

E-mail replied. Thanks!

MarshallJMP · September 08, 2014, 12:14:50 PM

Well now i see the pics,mmmm strange.

Anyway,the rear jack mod posted on the forum is an old one and way too difficult to perform.Dante or Rnolan could you replace it with the correct one if i send it to you?I think kflower8 would agree if i say way too complicated.

rnolan · September 08, 2014, 11:54:25 PM

Hey MJMP, no worries, send me a copy and I'll swap it out, although you can do as much as I can LOL
Cheers R

kfowler8 · September 09, 2014, 05:34:51 AM

I rewired it using MJMP's method last night. Everything works fine. I'm up and running. I spent more time de-soldering everything than I did hooking up the new wires. Defintely easier.

RobbHell · September 09, 2014, 12:14:37 PM

Did you have to put those two resisters back in? What up with HB's work? I have a 3TM from him and seen a few interesting things to put it. Lol

kfowler8 · September 09, 2014, 01:13:59 PM

Quote from: RobbHell on September 09, 2014, 12:14:37 PM
Did you have to put those two resisters back in? What up with HB's work? I have a 3TM from him and seen a few interesting things to put it. Lol

I replaced the resistors with the originals. Not sure if that's what was causing the squeal.

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MP-1 high pitch squeal