Marshall MG10-CD Help Wanted

[jagora]

Hello,
Not sure if I am suppose to post a message in this manner? But if I am breaking any rules Please feel free to educate me. At any rate, I bought a great little Marshall practice amp at a swap meet and the clean channel worked fine. When I push in the Overdrive button it sounds really good, that classic rock dirt sound, BUT No volume control at all. From what I've read about this amp is that it's engineered using a FDD Circuitry(in other words,an emulator) The other problem is the Volume knob for Contour/and Overdrive mode was broken off. I haven't tried opening it up yet but wondered if anyone else has any experience with this make and model?

Thanks in Advance
Joe

[J M Fahey]

You are very lucky

Somebody thought the MG10 was a popular amp and did a **full** analysis of it, very detailed, read it :
ElectroSmash - Marshall MG10 Analysis.

From what I see in the schematic you seem to have a broken distorted channel volume pot or maybe it got hit/kicked and solder or oads or tracks cracked.

Open the amp, look closely to that area with good light and glasses and resolder or replace potentiometer as needed.

[Jazz P Bass]

Here is a gut shot of the amp:

When removing the main board, you may also want to unscrew the TDA2030 output IC from the chassis.
Be careful that the milar isolator is not damaged & is reinstalled to keep the IC backplane away from chassis ground.

Note: that is a real fine piece of work ElectroSmash did.

[jagora]

Fantastic, Thank you for the positive words of encouragement. I have many other amps I need to fix as well, including my Crate, and an old "Charvel". I have two Fender Front mans and wondered if it's advisable to remove parts from a broken circuit board to use on another board of a different model assuming it's the same type of part; example - TDA 2030, resistors, IC Chips?

Thank you Again Mr. Fahey

Sincerely
Joseph

[jagora]

O.K. Thanks for the advice and I'll let you know what happens when and if I open it up. I have to be in the mood to do the repair. Often times I get into the garage and end up playing my guitar instead.


Thanks Always,
Joe

[jagora]

Pop-Up Blocker Disengaging

Can anyone tell me how I can view a personal message on the forum? I received a "Pop-Up" blocker advisory, probably because my computer operating system is out dated? I am using "Windows Vista" Home edition.


Thanks to everyone
Joe

[g1]

Try clicking on the 'notifications' button at the top of the page. Then click on inbox. Then click on the message.
Otherwise, when it notifies you of a new message, it will ask if you want to open in a new window. If you say yes it may trigger the pop-up blocker.

[Jazz P Bass]

The OP sent me a text asking where he could purchase the potentiometers.

Why he did not post it here I do not know.

I suggested Parts Is Parts.

https://www.guitar-parts.com/catalog...all-parts/pots

[J M Fahey]

Pop Up blockers are a safety measure but sometimes annoying and not needed in certain safe places .... such as MEF.
I suggest allowing MEF so send Pop Ups ... I do
Not sure about specific instructions but I am certain Windows Vista help will explain it.

FWIW I am using W7, just opened Control Panel, typed "popup" in the search box and it sent me to "Internet Settings", it has an on-off check box and on "settings" it opens a window asking which pages are allowed to send Popups, in this case music-electronics-forum.com
It canīt be much different on Vista.

[jagora]

Ah, O.K. you are correct about this matter. I'd like to add you to my email list too.

Thank You
Joe

[jagora]

Mr. Fahey,
That sound really easy and I'll give it a try. Thanks for your continuous patience and support


Joe

[Jazz P Bass]

Here is a link to the 'Contour' control: https://www.ebay.com/p/?iid=282260853433&&&chn=ps

Here is a chart of the Marshal MG controls:
mgpots.pdf
(Note: the OD Gain pot is shown as an 'A' taper. This info is from the supplier, not Marshall.)

I find the 'Overdrive Gain' control hard to find.
From Marshall it is a 'G' taper.
Which means: "G taper is reverse audio till midpoint and regular audio after that."

[J M Fahey]

(Note: the OD Gain pot is shown as an 'A' taper. This info is from the supplier, not Marshall.)
I find the 'Overdrive Gain' control hard to find.
From Marshall it is a 'G' taper.
Which means: "G taper is reverse audio till midpoint and regular audio after that."

I always called them "S" taper, might make them easier to search and find.
"S" is not a designation per se but refers to the resistance curve shape. itīs what you need for certain active gain controls and for graphic equalizers ... include Parametric equalizer gain controls too.

Resistance on "5" is 50% of total, but is logarithmic both ways ... which makes one half Log and one anti-log.
In such activ gain controls, it provides the smoothest variation end to end.

I made a batch of them, technically no big deal, resistive paint is metal roller applied to track surface; for linear pots is one paint end to end, for Log or Reverse Log full width is covered with high resistance paint, then half with a low resistance topcoat; "S" pots have center strip one value, ends another.

I had to pay for 500 tracks although only fully assembled 100 pots.

So Alpha Pots or anybody else can make any curve they wish, at practically same price, only they canīt be bothered with less than, say, 10000 of each.

[jagora]

Jazz P Bass,
So if I am looking on-line for a potentiometer for the Marshall "gain" volume. Must I specify my selection as an "A" Taper? I don't have a clue yet, BUT I am Ready, Willing, and Able to learn everything I can about audio circuits and what it takes to make those unique tones all of us guitar player love

Joe

[The Dude]

This might help:

http://amprepairparts.com/mgpots.pdf