Fixing the Musicmaster Bass Amp

taylornutt · Post by **taylornutt** » Sun Feb 20, 2011 10:42 pm

I am having some Volume and tone issues with my 1975 Musicmaster Bass amp. The volume pot turns really slow and smooth and the tone pot has very little resistance and turns really quick when I adjust it. Here is a video showing how the pots affect the sound of amp. I am guessing dirty pots but would love some feedback. Will photograph/video once I get it apart.

[youtube][/youtube]

Sidney Vicious · Post by **Sidney Vicious** » Sun Feb 20, 2011 11:33 pm

1) clean your pots - can't hurt and easy enough to do;
2) I notice you are plugged into the number 2 input
3) ok so your volume starts late . . . how does it end up?
4) the tone pots on those amps are famously ineffectual -

So, I tend to think there is nothing wrong with the amp that plugging into the first input and cleaning the volume pot won't cure.

Billy3000 · Post by **Billy3000** » Mon Feb 21, 2011 1:00 am

I would definitely try cleaning them first. But the fact that nothing happens before you hit 3 kind of tells me that something is wrong with the wiper in the pot.

taylornutt · Post by **taylornutt** » Sat Mar 19, 2011 5:03 am

I went and jammed with a buddy tonight and took the MMB amp along. Both my guitars were buzzing pretty loadly and the buzzing went away when I would touch the strings. I plugged both guitars into my friend's Fender Deville and there was no buzzing or grounding. It also made a crackling noise when nothing was plugged into it or plugged into channel 1. I hope to take it apart tomorrow and see if we can figure out the issues.

Sloan · Post by **Sloan** » Sat Mar 19, 2011 6:36 am

taylornutt wrote:It also made a crackling noise when nothing was plugged into it

this may be a microphonic preamp tube.

also, if your getting super excessive hum, you may need new filter capacitors. this is more common than a lot of people think. caps only have a real shelf life of like 10 years, but they generally last longer. i have done cap jobs on amps from like the 90's.

Haze · Post by **Haze** » Sat Mar 19, 2011 7:16 am

Change those power filtering caps! Its easy if you know how to solder and follow basic instructions so you don't shit yourself when a cap discharges on your hand ala sloan

Rule of thumb is evry 10 years. the caps on my 76 bassman were og and looked like they sit themselves 20 years ago and te amp sounded it.

Haze · Post by **Haze** » Sat Mar 19, 2011 7:18 am

Also, 3 prong that shit if it isn't already. Do that and ill bet you the humming and buzzing goes away. If not then kindly ship me the amp and ill fix it/rock out in small tube amp bliss

timhulio · Post by **timhulio** » Sat Mar 19, 2011 9:08 am

Both inputs are the same on this amp.

taylornutt · Post by **taylornutt** » Sat Mar 19, 2011 12:59 pm

timhulio wrote:Both inputs are the same on this amp.

The second input has slightly more gain than the first. Most 2 input amps I have seen, the second input is has more gain or is darker. Until I go through it and fix the problems I can't be sure.

taylornutt · Post by **taylornutt** » Sat Mar 19, 2011 1:00 pm

Haze wrote:Also, 3 prong that shit if it isn't already. Do that and ill bet you the humming and buzzing goes away. If not then kindly ship me the amp and ill fix it/rock out in small tube amp bliss

It already has a 3 prong installed, though it's pretty beatup. I might consider replacing the 3 prong with a newer one.

timhulio · Post by **timhulio** » Sat Mar 19, 2011 1:57 pm

taylornutt wrote:
timhulio wrote:Both inputs are the same on this amp.
The second input has slightly more gain than the first. Most 2 input amps I have seen, the second input is has more gain or is darker. Until I go through it and fix the problems I can't be sure.

No, they're identical. Look:

taylornutt · Post by **taylornutt** » Sat Mar 19, 2011 2:14 pm

I am not arguing that they should sound the same, but my 2nd channel is louder and slightly gainer right now. That could be a result of the problems I need fix. Once I sort all the problems out, it will probably revert back to what it's suppose to be.

taylornutt · Post by **taylornutt** » Sat Mar 19, 2011 3:05 pm

Haze wrote:Also, 3 prong that shit if it isn't already. Do that and ill bet you the humming and buzzing goes away. If not then kindly ship me the amp and ill fix it/rock out in small tube amp bliss

I will give it a go. Maybe today I can try when my kids are napping. Hopefully I don't have to send it to you, but I appreciate the offer.

I will take pics and try to locate the power caps you are refering to. Can I get those at Radio Shack?

Do you recommend removing the tubes while I work on the amp?

taylornutt · Post by **taylornutt** » Sat Mar 19, 2011 10:02 pm

I took the amp apart, sprayed contact cleaner in the pots, photographed everything and put it back together.

Nothing changed as far as the pots. I noticed that the Volume pot had a metal shaft and the Tone pot had a white plastic shaft, which means one of the pots is probably not stock and why they don't turn with the same resistance. I could be mistaken, but I thought I saw the back of the Volume pot that it said 1 Meg and the wiring diagram says the Volume should be 250K, which means both pots would be 1M. Not sure what that would do to the circuit if it's true. I may need to replace them both.

The buzz is still present. Input 2 is much louder than Input 1. Here are some photos of the interior

► Show Spoiler

Sloan · Post by **Sloan** » Sat Mar 19, 2011 10:07 pm

those white caps definitely look like they should be changed. also, the orange one is a likely culprit. ive noticed those silver mallory caps usually don't show leaks at the ends like other ones do, but i switch them out anyway. a cap job will make a shit amp sound great.

hotrodperlmutter · Post by **hotrodperlmutter** » Sat Mar 19, 2011 10:12 pm

FCUK IT

just sell it to me

taylornutt · Post by **taylornutt** » Sun Mar 20, 2011 1:50 am

Sloan wrote:those white caps definitely look like they should be changed. also, the orange one is a likely culprit. ive noticed those silver mallory caps usually don't show leaks at the ends like other ones do, but i switch them out anyway. a cap job will make a shit amp sound great.

In addition to the 2 bad pots, I need to change out 3 white caps, 1 orange cap and the silver mallory caps. Anything else?

cobascis · Post by **cobascis** » Sun Mar 20, 2011 1:55 am

bring it to an amp tech dude, rather than having sloan guess via pictures. you won't regret spending a little money bringing it in.

hotrodperlmutter · Post by **hotrodperlmutter** » Sun Mar 20, 2011 2:39 am

THE SLOAN DOES NOT GUESS

THE SLOAN MAKES AN EDUCATED DECISION

taylornutt · Post by **taylornutt** » Sun Mar 20, 2011 3:04 am

Can I check any of these with a Multimeter to see if they are bad? I found an amp tech local, but his prices seem kinda high.

Dabeck Electronics