DC-10: hum and electrical noise

[bricklayer]

Hello, I am new to the forum and not an amp technician, so forgive me for some possibly naive questions.

I recently bought a used DC-10, and in general the sound is amazing. However, I noticed that the amp is a little noisy. What I mean is that when the amp is on and no instrument is connected, I hear an audible hum. Not terribly annoying, but read on.

When plugged in, I find the amp is very sensitive to electrical noise. [BTW I don't think the problem is my guitar.] If I am plugged straight in, there is some static in addition to the hum. Again, not terrible, but it (not surprisingly) gets worse with higher gain--somewhat annoying if boost switch is used on clean channel or if lead channel is selected. When I run my guitar through pedals (e.g., arion stage tuner, boss dual overdrive, it doesn't really matter), the noise is increased. The noise gets very very annoying when I am using my one-spot AC adaptor to power my pedals. I also noticed the noise sensitivity when I first tried out the amp--it got quite bad when I was touching a lamp!

This is my first high gain amp (before this, I used a fender '65 blackface dual showman), so is this noise sensitivity just what you have to deal with when using a high gain amp? If not, what should I look into? Would it be necessary to replace any of the pre-amp tubes?

Sorry for the long post, and thanks in advance for any advice you might have!

 

[metalblitz84]

The tubes are usually the first things you want to look into. You said you bought it used, do you know how long it's been since they were chaged out? If it's been a long time (about a year or more) I would just replace all of the pre-amp tubes. You can buy them directlly off of Mesa's website. Usually when you get a lot of squealing and humming noise, it's due to an old worn out tube. Good luck!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

http://mesa.stores.yahoo.net/mesboogtub.html

 

[bricklayer]

Thanks for the quick reply! The guy I bought it from said that he hadn't replaced the preamp tubes the whole time he had it, which was at least 5 years. So I guess I should invest in some new tubes.

Do you recommend Mesa tubes? I know that they do a lot of rigorous testing on their tubes, but I've heard a lot of complaints about them in Harmony central reviews (mostly related to tone). I've heard some good things about JJ tubes, but then again I'm not sure how seriously I should take those posts on HC

 

[Buddy]

Turn on the amp , allow to warm up , and with your normal settings , tap on the pot's . If the noise presents itself , well , time to clean 'em .

As for the hum , try plugging it in a different outlet/room . Could be miswired .... Could be a grounding problem in the amp or house . Or maybe tech time .

Congrats on your "new" boog and welcome to the forum .

 

[mrmax]

I've got 2 DC 10's ,in the combo I'm using JJ's in the power section, in the head EH. The JJ's are livelier although both sound good.

 

[bricklayer]

Based on metalblitz' suggestion, I started looking at the preamp tubes. I haven't had a chance to buy a new set of preamp tubes yet, but I took a look at the current ones in the back of the amp and noticed that the one on the far right (v1?) was not lit up. I don't know if that's normal, because I could still get sound out of the amp with no problem.

So as a test, I pulled out that tube and switched it with a sovtek 12ax7 from my showman (not the best comparison, but...). This tube lights up nicely, and the sound has definitely changed. Only the clean tone is very muddy now. There is still some slight hum and electrical noise (although bad when boost switch is pulled), but I think it's improved. Looks like I should probably replace the whole set.

btw. I dont think its a power issue, because my house has a pretty well-grounded power supply, and the noise was apparent in 2 other places.

Buddy, for the tapping on the pots, do you mean I should pull the amp out of the frame and tap on the back of the pots, or just on the front of the knobs?

Also, another dumb question: is it necessary to pull the amp out of the frame to replace the preamp tubes? I found that I had to do that because they were so **** hard to reach, but I wonder if there is a simpler way that I just missed.

Thanks again for all your helpful suggestions. This is a great group!

Thanks again for the great suggestions

 

[Buddy]

Just grab the knob and give it a side to side shake . They will get dirt/oxidation in them over time and cause a 'static' noise .
To clean them you will have to pull the chassis out . (A short squirt of quality contact cleaner , then work the pot 20+ times .)
Its always a good idea to take a look see inside for any other problems . :wink:

 

[Boogiebabies]

I recently bought a used DC-10, and in general the sound is amazing. However, I noticed that the amp is a little noisy. What I mean is that when the amp is on and no instrument is connected, I hear an audible hum. Not terribly annoying, but read on.


Your input jack shorting plug is bent. You should hear nothing or some barely audible white noise. It needs to be bent back. A perfect excuse for a pot cleaning and preamp tube swap.

 

[mrmax]

I've found that turning the amp upside down & shining a flashlight through the small opening on the bottom of the amp(reverb cavity) works for me, for preamp tube replacement.