DC-5 feedback noise

[espexp]

I've got some serious noise issues going on and I need some help locating the problem. Here is my chain: Guitar w/EMG 81/60 into DC-5 head with a Gmajor in a modded to series loop. Not a very complicated setup. Here is the problem: I get uncontrollable feedback and noise on the lead channel. All the tubes are new mesa spax7, I changed them because I thought that was my problem. I only get noise with the guitar plugged in and the volume knob turned up anywhere past about 25%. I've tried 3 different guitars with the same results.
My settings on the lead channel are:
gain 8.75
treble 5.5
mid 2.5
bass 2
pres 2.25
master 3.5
output 2
EQ in a modified V
I wouldn't call these extreme settings. Can anyone give me a clue as to where to go from here. Thanks in advance

 

[Monsta-Tone]

Well...try some of these and let us know if any of them help....Try them one at a time.

Try swapping a known good tube with each preamp tube 1 at a time. Swap the tube and play the amp. If it doesn't help, move on to the next one.
Just because you have new tubes does not necessarily mean that they are good.

Try lowering the highs and lows on the GEQ.

Try lowering the gain a little.


You should not have feedback in your amp unless you have bad tubes, too high of an EQ setting, or something wrong with the amp.
I run mine like this and it has absolutely no feedback, even when facing the amp with my guitar turned up.
I also have a More Gain mod in mine.
Gain - 10
Treble - 6
Mids - 5
Bass - 6
Rev - off
Pres - 10
Master - 3

GEQ - usually only used for a solo boost.
80 - middle line
240 - 1/16" up
750 - 1/8" up
2200 - 1/8" up
6600 - top of slider on middle line


I run it through a Mesa Stiletto 4x12 slant with 2 Vintage 30's and 2 Heritage 30's.
I also run it through a custom cab from my Mojo with a BV30H & BV30V Mojotone British Vintage speakers.

The other day I tried these crazy settings because our baby put them here and I didn't notice. It sounded really heavy!
Gain - 7
Treble - 1
Middle - 10
Bass - 2 1/2
Pres - 10
Rev - 0
Master - 3

 

[espexp]

Thanks for the suggestions Monsta, I knew you would try to help.

Earlier today I tried lowering the gain as low as 4 and I still was getting feedback, I could control it better but it was still there. My EQ is set up with all the sliders within 1/4" of the center, except the middle one that is on top of the bottom line. I'll have to try swapping some tubes in the morning. It could only be V1-V4 right? V5 is the reverb and V6 is the phase inverter correct?

 

[Monsta-Tone]

There should be a tube chart in your manual. If not, let me know and I can email you one.
V1 - 1st Gain stages for both channels
V2 - 2nd & 3rd Gain stages for lead channel
V3 - 4th Gain stage for lead channel (A), and FX Return
V4 - 2nd & 3rd Gain stages for clean channel
V5 - Reverb
V6 - Phase Inverter

The tubes that can cause feedback in the lead channel:
V1
V2
V3
V5
V6
Power Tubes

Try using the channel without the Graphic EQ, this will let you know if it is before V3 or after.
If the feedback goes away with the EQ off, then it would be V3 or V5 or V6.
If the Reverb is off, V5 is most likely not the culprit, but could still be.

Don't underestimate the power tube's ability to create feedback or noise either!
Let me know if any of this helps.

 

[espexp]

OK, so I tried swapping tubes but that doesn't seem to help. I unplugged my guitar and turned up the master and output level to see if I could hear anything strange. I'm getting a consistent low pitched hum coming from the speaker. Also, at very low volume(below where the feedback occurs ) with my guitar volume up I'm getting a consistent medium to high pitched buzzing.
Could this be a supply voltage issue? I tested the outlet and it has a good ground.

 

[Monsta-Tone]

Well, the hum may be just part of the amp. Any tube amp will make noise if you crank it up.
My DC-10 is way more quiet than my Tremoverb though.

You might try the amp and same guitar/cables at another house and see.
I've never seen low voltage cause feedback though.
Did you use a plug tester: http://www.mcmelectronics.com/product/74-300&CAWELAID=220586716
This will tell you if the plug is properly wired, but will not tell you if you have the proper voltage.


I think we asked this, but have you checked your cords?
I sold a Crate half stack to a friend's son years ago when we had a music store. He tried it in the store and it worked perfectly.
He took it home and it squealled like a stuck pig. After a few angry phone calls from him, I asked him to describe exactly how he had it set up.
Come to find out, he was using a speaker cable that looked just like an instrument cable between the guitar and the amp.
This caused the most god awful feedback in his distortion channel, but not the clean channel.
I've actually done this myself, so I know how easy it is to do. You might double check this.

Other than that, if you replaced the power tubes and preamp tubes and it still squeals, and if you have the right cables, then it may need a trip to the amp tech.
I had a DC-2 that sounded phenomenal at lower volumes but cut in and out and squealled mercillessly at higher volumes. Turned out to be an output transformer. But, that is the only blown output transformer I have ever encountered. Usually it's something simple.

I hope my pre-coffee ramblings have helped in some way!

 

[espexp]

I got 1 more for ya, Monsta. I let the amp stay on with my normal settings and nothing plugged into the amp except the speaker and listened. Every couple of minutes the normal amp noise and light low pitched hum goes away completely as if there is no signal at all and then it gradually comes back in a couple of seconds.
As for the cables, I've tried 5 different cables and they all do the same thing.

 

[Monsta-Tone]

Hmm!
Sounds like it needs to go to the tech. Is there anyone around you that you can take it to?

Might be a bad solder connection or filter cap, hard to say without someone looking inside though.

 

[espexp]

I've never been very impressed with my local mesa tech.

That being said, I opened up the amp and looked around. I don't see any burned resistors or loose solder connections. I put my multimeter across my caps and got 0 volts. Does the resistor just outside the large blue caps discharge them when the amp is put on standby? It looks like there is 1 resistor per cap just for this purpose.

Anyway, I noticed that the power tube jacks have a lot of play in them, meaning, the individual terminals move around quite easily in the ceramic jacket. Is this normal?

Are there any other specifics I should be looking for?

Thanks Monsta, I know I'm a pain in the a$$!

 

[Monsta-Tone]

Here is unfortunately where I am gonna have to draw the line. Amps are not very safe to reach into. The big blue filter caps usually have around 500 volts DC on them. This does not feel good if you **** up!

When the amp is on Standby, you should have a higher voltage on them because the current has nowhere to go yet and nothing has caused a voltage drop.
The rest of the blue caps, 30 mf @ 300 volts should have no voltage across them in Standby.

You are probably reading 0 volts because the meter is set to AC and not DC volts.

Please, if you don't know what you're doing in an amp, read some articles 1st or take it to someone or send it to me. I don't want anyone getting hurt because I did not caution them.

If you absolutely insist on looking in the amp yourself.......
Start here: http://aikenamps.com/SafetyTips.html

 

[espexp]

Sorry Brother I didn't mean to make you nervous. I work with electricity every day and I understand how capacitors work and how to discharge them. I just found it odd that I had 0 volts after only about an hour after shutdown, then I remembered out of habit that I used my analog tester on the caps first which discharges them in about 5 seconds. It's the first thing I do every time I open up the chassis.

 

[Monsta-Tone]

:lol: Good! :lol:

Just wanted to make sure you weren't a plumber!

 

[espexp]

Well I replaced the filter caps, the 5 big ones anyway and it made the amp a lot quieter with nothing plugged into it. I didn't notice any hum or cutting out intermittently like it was doing before. While I was in there I replaced the send jack on the effects loop (something I should have done when I modded it to series). The amp seems to have a ton more bottom end and I'm going to have to reset all of my settings but I like the difference it made.

Now my only problem is when I have my guitar is plugged in I still am getting feedback when I turn the volume up on the guitar. The feedback is happening on both channels with the gain pulled and dimed on the clean channel and on the lead channel with the gain at 5 or higher. Along with the feedback I get an electronic buzzing sound that goes up with the volume on the guitar. 3 guitars, same pickups EMGs, same problem. Maybe I need a really good cable? I'm using a Live wire cable right now.

 

[Monsta-Tone]

3 guitars, same cable? I would really think about getting another one!

Good deal on the jack and caps. A lot of people think it's mojo bullshit, but I whole-heartedly believe in changing the caps when they get older, say around 15 years or so. I know you don't have to, but I don't have to clean the fuel injectors on my truck every 50,000 miles either. It will run either way, but it won't run the way I want it to without it! :mrgreen:

 

[espexp]

Now that I have new caps and no hum I was able to figure out that V2 was causing a lot of noise. This was a brand new mesa spax7. It seems that every time I buy new preamp tubes, half of them are junk right out of the box. With the price of preamp tubes these days you would think they would have some quality control.

On a happier note, I couldn't be more pleased with the new filter caps. The hardest part about changing them is cutting the glue that holds the old ones down. A couple of things I've noticed are:
1) more clarity, I didn't realize how mushy my tone had become
2) Tons of tight bottom end
3) actually sounds more "recto" than it ever has
4) more headroom
It feels like I've got a new amp, not one that I've had for 12 years!

 

[Monsta-Tone]

Right on! I know there are a lot of arguements against changing filter caps, but I have never seen an amp sound worse, or even the same afterward! They always sound bigger, deeper and have way more clarity!

Glad you got it all figured out!