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PostPosted: Sat Mar 07, 2009 10:25 pm 
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Bottle Rocket

Joined: Fri Oct 05, 2007 7:53 pm
Posts: 19
Location: Bedford, Texas
My DC-5 has developed a very muddy sound on the rhythm channel. I have replaced all pre-amp and power tubes, tried another cabinet, different guitar chords, different power sources and swapped out the slow-blo fuse. The problem is only slightly noticeable on the lead channel.

Here is an audio/video clip so you can hear it for yourself:
http://www.youtube.com/watch?v=wpwE-YMoNVA

Any ideas?
Thanks in advance!!!

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1996 Mesa/Boogie DC-5
2005 Mesa Rectifier Slant Oversized
1996 Fender USA Stratocaster w/'54 pups
2006 Fulltone OCD
2006 Fulltone OctaFuzz
2001 Dunlop Uni-Vibe w/foot-controller
1976 ElectroHarmonix Electric Mistress
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PostPosted: Sun Mar 08, 2009 4:13 am 
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Mark III

Joined: Thu Jun 07, 2007 7:26 am
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Location: Southwest Louisiana Tone Swamps
Hey, sucks that no one has replied to this at all. Seems you have having way more success on the youtube page itself with like 12 replies or so... Maybe you should just send it to Mesa and have them look at it? That sounds like the sound is fluttering almost from the video... like it's warbling really fast.. Is that how it is in person?

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PostPosted: Sun Mar 08, 2009 9:36 am 
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Mark II

Joined: Mon Nov 24, 2008 12:12 pm
Posts: 90
you said you had the Master set at 1. Im pretty sure mesa notes that you will get some undesired distortion when running the master that low. Try running the master between 3-4 and adjust your preamp side for volume. I get about the same results on my amp when i am trying to play at really low bedroom levels. I end up just not using my DC5 for the bedroom and only use when i am getting up in volume when the wife is out. Try giving the master a boost and see if that gets rid of it


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PostPosted: Sun Mar 08, 2009 10:47 am 
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Bottle Rocket

Joined: Fri Oct 05, 2007 7:53 pm
Posts: 19
Location: Bedford, Texas
mikeymike wrote:
That sounds like the sound is fluttering almost from the video... like it's warbling really fast.. Is that how it is in person?


The camera is recording the sound EXACTLY as the human ear hears it. I made sure of this before making the clip.

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1996 Mesa/Boogie DC-5
2005 Mesa Rectifier Slant Oversized
1996 Fender USA Stratocaster w/'54 pups
2006 Fulltone OCD
2006 Fulltone OctaFuzz
2001 Dunlop Uni-Vibe w/foot-controller
1976 ElectroHarmonix Electric Mistress
1994 Dunlop Cry-Baby


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PostPosted: Sun Mar 08, 2009 10:51 am 
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Bottle Rocket

Joined: Fri Oct 05, 2007 7:53 pm
Posts: 19
Location: Bedford, Texas
adam972 wrote:
you said you had the Master set at 1. Im pretty sure mesa notes that you will get some undesired distortion when running the master that low. Try running the master between 3-4 and adjust your preamp side for volume. I get about the same results on my amp when i am trying to play at really low bedroom levels. I end up just not using my DC5 for the bedroom and only use when i am getting up in volume when the wife is out. Try giving the master a boost and see if that gets rid of it


The "fluttering" sound occurs at volume, at any combination of volume and gain settings. I tested this with the channel volume at 5, and the gain at 1. It's clean at that setting, but when I turn up the gain to about 3, the fluttering sound kicks in again.

Thanks for the suggestion, man!

_________________
1996 Mesa/Boogie DC-5
2005 Mesa Rectifier Slant Oversized
1996 Fender USA Stratocaster w/'54 pups
2006 Fulltone OCD
2006 Fulltone OctaFuzz
2001 Dunlop Uni-Vibe w/foot-controller
1976 ElectroHarmonix Electric Mistress
1994 Dunlop Cry-Baby


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PostPosted: Sun Mar 08, 2009 11:58 am 
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Mark II

Joined: Mon Nov 24, 2008 12:12 pm
Posts: 90
i think i got what you were saying, i just wanted to make sure you were running the OUTPUT VOLUME pot at 2-4 and not 1.

i see that you changed the tubes, but did you pull them one at a time, let them warm up and then see if removing of a certain tube fixed the problem? The problem might not be the actual tube, but it might have to do with the part of the circuit connected to a certain preamp tube.

i would start and remove V1, closest to the input jack, try and play through the amp..and work your way down the line. V1 and V2 are going to be the primary preamp tubes. V3 is half connected to the drive channel and have connected to the FX return. V4 is the secondary section of the rhythm channel, V5 being for reverb, and v6 being the phase inverter. you could be getting that ossilation in any of these.

here is a good test. Using your FX return as a guitar input, turn the control for FX all the way to 100% wet and jack your guitar in there. When you do this, the only active controls will be OUTPUT VOLUME, the PRESENCE of the selected channal, and the EQ if you ahve it engaged. You can crank up the output volume a bit and play. If you dont get any of the ossilation, then you know that the problem has to be coming from further up in the preamp. the FX return, which uses half of the V3 tube, patch the signal in and puts it directly into the power amp section, thus it is bypassing V1,V2,and V4( which comes after it numerically, but really is before it in the signal chain), and v5 the reverb tube.

IF YOU DO HAVE OSSILATION while patching into the fx return, then i bet it is most likely ossilation coming from the phase inverter. If ossilation is occuring at this point, as traced above, you signal is really just running from V3 into V6, and then to the power tubes, so you will know where the problem is confined.

So what do you do with this? If you can narrow down that the problem exists high up in the preamp section, or way down in the power amp section, you can save your amp tech some prodding time, and save your sself a lot of money for him not having to do it.

let me know what you find from the test above


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PostPosted: Sun Mar 08, 2009 3:29 pm 
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Bottle Rocket

Joined: Fri Oct 05, 2007 7:53 pm
Posts: 19
Location: Bedford, Texas
MarkII,

Yeah, my first guess was V6 (phase inverter), but after multiple tube swaps, nothing has changed.

The tubes are all new, but I can't wait to to try the FX loop input test. I am curious to see how loud I can get before the problem kicks in (if at all). Right now, I'm also thinking the problem is in the power section somewhere.

The amp is in our rehearsal space, so I will do the test one evening this week.

Thanks again for the reply!

_________________
1996 Mesa/Boogie DC-5
2005 Mesa Rectifier Slant Oversized
1996 Fender USA Stratocaster w/'54 pups
2006 Fulltone OCD
2006 Fulltone OctaFuzz
2001 Dunlop Uni-Vibe w/foot-controller
1976 ElectroHarmonix Electric Mistress
1994 Dunlop Cry-Baby


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PostPosted: Wed Mar 11, 2009 10:37 am 
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Bottle Rocket

Joined: Fri Oct 05, 2007 7:53 pm
Posts: 19
Location: Bedford, Texas
GOOD NEWS!

After discussing the issue with a Mesa/Boogie technician (Marcus), it was determined that one possible cause could be in a problem in the power supply. More specifically, a capacitor failure. Typically, capacitors last 20-25 years, so it was a stretch.

I removed the chassis, and did a visual on the circuit board. It only took seconds to notice a problem. The "pressed" connector on the positive terminal on one of the large 220uF/300VDC caps had disconnected itself. Don't ask me how! I baby this amp. My guess is the capacitor was installed with stress/tension, and light corrosion contributed to the failure.

I soldered it back together, and I'm rockin' again!

Thanks again for the help/suggestions/feedback.

_________________
1996 Mesa/Boogie DC-5
2005 Mesa Rectifier Slant Oversized
1996 Fender USA Stratocaster w/'54 pups
2006 Fulltone OCD
2006 Fulltone OctaFuzz
2001 Dunlop Uni-Vibe w/foot-controller
1976 ElectroHarmonix Electric Mistress
1994 Dunlop Cry-Baby


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PostPosted: Wed Mar 11, 2009 10:45 am 
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Donating Member
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Joined: Mon Jun 04, 2007 7:58 am
Posts: 4431
Location: Greenville. SC
motorpsych0 wrote:
GOOD NEWS!

After discussing the issue with a Mesa/Boogie technician (Marcus), it was determined that one possible cause could be in a problem in the power supply. More specifically, a capacitor failure. Typically, capacitors last 20-25 years, so it was a stretch.

I removed the chassis, and did a visual on the circuit board. It only took seconds to notice a problem. The "pressed" connector on the positive terminal on one of the large 220uF/300VDC caps had disconnected itself. Don't ask me how! I baby this amp. My guess is the capacitor was installed with stress/tension, and light corrosion contributed to the failure.

I soldered it back together, and I'm rockin' again!

Thanks again for the help/suggestions/feedback.


Nice catch! Glad you got it back up and rockin'!

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PostPosted: Wed Mar 11, 2009 11:26 am 
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Mark III

Joined: Thu Jun 07, 2007 7:26 am
Posts: 189
Location: Southwest Louisiana Tone Swamps
Dude that is totally awesome. I'm so glad yo got it working. You should post a video of it now that it works. I am interested in the tone of the DC-5. :)

I did a similar thing with my 2:100. A screen grid resistor was blown. It feels so good to fix it though :)

_________________
Ibanez:
1998 RG-550 DY
2001 RG-520 QSTB with EMG 81/85
2001 RG-770 FM DRD ("reissue" available in Japan and Europe only)

Line6 Pod XT Pro
Mesa Recto Recording Pre
Mesa 2:100
Mesa Oversize 4x12


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PostPosted: Wed Mar 11, 2009 11:40 am 
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Mark II

Joined: Mon Nov 24, 2008 12:12 pm
Posts: 90
so simple its awesome! I will say however that Electrolytic capacitors are not really supposed to last that long. They are very fickle and lend themselves much easier to going bad than other types. They are usually rated to be sitting on a shelf for 5 years are so, and then used for 5 years. But overheating can cause them to fail earlier. I have noticed the temp in my DC-5 to by much hotter than some of my other amps. I think that is mainly due to the tubes being mounted horrizontally under the board. Not to say this is a bad layout, i have just noticed that my tweed amps, with a verticle set up, seem to be less hot after running for a while.

Not to mention is is pretty cheap and easy to swap out all the caps. I would def recomend buying them from mouser, as you will save lots of money. My DC5 has ATOM caps in it for the filtering section and after replacing them with Illinois caps, i did not notice any change ( The ATOM caps are much more expensive now and often hard to find in the same ratings.)

If you do recap, you should notice upfront that capacitors are getting smaller and smaller, even for the exact same rating and duty. The IC caps that i got to replace the two main ATOM filter caps were about half the size as the ATOM caps.

And to add some third hand knowledge i heard online, that the ATOM caps have been end of lifed...which makes me wonder how long the ATOM caps that are out there have been on the shelves...

Bottom line, if you are going to recap, save youself some cash and go with the IC caps for the filtering section. They work great.


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PostPosted: Wed Mar 11, 2009 11:41 am 
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Mark IV
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Posts: 565
Location: Edgewood, KY
Hell yeah gratz on the repair, im glad it was a simple repair and things are back to quality :D

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PostPosted: Wed Mar 11, 2009 12:23 pm 
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Mark III

Joined: Thu Jun 07, 2007 7:26 am
Posts: 189
Location: Southwest Louisiana Tone Swamps
adam972

that's very useful information!

_________________
Ibanez:
1998 RG-550 DY
2001 RG-520 QSTB with EMG 81/85
2001 RG-770 FM DRD ("reissue" available in Japan and Europe only)

Line6 Pod XT Pro
Mesa Recto Recording Pre
Mesa 2:100
Mesa Oversize 4x12


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PostPosted: Wed Mar 11, 2009 6:17 pm 
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Mark III

Joined: Thu Apr 05, 2007 7:21 pm
Posts: 455
Location: Medford Oregon
I love my DC-5. My favorite Mesa so far and I've owned a bunch.

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