Possible issue with Titan V12

[SeanSaliSE]

I've owned a Titan V12 for over a year now (on a previous occasion shortly after purchase it was sent to Mesa headquarters for upgrades. Addition of a fan, replaced transformer, additional vents in chassis, etc.)...

Just recently (September 2nd) I was playing a gig and I think my amp developed a problem. Everything was operating fine during sound check, but when it came time later in the evening to start our set, channel 1 (my clean channel) sounded like it was at half of it's volume. At this time when I switched to channel 2 (my dedicated overdrive channel) the volume jumped back to 'normal' levels and the difference in output was so wide that I had to play in the quieter channel 1 so I didn't blow anyone's ears (we play using in-ear monitors).

Between each song I was checking my levels to make sure nothing was bumped or unexpectedly moved. All my dials were untouched. Changing the 1/4 inputs didn't cause anything different. All my connections were solid and exactly like they are every day of the week. Everything was as it should have been except for the fact that my main channel was weak. Because we use IEMs everyone was hearing the XLR direct out signal of the amp through all of this.

About a week later I got to set up the amp again at my jam space to further investigate the problem, once again making sure the knobs hadn't been moved. When I switched channels from 1 to 2, this time there was no massive output gap. It seemed the whole amp's output now was weaker regardless of its channel. I confirmed this by listening both to the output from the speaker cabinet (4 ohm load PH1000), and through my in-ear monitors. The master output knob on my Titan is normally set at 9 o'clock, with both channel 1 and 2 volumes set at 10:30 (channel 2 overdrive level adjusted to match channel 1 output). I had to turn the amp almost past 12 o'clock to get CLOSE to the level of volume it would output before, and my guitar player STILL said I wasn't as loud... argh!

I did some research and the only piece of info I found was in the user manual that suggested that it could be an issue with the amp's driver tube, which MAY cause a weakened overall output in the amp. However my sound is clean. No cackling or popping or any other characteristics of faulty tubes other than weak output.

I was hoping anyone on this forum with Titan V12 experience may be able to enlighten me a little bit on what my problem may be and the best way to fix it. I'm no amp tech.

PS. I know everything about my amp when it comes to inputs, levels, knobs, switches... I assure everyone I've quadruple-checked all the parameters of my setup (which has been the same since I've owned the amp) and nothing on the outside was different. So before someone posts the response... YES IT WAS PLUGGED IN ALL THE WAY.

http://tb1.talkbasscdn.com/smilies/colors/wink.gif

[B-string]

A tube having a weak output does not normally distort, but can be sensitive to incoming gain.

[SeanSaliSE]

Originally Posted by B-string

A tube having a weak output does not normally distort, but can be sensitive to incoming gain.

I was curious if that was the reason the overdrive channel was still kicking full tilt when the problem first started.

I'm a little nervous opening up the chassis of the head... but then again I'm sure replacing one tube isn't rocket science. They're not too expensive and at least it will tell me if the driver tube really is the culprit.

[B-string]

Originally Posted by SeanSaliSE

I was curious if that was the reason the overdrive channel was still kicking full tilt when the problem first started.

I'm a little nervous opening up the chassis of the head... but then again I'm sure replacing one tube isn't rocket science. They're not too expensive and at least it will tell me if the driver tube really is the culprit.

Exactly, tubes are not light bulbs they can fail in strange ways.

[Caca de Kick]

While my Titan was in getting the updates and a few other things looked at, they also installed new preamp tubes while it was there.
A week after I got it back, one of the new preamp tubes failed bringing the amp to making no sound at all.
Now, I never like the Mesa factory tubes, so out they came and I installed some favorites, been working great since.

The lid is easy to remove, just a lot of screws! The pre tubes are very accessible.

[Bassorama57]

Subscribed.
I've had some wierd issues with my V12 over the past several years as well....noteably on gigs. Very similar to what you've described, with the dirty channel going out; but eventually 'coming back, but weaker' after having switched back to the clean channel. Wound up replacing the O/D tubes...and still took it into a very good local tech (Music Technology/Springfield, VA); apparently some of my MOFSETS had wiggled loose from the board. To paraphrase the tech (who himself is a bassist): "Mesa guys built it to be repairable - the MOSFETs are plugged into, but not soldered to the board - makes my job easier if one goes out, but a few of them can and apparently did partially wiggle loose." So what I was experiencing was MOSFETs sometimes connected, sometimes not. There's TWENTY TWO of them in there so...that's 22 opportunities for loose connections.

Now if that's all that's wrong with yours, you could unscrew everything and (after assuring you've discharged all the static charge, capacitor residuals, yada yada) gently nudge all of them to be sure they're seated in place, but an amp tech probably wouldn't charge too much over 1 hour of shop time or a diagnostic fee to do the same thing.

[Caca de Kick]

Originally Posted by Bassorama57;

apparently some of my MOFSETS had wiggled loose from the board. To paraphrase the tech (who himself is a bassist): "Mesa guys built it to be repairable - the MOSFETs are plugged into, but not soldered to the board

Hmm,
Funny you mention the mosfets. When I posted that I sent mine back for the updates, Mesa told me it had several damaged mosfets, so they replaced the whole block of them. Mine was only 2 months at the time.
So I guess for future reference I'll look at them myself if I ever get into a situation again. Thanks.

[SeanSaliSE]

Originally Posted by Bassorama57

Subscribed.
I've had some wierd issues with my V12 over the past several years as well....noteably on gigs. Very similar to what you've described, with the dirty channel going out; but eventually 'coming back, but weaker' after having switched back to the clean channel. Wound up replacing the O/D tubes...and still took it into a very good local tech (Music Technology/Springfield, VA); apparently some of my MOFSETS had wiggled loose from the board. To paraphrase the tech (who himself is a bassist): "Mesa guys built it to be repairable - the MOSFETs are plugged into, but not soldered to the board - makes my job easier if one goes out, but a few of them can and apparently did partially wiggle loose." So what I was experiencing was MOSFETs sometimes connected, sometimes not. There's TWENTY TWO of them in there so...that's 22 opportunities for loose connections.

Now if that's all that's wrong with yours, you could unscrew everything and (after assuring you've discharged all the static charge, capacitor residuals, yada yada) gently nudge all of them to be sure they're seated in place, but an amp tech probably wouldn't charge too much over 1 hour of shop time or a diagnostic fee to do the same thing.

This is a great piece of information! It makes a lot of sense that I could be having this exact problem, since my head sits on top my cab (unheard of I know!!) and is subject to heavy vibrations for hours several times a week.

Now... before I attempt open-heart surgery on my beloved (and now discontinued) Titan, how the heck do I go about doing all that discharge mumbo jumbo to protect the integrity of the sensitive mosfets?

[Bassorama57]

Originally Posted by SeanSaliSE

.. how the heck do I go about doing all that discharge mumbo jumbo to protect the integrity of the sensitive mosfets?

Oh gosh golly I hate to even start to say as I'd fail to mention something. A long time ago I zorched myself with my B-15 so I generally know where to not stick my hands, but perhaps someone else will contribute. You'll know them when you see 'em though, flat chip thingies plugged into the board.

Also forgive me for continually gooning it up - MOSFET, MOFSET..can't get it straight. Technically its:

"The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a transistor used for amplifying or switching electronic signals." Moss-Fet. I have to get that straight eventually..

[BassmanPaul]

This makes little sense to me. A MOSFET, like any other SS output device, needs to be bolted against its heat sink. if it come loose it will overheat and be destroyed. Socketed output devices are nothing new and I simply cannot see them coming loose without failing. Perhaps a picture of the output bank will explain things.

[dmusic148]

Sure-they're screwed down but the legs are just stuck into sockets. So they can corrode, or vibrate loose.

[Bassorama57]

The V-12 has had a few issues...not sure if that's why Mesa discontinued it, but in general it's too powerful for it's own good. There are other report of this issue (MOSFETs coming loose/burning/etc.) this forum as well as others. Happens!

[BassmanPaul]

Originally Posted by dmusic148

Sure-they're screwed down but the legs are just stuck into sockets. So they can corrode, or vibrate loose.

Sorry then the thing is poorly designed and executed!

[juggernaut1]

Originally Posted by Bassorama57

Subscribed.
I've had some wierd issues with my V12 over the past several years as well....noteably on gigs. Very similar to what you've described, with the dirty channel going out; but eventually 'coming back, but weaker' after having switched back to the clean channel. Wound up replacing the O/D tubes...and still took it into a very good local tech (Music Technology/Springfield, VA); apparently some of my MOFSETS had wiggled loose from the board. To paraphrase the tech (who himself is a bassist): "Mesa guys built it to be repairable - the MOSFETs are plugged into, but not soldered to the board - makes my job easier if one goes out, but a few of them can and apparently did partially wiggle loose." So what I was experiencing was MOSFETs sometimes connected, sometimes not. There's TWENTY TWO of them in there so...that's 22 opportunities for loose connections.

Now if that's all that's wrong with yours, you could unscrew everything and (after assuring you've discharged all the static charge, capacitor residuals, yada yada) gently nudge all of them to be sure they're seated in place, but an amp tech probably wouldn't charge too much over 1 hour of shop time or a diagnostic fee to do the same thing.

Bassorama, did they do that work under warranty? My Titan has been to Mesa 3 times. It was ok for a little while, then it started cutting out again on the last gig.

[juggernaut1]

[quote=BassmanPaul;11479465]This makes little sense to me. A MOSFET, like any other SS output device, needs to be bolted against its heat sink. if it come loose it will overheat and be destroyed. Socketed output devices are nothing new and I simply cannot see them coming loose without failing. Perhaps a picture of the output bank will explain things.[/QUOTE

if these are the mosfets,they are all soldered in and bolted. There are 2 rows of 11 each.

[BassmanPaul]

That's kinda what I was expecting. They should not come loose unless they were incorrectly torqued. I've worked on quite a few MOSFET amps and have never come across a loose output device.

[tombowlus]

As I recall, Mesa and some other companies using MOSFETs had some trouble for a while getting good parts when one of the leading manufacturers of MOSFETs split the company in two. Some of the Titans may have gone out with the "bum" MOSFETs before they realized that they had a quality issue.