Problem with new LSS Ch 2...help!

[pcos]

Hi Folks,

Looking for a little help.

Just got a new LSS - about 1 week old and I have been lvoing it.

Clean on Ch 1 blows me away, and the reverb is about the best I have heard. Everything seems just fine on ch 1.

But - a problem has cropped up on ch 2. On certain notes I have noticed a low level static kind of sound occationally. If I hold a note and let it sustain, I can also hear occational changes in the volume control. Finally, when this is happening, the reverb can intermittenly drop out. All of this is intermittent - and not overly pronounced - but clearly there.

This happens only on channel 2 - regardless of power level, drive or clean swith position, drive or gain setting, or anything else I can determine.

Channel 1 sounds just wonderful and not problems with the reverb or volume on sustained notes.

I am assuming I have a tube (preamp?) going bad.

Any thought or suggestions/

Thanks in advance!

 

[Brewski]

You might try to replace your pre-amp tube by switching one at a time with a new tube, just to make sure. The one that is driving your your channel two gain could be marginal. That's usually a good place to start, as well as the simplest. Also, check your power tubes . It doesn't hurt to have a spare anyway.

 

[pcos]

Good Suggestion - thanks.

Anythoughts as to why the reverb might be randomly dropping out? I can understand the idea that a preamp tube could be messing with a single channel, ut its unclear to my why this would cause the reverb to drop out.

Then again.... there's a LOT about tube amps that is unclear to me - but .....I'm trying to learn.

Thanks again!

 

[timmerel]

Could your reverb level knob be dirty from the factory, or there be a dry solder connection? You would need a tech to check, unless you are good with a screwdriver.

 

[Ducky]

Hey Pcos,

I don't think that it could be your tubes. Reason I say that is cuz only your V1A (first half of tube) is different between the two channels. Every other tube is used for both. So if your Ch1 is ok, then it might be your v1, but you said that it occurs with the drive off? correct? Cuz with this off, "techinally" it is the same as Ch1.

I would say give Mesa a call. And report back to us I got a LSS too, and hopefully its not a prob with design.

 

[pcos]

Ducky,

You raise a good point. I was looking through the manual this morning, and I came to the same conclusion. I went back and tried to see if it would happen with the drive switched off and I was not able to detect a problem.

I typically use ch 2 with the drive, but as I was debugging this, I thought I had flipped the drive off and still heard it. Now I am begining to wonder about that -it was late at night when I did it, perhaps I was begining to drop a few bits myself.

If V1 was bad, and it this problem is tied to the drive, then swapping that out should do the trick. I was going to try to call Mesa today but discovered that they are open only open Monday-Thursday 8-5pm PST, so I have to wait.

I went to the local guitar center and got an extra preamp tube and an extra EL84 so I could have a backup and use them to debug further. I will try that tomorrow and see what that does.

Still can't fugure out why the reverb would dropout though. The reverb is a tube driven circuit, and it would use the same tubes with either channel 1 or 2. Since I have no problems whatsoever on ch 1, this would suggest that the reverb is ok. Since if comes after the the preamp (which I assume) I would think that what would happen is that I would have ch2 with some noise being rendered throught the reverb. So why the dropouts?

At any rate I will be calling Mesa Monday - even if I fix it - if its V1, I'll want a new tube via the warrentee. I'll get their take on it.

I'll let you know what I find out.

Thanks,

 

[Ducky]

Hey pcos,

Yeah it does sound like your v1. Were you able to reproduce it with the new tube in there?

As for the reverb, if your v1 is bad, then maybe that's the cause.

I've had a couple of probs with my amp. And all of them are due to tubes.
I put in new tubes, bingo, back to musical blyss.

 

[pcos]

I finally got a chance today to try some tube swapping.

I popped out the 12AX7 that was in V1 and put in a new SPAX7 ("a high grade subsitute for the 12AX7" - my local guitar center was out of Mesa-Boogie 12AX7s).


Problem gone!

No funky static noises on ch 2 drive, and no more reverb dropouts.

Plus the sound seems pleasantly "smoother".

Given that the old tube clearly had a problem, I have no idea if the improved sound is because of I now have a good tube, or because of any subtle differences contributed by the SPAX7 tube itself.

Bottom line - problem solved - my ears ar doing a happy dance....

I'll call Mesa tomorrow and see if they can send me a new tube under warentee.....

Thanks for the help and advice guys - muchly appreciated!