Little Mark III Problem - I'm Really Confused

[woodsideh]

A couple of weeks ago I picked up a LMIII at Guitar Center. That weekend I played an outdoor festival.

My rig that night:
LMIII (racked) (DI)
X2 Wireless
Tuner
compressor
2-Avatar SB112s (1 with tweeter turned up pretty high)

About 30 minutes into the gig the LMIII shut down. There was nothing coming through the cabs but strangely enough I was still coming through the FOH. After the song I turned the amp off and back on. It came up with no problem. About 3 minutes into the next song it goes down again. This repeated several times. On the way back from the gig the next day I stopped by Guitar Center and returned the amp. They had another one shipped to me the last week.

I played another outdoor gig last night.

My rig last night:
New LMIII (racked) (DI)
X2 Wireless
Tuner
1-Avatar B212 (with tweeter turned up pretty high)
I even played a different bass.

After about 45 mins into the gig this one shut down. Again I was still coming through FOH. This time I disconnected the wireless and the tuner. I also turned the tweeter back to about 1/2. The amp seemed to do fine for another 45 minutes. Then it shut down again. At the break I switched heads to an old reliable GK.

I am really confused. I have no idea what is going on here.

[ga_edwards]

Poweramp overheating perhaps? How much space do you have around the amp? Are the side vents and and rear fan obstructed?

Not ideal, but I'd try taking it out of the rack next gig and see how it performs.

[BassmanPaul]

Check you cables for a start. Next check the impedances of your cabinets.

Paul

[rhopper]

Originally Posted by ga_edwards

Poweramp overheating perhaps? How much space do you have around the amp? Are the side vents and and rear fan obstructed?

Not ideal, but I'd try taking it out of the rack next gig and see how it performs.

I agree, sounds like an overheating issue.

[yamaha]

Happened to me once also. Powered down, then on again. Never happened again.

IIRC, I commented on this on a tread, and I had quite a few similar stories. Guess the LM might be sensitive to ohms/heat, but as 99.9% of the reviews are thumbs up, I still consider it a top, and that's why I have a LM2, F1, and planning on buying a cmd combo.

[woodsideh]

Originally Posted by ga_edwards

Poweramp overheating perhaps? How much space do you have around the amp? Are the side vents and and rear fan obstructed?

Not ideal, but I'd try taking it out of the rack next gig and see how it performs.

There is at least 6 inches on each side of the amp. There is also space below and above. The fan is not obstructed in the rear. If it is overheating would the direct still work?

Originally Posted by BassmanPaul

Check you cables for a start. Next check the impedances of your cabinets.

Paul

The cables are good. Two weeks ago I used 2-8 ohm cabs. Last night I used 1-4 ohm cab. The cables seemed to work fine when I changed amps.

[KJung]

Originally Posted by woodsideh

There is at least 6 inches on each side of the amp. There is also space below and above. The fan is not obstructed in the rear. If it is overheating would the direct still work?



The cables are good. Two weeks ago I used 2-8 ohm cabs. Last night I used 1-4 ohm cab. The cables seemed to work fine when I changed amps.

Yes, the power amp limiting would not impact the preamp or DI. If this happened with two LM's, and since you rarely hear about this with the thousand or so others that are using and posting about this head, either you are just pushing it beyond its limits volume-wise, or there is something funky in your signal chain (i.e., maybe your 4ohm cab is actually significantly under 4ohm nominal impedance.

If it happened with two LM's, it sounds like the amp might not work for you. So many of us have POUNDED the LMII (and I assume III) at very high volumes through big 4ohm cabs outside, etc., that something does not feel right here.

[woodsideh]

Originally Posted by KJung

Yes, the power amp limiting would not impact the preamp or DI. If this happened with two LM's, and since you rarely hear about this with the thousand or so others that are using and posting about this head, either you are just pushing it beyond its limits volume-wise, or there is something funky in your signal chain (i.e., maybe your 4ohm cab is actually significantly under 4ohm nominal impedance.

If it happened with two LM's, it sounds like the amp might not work for you. So many of us have POUNDED the LMII (and I assume III) at very high volumes through big 4ohm cabs outside, etc., that something does not feel right here.

I run the gain around 11 o'clock and the volume between 9-11 o'clock. I'm not sure what the volume limits are.

I am assuming the ohms listed on the cabs is correct. Does anyone have any experience with an LM / Avatar combination?

[THORRR]

You may also want to set up your rig exactly the same way, but with a reliable power source (like maybe a 20amp line at home) and see if the problem repeats itself.

The only time I've ever had an issue like yours with my Markbass LM 800 was when the power being supplied wasn't enough or wasn't constant. A power conditioner might also help.

The amp cutting out could be safety circuits protecting it from damage due to an unreliable power source.

[craig.p]

My guess is that the amp's power section doesn't like the impedance offered by those two cabs' crossovers. Wouldn't be the first time one lightweight got kneecapped by a reactive load while another one simply laughed at it.

[woodsideh]

Is anyone using a LMIII with Avatar cabs?

[Lester4string]

Happened to me when I was running two 4 ohm cabs in Series (for 8ohm impedence) Power amp cut out when I pushed it real hard. I never had that problem running single 2x10 at 4 ohms, or 4x8 at 8 ohms.

Also I never pushed it that hard at a gig, just testing out all my different cab combinations.

[DWBass]

Originally Posted by woodsideh

Is anyone using a LMIII with Avatar cabs?

I am. I run 2 Avatar cabs (a 2x10 and a 1x12). Have had no issues so far! I run the gain about 12noon and the master volume around 9 o'clock into a 4ohm load.

Check your cables (speaker and instrument) for shorts. Did the amp actually go into protect mode or did you just drop sound? Check your bass electronics as well.

I don't think these amps are best suited for rack mounting in my honest opinion. Even though you have enough space in your rack, air flow may still be impeded.

Lastly, how was power provided for your gig? Standard AC feed or generator? If it's generator, I think that may be the problem. I had it happen (different amp though) before.

[woodsideh]

Originally Posted by DWBass

I am. I run 2 Avatar cabs (a 2x10 and a 1x12). Have had no issues so far! I run the gain about 12noon and the master volume around 9 o'clock into a 4ohm load.

Check your cables (speaker and instrument) for shorts. Did the amp actually go into protect mode or did you just drop sound? Check your bass electronics as well.

I don't think these amps are best suited for rack mounting in my honest opinion. Even though you have enough space in your rack, air flow may still be impeded.

Lastly, how was power provided for your gig? Standard AC feed or generator? If it's generator, I think that may be the problem. I had it happen (different amp though) before.

Thanks for replying. I'm not sure wht the difference is in protect mode and just dropping the sound. The sound did go away until I shut the amp down and turned it back on. I will check the cables again. They worked fine after I changed to the GK head. As for power, both gigs had a standard AC feeds.

[craig.p]

Would be interesting to test it again but this time with the tweeter level turned down. Could be some tweeter-protection mechanism (if there even is one) is offering some sort of intolerable impedance to the MB -- something that another brand head might be able to handle. Just thinking out loud about possible causes.

[DWBass]

Originally Posted by woodsideh

Thanks for replying. I'm not sure wht the difference is in protect mode and just dropping the sound. The sound did go away until I shut the amp down and turned it back on. I will check the cables again. They worked fine after I changed to the GK head. As for power, both gigs had a standard AC feeds.

Geez, that's odd then! We play generally at the same volume. Hmmm.........how about the speaker connections? Speakon to Speakon or Speakon to 1/4"? If 1/4", do they fit into the cab snugly?

[KJung]

Originally Posted by craig.p

Would be interesting to test it again but this time with the tweeter level turned down. Could be some tweeter-protection mechanism (if there even is one) is offering some sort of intolerable impedance to the MB -- something that another brand head might be able to handle. Just thinking out loud about possible causes.

I do believe the MB stuff is very sensitive to 'under 4ohm impedance', since there were shutdown issues when used with the EA NL210 cabs, which have lower than 8ohm nominal impedance.

Since two LM's did this with the OP, and since these heads are SO solid for the vast majority of users, I tend to agree that something is funky with that particular cab (which might not impact a different head).

Since the head shuts down and then comes back up when turned on and off, that is almost surely the 'safety protect' circuitry kicking in.

[DWBass]

Originally Posted by craig.p

Would be interesting to test it again but this time with the tweeter level turned down. Could be some tweeter-protection mechanism (if there even is one) is offering some sort of intolerable impedance to the MB -- something that another brand head might be able to handle. Just thinking out loud about possible causes.

I have both my Avatar cabs tweeters set at 12noon and we play pretty much at the same volume. I've had no issues to date.

[DWBass]

Originally Posted by KJung

I do believe the MB stuff is very sensitive to 'under 4ohm impedance', since there were shutdown issues when used with the EA NL210 cabs, which have lower than 8ohm nominal impedance.

Since two LM's did this with the OP, and since these heads are SO solid for the vast majority of users, I tend to agree that something is funky with that particular cab (which might not impact a different head).

I was just thinking this as well. Test the impedances on both your cabs to be sure both are 8ohm cabs.

[woodsideh]

Originally Posted by DWBass

I was just thinking this as well. Test the impedances on both your cabs to be sure both are 8ohm cabs.

What is a good way to test the impedance without taking it to a tech?