Markbass LM2 Issues

[ebenezer]

Played last night and my LM2 started loosing power....lost half the volume and just sounded weird,  like an oscillating type sound....using 2 vanderkley 112s...any ideas would be appreciated. 

[Jonge McLengo]

I had the exact same issue with my LM2 after playing a venue with a dodgy power supply - volume would change randomly without warning. I took it to a tech who replaced some components to do with the power which still didn't fix it. Sorry to be doom and gloom but I just ended up getting rid... would be curious to know if you do figure out the actual solution!

[sandy_r]

1 hour ago, ebenezer said:

Played last night and my LM2 started loosing power....lost half the volume and just sounded weird,  like an oscillating type sound....using 2 vanderkley 112s...any ideas would be appreciated. 

 

there are a couple of things you could do which might narrow down the affected  section of the amp (visual check - with power off, and NO poking - of Power supply, Power Amp stage, etc. for evidence of new ventilation holes/magic smoke release in caps & power semiconductors; trying Preamp Out to FX send; trying FX In to Main Amp) ...but ultimately it's a question of weighing up a repair estimate from nearest amp tech centre with cost of replacement gear

 

Edited December 4, 2023 by sandy_r

[ebenezer]

Cheers guys, had the lid off and nothing to see tbh....cleaned the jack sockets on the back with switch cleaner....if no better I think I will cut my losses and buy a new amp...

[BassmanPaul]

Does the amp have an effects loop? If yes connect send and return with a short signal cable and see if that helps.

 

[ebenezer]

Will do cheers. 

[BassmanPaul]

On 04/12/2023 at 16:51, ebenezer said:

Will do cheers. 

And?

 

 

[ebenezer]

The amp seems to work OK, have left the patch lead in....have since bought a LM3....have a gig on Friday night so will try the LM2 at volume and see what happens...fingers crossed. 

[Downunderwonder]

Flat battery in active bass?

[Chienmortbb]

On 04/12/2023 at 09:54, Jonge McLengo said:

I had the exact same issue with my LM2 after playing a venue with a dodgy power supply

I doubt whether the mains at a venue could damage your amp. Can you explain? UK mains power is rarely "dodgy".  As I understand thugs, in the USA, this was not always the case, hence the creation of power conditioners. I am sure that @agedhorse or @Passinwind could correct me on that.

[Jonge McLengo]

8 hours ago, Chienmortbb said:

I doubt whether the mains at a venue could damage your amp. Can you explain? UK mains power is rarely "dodgy".  As I understand thugs, in the USA, this was not always the case, hence the creation of power conditioners. I am sure that @agedhorse or @Passinwind could correct me on that.

 

There is definitely some variation in the power supply in the UK; friend of mine lives just down the road from a substation and gear that worked perfectly well and quietly for me was forever buzzing and occasionally going wrong at his.

 

The venue in question was a portakabin-esque place of dubious permanence. There were 3 or 4 bands on the bill, all of whom had their amps going from a single socket and all of whom left them turned on while we soundchecked. The guitar player had similar issues with his amp until we persuaded the other bands to turn their amps off until they got on stage - I believe his amp later had to have some tubes replaced. Mine started fluctuating in volume during that soundcheck and kept doing it from that moment on - that’s why I suspected it was something to do with the power supply.

[agedhorse]

Power conditioners are in general, non-solutions to problems that need to be correctly fixed, and also are markets to extract the most money possible from purchasers.

[Chienmortbb]

7 hours ago, agedhorse said:

Power conditioners are in general, non-solutions to problems that need to be correctly fixed, and also are markets to extract the most money possible from purchasers.

Those were my thoughts exactly, but as I have no real idea of the quality or otherwise of power in the US or whether it varies State to State. I did have one amplifier where the overvoltage protection was set for 240V, but our mains voltage, at my house, is usually 245V. Luckily it was a prototype I was checking, and the production units were fine up to and beyond 253V AC.

Edited December 15, 2023 by Chienmortbb

[agedhorse]

Power quality varies in the US just the same as in the EU and UK. 
 

For an audio product to be compliant to the IEC 62368 standard (Europe), it must be able to operate at the nominal voltage +/-10%. In the UK, the mains voltage is officially 230V +10/-6% which makes the legacy 240V harmonize with the EU’s 230V +/-10%.

 

The required high line testing, if the product is approved for 240V markets (like AU/NZ) is 264V. If limited to 230V markets it would be 253V.

[BassBunny]

On 13/12/2023 at 20:08, ebenezer said:

The amp seems to work OK, have left the patch lead in....have since bought a LM3....have a gig on Friday night so will try the LM2 at volume and see what happens...fingers crossed. 

So it looks like a bit of corrosion in one or both of the effects loop jack sockets. It's a pretty common problem if you never use them. 

Either:

1. Plug a jack in and out of each socket repeatedly to try and clean them up 

2. Leave it as it is.

3. Get some switch cleaner and give it some wallop. Which you've done.

4. Get the jack sockets changed.

I'd do a combination of 1&2. After a bit of In/Out action just leave a nice short patch lead in the effects loop.

[agedhorse]

Don’t give it a wallop, only the tiniest amount possible or you can create new problems when the “cleaner” gets into places it doesn’t belong.

[ebenezer]

Thanks guys

 

[BassmanPaul]

On 15/12/2023 at 20:45, ebenezer said:

Thanks guys

 

Nice to see you not being a Scrooge with your thanks!

[Chienmortbb]

On 15/12/2023 at 20:57, agedhorse said:

Don’t give it a wallop, only the tiniest amount possible or you can create new problems when the “cleaner” gets into places it doesn’t belong.

Agreed. A little on a plug inserted and rotated. I remember that you could buy dummy plugs that were slightly abrasive, but I have never used them myself.

[barkin]

How does dirt/oxidisation on the barrel (or ring/tip contacts) of a jack socket cause problems if there's normally nothing plugged in to it? 

 

More likely the problem's on the (normally made) switching contacts, and breaking them a few times by inserting a jack plug cleans the contacts sufficiently to get rid of the problem. No gloop squirting required - although I guess some of it may find its way to where it's really needed. 

[BassBunny]

49 minutes ago, barkin said:

How does dirt/oxidisation on the barrel (or ring/tip contacts) of a jack socket cause problems if there's normally nothing plugged in to it? 

 

More likely the problem's on the (normally made) switching contacts, and breaking them a few times by inserting a jack plug cleans the contacts sufficiently to get rid of the problem. No gloop squirting required - although I guess some of it may find its way to where it's really needed. 

The effects loop have make/break jacks. If you don't use them the contacts, which are normally made, can oxidize and go high resistance causing a loss of signal.

[barkin]

1 minute ago, BassBunny said:

The effects loop have make/break jacks. If you don't use them the contacts, which are normally made, can oxidize and go high resistance causing a loss of signal.

Yes, that's exactly my point... 

[BassBunny]

It's a bit difficult to explain. It's not the tip or ring where a jack would touch. It's a set of contacts that break when the jack is inserted. I'll try a get a pic of the type of socket used.

[barkin]

1 minute ago, BassBunny said:

It's a bit difficult to explain. It's not the tip or ring where a jack would touch. It's a set of contacts that break when the jack is inserted. I'll try a get a pic of the type of socket used.

No need, I know. Maybe read my post again? 

Edited December 18, 2023 by barkin

[BassBunny]

1 hour ago, barkin said:

More likely the problem's on the (normally made) switching contacts, and breaking them a few times by inserting a jack plug cleans the contacts sufficiently to get rid of the problem. No gloop squirting required - although I guess some of it may find its way to where it's really needed. 

Gotcha, my bad. 

That's exactly the "cure". It's inserted/removing of a jack plug that disturbs any crud. A bit of switch cleaner just ensures you get a nice clean jack socket at the end but certainly not always necessary.