Mysterious Mesa amp(s) problem, I'd appreciate some help

[Beedster]

Folks

 

I've recently sold two pretty nice Mesa Boogie amps to two highly trusted members on here. On being played by the respective buyers both have been faulty. The first, an M6 Carbine had very low output volume for a few hours that seemed to resolve and I'm assuming all is fine now although it was a worrying few hours for the buyer and me! The other an M-Pulse 600 appears to have started life in its new home with the same symptoms! Worryingly 24 hours later it is not playing ball and continues to produce low volume and distorted tone into multiple cabs. The M6 was collected in person and the M-Pulse was delivered by me, so there's no courier abuse involved, and both units were working fine at my place before they left.

 

OK, these two things could be completely random, unconnected and just bad luck/bad timing, but in almost 40 years of playing I've not had anything like this. 

 

I'm wondering whether there could be an issue with the power supply here. Both amps were played (and tested before sale) in my rehearsal room that runs from a separate power supply to my house. This is because the house is very small and there siomply is no room for large bass amps/speakers. I had a decent sparky over when we first started using the room a couple of months after we moved in to the house, he thouroughly checked the power supply and wiring in the room, replaced some sockets and switches, and gave it the all clear. Even so a few weeks later an all-tube guitar amp that had previously worked fine ran very noisily and oddly on that separate power supply. It didn't worry me too much as the time but has me wondering now. 

 

The amps have been stored cold but dry, in much the same conditions as I imagine a lot of audio gear is kept when warehoused, so I doubt that damp could be a problem, and either way they worked fine before they left. The M-Pulse which seems to be the bigger of the problems was also stored in an SKB airtight shock-mount case so pretty well protected. 

 

I'm at a bit of a loss, thoughts most welcome?

 

 

[wateroftyne]

Temporarily connect the FX send and return with a jack lead and report back…

[Beedster]

11 minutes ago, wateroftyne said:

Temporarily connect the FX send and return with a jack lead and report back…

 

Thanks Michael we've done that one sadly (the buyer had a similar issue with his BB750 which was resolved in similar fashion at @agedhorse suggestion). 

 

As I just said to the buyer, I kinda regretted selling it anyway despite no longer gigging electric bass (I did tun a mag PUP from my DB through it a while back and it was rather massive), so this could simply be fate's way of telling me I must always own at least one Mesa rig, and who am I to disagree with fate (I'm sure many here would concur it's a reasonable hypothesis)  

[Steve Browning]

Blimey, that's weird. 

 

I sold an M-Pulse 600 that made a lot of noise despite being fine when sold. As in your case, to a very decent BCer.

 

It turned out a replaced input jack solved the problem. 

 

Very odd that the same problem manifests itself in both amps.

 

Paging @agedhorse for his thoughts. Hopefully it's something straightforward. 

[Downunderwonder]

The odds both buyers are nitwits with flat batteries in their basses could be about as long as two Mesa's breaking down. Worth checking.

[binky_bass]

7 hours ago, Downunderwonder said:

The odds both buyers are nitwits with flat batteries in their basses could be about as long as two Mesa's breaking down. Worth checking.

I'm the M-Pulse buyer. And to confirm, about everything that can be troubleshooted has been troubleshooted. Different basses, different cables, speaker leads, kettle leads, different cabs, different sockets. I've opened it up and there does look like a potential 'dodgy' valve (the silver cap on one is in tact, on the other its whited out) but both glow and warm up and neither have broken filaments. I've run a bass through the FX return to bypass the pre-amp and the power section seems OK, and as mentioned above I've tried the trick of running a shorted patch through the effects return to bypass the problem that the BB750 had. Unfortunately the amp doesn't seem to want to produce the volume it should. With the gain at 50%/60% and the master volume all the way up I can comfortably talk over it, which shouldn't be the case! @Beedster has been an absolute gent with all of this, we've agreed the best course of action is to rewind the sale as taking it to a Mesa Authorised repairer is never cheap! There is the outside possibility it's something in my environment however in that environment is an Ashdown CTM300, the Mesa Big Block, a Blackstar Series One, a Marshall JVM410, a Friedman JJ20 and an 800w PA system all currently doing as they should. Tis curious indeed. 

[Beedster]

8 hours ago, Downunderwonder said:

The odds both buyers are nitwits with flat batteries in their basses could be about as long as two Mesa's breaking down. Worth checking.

i think both were sufficiently experienced to exclude such factors pretty early in the process 👍

[Beedster]

35 minutes ago, binky_bass said:

I'm the M-Pulse buyer. And to confirm, about everything that can be troubleshooted has been troubleshooted. Different basses, different cables, speaker leads, kettle leads, different cabs, different sockets. I've opened it up and there does look like a potential 'dodgy' valve (the silver cap on one is in tact, on the other its whited out) but both glow and warm up and neither have broken filaments. I've run a bass through the FX return to bypass the pre-amp and the power section seems OK, and as mentioned above I've tried the trick of running a shorted patch through the effects return to bypass the problem that the BB750 had. Unfortunately the amp doesn't seem to want to produce the volume it should. With the gain at 50%/60% and the master volume all the way up I can comfortably talk over it, which shouldn't be the case! @Beedster has been an absolute gent with all of this, we've agreed the best course of action is to rewind the sale as taking it to a Mesa Authorised repairer is never cheap! There is the outside possibility it's something in my environment however in that environment is an Ashdown CTM300, the Mesa Big Block, a Blackstar Series One, a Marshall JVM410, a Friedman JJ20 and an 800w PA system all currently doing as they should. Tis curious indeed. 

 

Thanks Russ, likewise you've been a real gent about all this also. It's all a but strange. I messaged thew buyer of the Carbine last night and his is still running trouble-free despite a similarly shaky start, the plot thickens.  I hope this thread provides some clues and potential solutions 👍  

[Downunderwonder]

8 hours ago, Steve Browning said:

turned out a replaced input jack solved the problem

A clue!

 

Do you use Monster cables? They may have upped their game but they used to sell cables with 1/4+a tad" plugs which gave them a really solid plug in and buggered the jack for anyone coming along with a standard lead.

[sandy_r]

49 minutes ago, binky_bass said:

I've run a bass through the FX return to bypass the pre-amp and the power section seems OK,

 

...so the problem is in the preamp, between the Input and Send jacks?

 

[binky_bass]

3 minutes ago, sandy_r said:

 

...so the problem is in the preamp, between the Input and Send jacks?

 

Honestly, I don't know enough about the inner workings of amps to comment further than I have. Potentially you're correct, but I don't know! 

[sandy_r]

1 minute ago, binky_bass said:

Honestly, I don't know enough about the inner workings of amps to comment further than I have. Potentially you're correct, but I don't know! 

 

ok, to clarify then: when you say the power section is "ok" (when feeding a bass into the Return jack), are you saying that the power section produces the expected ouput volume?  And, also, were you feeding the bass in direct, or through a separate preamp/pedal? thanks

 

[binky_bass]

@Beedster suggested running a bass through the FX return - I've never actually done that before so had no frame of reference for what it should be telling me. 

 

When going into the FX return of the M-Pulse, it was quiet, a volume that you can talk over, and nothing on the front panel impacted the sound, but as it's bypassing the pre-amp, that's to be expected. I did the same with my Big Block as an A/B test and had a similar result in terms of volume, so I presume that going into the FX return won't give you masses of volume. 

 

And yes, Direct in. Nothing in the chain expect bass, amp and cab for all troubleshooting tests. 👍 

Edited January 6 by binky_bass

[sandy_r]

1 hour ago, binky_bass said:

@Beedster suggested running a bass through the FX return - I've never actually done that before so had no frame of reference for what it should be telling me. 

 

When going into the FX return of the M-Pulse, it was quiet, a volume that you can talk over, and nothing on the front panel impacted the sound, but as it's bypassing the pre-amp, that's to be expected. I did the same with my Big Block as an A/B test and had a similar result in terms of volume, so I presume that going into the FX return won't give you masses of volume. 

 

And yes, Direct in. Nothing in the chain expect bass, amp and cab for all troubleshooting tests. 👍 

 

ok, thanks - well, you could try 2 other quick tests, if you wished, to narrow down the problem; try the chains:-

 

A) bass - i/p of Big Block - Send Out from BB - Return In on M-Pulse;

B) bass - i/p of M-Pulse - Send Out from M-Pulse - Return In on Big Block

 

Do you get full volume o/p from M-Pulse in A)  and quiet o/p from Big Block in B)?

 

Edited January 6 by sandy_r

[sandy_r]

might be an idea also to report all your toggle-switch settings on front and rear panels - and are you/ have you been using a footswitch and the Solo control (try varying this, in case its working with no footswitch)

 

[Beedster]

Thanks for your help @sandy_r and @Downunderwonder. Quick answer to some of the above; as far as I know I haven't used monster cables, and despite @Steve Browning very very kindly sending me a Mesa footswitch a while back I was never able to use it as apparently there were two version of the M-Pulse (I meant to open a thread here asking whether the cables could be switched but for some reason never got around to it). I think examining toggle positions might be helpful if Russ has the time and patience to do so, if not I'll continue this once I've collected the rig 👍

 

I have a strong sense that something I was doing here has led to these problems with the two previously trouble-free units, although much like the final scene of Burn After Reading (which if you've not see you really should), I'm damned if I know what the hell it was 🤔 

 

Thanks again folks 👍

[binky_bass]

No footswitch provided and the solo dial does nowt without it! All the same I have rolled it up and down just to be sure! Genuinely have played around with all settings etc. to no avail. It could very well be the valve I mentioned, not entirely sure of the impact a faulty valve would have on an M-Pulse. You can see below the silver cap on one is distinctively different to the other, potentially a failed pin seal?

 

[binky_bass]

Either which way, it's a massive testament to the community on Basschat to be able to comfortably and openly discuss such things between the seller, the buyer and others with knowledge to share to help resolve these things! 😁

[Beedster]

6 minutes ago, binky_bass said:

Either which way, it's a massive testament to the community on Basschat to be able to comfortably and openly discuss such things between the seller, the buyer and others with knowledge to share to help resolve these things! 😁

 

Nicely put mate and I agree 100%, as we said when we met, it felt like two old friends meeting up despite having never actually met in the first place 👍

[sandy_r]

38 minutes ago, binky_bass said:

and the solo dial does nowt without it!

 

...when everything is working correctly! 😉

 

[Steve Browning]

Reading this is similar to watching someone trying to unravel a twisted cable. You want to jump in and try doing it yourself!

 

Bound to be something ridiculously simple in the end. 

[binky_bass]

4 minutes ago, Steve Browning said:

Reading this is similar to watching someone trying to unravel a twisted cable. You want to jump in and try doing it yourself!

 

Bound to be something ridiculously simple in the end. 

Probably! 

 

I have genuinely tried everything I could think of... even to the point of removing all other amps from the environment. Removing all cables and leads from the area (just in case the plethora of wires/cables and speakers somehow was generating some kind of interference) with no change. I've chased these rabbits down holes before over the years and most of the time find the problem, but as it stands, the resolution evades me! 

Edited January 6 by binky_bass

[Beedster]

 

Rabbit seeks solution to Mesa problem 😆

[Beedster]

26 minutes ago, Steve Browning said:

Reading this is similar to watching someone trying to unravel a twisted cable. You want to jump in and try doing it yourself!

 

Bound to be something ridiculously simple in the end. 

A fine observation Steve, I get the funny feeling that by the time it gets back to

mine, like the Carbine, it will have resolved and we’ll never know what was going on. Upside, I will have a Mesa rig again (although Russ if we do resolve this in the meantime you can of course choose to retain ownership should you wish) 👍

[spyder]

1 hour ago, binky_bass said:

No footswitch provided and the solo dial does nowt without it! All the same I have rolled it up and down just to be sure! Genuinely have played around with all settings etc. to no avail. It could very well be the valve I mentioned, not entirely sure of the impact a faulty valve would have on an M-Pulse. You can see below the silver cap on one is distinctively different to the other, potentially a failed pin seal?

 

The valve with the white top is faulty.

There is an air leak.

From the web......

 

White getter on a bad tube VS a healthy tube getter

The second thing to look for is the condition of the getter. This is the greyish coating usually found at the top of a tube, but can be on the sides, or both top and sides, depending upon the tube type. Any color from grey/silver, to black is healthy. When a vacuum tube develops an air leak (a small crack or bad seal by a pin for example) this getter color will change to pure white. 

 

Hope this helps.

Edited January 6 by spyder