Mesa Boogie V-twin krackles and stutters...

[Muziekschuur]

I have a mesa V-twin wich crackles and stutters when connected to POWER AMP OUT and TO HEADPHONES/MIXER. The unit works fine out of the TO GUITAR AMP... I'm afraid if I were to use it longer with the unfixed outputs in place and the unit only using with GUITAR OUT....

Is this a job wich I could fix? Or will this involve IC repair?

I can dome simple repairs.. But I'm no electronics wizard. If I were to send it out to a Mesa repair center in Holland I would miss it for at least three weeks... I'd like to avoid this ....

[Jazz P Bass]

You will most certainly have to do a bit of troubleshooting to find the problem.
The 'Guitar Out' is simply the guitar signal straight out to the jack.
The 'Power Amp Out' and the 'Headphones/ Mixer' are derived from the whole circuit.
Simply put, it could be anything.
Link: http://tubefreak.com/v-twinp.gif

[Muziekschuur]

I'll have a peek then. Maybe the importer can give me a quote... But haven't heard from him yet...

[52 Bill]

The 'Guitar Out' is simply the guitar signal straight out to the jack.

Check that, the Guitar Out signal is either bypass or through the circuit.

The other two outputs share some common circuitry that could be the cause of the noise, like U1B and U3A.

[Muziekschuur]

Those are TL072 chips.... right? If I'm not mistaken those chips are microphone preamp chips made by Texas Instruments... If it are those, they are in my D&R Dayner mixing console.

The original power supply got quite hot..... When I tested with that supply. My V-twin is part of a pedalboard where it is fed by a Harley Benton Powerplant. Wich delivers max... 500 mA. But it worked so I use that. I wonder if underpowering this pedal could have led to the current damage....

[J M Fahey]

Not a wise decision.

But no, it wouldn't have hurt the pedal, it would simply have behaved very poorly.

[Mick Bailey]

You could narrow it down by using a simple audio probe. I'd do a listening check on the output of U3A and U1B (as per 52 Bill's suggestion) with an input signal - either guitar or some other similar level audio source. You should be able to hear where the signal breaks up. When you take out an IC it's worthwhile installing a socket, but you need to make sure you don't damage the tracks or pads when you remove components. You can make things easier by snipping out the component with a fine pair of cutters and then removing the pins individually.

As these pedals have increased in value quite a bit you need to be confident you can carry out any repair effectively. Don't forget that the pedal steps up the power supply voltage internally to 'real' preamp tube voltages, so it isn't quite the same thing as working on (say) a Tubescreamer.

[dbdoc]

I would certainly eliminate the 2 tubes and dirty/bad socket connections before getting in too deep.

[Muziekschuur]

I did test with swapping tubes. And over "To guitar" the sound was allways great in either clean or crunch/Lead mode.

I will open her up as I have not yet heard back from the Importer...(Roos electronics in Holland).

[Mick Bailey]

Unlikely to be the tubes as they'd affect all of the outputs. Could be dirty sockets, though - especially if they don't get used much. It has to be something common to both faulty outputs and I reckon the signal is good up to U3A pin 3.

[Muziekschuur]

Thank you Mick Bailey.... for these encouraging words.... I haven't got the nerf to crack open the case.... Maybe later this week...

[TVPC]

I have the same problem with mine

Thank you Mick Bailey.... for these encouraging words.... I haven't got the nerf to crack open the case.... Maybe later this week...

Just bought one off ebay and this is the exact same problem that I have... the headphones/mixer sounds AWFUL and crackly. It's useless, and the headphones out is the main reason I got this preamp for direct recording...

Whatever happened to your unit? Were you able to fix the problem? Please help!!

[52 Bill]

Welcome to the place.

Just bought one off ebay and this is the exact same problem that I have... the headphones/mixer sounds AWFUL and crackly. It's useless, and the headphones out is the main reason I got this preamp for direct recording...

What exactly are your symptoms? Does the guitar amp output work correctly? How about the power amp output?