My amp has a subtile distortion even clean!?

Mark I's, II's, III's and the almight IV

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arnek85
Bottle Rocket
Posts: 10
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Location: Kiel, Germany
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My amp has a subtile distortion even clean!?

Post by arnek85 » Wed Jan 10, 2018 3:48 am

Hey everybody,

I have got a Mark III blue stripe and since last week it adds a slightly subtile distortion to the signal. Even at super clean settings.

Anyone an idea? I guess it's a problem in the preamp section.

Cheers!

Promethean
Mark II
Posts: 82
Joined: Wed Nov 13, 2013 7:53 am

Re: My amp has a subtile distortion even clean!?

Post by Promethean » Wed Jan 10, 2018 6:31 pm

Could just be a bad tube... tried swapping one at a time?

There was a known reverb glitch which caused a slight distortion in the background of my Purple Stripe at any clean setting if reverb was used. Mesa sent me a note with a fix - an extra earth connection. Dont know if the Blue Stripes had same problem but might be worth checking re. ‘Mkiii reverb glitch’

GJgo
Mark III
Posts: 247
Joined: Sun Mar 06, 2016 10:38 am
Location: Western Colorado

Re: My amp has a subtile distortion even clean!?

Post by GJgo » Sun Jan 14, 2018 12:44 pm

Could also be time for new caps.

darkbluemurder
Mark II
Posts: 104
Joined: Fri Jul 28, 2006 5:58 pm
Location: Europe

Re: My amp has a subtile distortion even clean!?

Post by darkbluemurder » Tue Jan 16, 2018 9:45 am

My understanding was that the reverb glitch was fixed in the Blue and Green Stripes.

I also believe that we discussed the power supply caps in another thread.

Other potential causes for what you describe could be a faulty optocoupler. The lead circuit has one at the input and one at the output. If either of them does not break the circuit clearly when in clean mode you could have spill over. Try the following: put the amp in clean mode, play a guitar and turn the lead drive and master. Does the distortion you hear increase? If no, the optocouplers should be fine.

Good luck,
Stephan

GJgo
Mark III
Posts: 247
Joined: Sun Mar 06, 2016 10:38 am
Location: Western Colorado

Re: My amp has a subtile distortion even clean!?

Post by GJgo » Tue Jan 16, 2018 9:56 am

When Mike B. serviced my blue stripe he performed the reverb mod to it.

darkbluemurder
Mark II
Posts: 104
Joined: Fri Jul 28, 2006 5:58 pm
Location: Europe

Re: My amp has a subtile distortion even clean!?

Post by darkbluemurder » Tue Jan 16, 2018 10:18 am

In that case I stand corrected.

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