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markbass tube 800 scratchy pots

F

falconbob

Jul 6, 2007
2
0
#1
anyone experience this...adjust the volume,gain,or eq knobs and get static scratchy noise out of the speakers ? ive had 2 of these amps,both out of the box do the same, i removed case to try to spray cleaner in the pots but they are sealed. ive sent 2 emails to markbass with NO REPLY. are these amps just s**t and paying off artists to sell these keeps people quiet ?
i would like some answers or advice as this #2 amp is gonna hit the trash can.
 
#3
It's not going to work on the sealed pots that many manufacturers are now using.

Generally, when this happens to a sealed pot, there may be other things within the circuit responsible for these symptoms. Otherwise the pot needs to be replaced, and you need to know what you are doing because it's easy for a hack to ruin an otherwise perfectly good PCB. Yes, I see it all too often.
 
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#5
falconbob said:
i cant believe that im the only one with this problem, 2 brand new amps,scratchy pots right out of the box and continued for 6 months each amp...still no replies from markbass.
Click to expand...
You are aware that Italy was hard hit by the Coronavirus, right?

Give them some time, work with them to get your issue resolved. If you attempt to repair it yourself, you may find that you have no warranty and that yo are on your own.

If you are outside the EU, contact your dealer or the importer of record. In the US, there is an authorized service depot that handles all MarkBass products as well. Since your profile doesn't indicate where you are located, that's all the help I can provide.
 
#7
Sometimes slightly scratchy pots are due to the resistive surface not being burnished smooth from use. It doesn't take much surface roughness for this to be apparent.

I have also seen a little of this on pots that use a hardened (longer life) resistive element, takes longer to burnish in. My experience is that ~50 turns of the pot gets you pretty close to worn is, depending on the number and pitch of the wiper fingers.
 
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#10
falconbob said:
anyone experience this...adjust the volume,gain,or eq knobs and get static scratchy noise out of the speakers ? ive had 2 of these amps,both out of the box do the same, i removed case to try to spray cleaner in the pots but they are sealed. ive sent 2 emails to markbass with NO REPLY. are these amps just s**t and paying off artists to sell these keeps people quiet ?
i would like some answers or advice as this #2 amp is gonna hit the trash can.
Click to expand...
I bought a month ago a used LMT800, the Gain 1 was very scratchy and also the Master Volume. Since I know that they are sealed pots I removed the knobs and saw that there was a very small hole at the base of the shafts. So, this morning I sprayed DeoxIt D5 in these small holes and turn the shaft of the pots for about a minute or so and voilà no scratchy noise anymore. Hoping this will help those having this problem.
 
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#12
GUY DES ROSIERS said:
I bought a month ago a used LMT800, the Gain 1 was very scratchy and also the Master Volume. Since I know that they are sealed pots I removed the knobs and saw that there was a very small hole at the base of the shafts. So, this morning I sprayed DeoxIt D5 in these small holes and turn the shaft of the pots for about a minute or so and voilà no scratchy noise anymore. Hoping this will help those having this problem.
Click to expand...
Yesterday I forgot to mentioned that my first idea was to get the cleaner in the pots by spraying the shaft hoping the cleaner will get in the pots that way. I did that also so not sure if the cleaner got in that way only or both ways (Shaft + the small hole at theb ase of the shaft). The important thing is it worked.
 
#16
To contribute to a zombie thread, I just got a Markbass Players School 1x15 combo and the gain knob was exceedingly scratchy/intermittent/distorting. I went with @DWBass's suggestion and fully swept the knob back and forth 51 times and it is totally silent now. If it happens again, I'll try an electrical cleaner in the pat as GUY DES ROSIERS suggested. Hopefully it won't come to that because those knobs are difficult to remove without gouging the plastic.
 
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#17
To further contribute to a zombie thread, I have the same scratchy issue on a LMT800 and was planning to change it. I'll send it to a friend that knows what he's doing but I plan to buy the pot first and send with it altogether. Does anyone know what type it is, can someone post a link with it from an online shop or something? Thanks!
 
#18
I just got my LMIII back from repair. They replaced the preamp board which houses all of the pots.
Two of them are a little scratchy but only when a signal is going through them as I turn the pots up and down.
I'm afraid if I send it in again I'm going to have the same issue anyway. It's not a show stopper the way it is.
It doesn't scratch when I play. I'll probably just live with it.
 
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#19
BassNGuns said:
I just got my LMIII back from repair. They replaced the preamp board which houses all of the pots.
Two of them are a little scratchy but only when a signal is going through them as I turn the pots up and down.
I'm afraid if I send it in again I'm going to have the same issue anyway. It's not a show stopper the way it is.
It doesn't scratch when I play. I'll probably just live with it.
Click to expand...
I have the same problem and found it occurs very often with Markbass: scratchy pots ONLY when a signal is going through. I talked to a tech and he says it's DC leaking in the board. It's all too tiny and crammed to fix it, that's why Markbass just puts in a new preamp under warranty. Since mine is out of warranty, I also just have to live with it.
If anyone has had this and has left it as is, I would like to know if it got worse or damaged other things in the long run.
 
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#20
Martelino said:
I have the same problem and found it occurs very often with Markbass: scratchy pots ONLY when a signal is going through. I talked to a tech and he says it's DC leaking in the board. It's all too tiny and crammed to fix it, that's why Markbass just puts in a new preamp under warranty. Since mine is out of warranty, I also just have to live with it.
If anyone has had this and has left it as is, I would like to know if it got worse or damaged other things in the long run.
Click to expand...

Fyi - I posted this issue on FB in Basses And Amplification and got a very interesting answer from someone, some of these guys are techs:

"Yes, slightly scratchy pots are normal for MB amps. The problem is not the pots per se, but the fact that they use JFET op-amps with high input impedance, which makes the circuit very sensitive to even a slightest change of the pot's resistance. Which also causes a lot of hiss if you crank up both gain and master even with EQ pots in neutral position, especially if your cabinet has a tweeter."
 
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