Mesa 50 cal. volume/gain issues

[JMaynard]

Greetings.
I have a Mesa 50 caliber + that has a problem with volume/gain. Power section is fine. Tubes are good. Loop is good. Amp sounds nomal except that after about 50% on the push/pull volume pot, the volume gradually drops to near nothing then increases dramatically at 100%. Also generates noise when increasing or decreasing level. I have replaced the pot but same symptoms occur. Any thoughts on this would be appreciated.

[52 Bill]

...except that after about 50% on the push/pull volume pot, the volume gradually drops to near nothing then increases dramatically at 100%. Also generates noise when increasing or decreasing level. I have replaced the pot but same symptoms occur. Any thoughts on this would be appreciated.

Sounds like a parasitic oscillation problem.

What happened before this symptom occured? What have you done so far?

[JMaynard]

Thanks for your response. Can't say what happed leading up to the problem. The amp has exibited these symptoms since I purchased it some time ago. The pot I replaced was physically damaged so I assumed that was at least part of the problem. Replacing the pot made no difference. I have only tested the power section, effects loop and swapped tubes to rule out that possibility.

[izzybell2810]

Thanks for your response. Can't say what happed leading up to the problem. The amp has exibited these symptoms since I purchased it some time ago. The pot I replaced was physically damaged.

Have you considered that the board may also be physically damaged too, causing the intermittent problem you've described?

[JMaynard]

Thanks for your response. There is no damage to the board and the problem is constant.

[txstrat]

I'd had the problem with a weird acting pot like this too. It was a ground issue. The stage prior to the pot had a bad soldering joint.
Just a thought.

[Davemob]

I have only tested the power section, effects loop and swapped tubes to rule out that possibility.

I own a 50 Cal+ 1x12 combo and am experiencing the same issue with volume cutting in and out. I spoke to an authorized Boogie tech about the issue this morning. While I will still get my amp to him to clean the scratchy pots, he suggested a possible solution: put something in the f/x loop. I put a standard 6'' patch cable in the send/return jacks on the rear of the chasis. No more volume cutting. The tech says that the effects loop runs through the signal chain at all times with this model. Although there is obviously another issue to resolve, shorting the f/x loop appears to solve my problem. Give it a try and let us know if shorting the f/x loop works for you. BTW, I also put a delay pedal in the loop while practicing this evening and did not experience any volume fluxuations.

[tim]

If shorting the FX loop fixes the problem then it's time to either clean or replace the return jack. I usually replace them but you can try cleaning it with a contact cleaner like Caig D5

[JMaynard]

I'd had the problem with a weird acting pot like this too. It was a ground issue. The stage prior to the pot had a bad soldering joint.
Just a thought.

Thanks for your reply. Ground issue was my first thought.

[JMaynard]

If shorting the FX loop fixes the problem then it's time to either clean or replace the return jack. I usually replace them but you can try cleaning it with a contact cleaner like Caig D5

Thanks for your response Tim. Symptoms are associated with the volume/gain pot when rotated beyond 50%. Effects loop functions perfectly.

[JMaynard]

I own a 50 Cal+ 1x12 combo and am experiencing the same issue with volume cutting in and out. I spoke to an authorized Boogie tech about the issue this morning. While I will still get my amp to him to clean the scratchy pots, he suggested a possible solution: put something in the f/x loop. I put a standard 6'' patch cable in the send/return jacks on the rear of the chasis. No more volume cutting. The tech says that the effects loop runs through the signal chain at all times with this model. Although there is obviously another issue to resolve, shorting the f/x loop appears to solve my problem. Give it a try and let us know if shorting the f/x loop works for you. BTW, I also put a delay pedal in the loop while practicing this evening and did not experience any volume fluxuations.

Thanks for your reply. Symptoms are associated with the volume/gain pot when rotated beyond 50%. Effects loop functions perfectly.

[tim]

Thanks for your response Tim. Symptoms are associated with the volume/gain pot when rotated beyond 50%. Effects loop functions perfectly.

I was more referring to Davemob's problem...hope you get yours ironed out...I hate those kinds of problems...