Thin Sound on VM 2466

[macsmith]

Hello

I am using the VM for some years. Great amp.

Now i have this problem: after power up the amp and engaging the standby switch the sound is normal. After a few minutes playing sound will be thin and a litte less volume. If i switch the standby off, waiting some seconds and turn it on, the sound is again normal. What can be wrong?

Thank you very much for your effort

Michael from Germany

[Soulcaster]

You might have a tube on it's way out.....?

[macsmith]

The tubes are not very old. I have pulled all tubes in and out and embraced the input jack with WD 40. It seems that the amp is working well now. I have to take a look at it. But thank you for your answer.

[sugarkane]

Could be many things.

But that's exactly what happens when the effects loop jacks get dirty. Give them a good clean out before trying more complicated fixes.

[macsmith]

The effect ist there again.
@ sugarkane: i dont use the effects loop. Is it anyway possible that the fx loop can be the problem?

[sugarkane]

Yeah, it happens all the time with amps. Is is the most likely? No, I can't say that but it's something you can easily found out for yourself before the time and trouble of going to a tech.

After a few years or so any contacts on the pots or loop can get grimy from everyday dust and useage and cause cut-outs and thinness. The results sound disastrous but are the easiest fix in the world.

Good luck with it.

[surfnorthwest]

The only way to rule out the tubes is to change each preamp tube and see if that fixes it. Then connect a voltage meter and check to make sure your bias is in the optimum range.

If that all checks out, take a look at anything you might have recently changed in your chain... cables, pedals ect. If that all looks good then I am afraid it is service time.

[macsmith]

Yesterday i played the VM and after a few minutes there was the discribed effect. I looked to the rear panel and saw thet the loop was enabled. During playing the amp i pushed the loop button and the sount was ok. Pusching the button once again the sound was crap. I think that was the solution.
Is it right there is a contact in the loop jack to make the connection if no plug is in the jack?

[SteveD]

If the loop is enabled but nothing is plugged into it then there is indeed a connection from the send to the return jack socket that enables the signal to pass through anyway (Otherwise there would be no sound because it is a series loop).

When the loop is disengaged by the push switch it is completely out of the signal path true bypass style.

The switching contact that may have oxidised or become dirty thereby causing reduced signal integrity is on the return socket. Try spraying electrical cleaning fluid on a jack plug and inserting it into the return several times in rapid succession. Hopefully this will clear the problem. If not there may be an issue with the loop circuit itself. If you never use the loop, disengage it.

[sikter]

You probably just need to clean the contacts inside the socket but if you don't
use the loop just turn it off. I would try to plug/unplug jack several times to wake up switch inside. You can also enable loop and connect send and return with short patch cable.
That will ensure you that the loop is working fine...

EDIT:
If I only new Steve was typing in the same time. :-)