New build goes to full volume and stays

[pjd3]

It was sounding great - for about 30 minutes then,

I started to hear some noise of sorts, as when you have a grounding issue on your guitar. Then a minute later the volume went instantly to full volume. The volume knob no longer had any effect whatsoever. Ahhhhhhhh. Was so excited about the new amp then this.

I was hoping to pick some brains about this and take some guidance to the amp. Right off, I would be looking at things very early in the preamp stage, any wires that have come off a potentiometer, maybe a bad pot (these are CTS from Mojotone). I did have to do a bit of drilling and banging on things while mounting this Princeton reverb chassis in a Bogner Alchemist cabinet. Perhaps that jarred something loose.

Any ideas of where to look for the "volume goes to 10 instantly" would be very appreciated! Damn!

Thank you,
Phil D.

[pjd3]

I should mention that this is a 6L6 Blackvibe, a single channel Vibroverb from Rob Robinettes site.

Phil D.

[sluckey]

Check the ground connection to the volume pot. Make sure it reads zero ohms.

[pjd3]

Hey Slucky, I was just ready to remove the chassis to look inside and decided to power it up.

To my big surprise, everything is back to normal. I was going to look for a fallen wire, and yup, particularly a ground. I've seen that before when a ground falls off and you lose the voltage divider thus getting full signal. I full expected to see that but, I feel confident that no wires re-attached themselves during my "nap of disappointment".

The amp is on now and I'm looking to see if any thing crops up. A few folks on internet were suggesting a tube issue to others with volume fluxuation issues OOOOH! There it is! It just went all the way up! Now down. WTF

As I pull in and out on the volume knob, the volume completely cuts in and out, up and down. It looks like I lucked out with a bad CTS volume pot. I thought the shaft had some play in it to begin with. Didn't expect a bad CTS pot but, looks like that is it.

Phil Dl

[pjd3]

It then appeared to be the pot as you could manipulate the knob/post and cause drop outs, noise, buzz, up to 10, but then all of a sudden it would be like the amp would fix itself, then you could not cause any aborrations whatsoever even when aggressively manipulating the pot/shaft.

So, back to a little confusion. Its just not being consistent in its fault modes.

you could also (and still can) cause all this commotion by whacking the cabinet with your hand, or tapping the cabinet with a wrench. I guess I still believe it can be a bad pot, I just didn't bargain on a pot fixing itself momentarily, then going crazy again all by itself without even being near it.

Confused first amp build,
Phil D.

[pjd3]

Well, one thing for another.

Discovered the ground wire from the volume pot was not sufficiently soldered to the preamp buss wire. It looked like a good solder joint visually. I got that 18 awg from work and it looked somewhat colored or yellowed to me, tinged. And a fellow employee joked that "some of the stuff is older that we are around here". I reflowed every connection to the buss wire, adding in much more solder and longer heating time to ensure that the surface of things got cleaned adequately and that the solder adhered. that took care of that problem, as I suspected it would. But then, around 20 minutes into playing this nasty distortion, breakup occurred when I struck chords hard. It wasn't a "tube" distortion, it sounded like the sound was totally falling apart, and it took time for the sound to recover, as if something was being depleted. So disappointed.

I'll start a new thread on this new problem. I'll take a try at making a fix to this but, if I find its out of my leage, I'll turn the amp over to the local amp tech.

This amp is something I build to gig with every week.

Phil D