Input Jacks

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jimsz
Posts: 53
Joined: Tue Sep 21, 2010 7:25 pm

Input Jacks

Post by jimsz »

While I've had my Weber amp kit up and running for some months now, recently if I plug into the "Normal" channel, there is some background noise and the volume increases but remains at a certain level. No matter how much I turn the pots on that channel, nothing happens. I suspect there is something wrong with the input jack.

I was told by one guy to run the plug in back and forth a few times and this help. It didn't.

Has anyone else had this problem?
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rp
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Re: Input Jacks

Post by rp »

Bypass the jack with alligator clip jumpers from the guitar cable directly to ground and the jack side of the input resistor. That'll eliminate the jack. You need to stick something in the jack that'll open it. I doubt that's the problem, but I recently had 2 bad jacks that kept me busy for while as I refused to believe that was the problem.
jimsz
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Joined: Tue Sep 21, 2010 7:25 pm

Re: Input Jacks

Post by jimsz »

rp wrote:Bypass the jack with alligator clip jumpers from the guitar cable directly to ground and the jack side of the input resistor. That'll eliminate the jack. You need to stick something in the jack that'll open it. I doubt that's the problem, but I recently had 2 bad jacks that kept me busy for while as I refused to believe that was the problem.

Bad jack? Yeah, I'm starting to get that impression too.

It's really a bit of a chore to pull the chassis out of the cabinet on these kits and didn't want to do that unless I was relatively convinced it was a bad jack that need replacing.

I had even read to spray some Deoxit on the plug and run that back and forth in the jack. I don't that will work, either.
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Structo
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Re: Input Jacks

Post by Structo »

That won't do any good if the switching part of the jack is messed up.

It's like a little leaf spring that contacts the ground to the input when a plug is not present.
Tom

Don't let that smoke out!
jimsz
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Joined: Tue Sep 21, 2010 7:25 pm

Re: Input Jacks

Post by jimsz »

Structo wrote:That won't do any good if the switching part of the jack is messed up.

It's like a little leaf spring that contacts the ground to the input when a plug is not present.
Any idea what causes these messups, I don't recall there being anything observably wrong with the jack.
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M Fowler
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Re: Input Jacks

Post by M Fowler »

I would look for solder joint problems areas and the wire from the preamp tube to the volume pot.
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rp
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Re: Input Jacks

Post by rp »

Have you proved it's the jack yet by testing / bypassing? Maybe Weber uses those terrible cheap switchcraft knock offs so it's possible. But in a homebrew it's unlikely it's the jack, you probably made a mistake somewhere.

My two Re'ans tested fine when pulled, obviously I put them back in, where they again didn't work. I still refuse to throw them out.
Any idea what causes these messups, I don't recall there being anything observably wrong with the jack.
Gremlins.
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Firestorm
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Re: Input Jacks

Post by Firestorm »

Switchcraft type jack? There's some inconsistency in the diameter of guitar cord plugs. On some, the tip is not quite big enough (or the groove is located a lttle to far back from the tip) to fully release the shorting contact. Over time (even a short time) it's possible that the tip contact deformed slightly and began causing the problem. If you have other brands of cables, you could try those.

If it is the jack, you can test for a shorting contact problem (once the chassis is out) by plugging in and checking whether you can insert a strip of index card stock between the shorting contact and the tip contact. If inserting a cable doesn't clear the shorting contact, don't try retensioning the leaf spring itself (get it wrong and it will never be right again). Instead, use needle nosed pliers to open up the "hook" on the tip contact (just a tiny bit).

Of course, it might be a cold solder joint or a bad ground. But you will have to pull the chassis.
jimsz
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Joined: Tue Sep 21, 2010 7:25 pm

Re: Input Jacks

Post by jimsz »

Thank you gentlemen, you've given me some very good ideas to work with, I'll put them to the test and let you know the results.
jimsz
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Re: Input Jacks

Post by jimsz »

Gents, my apologies for getting back so late on this, it's amazing that no matter what intentions you may have of doing something, family members tend to make other things happen for you, instead.

Anyways, I'm rather puzzled but also happy with the results, at least, so far.

After doing the simple troubleshooting solutions of swapping cables, it was apparent I would have to open up the cabinet and pull the chassis.

After doing so and spending time with the ole chopstick poking and a prodding around, I found that if I pressed down on most areas of the circuit board, I could easily reproduce the noise. Of course, that really didn't help me to isolate the problem.

But, thanks to M Fowler's suggestion of having a look at the volume pot wires, I decided to start with the solder joint going to ground just below the volume pot that had 2 resistor, 2 capacitors and 3 wires attached, one of them was the ground from the volume pot while another was a ground from the input jack. Other than the suggestion from Fowler, it was merely a complete random place to start.

So, I resoldered the joint, turned on the amp and viola, the noise was gone. I was absolutely shocked. And, no amount of bending and prodding of the circuit board could I in any way recreate the noise.

At this point, I am now at the crossroads of the deciding on whether or not I'm just going to accept the fact that this was indeed an amazing coincidence, that I actually solved the problem and can put the chassis back in the cabinet and pat myself on the back, oh... and pat M Fowler's back, too. Or, do I wait a day and go back and keep prodding and testing until I either recreate the noise or break something.

This decision was not an easy one considering Murphys law, put it back together and the noise comes back, right? I mean, I spent many an hour on troubleshooting this rig in the first place trying to find the little issues that required tweaking to make this amp work properly. Sometimes, the solutions were not even what you may have thought they were, something completely different.

But, considering how proud I felt and how utterly huge my ego was at that time for thinking that I just fixed the problem from the get go, I decided to go for it and put it back together.

Well, so far so good, it works great. For a newbie like myself in the amp building world, I am utterly stunned at how it all came together so easily.

Of course, you guys are to be thanked immensely for the help you offer.

Thanks a million, guys!
:D
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