Finished crack kit, potentiometer makes buzz in left channel at certain position

[12AU7-6SN7]

The resistance check and voltage checks ok... the pot will make a scratchy noise around 8 o clock on the dial and buzzes and cuts the output volume  a little, all in the left channel... if I go just above or just below the problem position of the pot it works fine. I reflowed some solder joints and it improved but I can’t get it eliminated.

 

[Paul Birkeland]

Can you post some photos of the pot and the area around it?

-PB

 

[12AU7-6SN7]

A little embarrassed of my substandard work

http://imgur.com/a/n5reCL3

No shorts on those wires or anything from what I can tell.. amp sounds beautiful everywhere but 8-8:30 on the dial.

 

[Paul Birkeland]

The lower ground lug (black wires) on the volume pot looks like it might be a problem.

If you are using a small soldering iron (under 35 watts), I'd spend $5-10 on a 40-50 watt iron so you can really get those joints hot.

 

[12AU7-6SN7]

I’ve got a really nice soldering iron station. My pop was a tech and it was his.

I’ll try redoing those ground lug joints tomorrow and see if it helps the issue... might just be the pot itself, we’ll see... enjoying the music right now... this thing makes these ZMFs sing!

 

[Paul Birkeland]

If you have a station, be sure the temperature is turned all the way up.

 

[12AU7-6SN7]

If soldering “station” means it is adjustable, I guess I had the wrong terminology. It’s a decent quality single temp (as far as I can tell) Weller with a base power unit and stand. Temp isn’t a problem, I may have just done a crappy job there. I think the pic looks worse than it is, since it was shiny... the iron is at another location right now, so I’ll take the amp over there in the morning and see if it fixes it or not.

Thanks for your help Paul.

Edit: I think it is a 60 watt unit.

 

[12AU7-6SN7]

The lower ground lug (black wires) on the volume pot looks like it might be a problem.

If you are using a small soldering iron (under 35 watts), I'd spend $5-10 on a 40-50 watt iron so you can really get those joints hot.

The actual solder joint on that lug was beautiful and shiny. I redid it anyway to no effect, along with the others on the pot. Still scratches at the one narrow spot on the dial.

It’ll do for now since it works perfectly otherwise, and I hope the new alps blue velvet should fix the problem when it arrives next month.

 

[Doc B]

Try exercising the pot.

 

[12AU7-6SN7]

Try exercising the pot.

Did that, also tried some chemtronics cleaner/water displacement/lubrication spray my pop used to use at work on potentiometers. Didn’t work either.

 

[12AU7-6SN7]

Alps pot fixed the issue. Good grooves time.