concert bass crackling after about an hour or 2

[sunn]

Anyone else have this problem where if you leave a concert bass amp on long enough it starts crackling and buzzing randomly for no reason no matter where you plug things in or out?

Anyone know what it could be?

[TubeMan]

sounds like it could be arcing.
its not unusual for old dirty parts in our beloved vintage equipment to become unstable and begin arcing when they heat up.

usually you can open it up and look for a little carbon trail on the parts that have been arcing and take care of it

[JoeArthur]

Arcing usually applies to equipment operating with high internal voltages...  Tube amps can arc, being operated with a B+ of 450 volts or higher... but that usually doesn't apply to solid state operating at around 70 volts... less than the supply line voltage.

The Concert series is constructed using wire lugs interconnected with "jumper wires".  The jumper wires "push" over PC board lugs.  These are essentially "loose connections".  Heat does affect the quality of these type of connections.  Sometimes it gets better and sometimes it gets worse... over "on" time.

The only way I could eliminate the hissy crackling of my concert lead was to clean and solder all of these interconnections.  It corrected all of the problems... except for a volume control that was so worn it needed replacing.

As a side note, this construction method (lug to jumper wire) only benefits servicemen replacing entire boards... not an option to many that own these amps... these days.

[Babs]

I have a similar crackling problem that may be similar to what's been talked about. Although mine starts immediately and is accompanied by sudden volume dips and rises. I am going to give the soldering the lugs fix a try.

I also have the dreaded buzzing. I saw a quote by someone saying the CB is a great antennea; I agree! Has anyone ever tried to sheld the electronics? I was thinking to try and add a metal screen material over all area exposed when the wood top cover is removed. My fear is that the shelding problem is between components of the elctronic themselves, which I assume means we are SOL.

Post if you have any hints on removing the buzz. Thanks.

[JoeArthur]

I've never had "dreaded buzzing" problems with my concert lead.  Sure I realize you are talking about a concert bass... but there really ain't much difference than the reverb I have but don't use on one channel.

The volume fluctuations are probably caused by a bad volume control.  I have seen a lot of this happening on these amps, plus the possibility of the bass control being bad... also causing volume fluctuations.  My volume control was so bad that I could push on it to get the volume back, but when I let off the pressure, the volume loss came back.

If you want to shield the wood enclosure, then you could use a metal screen, copper foil or even aluminum foil (the kitchen kind).  Staple it to the inside of the wood... but it will only work effectively as a shield if it is grounded.  A small wood screw into the wood, with a large washer making contact with the shield, and a wire from that to some existing screw on the chassis should handle that.

But it bothers me... I wouldn't consider any member of the concert series a "great antenna"... certainly not by the nature of it's design.  Since most of these amps are probably in the 25+ year old range... the age of the amp, and most likely the dirt and various accumulations over the years are the culprit.  If your cables are good, and you are using a good grounded three prong outlet, then you might want to apply some contact cleaner to the input jacks, even replacing them if they are so badly worn.

Sometimes, the input jacks get loose.  Before they are tightened, sometimes dirt can get between the jack and the chassis.  Over time, this dirt can build up to prevent a good electrical connection between the jack body and the chassis.  What should be ground... the inside of the jack that connects with the cable may now be at a level above ground.  This can cause some strange sounds to result.  At the least, take off the nut holding the jack to the chassis and clean behind it.

Hope this helps!!

Joe

[Geoff]

Joe is certainly right about dirt accumulating over the years.  If you give any of your jacks (or PC board male connectors) a good cleaning with a contact cleaner and a cotton swab, you may be shocked to see what comes off.  Try it on your instruments too -- might be the same story.  I try to run a tight ship in the gear department but periodic jack and contact cleaning often reveals a dark residue from cruft, dirt, and oxidation.

CAIG DeoxIT on a Q-Tip and you're good to go.  Some may consider cleaning jacks/plugs sort of anal retentive or unlikely to produce noticeable results -- but it gives me piece of mind and I am confident all my contacts are good once I've ruled out things like bad jack tension, sketchy grounds, etc.

Good luck!

[Geoff]

...I meant "peace of mind", not "piece of mind".  Sorry - I need more sleep before posting.

[Babs]

Thought I'd update... I took the amp in the basement and gave it a try, assuming if outside RF was causing the problem that I wouldn't hear it (or it would be much less) below ground. No difference. Thus, I think shelding is a waste of time.

I am convinced that the internal lugs being loose or having bad contacts, dirt and grime buildup, etc. are the cause. I also have at least 4 electrolytic capacitors that have fuzzy whitish bubbles near the positive terminals of the cap. I assume these are pretty much shot (not surprising for a 29 year old amp). I am going to start by replacing as many of the these capacitors as I can, including the power supply filter caps. I'll clean and solder the lugs and clean the other contacts. Lastly, I want to replace the potentiometers and am looking for advise here (manufacturers, suppliers, etc.)!

I'll post when I have some results.

[sunn]

of course, wouldn't you know it, i take my concert bass amp in to have someone look at it and they can't seem to replicate the crackling problem.  the guy said i have 2 filter caps leaking really bad though, could that be it?