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View Full Version : My amp is farting - why, why, why?


S Effren
10-18-2008, 12:58 PM
I have a Gries 40w with a Jensen Neo 100. It's make a progressively worsening farty-type distortion (now) at all volume levels.

I replaced the entire tube complement with no change noted. The only tube I didn't have a replacement for was the rectifier 5AR4. I did have one of those Weber Copper Top Equivalents that I put in it's place. Made no difference.

Could the speaker be blown? It's rated a lot higher wattage handling than my amp puts out. I haven't been pushing it hard at all recently. Lower volumes, in fact, as I've been sitting in front of the amp and playing instead of standing while recuperating from ankle surgery.

Any other thoughts on what could be wrong? Debating popping for a new speaker vs. taking it in for service (a 6-hour roundtrip for me for drop-off and pick-up to Orlando.)

As always, your help is always appreciated.

gkoelling
10-18-2008, 02:35 PM
Do you have access to an 8 ohm cabinet? If so, unplug the internal speaker and try the extension cab. If the noise is gone, it's probably the speaker. If not, it's tubes.

quinnamps
10-18-2008, 02:55 PM
Filter cap going south?

Mikey Likes It
10-18-2008, 03:06 PM
Maybe it's GASSING for a new guitar.

RedRock
10-18-2008, 03:09 PM
GAS-X, at your local grocery store.

orogeny
10-18-2008, 03:10 PM
Do you have access to an 8 ohm cabinet? If so, unplug the internal speaker and try the extension cab. If the noise is gone, it's probably the speaker. If not, it's tubes.
good idea.

might not be the tubes though. . .

Mickey Shane
10-18-2008, 03:52 PM
If you are drop tuning and have the Bass knob turned up high, turn down the bass. Speaker farting is well known by bassists. Guitarists not so much.

S Effren
10-18-2008, 08:00 PM
I have a bass amp cab I'll check the impedence on and try it out if compatible. Nope, no drop tuning. Stay tuned.

leofenderbender
10-18-2008, 08:39 PM
Install a CERAMIC speaker - farts no more...

gkoelling
10-18-2008, 09:52 PM
Install a CERAMIC speaker - farts no more...

This and the bass possibly up too high could be the culprits.

I have a Gries 35 (there is no 40) and there's a lot of bass on tap in that amp.

Also, find a Tonker (original equipment in the amp) or Swamp Thang. Either of those speakers are amazing in the 35.



Good luck to you.

crosse79
10-19-2008, 02:56 AM
You fed it baked beans didn't you?

riffmeister
10-19-2008, 07:27 AM
Install a CERAMIC speaker - farts no more...

Neodynium magnets are used in bass amps, the 100W Jensen Neo is not the problem (unless it's defective).....

ericb
10-19-2008, 07:30 AM
Neodynium magnets are used in bass amps, the 100W Jensen Neo is not the problem (unless it's defective).....

Exactly, the speaker won't cause that unless it's blown... Also if it had cone cry I wouldn't describe that noise as 'farting' , it's more like screeching and howling!! Just 1 thing I haven't seen anyone bring up , but the tube sockets in my 70 Twin ended up needing some adjustment and cleaning and if the tubes have some intermittent connecting , the 'farting' noises will appear! Just another thought but more than likely when you retubed your amp you would 've figured out which socket(s) were bad. Good luck

Eric

S Effren
10-19-2008, 01:27 PM
OK. I tried another speaker cab and the same thing happened. Started out sounding fine then gradually deteriorated into this flabby, farty distortion. So it's not a blown speaker. It appears to be the amp itself.

It's been suggested above that it could be a bad cap. Does that sound about right to everyone? If so, any way to isolate the bad one. I have a multi-meter but must proclaim ignorance on how to use most of its functions. Really only use it for biasing. I pretty decent with a soldering iron. My problem is generally in knowledge deficiency. Solder what to what kind of stuff. I may be able to replace the damaged part if I could figure out which it is (and it's value. hopefully printed on the part???). Could always bring it to GC. Man I hate to ship it back to Gries. Hate shipping amps generally.

P.S. I filled the reverb tank with pepto bismol. Still farty. I advise against this technique.

S Effren
10-19-2008, 01:32 PM
Oh, yeah. I did notice that some (most) of the pre amp tubes were a little loosey goosey in their sockets. That could do it, huh? How do I know for sure? Would bending the tube pins eccentrically a tiny bit make them fit more snug in the sockets?

Roccaforte Amps
10-19-2008, 01:38 PM
I have a Gries 40w with a Jensen Neo 100. It's make a progressively worsening farty-type distortion (now) at all volume levels.

I replaced the entire tube complement with no change noted. The only tube I didn't have a replacement for was the rectifier 5AR4. I did have one of those Weber Copper Top Equivalents that I put in it's place. Made no difference.

Could the speaker be blown? It's rated a lot higher wattage handling than my amp puts out. I haven't been pushing it hard at all recently. Lower volumes, in fact, as I've been sitting in front of the amp and playing instead of standing while recuperating from ankle surgery.

Any other thoughts on what could be wrong? Debating popping for a new speaker vs. taking it in for service (a 6-hour roundtrip for me for drop-off and pick-up to Orlando.)

As always, your help is always appreciated.






I'm not a big fan of current production Jensens for this reason,
try another speaker.

ericb
10-19-2008, 02:11 PM
Oh, yeah. I did notice that some (most) of the pre amp tubes were a little loosey goosey in their sockets. That could do it, huh? How do I know for sure? Would bending the tube pins eccentrically a tiny bit make them fit more snug in the sockets?

Hi , the preamp tubes won't do it. .If it would, you just move them with your fingers while playing and you'll hear the noise. . Then you keep moving them until the noise stops. If it makes no noise while moving them , there's no problem with their contacts. I was referring to the power tube sockets in my '70 Twin causing the noises.

Eric

ericb
10-19-2008, 02:19 PM
I'm not a big fan of current production Jensens for this reason,
try another speaker.


He already did and posted that the same thing happened.. It's nothing to do with the Jensen. Eric

S Effren
10-19-2008, 03:45 PM
Yup, definitely ruled out the speaker as the cause. That being said, the Jensen has been a tremendous speaker for me. Bought it on a whim out of curiosity (my first neo mag) knowing that new production Jensens have been poo pooed and not having had high expectations. I don't know how reliable it is but it sounds like heaven!!! Kicks the crap out of the Tonker or whatever the hell was in there (I forget) when I bought it. It sounded like crap and got changed out immediately upon purchase. I digress.

As for the tubes, the power tubes weren't loose at all.

Thanks for all the replies as well.

shizzaq
10-19-2008, 08:19 PM
I had a Gries 35 that had a problem very similar to this. The sound would come through other speakers so I eliminated the speaker in the Gries. I recorded the sound and emailed the recording to Dave Gries and he sent me a shipping label to send the amp to him. He fixed the amp and told me it was a blown cap. It was a weird electronic type distortion almost like a crappy car stereo being pushed beyond its capacity. I hope this helps.