HELP!! Amp "farting"

[awilkie84]

I can't quite tell where the problem is coming from, as I don't have any alternatives at this time for testing.

I have a Fender P-bass with Seymour Duncan SPB-3 pickup & 250k vol/tone CTS pots. I run this into an Ampeg PF-500 that had its board replaced earlier this year. The PF-500 is run into a Traynor 2x10/1x15 cab (all speakers in 1 cab) run at 4Ohms. I've tried both a Speak-on & a 1/4" cable. Both have the same issue.

When I play aggressively on low notes (mostly from 4th fret down on the E), I can hear the sound starting to distort. I've also noticed that the sound is VERY boomy and it doesn't sound like I can hear the 10" speakers. This might be because the 1x15 is pushing more air than the 2x10.

I've never abused my equipment, but I got the cab on trade in the summer for my Hartke 410XL (I wanted a 4Ohm cab).
I've tried my EQ at many different settings on the PF-500, but I can't get rid of this distortion.

Is it coming from the head, the cab, or possibly the bass itself? Any ideas on how to go about testing this?

 

[KeddyLee]

Does your amp have a tube? Very common "farting" from a bad tube.

My Hartke recently had this problem. I had a bad solder connection. Ran OK most times but when vibration hit (like that doesn't happen) it loosened the connection and *faaaart!*.

Get her checked out.

 

[monkeyfinger]

Most likely the cab. Easiest way to tell is try another cab. The farting sound is from speaker over-excursion, (exceeding xmax). This is the most common way bass cabs get damaged.

 

[P-oddz]

Your pickups might be sending a pretty hot signal to the preamp, no? Have you tried messing around with the on-board compression or db pad? Is it still happening?

 

[BurningSkies]

You've found the limit that your cabs can take.

You can probably figure out which one has reached its excursion limits if you try to reproduce what its doing (try putting the 15 on top of the 210 and see if that makes it more obvious which one is running out of gas).

With those cabs, your best bets to avoid over excursion are:
-Turn your volume down.
-Reduce the amount of bass from your EQ.

 

[P-oddz]

Also (as just a side thought), how is the pickup height towards your E string?
Maybe backing it off a little will improve a more even response if you still find yourself hitting a wall with the speaker and EQ adjustments.

 

[awilkie84]

Does your amp have a tube? Very common "farting" from a bad tube.

My Hartke recently had this problem. I had a bad solder connection. Ran OK most times but when vibration hit (like that doesn't happen) it loosened the connection and *faaaart!*.

Get her checked out.

No tubes in this head. All class D solid state. The sound seems to get boomier as the head warms, though.

Most likely the cab. Easiest way to tell is try another cab. The farting sound is from speaker over-excursion, (exceeding xmax). This is the most common way bass cabs get damaged.

I wish I had another cab to try. Maybe I can take my head into the local store & plug it into something else.

Your pickups might be sending a pretty hot signal to the preamp, no? Have you tried messing around with the on-board compression or db pad? Is it still happening?

I've tried playing with the compression, but haven't tried the dB pad, as it's a passive bass.

You've found the limit that your cabs can take.

You can probably figure out which one has reached its excursion limits if you try to reproduce what its doing (try putting the 15 on top of the 210 and see if that makes it more obvious which one is running out of gas).

With those cabs, your best bets to avoid over excursion are:
-Turn your volume down.
-Reduce the amount of bass from your EQ.

It's a combined cabinet. There are input/outputs on the back but it doesn't seem to matter which one I plug into. I've tried turning the bass down to about 10 o'clock. I shouldn't need to go lower than this, should I?

Also (as just a side thought), how is the pickup height towards your E string?
Maybe backing it off a little will improve a more even response if you still find yourself hitting a wall with the speaker and EQ adjustments.

I had thought of that, but the volume level across all strings is the same, it just seems to be the frequency that's breaking up.

 

[BurningSkies]

No tubes in this head. All class D solid state. The sound seems to get boomier as the head warms, though.



I wish I had another cab to try. Maybe I can take my head into the local store & plug it into something else.



I've tried playing with the compression, but haven't tried the dB pad, as it's a passive bass.



It's a combined cabinet. There are input/outputs on the back but it doesn't seem to matter which one I plug into. I've tried turning the bass down to about 10 o'clock. I shouldn't need to go lower than this, should I?

I see. In that case, it really doesn't matter which speaker is doing it since it's part and parcel of the same cab. You're reaching over excursion either way.

The thing is this, speakers can only take so much power before they reach their maximum amount of excursion. Most cabinets are rated by thermal limits rather than excursion limits, mostly because most cabs have a lesser excursion limit. Also, its a bit of a moving target, because more bass takes more 'power' and takes more speaker movement to produce.

 

[monkeyfinger]

I would take it to a local store and try other cabs. Bring your cab too.

 

[dannster]

Years ago I had an Ampeg IsoVent cabinet. 2x10 and a tweet angled up above a couple of clam-shelled 15's. The 10's could not keep up with those 15's and farted out all the time if pushed to moderate levels. I suspect it is probably your cab and it's design.
As far as your amp there has been some problems with those but this doesn't sound like the common issues.

Try the cab with another amp. and try your amp with another cab.

 

[awilkie84]

The odd thing is that my cab is rated at 100W above what my head is. My volume's never up over 1 o'clock, either.

I guess I'll take it in & see what my tech says. He'll let me hook it up to whatever he has in the store, too.

 

[KeddyLee]

Could be a bad connection to the actual speaker itself too.

I doubt the repair will be a big deal unless the speaker is actually blown.

 

[BurningSkies]

The odd thing is that my cab is rated at 100W above what my head is. My volume's never up over 1 o'clock, either.

A couple things here...make this 'not odd'.

1. Your cab's thermal limit is the 'rating'. The excursion limit is predictably less than the thermal limit. Often times its a fraction of the limit.

2. Volume controls on amps are hardly ever linear. Your amp may be producing its full rated wattage (or even more) well before you max out the volume knob. In many amps, that can happen before it hits 'noon'.

 

[B-string]

So take the cab "rating" divide that by two for the usable amount of low bass frequencies power it will take. So you have 200 watts more available than the cab can handle, fart city at 1:00 on the master as most amp heads that is the end of the clean power with good gain coming from the preamp.

By the way 210s are about as capable as a 115 so if you can't hear the 10s they have probably blown.

 

[eriky4003]

I'm surprised none of the usual suspects haven't chimed in on this thread.
The cab being rated at 100W more than the head is for thermal limits (eg. when you'll fry the speakers). The rule of thumb around here is multiply the thermal limit by 50 to 60 percent to get what the cab or speaker will take before it mechanically fails (eg. you rip the cone of the speaker(s) from trying to reproduce the sound).
Try reducing the bass knob on your amp and increase the midrange. Your cabinet will probably do better with this arrangement. Good luck!

Ahh, B-string (one of the usual suspects) comes riding to the rescue.

 

[BassmanPaul]

I've used one of those cabinets in the past and it was not a good experience. The Hartke cabinet you traded for it would be considerable better.

A lot of folk think that they have to wring every last watt out of their amps. This is a fallacy. You would have been louder at 8Ω through the hartke than you are with the Traynor. I think you made a poor trade.

You also have to remember that an average speaker cabinet's power rating is THERMAL, or the point at which it starts to melt. It will run out of excursion, or how far the cone(s) can move safely, at about half of that thermal power. If the cabinet has a power rating of 600W then it can actually use only about 300W

 

[awilkie84]

So, realistically, my cab should be rated at DOUBLE my head's value!? That seems a bit ridiculous...and is really going to drive up the cost of my rig. Turning down below 1:00 means I'm not heard with the guitar/drums. I really hope it's more of a problem with the speakers/wiring than it is head/cab compatibility.

I've used one of those cabinets in the past and it wan not a good experience. The Hartke cabinet you traded for it would be considerable better.

A lot of folk thing that they have to wring every last watt out of their amps. This is a fallacy. You would have been louder at 8Ω through the hartke than you are with the Traynor. I think you made a poor trade.

You also have to remember that an average speaker cabinet's power rating is THERMAL, or the point at which it starts to melt. It will run out of excursion, or how far the cone(s) can move safely, at about half of that thermal power. If the cabinet has a power rating of 600W then it can actually use only about 300W

My Hartke at 8ohms was NOT louder than my Traynor. In fact, with the Hartke, I had to dial up to 3-4:00 on the volume to be heard. That's more juice than this Traynor seems to need.

The Hartke was also only rated at 400W, so that's 200W by your math...much less than the 300W on the Traynor.

 

[PhatRon]

are you positive this is speaker farting? could you be pushing the pre too hard? I'd try lowering your gain stage and then push it hard. 1/4 pounders are very hot pups, try lowering the pup under the E string. Not saying it's not speaker fart, just try to verify.
like others have said try with another cab

 

[Joedog]

I've tried turning the bass down to about 10 o'clock. I shouldn't need to go lower than this, should I?

You might. EQ needs to be set with ears, not eyes. Try it, you MAY be surprised, and it costs nothing to try. I'd roll it ALL the way down, see what happens, and if that works (eliminates the farting and boominess), slowly work it back up, to see what happens. Why assume without trying? You might need to boost the mids to compensate, but leave them the same until you try the above.

 

[awilkie84]

are you positive this is speaker farting? could you be pushing the pre too hard? I'd try lowering your gain stage and then push it hard. 1/4 pounders are very hot pups, try lowering the pup under the E string. Not saying it's not speaker fart, just try to verify.
like others have said try with another cab

My gain stage is at 11:00, if I run with my volume at 1:00. If I dime the volume, my gain is at 8:30. I had the same issue with a Squier Jag5 (bass boost rolled off), so I'm thinking it's not the bass (but could be wrong).