ShortScale.org

So, I recently had my '74 Vibrolux brought back from the dead. I bought it in really rough shape and never got to hear it before it was restored. I really like the way it sounds, you know, like a Fender. Except when I get above 3 or so on the volume there is some pronounced speaker fart. whomp whomp whomp. I don't mind the low end losing clarity and definition when the amp is pushed to distortion, but this thing straight up farts and it's not cool. The speakers are new Jensen P10R's ( I think, I can double check) rated at 40w a piece. It's a 40w amp, so there is enough speaker there to handle the load. I haven't gotten to play it a lot but one would think enough to have let the farts run their course. I guess my question is, do I need new speakers? Or should I just give it more time?

Check the speakers for remains of packaging first. :/ You know, stupid looking things can happen.

I will check this evening. But it definitely has the sound of a speaker exceeding its capacity. Like Bone Thugs & Harmony blasted through the stock speakers of a 1988 Ford Escort. Shit's just farty.

I guess it's possible that the speaker was overloaded. When an amp's rated at a certain wattage on paper, I've been warned that they can produce a little more than that in real world situations. If amp and speaker are both rated the same then, you could overload the speaker if you run the amp flat out for too long.

Yeah... You generally want to pair an amp with speakers that can handle at least a bit more power than the amp can output for that very reason. I have no idea what that vintage of Vibrolux packed out of the factory but I doubt they were living that close to the edge.

As I understand it, you want your total speaker wattage to be at least 1.5 times the wattage of the amp. You have 2x40W speakers?

I've read a few articles on this lately as I've been fantasising about getting a 412 made. Can't find any article that aren't ultimate-guitar though, and I'm normally loth to link to that site given that it's mostly written by 13 year olds who pretend to have been playing for 40 years and have been blown away by how much better there Squier Affinity is that all the Gibsons and Fenders they played back in the day.

http://www.ultimate-guitar.com/columns ... _amps.html

http://brain21.net/blues/blog/?p=432

Yeah, I have 2 40w speakers for a 40w amp. It's not that my speakers aren't rated for the amp. At least on paper. As I understand it the Jensen P10R is the "vintage voiced" speaker, while a P10q(?) would be a more modern voicing. I opted for the vintage voicing because it's a vintage amp. Either way I don't think the speakers ought to be farting out unless a)they aren't broken in yet or b)I ruined them by rocking too hard right outta the box. Or maybe the vibrolux is just farty, but i doubt that. I'm not particularly keen on the notion of trying out all manner of speakers until I find the right ones, but I spent good money on the amp and it should not fart when the going gets tough. I'm hoping that someone could shed some light on the speaker break in period, as the general wisdom to be had on guitar nob sites (not this one, it's not nobby at all) is all over the map. Some accounts lead me to believe that it will come out of its current state in time with more hrs of play, while others say the opposite.

Maybe the output bias is set too cold, I googled this problem and it found a link on (apologies), but anyways this is what that person said:

I have a hunch that this is not a tube issue. "Farty" usually means crossover distortion (output tube bias far too cold), or blocking distortion (blackface and silverface Fenders are real susceptible to this, particularly if the output stage coupling capacitors have drifted too high, if there's insufficient output tube bias, if the bias feed resistors have been replaced with a higher value or have drifted too high, there's too much negative feedback due to a feedback resistor that's drifted low, etc etc etc.

Try it out through some other speakers if possible, the best way to pinpoint the problem is by eliminating possibilities.

Totes longshot: are the speakers wired together correctly to match the impedance the amp wants?

Sounds like Smallbox might have nailed it for you, though.

71Smallbox wrote:Maybe the output bias is set too cold, I googled this problem and it found a link on (apologies), but anyways this is what that person said:

I have a hunch that this is not a tube issue. "Farty" usually means crossover distortion (output tube bias far too cold), or blocking distortion (blackface and silverface Fenders are real susceptible to this, particularly if the output stage coupling capacitors have drifted too high, if there's insufficient output tube bias, if the bias feed resistors have been replaced with a higher value or have drifted too high, there's too much negative feedback due to a feedback resistor that's drifted low, etc etc etc.

Try it out through some other speakers if possible, the best way to pinpoint the problem is by eliminating possibilities.

????? If you hadn't pre-apologized I'd be pissed. I have another amp with a couple of 12" rated at 50w. I should try it out with those. If that gets rid of the nastiness, I'm gonna have to carry around bothamps

Or it could be that super technical thing you said, which would suck.

Doog wrote:Totes longshot: are the speakers wired together correctly to match the impedance the amp wants?

Sounds like Smallbox might have nailed it for you, though.

Will absolutely check the wiring when I try it out with my other speakers.

robrtnickerson wrote:

Doog wrote:Totes longshot: are the speakers wired together correctly to match the impedance the amp wants?

Sounds like Smallbox might have nailed it for you, though.

Will absolutely check the wiring when I try it out with my other speakers.

also make sure the impedance matches for the speaker load!

So, I haven't done any of the things that you guys suggested that I try. Except I did look at these speakers for visual damage and checked for ohms etc.

I have been playing through the amp a fair amount at moderate to low volumes, never pushing the speakers or using my sub octave pedals or playing the baritone on it. I played it yesterday in a band situation with the volume up to about 8 or 9. The flubbies seem to be gone. The bass response is mushy, but it's not pushing the speakers too far. No farts. I expected the bass response to be different than what I was used to, being a lower wattage 2x10 combo, so I am not concerned with what I'm hearing. It's just a matter of preferences at this point.

Thanks for all of the advice though! I'm just glad that it doesn't appear as though I'll need it.

Since it's an old Fender, keep your bass knob only at 2 or lower, if you set it higher it will sound flabby and eventually fart out.

71Smallbox wrote:Since it's an old Fender, keep your bass knob only at 2 or lower, if you set it higher it will sound flabby and eventually fart out.

Noted and done!

I've been playing it in a band type situation where we all play too loud, last week I finally tilted it back on its legs and pointed it where I could actually hear it. Turning the bass down to 2 did make a difference on the looseness of the bottom end. I didn't mind it sounding that way, but I feared it might hasten the amps demise.

On a side note, these things are awesome sounding amps. I would prefer if there were mids in the eq section, but oh well. I can turn it up enough to get the amp to break up and not be overbearingly loud like every other fender amp I've played.