grease42
Sorry, I know this is off topic, but I’m looking for some input. I bought a QSC GX7 amp a few years ago and I loved it. However, one night it started clipping one side out. We sent it back to QSC to have them go through it, they fixed it, but then I started blowing out baskets left and right. I was told something probably created a brown out. I’m looking to get another amp, but I’m being recommended the same one I had. I don’t wanna spend alot, because I’m starting to slowly phase out, but I was just curious what everyone recommends or uses, and what the cost is. Thank you in advance.
Posté Wed 14 Jul 21 @ 11:29 pm
SuperHarry Kingmaker
Hi Grease,
From a distance, it's hard to tell whether the speakers blowing up was caused by overload or simply a faulty amplifier. The QSC brand is an excellent brand in itself (JBL has used QSC electronics in their own amplifiers for a long time), but the amplifier you have chosen is an "entry-level" model, a model in a low price range. They don't necessarily have to be bad, but often the technical structure is a bit basic, the power supply is a bit tight, the cooling is mediocre and the protections are slow. They are also usually not comparable to the more expensive series in terms of sound. The choice of an amplifier should not be judged solely on the power it can deliver.
If your amplifier is not defective and you still blow up speakers, a user error will usually be the cause. First, does the input sensitivity match the output voltage of the driving mixer? Most mixers drive +4dBV (1.23V, some even +6dBV) on the meters at 0VU, while the input sensitivity of many professional amplifiers is 0dBU (=0dBv, 0.775V). This results in clipping very quickly if you neatly play your VU meters on the mixer "in the green" but has fully opened the gain controls on the amplifier. Good cone speakers can handle the occasional soft clip without any damage, but they don't like heavy clipping for a long period of time. Clipping means that the power supply is at its limit and can't supply enough clean voltage to the output stages, which in turn will "truncate" the peaks. That "clipping" results in a kind of pulsating DC voltage and you should know that when DC voltage applied to a speaker's voicecoil makes the cone stand still for short periods of time (virtually). So, the moment that the cone "pauses", it’s no longer cooled through the (usually moving) central "dome cap" and damper glued on the center of the cone and gets too hot, worms, jams or burns out.
Secondly, too large and/or uncontrolled cone movements: obviously, the voice coil will be damaged by simply hitting the stop in the gap of the magnet and will jam. This can simply happen by driving too much power to the speaker, or clipping as already described, or here it comes: when choosing an amplifier for a specific task it is also important to look at a few other technical data such as the working impedance, the damping factor and the slew rate. Especially the damping factor is underestimated. This damping factor shows how stably the amplifier transports the power to the speakers (and back). Yes, also back in reverse, because if a cone moves back to its resting point after a cycle, the voice coil drives the amplifier in return. This has to be processed and handled by the amplifier. You’ll understand that if the amplifier handles it badly, the loudspeakers can start making uncontrolled movements, especially low frequency drivers (woofers). Perhaps you have seen it sometime, such a "fluttering" woofer. By the way, always use your speaker cables as short as possible (and not too thin), because the length and thickness of the cable is directly related (and added) to the damping factor. A very technical story, and this was just a start, because we haven't even talked about cooling yet. Anyway, I hope you have gained an insight that it is not easy for an amplifier to drive those speakers in a good way, and to keep them intact, nor is it easy for the engineer to let the system work for hours and hours and having no damage afterwards. There are many good amps for sale out there. We DJ's and PA- engineers, as well as the equipment have to work under harsh conditions (rooms with high temperatures and humidity, sunny and rainy outdoors), so I would not choose an "entry-level" model for the simple reason that manufacturers often have make too many concessions on the quality or design of the thing to try to make it "affordable"... Anyway, QSC is certainly an excellent brand in itself, like so many...
Good luck , Harry
From a distance, it's hard to tell whether the speakers blowing up was caused by overload or simply a faulty amplifier. The QSC brand is an excellent brand in itself (JBL has used QSC electronics in their own amplifiers for a long time), but the amplifier you have chosen is an "entry-level" model, a model in a low price range. They don't necessarily have to be bad, but often the technical structure is a bit basic, the power supply is a bit tight, the cooling is mediocre and the protections are slow. They are also usually not comparable to the more expensive series in terms of sound. The choice of an amplifier should not be judged solely on the power it can deliver.
If your amplifier is not defective and you still blow up speakers, a user error will usually be the cause. First, does the input sensitivity match the output voltage of the driving mixer? Most mixers drive +4dBV (1.23V, some even +6dBV) on the meters at 0VU, while the input sensitivity of many professional amplifiers is 0dBU (=0dBv, 0.775V). This results in clipping very quickly if you neatly play your VU meters on the mixer "in the green" but has fully opened the gain controls on the amplifier. Good cone speakers can handle the occasional soft clip without any damage, but they don't like heavy clipping for a long period of time. Clipping means that the power supply is at its limit and can't supply enough clean voltage to the output stages, which in turn will "truncate" the peaks. That "clipping" results in a kind of pulsating DC voltage and you should know that when DC voltage applied to a speaker's voicecoil makes the cone stand still for short periods of time (virtually). So, the moment that the cone "pauses", it’s no longer cooled through the (usually moving) central "dome cap" and damper glued on the center of the cone and gets too hot, worms, jams or burns out.
Secondly, too large and/or uncontrolled cone movements: obviously, the voice coil will be damaged by simply hitting the stop in the gap of the magnet and will jam. This can simply happen by driving too much power to the speaker, or clipping as already described, or here it comes: when choosing an amplifier for a specific task it is also important to look at a few other technical data such as the working impedance, the damping factor and the slew rate. Especially the damping factor is underestimated. This damping factor shows how stably the amplifier transports the power to the speakers (and back). Yes, also back in reverse, because if a cone moves back to its resting point after a cycle, the voice coil drives the amplifier in return. This has to be processed and handled by the amplifier. You’ll understand that if the amplifier handles it badly, the loudspeakers can start making uncontrolled movements, especially low frequency drivers (woofers). Perhaps you have seen it sometime, such a "fluttering" woofer. By the way, always use your speaker cables as short as possible (and not too thin), because the length and thickness of the cable is directly related (and added) to the damping factor. A very technical story, and this was just a start, because we haven't even talked about cooling yet. Anyway, I hope you have gained an insight that it is not easy for an amplifier to drive those speakers in a good way, and to keep them intact, nor is it easy for the engineer to let the system work for hours and hours and having no damage afterwards. There are many good amps for sale out there. We DJ's and PA- engineers, as well as the equipment have to work under harsh conditions (rooms with high temperatures and humidity, sunny and rainy outdoors), so I would not choose an "entry-level" model for the simple reason that manufacturers often have make too many concessions on the quality or design of the thing to try to make it "affordable"... Anyway, QSC is certainly an excellent brand in itself, like so many...
Good luck , Harry
Posté Thu 15 Jul 21 @ 9:38 am