Is there no manual for s? It is strange that there is no manual anywhere to be found. What's that all about? Steve Guttag We forgot the crackers Gromit!!! As to the series 1 owners manuals, I believe they predate pdf's use by a bit and thus would probably need to be scanned. Originally, they were in "booklet" form too with very tiny type.
I think it's the usual problem that the engineers are different from the people who maintain the web site, and they haven't made it a priority to put a link to the manual up on the web. This is a common problem, and somewhat understandable. Remember the supply is not referenced to ground, so if the output transistor shorts, it just hauls the rails way offset. Measured to ground. Measure across the bridge it will be v - or whatever - all the time regardless.
I yanked all the output devices out and they all test fine! So i yanked both drivers and brought it up very very slowley and just enough to get some juice in it and yes i find the power supply to be off.
Need to get some parts and i will sork on it some more. Found several and put it on my server I found several docs including the schematics and put it in a zip file on my server.
Scan the file before opening it as you always should! Hi guys. The sound is very delightful and I tried to build the PCB as compact as possible with discrete components. QSC power supplies float at the speaker voltage, so each channel has to have it's own power supply.
Another advantage is that the drivers need only drive enough voltage to drive the BE input of the output transistors. This suits op-amp based circuits.
Crown took the idea another step by combining this with a bridged pair riding the moving rails, so you get a bridged amp that you can bridge again to get 4x the supply peak voltage. That was in the 70s, 80s because I moved to computers in 86, so I dunno what happened with amps later. It looks like QSC no longer has Service manuals on line, just user manuals.
But I found some old schematics else where and I note that this one uses Collector facing outputs, which meant that all the power transistor Collectors were grounded and therefore did not need sil-pads to isolate them, making for better heat transfer. Last edited: pm. I did put them all in a zip file and on my server if people are having trouble finding them. But here we should note that QSC are able to get away with this elegant arrangement, simply because the output terminals are AC coupled; in other amplifiers, the relay has to be placed at the output, for positive protection against DC faults.
The QSC comes fitted with an internal fan. The thermal design isn't outstanding - for instance, the fan's main airstream misses out each end of the heatsink. But the ducting is excellent, if the size of the holes on the back panel is anything to go by, and it's fair to say that this amp won't suffer from dust accumulations. The fan runs at two speeds: normally slow and relatively quiet, it speeds up when tripped by a thermal sensor, which comes in when the amp is driven hard and begins to heat up.
Table 1 gives the power versus load impedance and associated sensitivity data. Note that the sensitivity is 6dB lower than indicated if you operate unbalanced, going up pins 1 and 2 or on the sleeve and tip viz. The overload LEDs don't have a definitive threshold - they become progressively brighter over a 2dB range. Moral: keep spotlights off this amp if you want to see the LEDs in action.
In suitably dim lighting, the QSC's overload LEDs are accurate regardless of the speaker loading, and may be read with confidence. Protection is also positive: we grossly overloaded the amplifier by driving it in bridgemode with sine waves, into a 4 ohm load. After the heatsink temperature had shot up, the breaker tripped out, killing the mains juice. Sadly, this stops the fan - at least until you reset the breaker.
If QSC rewired the fan to bypass the circuit-breaker, the big cool-down would be usefully hastened. This is particularly important for PA work. A big plus point however is that the breaker replaces complex electronic protection, which is apt to damage the sound surreptitiously when the amp drives speakers with awkward impedance curves.
Returning to the unique AC output coupling, one disadvantage of this topology is an above-average hum level, around dB relative to watts into 8 ohms, or dBu. This will only be relevant though if you're using unusually sensitive speakers in a quiet environment: you'll hear a dull buzz if you put your ear hard against the drive unit, otherwise not.
Having said that, for very critical listening, don't forget the subliminal effects of hum; even very low level buzzes can make people irritable or fatigued after a few hours monitoring. To a skilled eye, the QSC heeds all the rules-of-thumb relating to reliability in a rock'n'roll environment. But there's one area that begs answers: it's worth remembering that the amp's outputs come off the 70 volt supply rails.
In other words, the usual direct-coupled output, which is normally at zero volts but sometimes 'goes DC' is replaced here by an output which is held at zero volts solely by virtue of the series output capacitors. If one of these should go short, bang..! In mitigation, QSC have chosen high-spec Nipponese capacitors designed specifically to cope with the rigours of high temperatures, and massive peak currents.
But to play safe, it might be a good idea to have the output capacitors checked out for leakage or other degradation after 12 or 24 months of use. To sum up, this amp is definitely at home on the road. If the speaker's impedance dips, the amp won't limit or protect to the same extent as most Bipolar designs.
Table 1 bears this out - look at the 4 ohm stereo and 2 ohm bridge-mode figures. From this, we can deduce that the amp will be happy with nominally 4 ohm speakers, under all conditions. Regarding connections, you may need to rewire your feeds to take advantage of the balanced input, and do away with a potential hum loop. Otherwise, it's plug in and go - at least until you get around to replacing the output terminals with something more practical.
There are just two niggles for studio use. One, the gain controls. True, once set they may not need adjustment for a long time, but sometimes they're handy for muting purposes.
Two, the fan. It's certainly quieter than most, especially since it runs at half speed under normal studio conditions. But with the amp just ticking over, and no signal, fan noise is noticeable and even mildly irritating in a quiet room. To attune this amp fully to studio usage, QSC could consider incorporating a second thermal sensor, using this to switch out the fan when the heatsinking is close to its quiescent temperature.
In this way, the fan noise will usually only correlate with the amp being driven hard, and will therefore be obscured by music. This seller has not set a shipping cost for Germany. Please contact them to ask about shipping.
This item is sold As-Described and cannot be returned unless it arrives in a condition different from how it was described or photographed. Items must be returned in original, as-shipped condition with all original packaging. Your purchases also help protect forests, including trees traditionally used to make instruments.
We understand the importance of online privacy and are committed to complying with the EU General Data Protection Regulation. To reflect our commitment, we updated our terms and conditions.
0コメント