The other issue with "digital" type amplifiers is the output can only go 0 to 100. There is no 101+ peak power available like analog amplifiers are able to do. And many, but not all digital amplifiers don't do harmonics very well.
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Well... What the Q-Sys amps CAN do is to both bridge and Parallel Channels using FAST (TM) (C) or FLEXIBLE AMPLIFIER SUMMING TECHNOLOGY. I believe they can also send unused power from one channel to another for example if you are driving a 3 way speaker the unused HF power can be applied to the LF section dynamically but don't quote me on that part of it. -
CX-Q amplifiers have quite a bit more headroom than typical linear amplifiers. They run with 150V rails. When transients and bursts of audio come through, they deal with it better than linear amps.
Here is an oldie but goodie video by Barry Ferrell on DCA versus DPA-Q (same as CX-Q).
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I'll read it and get back to you, But going past the brick wall of max power out seems pretty impossible.Comment
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Older class D amps had issues with transient response related to the PWM reconstructing filters used in the power stage. The filters were necessarily steep to meet the EMI requirements of governments, and this coupled with the relatively low switching frequencies, meant that the filters would ring on transients. Higher switching frequencies and simpler filters resolved almost all of these issues. Noise can still be an issue if the design stage is not executed properly, but modern class d amps are pretty good, especially from reputable manufacturers. All my bench amps are class D, as well as the surround amp in my screening room. Its pretty hard to beat 4 channels in 1RU.
I appreciate the video link Steve! Good video, lots of good practical info.
JoshLast edited by Josh Jones; 03-26-2025, 06:58 PM.Comment
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It can but again I wouldn’t because all it will take is a power glitch or something to potentially lose the configuration and then you’re stuck until you can get someone back with a core to redo it.Comment
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Hi, I was wondering about the passive crossover. The VHF driver has a built in crossover. But the specs online don’t say at what frequency/slope it’s crossed. I was thinking i can build a 3- way crossover and leave the VHF as is. Anyone know this info?
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Spot on Josh! I've been involved with Class D stuff on and off since the Infinity Class D amplifier of the Mid 70's, and that is the main issue that amplifier had. The QSC thing sounds like an old design of a company that went bankrupt, but whose design was picked up by a semiconductor manufacturer. They originally offered two models before they went bankrupt. Their failure mode was very similar to what Steve said the QSC did. I have to research a bit later today for the name and the patent.Comment
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AM transmitter manufacturers went through the same growing pains with class D during the 70's and 80's. Their solution was to increase the number of PWM phases, thus raising the effective ripple frequency by the number of phases. This relaxed the filtering requirements, and allowed simpler filters that didn't ring, and therefore tighter modulation control.
Thanks for the note about QSC stock Steve! Hopefully 3 SC-412C's will be enroute soon.
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Josh, this is the one I was thinking of. Many major Audio manufacturers use Class T technology including Audio Research who still builds very high end tube amplifiers. There is a lot more on it out on the net.
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Just getting back to this project. I was thinking of using a QSC DPM-300 but not with DCM amps. Those have the proprietary DB15(VGA) data connections. I know I won’t get all the benefits of the presets etc but I have plenty of power amps with XLR or RCA inputs. I can get VGA connector boxes (see pics) and make my own cable adaptors according to the pin out. But this is where I’m a bit confused. Would anyone know how to go about ?
the pin out is in the DCP-30D manual. (See pics)
I can also make an XLR to DB25 analog cable to feed the DPM-300 from my Marantz AVR8802.
anyone who would know this please let me know.
thx
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Actually, I figured it out. It works !Comment
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Steve, They just rate the output level at a lower wattage and then again at say 2.5 to 3db higher for for the headroom. Also, the most important aspect of any amplifier is the slew rate, then the head room. Comparing an amplifier with 80 or 90 volt rails to one with 150 volt rails is not a good way to compare. There are linear amplifiers out there that have 150 volt rails. In fact the ancient Phase Linear 700 had 100 volt rails in 1972... . I'm not at all against digital, and I can see the advantage to this stuff in Cinemas and for use in Big stadiums.
CX-Q amplifiers have quite a bit more headroom than typical linear amplifiers. They run with 150V rails. When transients and bursts of audio come through, they deal with it better than linear amps.
Here is an oldie but goodie video by Barry Ferrell on DCA versus DPA-Q (same as CX-Q).
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No, you clearly are misunderstanding the ratings. They rate the amps with a continuous tone because that is how all amplifiers are rated. The burst/max power, on the CX-Q (DPA-Q) amps attains their level based on their higher rails that allow for the higher swing. The power capabilities of the output devices and storage in the capacitors still limit the amp in terms of the duration of the higher power output. However, the fact that their smallest amp in the series CX-Q2K4, it can handle 400 watts/channel into 8-Ohms but can be run, effectively as a 700-watt amp in all be the slimmest of situations (subwoofer playing a Nolan movie). You aren't going to get a linear amplifier to behave like that.
You can see this on their higher power amps like the CX-Q8K4. It has really high continuous power ratings (1250-watts) but their max/burst power is no higher on an 8-Ohm speaker because you are already at the rails. Now, if you get to bridge or parallel the channels, you can get some pretty incredible output levels because you are getting more swing.
I've found it very rare for slew rate to have any great impact. Crown would never have gotten out of the "D" series amps (D150, DC300, or D75) if slew rate was all that critical, they were notoriously slow compared to their contemporaries.
The power rails in a linear amplifier are dependent on their output rating. They aren't going to put a 150V power supply in an amplifier only outputting 200W as everything would have to scale up for it and for no benefit. The DCA 2422 has 99V rails and it is 425W/channel.
Phase Linear had their own demons (and oscillations). Bob Carver had lots of nifty ideals. I was always intrigued by the M400 series cube amplifier. It is nifty to have your amplifier powered by, essentially a dimmer! Crown and Carver are notorious for running their components right at their limits though (and sometimes just a bit over).Comment
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