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Review and Measurements of QSC DCA2422 Amp

amirm

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#1
This is a review and detailed measurements of the QSC DCS2422 "Digital Cinema" Power Amplifier. It is on kind loan from a member. It must be sold through specialty channel as I can't find it available much. From the bit of searching I did, it seems to go for US $550.

This digital cinema characterization applies to the connectivity of the box. Otherwise this is a normal power amplifier in rack mount configuration:
QSC DCA2422 Digital Cinema Amplifier Audio Review.jpg

There is a nice dial with wide range of gains you can dial in. I liked the clipping indicator.

There is a speed controlled fan which is good. What is not good in home hifi situation is that even in its slowest mode there is a whine to the fan that is audible from 6 feet away. If you are going to use this amp, it would need to be in an equipment closet.

The back panel shows the locking SpeakON speaker connectors and only a pair of XLR inputs:

QSC DCA2422 Digital Cinema Amplifier Back Panel Audio Review.jpg

Given the programmable gain you can use RCA to XLR cables. I won't go through the rest of the features, selectable with dip switches.

Power Amplifier Measurements
I set a gain close to what I typically see and dialed in enough input for 5 watts of output:
QSC DCA2422 Digital Cinema Amplifier Audio Measurements.png


As noted, channel 2 was fine but channel 1 was all over the place. Its SINAD (signal over noise and distortion) hit a low of 49 dB and a high of 83 dB (later in testing). There is some kind of instability there. I noticed that jiggling the speaker cable in that channel caused some variations too so maybe it is mostly the connector.

Channel 2 beats the THD+N spec so that is good.

Here is a warm up sequence although the unit was not at room temp before I started:
QSC DCA2422 Digital Cinema Amplifier Warm Up Audio Measurements.png


So Channel 1 even when "stabilized" still acts different from the other channel.

Using the dashboard average of the two channels, this is what we get compared to other power amps tested:
Best Audio Amplifiers 2019.png


Frequency response was very good with just a bit of droop at 20 kHz:

QSC DCA2422 Digital Cinema Amplifier Frequency Response Audio Measurements.png


FFT spectrum of 1 kHz tone tells us about the design of this DCA2422:

QSC DCA2422 Digital Cinema Amplifier 1 kHz FFT Audio Measurements.png


We see a spike a bit above 100 kHz. QSC does not indicate the topology of the amplifier but does say it has a switching power supply. The switching power supply substantially lowers the weight of this unit and brings high efficiency that way. I suspect the Amp is some kind of class G (multi-voltage class AB amplifier). The spikes we see are I think the switching frequency of the power supply bleeding through. They are comfortably above the audible range and unlike class D amps, at rather low levels. Overall, this is a much cleaner spectrum than I see on class D amplifiers (which use switching power supply and amplifiers).

Testing with 4 ohm load shows copious amount of power available:

QSC DCA2422 Digital Cinema Amplifier Power at 4 Ohms Audio Measurements.png


We can see channel 1's worse performance just the same here. Compared to our best ever measured power amplifier using Hypex NC400, we have tons more noise and distortion. But we also have far more power at much lower cost.

I finally took the time to properly mount my dummy loads in a rack mount case with a nice switch to select between 4 and 8 ohms so here are the results of latter:

QSC DCA2422 Digital Cinema Amplifier Power at 8 Ohms Audio Measurements.png


Unlike 4 ohm where we came up short, the 8 ohm measured power is actually better than the specs.

Perhaps it is best to compare the QSC to another commercial amp I have tested: the Crown XLS1502:

QSC DCA2422 Digital Cinema Amplifier Power at 4 Ohms Compared to Crown XLS1502 Audio Measureme...png


If QSC's Channel 1 had behaved better, it would have beat the Crown across the board. As it is, one channel is better, the other much worse. There is higher output power though (sorry the cursor is not set to read that properly from the graph).

Here is how intermodulation distortion rates at different power levels:

QSC DCA2422 Digital Cinema Amplifier IMD Audio Measurements.png


Fascinating how closely the QSC tracks the performance of Klipsch Powergate. It of course leaves it in the dust as far as power is concerned.

Conclusions
The QSC DCA2422 amplifier is the typical commercial power amplifier with tons and tons of power in a light and low cost enclosure. Unlike class D competitors, it seems to have a much more stable design. The issue with it is the one channel misbehaving. If that is typical of the rest of the production, then that is not good. If it is just an issue with this specific sample, then this is a good buy for a rack-mount install to drive subwoofers and such. The fan noise rules it out for any kind of "domestic" application.

------------
As always, questions, comments, recommendations, etc. are welcome.

In the process of crimping a bunch of connectors to build my dummy load, I realized how tough the ratchet style crimping tools are on high-quality yellow ring connectors. Searching for a power version, I found this wonderful tool:


Bad news is that as most things good in life, it costs money, lots of money! $500 to be exact. So Please help fund that by donating generously using:

Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
 

daftcombo

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#3
Hi Amir,
Thanks for this new good review. Too bad the bad channel isn't like the good one by a mile, otherwise it could have been a very good product.

I saw your graph with the "power supply frequency" artefacts. Could you explain us what they are about? I saw them on other reviews but don't understand why they appear, and if they are audible or not.
I've read on a review that such things at 120Hz for instance (here it is 110 probably) could make the amp sound "warm". What do you think?
 

amirm

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#4
When there is a linear power supply, there are diodes that convert the AC waveform from positive to negative, to two positive humps. This will then be smoothed out to become "DC."



The second waveform is post rectification. In US our mains frequency is 60 Hz. So if we see components that are 120 Hz, it usually indicates that the rectification noise from the power supply is bleeding into the output of the amplifier. If we have 60 Hz, that just means that frequency is also leaking into the amp.

In the case of QSC, it is a switching power supply. So it converts the AC to high voltage DC and then back to DC. The latter is done by switching the DC on and off. That switching noise is very powerful and if not filtered exceptionally well, will again bleed into the output of the amplifier as I showed in my graph (the 110 khz and harmonic tones).

Is this what you were asking?
 

andreasmaaan

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#5
Thanks again @amirm. It seems surprising there is such a performance disparity between the channels. Could the unit be broken perhaps?
 

daftcombo

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#6
When there is a linear power supply, there are diodes that convert the AC waveform from positive to negative, to two positive humps. This will then be smoothed out to become "DC."



The second waveform is post rectification. In US our mains frequency is 60 Hz. So if we see components that are 120 Hz, it usually indicates that the rectification noise from the power supply is bleeding into the output of the amplifier. If we have 60 Hz, that just means that frequency is also leaking into the amp.

In the case of QSC, it is a switching power supply. So it converts the AC to high voltage DC and then back to DC. The latter is done by switching the DC on and off. That switching noise is very powerful and if not filtered exceptionally well, will again bleed into the output of the amplifier as I showed in my graph (the 110 khz and harmonic tones).

Is this what you were asking?
Yes, thank you for this explanation. When is it audible, does it make the sound "warmer" or just distorded/bad?
 

Willem

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#7
QSC are quite a big player in the pro audio market, so I am a bit surprised by what seem like manufacturing shortcomings. Anyway, it makes me all the more curious to see measurements of the Yamaha Pxx00s series. The P35000s was tested with an AP analyzer by some French engineer, and the results were impressive. As I have said before, on the basis of that test I bought a 2x250 watt P2500s for my son, and it seems to perform impeccably. Unfortunately it would be prohibitive to send it in for a test, all the way from Europe, but there must be plenty of them in the US as well.
 

RayDunzl

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#8
When is it audible, does it make the sound "warmer" or just distorded/bad?
It would likely be a constant "hum" at 60 or 120Hz or their harmonics if audible, with or without the music signal.

I would not consider that to change the "sound" other than to add an extraneous noise.
 

Sythrix

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#9
I have 2 QSC RMX850s. I wonder how they compare.

I recently finished modifying one to change the fan to something more tolerable. (Noctua, but that required a step down converter because the stock is 24 V). Haven't actually used them yet, as I'm moving soon.

Thanks for the review!
 

amirm

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#10
Yes, thank you for this explanation. When is it audible, does it make the sound "warmer" or just distorded/bad?
You just get hum or buzz when it is audible.
 

amirm

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#11
Thanks again @amirm. It seems surprising there is such a performance disparity between the channels. Could the unit be broken perhaps?
The owner bought it used from someone else. So it may be so. I am waiting for him to give me permission to open it. I noticed that one of the speakOn connectors is not secure enough even when locked.
 
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#15
I'm liking this Amplifier SINAD graph. Could there be a complete master version of this posted somewhere as was done with the DAC SINAD graph?

I've been keeping an eye on the accumulating speaker amplifier reviews trying to find a nice budget two-channel amp (<$300).
 

apgood

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#17
The owner bought it used from someone else. So it may be so. I am waiting for him to give me permission to open it. I noticed that one of the speakOn connectors is not secure enough even when locked.
Did you end up opening it up and seeing if an internal fault was causing the differences in the two channels?
 

amirm

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#18
Did you end up opening it up and seeing if an internal fault was causing the differences in the two channels?
I did open it but nothing was revealing with respect to the connector. It was impressive to see so much electronics in there for so little money.
 

apgood

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#19
I did open it but nothing was revealing with respect to the connector. It was impressive to see so much electronics in there for so little money.
Pity I think it probably isn't normal to have that sort of variation between the channels. I have several of the lower power Class AB amps from the DCA series for home theatre use and haven't noticed any audible variations. Can't comment on measureable as only measured the end result with speakers on the end.

Yeah there's a bit of extra circuitry in there for monitoring through Dataport.
 

psemeraro

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#20
This is a review and detailed measurements of the QSC DCS2422 "Digital Cinema" Power Amplifier. It is on kind loan from a member. It must be sold through specialty channel as I can't find it available much. From the bit of searching I did, it seems to go for US $550.

This digital cinema characterization applies to the connectivity of the box. Otherwise this is a normal power amplifier in rack mount configuration:

There is a nice dial with wide range of gains you can dial in. I liked the clipping indicator.

There is a speed controlled fan which is good. What is not good in home hifi situation is that even in its slowest mode there is a whine to the fan that is audible from 6 feet away. If you are going to use this amp, it would need to be in an equipment closet.

The back panel shows the locking SpeakON speaker connectors and only a pair of XLR inputs:


Given the programmable gain you can use RCA to XLR cables. I won't go through the rest of the features, selectable with dip switches.

Power Amplifier Measurements
I set a gain close to what I typically see and dialed in enough input for 5 watts of output:
View attachment 26101

As noted, channel 2 was fine but channel 1 was all over the place. Its SINAD (signal over noise and distortion) hit a low of 49 dB and a high of 83 dB (later in testing). There is some kind of instability there. I noticed that jiggling the speaker cable in that channel caused some variations too so maybe it is mostly the connector.

Channel 2 beats the THD+N spec so that is good.

Here is a warm up sequence although the unit was not at room temp before I started:
View attachment 26102

So Channel 1 even when "stabilized" still acts different from the other channel.

Using the dashboard average of the two channels, this is what we get compared to other power amps tested:
View attachment 26109

Frequency response was very good with just a bit of droop at 20 kHz:

View attachment 26103

FFT spectrum of 1 kHz tone tells us about the design of this DCA2422:

View attachment 26104

We see a spike a bit above 100 kHz. QSC does not indicate the topology of the amplifier but does say it has a switching power supply. The switching power supply substantially lowers the weight of this unit and brings high efficiency that way. I suspect the Amp is some kind of class G (multi-voltage class AB amplifier). The spikes we see are I think the switching frequency of the power supply bleeding through. They are comfortably above the audible range and unlike class D amps, at rather low levels. Overall, this is a much cleaner spectrum than I see on class D amplifiers (which use switching power supply and amplifiers).

Testing with 4 ohm load shows copious amount of power available:

View attachment 26106

We can see channel 1's worse performance just the same here. Compared to our best ever measured power amplifier using Hypex NC400, we have tons more noise and distortion. But we also have far more power at much lower cost.

I finally took the time to properly mount my dummy loads in a rack mount case with a nice switch to select between 4 and 8 ohms so here are the results of latter:

View attachment 26107

Unlike 4 ohm where we came up short, the 8 ohm measured power is actually better than the specs.

Perhaps it is best to compare the QSC to another commercial amp I have tested: the Crown XLS1502:

View attachment 26105

If QSC's Channel 1 had behaved better, it would have beat the Crown across the board. As it is, one channel is better, the other much worse. There is higher output power though (sorry the cursor is not set to read that properly from the graph).

Here is how intermodulation distortion rates at different power levels:

View attachment 26108

Fascinating how closely the QSC tracks the performance of Klipsch Powergate. It of course leaves it in the dust as far as power is concerned.

Conclusions
The QSC DCA2422 amplifier is the typical commercial power amplifier with tons and tons of power in a light and low cost enclosure. Unlike class D competitors, it seems to have a much more stable design. The issue with it is the one channel misbehaving. If that is typical of the rest of the production, then that is not good. If it is just an issue with this specific sample, then this is a good buy for a rack-mount install to drive subwoofers and such. The fan noise rules it out for any kind of "domestic" application.

------------
As always, questions, comments, recommendations, etc. are welcome.

In the process of crimping a bunch of connectors to build my dummy load, I realized how tough the ratchet style crimping tools are on high-quality yellow ring connectors. Searching for a power version, I found this wonderful tool:


Bad news is that as most things good in life, it costs money, lots of money! $500 to be exact. So Please help fund that by donating generously using:

Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
Love the site and all that you do!!!

I have extensive experience with this series of QSC amps. The "Power Light 2" family. The family includes CX (basic install) DA (cinema) PLX 2 (premium music store/musician) and Power Light 2 (pro touring) I ran my sound company using the CX, which are available used for nearly nothing. New, the list price is several thousand per amp.

The amp you tested is the lowest power dual rail in the series, and actually my least favorite. Low voltage rail is 50 something volts and high if I recall is around 100. My two favorite amps from the series are the second from the bottom (CX502/PLX1602/DCA1622) 83v single rail, and the top of the series (CX1102/PLX3402/DCA3422) 83v bottom rail, 135v top rail. The CX502 uses the same transformer as the CX1102 but the high rail driver circuitry is missing.

The amp you tested would have delivered better 4 ohm performance (along with being more gentle to the wall power) if you populated the two missing 200v caps, which are available from QSC as factory parts. Also, the pro touring versions use 1000uf caps in the second stage of the power supply, where all the other amps in the series use 470uf caps. The 1000uf caps are also available from QSC as factory parts. Used the way I did,at its limit, driving double 18" ported subs down to 25hz hour after hour after hour... the extra cap storage makes a huge difference in both bass sound quality and how the amp draws power from the wall or distro. (We always used a proper distro!) Despite what the ad copy says... when driving subs at the limit, these amps want LOTS of AC current.

The CX502/PLX1602/DCA1622 with all six 200v caps installed and the secondary caps upgraded to the 1000uf "touring" version is a remarkable amp with lots of power and good current delivery. (The larger CX1102 version basically doubles power everywhere which is totally not necessary in a domestic environment unless your wall outlet can deliver tons of current and you want to brag about 700 - 1200 watts per channel in your hifi...

The basic topology is 115khz switching power supply feeding a class a/b output stage of one or two voltage rails. There are two electrolytic caps in the signal path - one before the volume control and one before the amp driver stage. I always removed the first (pre volume) cap as its there simply to prevent any dc from making the volume control sound noisy. Immediate subjective improvement in sound quality from removing that first cap. I have experimented (domestic use only!) with removing the second cap, swapping preamp opamp, (lm4562 sounds noticably better than the stock 33078!) film cap bypass on power supply caps, etc. and the amp does respond well to those tweaks. If I was trying to drive Maggies or similar the QSC CX properly modded would be my second choice go-to amp. (I currently use deeply modded Ashley FTX Series 3 amps. Fully discreet, all mosfet, thru-hole boards, etc.)

Used domestically, (properly modded) this series of QSC amps will lean toward the brighter side of neutral, with good stereo width, some stereo image depth, a playful "growl" to the bass, and an insistent sense of tons of power looking for a party.

Used domestically, and unmodded, the amps will sound very "matter of fact" with not much imaging depth (thanks to two electrolytic caps and 33078 opamp in the input section, plus a 5532 opamp if you engage the limiter.) The prodigious power will be obvious but if you're looking for holographic imaging, beauty of tone, etc. then these amps are not the droids you seek.

Regarding fan noise, this series of amps benefits from re-tightening the heat sink screws after a few years. As a classic a/b output stage with about 1 amp of idle current, the heatsinks need to be working correctly to keep the fans at their slowest setting in a domestic environment. At its slowest speed, the fan should be absolutely quiet. Maybe the amp you tested has a bum fan? (I've never had a fan issue with dozens and dozens of those amps working year after year in the worst possible environments imaginable.)

I've attached the schematic (PLX 2402 version) of the amp that you tested.
 

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