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Author Topic: QSC SPA series install amplifiers?  (Read 845 times)

Frank Koenig

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QSC SPA series install amplifiers?
« on: May 01, 2020, 11:43:36 am »

I have a little home-audio project for which a QSC SPA4-100 four-channel amp looks like a perfect fit. I like that it's small, no-fans, efficient and has auto-standby and single-pot remote volume. (It looks nice, too.) Curiously, QSC does not provide performance specs for noise and distortion, but I assume that these are beyond reproach.

I'd love to hear of any experience that any of you may have had with these. Thanks.

--Frank

https://www.qsc.com/systems/products/power-amplifiers/energystar-amplifiers/spa-series/spa4-100/
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Robert Healey

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Re: QSC SPA series install amplifiers?
« Reply #1 on: May 01, 2020, 02:44:40 pm »

I have a little home-audio project for which a QSC SPA4-100 four-channel amp looks like a perfect fit. I like that it's small, no-fans, efficient and has auto-standby and single-pot remote volume. (It looks nice, too.) Curiously, QSC does not provide performance specs for noise and distortion, but I assume that these are beyond reproach.

I'd love to hear of any experience that any of you may have had with these. Thanks.

--Frank

https://www.qsc.com/systems/products/power-amplifiers/energystar-amplifiers/spa-series/spa4-100/

I've had them go in a few recent auditoriums for BOH monitoring and paging speaker systems in 70V mode. No issues reported but I am not sure you could judge fidelity on a 4" Atlas ceiling speaker.

I am hoping for a "Q" version that is a native device in a Q-Sys system.
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Caleb Dueck

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Re: QSC SPA series install amplifiers?
« Reply #2 on: May 01, 2020, 04:37:07 pm »

I'd love to hear of any experience that any of you may have had with these. Thanks.

Not much to share other than - if you need a small/cheap amp and are using a lot of QSC anyway, such as QSys and background speakers and/or conferencing - they seem to work well.  If you're looking to drive small subwoofers or studio monitors - there are better options.  They're a price point option.
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Frank Koenig

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Re: QSC SPA series install amplifiers?
« Reply #3 on: May 02, 2020, 11:57:22 am »

...there are better options.  They're a price point option.

Thank you both for the replies. It sounds like there is no particular reliability problem with these and that they're out there being used which is a big plus. Having said that I'm in no way wed to this model and am very happy to hear alternatives.

My requirements are, roughly:

3 channels for stereo full-range and one sub. I expect this to be achieved with 4 channels 2 of which are bridged for the (8 Ohm) sub. This is for use with a TV on which I'll primarily stream movies (TV series) about people with problems. I expect to use a MiniDSP 2x4HD for processing.

>100 W into 4-8 Ohms. More is better.

Low-power standby with auto power-on in the presence of signal. This is a hard requirement.

Preferably no, or very low, fan noise and a compact package is a plus as it would allow me to locate it in the listening area rather than having to run wires to another room.

Freedom from dead-zone ("crossover") distortion that is audible at low power levels. I'm less concerned about THD near clipping.

Noise low enough that it won't bother me in a 200 sq ft room with, say, 95 dB sensitivity speakers. Pretty much anything beyond a crappy car-stereo amplifier should be able to meet this.

Budget $1500 tops. I feel that I should be able to get what I want for less, maybe a lot less. The QSC is ~$900. If I go to $1700 I can get into a Quattrocanali, for example, which is a nice piece, but it has a fan and is really more than I need. It costs more than the damn TV! But I would prefer a brand I've heard of :)

Many thanks.

--Frank
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Caleb Dueck

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Re: QSC SPA series install amplifiers?
« Reply #4 on: May 02, 2020, 10:20:20 pm »

It sounds like you're looking for a studio-focused amp, which I'm not as familiar with.  Otherwise the lower powered amps seem to be consumer focused or budget focused.

Powersoft Mezzo are worth a look.
Lab.Gruppen Lucia
Stewart as well, but most are lower power.
LEA, the new brand with ex-Crown guys.

I think there are some older Crown, Crest, Ashly, and Rane options targeted for this.

If there isn't an auto-stand-by - what about a relay, like a Furman PS-REL and CN-20MP?
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Frank Koenig

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Re: QSC SPA series install amplifiers?
« Reply #5 on: May 04, 2020, 12:22:11 pm »

Powersoft Mezzo are worth a look.

Caleb, thanks. I had overlooked the Mezzo. It appears to be directly competitive with the QSC SPA and costs only a little more. It ticks all the boxes for me. It has the interesting property that all channels are capable of utilizing the full output of the power supply over a wide range of load impedances so it makes efficient use of the supply for asymmetric loads. It also has some built-in DSP which could be useful for other projects. Alas it does not include FIR filters.

When it comes to power management, of course I could rig up a relay and remote switch (or get out the conduit bender), but auto-standby is really nice for me. I like that you can just turn off the TV with the remote and forget about it, especially since others may be at the controls.

--Frank
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Lee Douglas

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Re: QSC SPA series install amplifiers?
« Reply #6 on: May 04, 2020, 01:20:39 pm »

Otherwise the lower powered amps seem to be consumer focused or budget focused.

That's what I was thinking.  Frank, just curious; why not use consumer stuff?  For the cost of any of the amps suggested you could get a decent surround amp and a powered sub that would have a decent amount of DSP and use next to nothing in power when the TV was off.  They would certainly be quiet enough and would not need an outboard crossover.  I have two Yamaha surround amp in my house rack and they are on 24/7 and idle most of the time.  Hell, with the right remote, you could set up a macro to put them in standby with the TV.
« Last Edit: May 04, 2020, 03:26:50 pm by Lee Douglas »
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John Roberts {JR}

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Re: QSC SPA series install amplifiers?
« Reply #7 on: May 04, 2020, 01:32:52 pm »

I have a little home-audio project for which a QSC SPA4-100 four-channel amp looks like a perfect fit. I like that it's small, no-fans, efficient and has auto-standby and single-pot remote volume. (It looks nice, too.) Curiously, QSC does not provide performance specs for noise and distortion, but I assume that these are beyond reproach.
Don't ASSume... there is a spec sheet at the link you provided.  ::)

Install amps are generally cost effective (cheap) but these spec 100dB S/N and flat 20-20k response.

The amplifiers are modern class D so don't look for crossover distortion or other false bogeymen.
Quote
I'd love to hear of any experience that any of you may have had with these. Thanks.

--Frank

https://www.qsc.com/systems/products/power-amplifiers/energystar-amplifiers/spa-series/spa4-100/
I have no first hand experience but modern amplifiers, even these inexpensive install amps generally don't suck.

JR
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Frank Koenig

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Re: QSC SPA series install amplifiers?
« Reply #8 on: May 04, 2020, 02:48:12 pm »

Don't ASSume... there is a spec sheet at the link you provided.  ::)

Install amps are generally cost effective (cheap) but these spec 100dB S/N and flat 20-20k response.

The amplifiers are modern class D so don't look for crossover distortion or other false bogeymen. I have no first hand experience but modern amplifiers, even these inexpensive install amps generally don't suck.

JR

Thanks JR, I did find the noise spec, just missed it the first time. But so far as I can tell there really is no distortion spec, which just strikes me as odd. Even if it's  kind of useless it's a spec that consumers have expected to see since time immemorial. The frequency response spec is weird, too. +/- .1 dB, really? Even an $8000 Powersoft specs to -.5 dB, which is good enough for me, and everyone else it appears. I guess if you got it, flaunt it, and I know that these sheets are written by marketing folks after pressing the engineers for numbers.

As for distortion at low power, I was really only listing requirements as they came to mind. And while I agree that it should be a thing of the past I find it curious that some modern amps only spec THD above some power level, typically .1 or 1 W. Do you suppose that distortion really does go up, beyond the ability of the negative feedback to correct, as the on-time of the output switch goes to zero, or is it just a measurement problem, or something else? I have this superstition that my big Powersoft K-series are a little fuzzy sounding at very low power, but it may be just that. I could try to measure but it might be tricky with all the switching hash on the outputs. I don't know how my old HP Audio analyzer or the ADCs on my computer interface (for Smaart, etc.) would handle that. I might have to build and qualify proper filters, which is a bit of an undertaking.

Anyway, thanks for indulging me.

--Frank
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John Roberts {JR}

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Re: QSC SPA series install amplifiers?
« Reply #9 on: May 04, 2020, 08:16:18 pm »

Thanks JR, I did find the noise spec, just missed it the first time. But so far as I can tell there really is no distortion spec, which just strikes me as odd. Even if it's  kind of useless it's a spec that consumers have expected to see since time immemorial. The frequency response spec is weird, too. +/- .1 dB, really? Even an $8000 Powersoft specs to -.5 dB, which is good enough for me, and everyone else it appears. I guess if you got it, flaunt it, and I know that these sheets are written by marketing folks after pressing the engineers for numbers.

As for distortion at low power, I was really only listing requirements as they came to mind. And while I agree that it should be a thing of the past I find it curious that some modern amps only spec THD above some power level, typically .1 or 1 W. Do you suppose that distortion really does go up, beyond the ability of the negative feedback to correct, as the on-time of the output switch goes to zero, or is it just a measurement problem, or something else? I have this superstition that my big Powersoft K-series are a little fuzzy sounding at very low power, but it may be just that. I could try to measure but it might be tricky with all the switching hash on the outputs. I don't know how my old HP Audio analyzer or the ADCs on my computer interface (for Smaart, etc.) would handle that. I might have to build and qualify proper filters, which is a bit of an undertaking.

Anyway, thanks for indulging me.

--Frank
Class D amps are different animals with different behaviors... I don't have the time or energy to explain where their flaws may be hiding, but it is not crossover distortion.

JR

PS: FWIW I am using 6x class D amps for my living room TV surround system... Sounds good enough for me... (not QSC but I expect they are OK too).

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Frank Koenig

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Re: QSC SPA series install amplifiers?
« Reply #10 on: May 05, 2020, 01:06:42 pm »

I don't have the time or energy to explain where their flaws may be hiding, but it is not crossover distortion.

I know the feeling. But if you're ever in the mood I'm interested.

Just for grins, I took a look at the data sheet for a small, integrated class-D amp:

http://www.ti.com/lit/ds/symlink/tpa3116d2.pdf?ts=1588647708626

They give extensive distortion curves as a function of frequency and power. There is an uptick in distortion + noise at mid to low frequencies at power levels < ~1W. This could be the noise dominating the measurement. I believe distortion measurements, as made by Audio Precision, differentiate the harmonics from the noise by signal averaging but, now that I think about it, signal averaging may not work so well on the switching hash as it may be correlated with the test signal. It may be just damn hard to measure.

So I don't know, but this feature of the distortion curves may have something to do with amp manufacturers using a lower power limit when speccing distortion. Commercial amp users don't give a hoot about low power anyway since low power means they specced an amp that's bigger than it needs to be.

Enough for now from me. --Frank
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John Roberts {JR}

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Re: QSC SPA series install amplifiers?
« Reply #11 on: May 05, 2020, 02:51:51 pm »

I know the feeling. But if you're ever in the mood I'm interested.

Just for grins, I took a look at the data sheet for a small, integrated class-D amp:

http://www.ti.com/lit/ds/symlink/tpa3116d2.pdf?ts=1588647708626

They give extensive distortion curves as a function of frequency and power. There is an uptick in distortion + noise at mid to low frequencies at power levels < ~1W. This could be the noise dominating the measurement. I believe distortion measurements, as made by Audio Precision, differentiate the harmonics from the noise by signal averaging but, now that I think about it, signal averaging may not work so well on the switching hash as it may be correlated with the test signal. It may be just damn hard to measure.

So I don't know, but this feature of the distortion curves may have something to do with amp manufacturers using a lower power limit when speccing distortion. Commercial amp users don't give a hoot about low power anyway since low power means they specced an amp that's bigger than it needs to be.

Enough for now from me. --Frank
I was involved with class D back in the 80s (at Peavey) when they were far from mature and the device technology was not up to the challenge like it is this century. There are some subtle low level distortions but these are pretty much managed in modern chip sets.

My point was that saturated switching amps do not exhibit the classic problems associated with linear audio amps. 

Back when I was product manager for all Peavey's power amps and I had a class D amp that was lucky to spec 1kW... The limitation back then was power switching devices that could handle the voltage/current. Class D amp output devices do not behave well in parallel like typical analog output stages can. So the switching amp industry was at the mercy of power device manufactures waiting for fast, high current, high voltage devices. Now decades later that wait was rewarded (thanks a lot... :o ).

The modern generation of cost effective switching amps were after my time in the trenches so I have no hands on experience or inside information, but I can read the tea leaves (customer complaints) and they seem pretty serviceable. I can speculate they use standard IC manufacturer chip sets with cookbook application note designs.

My favorite modern class D amp for modest power is a EU product (Hypex) designed by Bruno Putzey (real deal engineer).

For TMI, I use a cute couple watt class D amplifier chip in my drum tuner. This class D IC sips current from my batteries and is about the size of a wood tick who is still hungry. You have to love modern technology (I do).  8)

JR
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Frank Koenig

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Re: QSC SPA series install amplifiers?
« Reply #12 on: May 22, 2020, 01:09:03 pm »

Here's the follow-up. I bought the Powersoft Mezzo 604A, which has 4 channels, a 600W power supply, DSP without FIR and auto-standby. I'm very pleased. It's a nice compact package that I mounted on the wall behind the TV with the business end close to one vertical edge of the TV so that it's accessible. It's super quiet both electrically and acoustically and, of course, sounds just fine. The auto-standby, which has a fixed -60 dB threshold, more-or-less instant-on and an ~30 min. hold, works perfectly. I'm using a miniDSP 2x4hd upstream for FIR filtering and remote-controlled preset selection (bass-boost on/off depending on program).

Thanks for the help, everyone.

--Frank
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Re: QSC SPA series install amplifiers?
« Reply #12 on: May 22, 2020, 01:09:03 pm »


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