New QSC amp ????

Re: New QSC amp ????

The PLD and CXD lines are 4-channel class D amps with built-in DSP and a set of processing presets (such as voicing, crossover, and protection for specific loudspeaker models, as well as various bi- and tri-amp configurations).

Power amps have long been bridegable (i.e., channels put in series) to boost output voltage capability. These amp channels can also be paralleled for boosting output current--something which typically couldn't be done with linear power amp stages without disconnecting the feedback loop on one of them.

The proprietary thing is the MOSFET output devices, and I'll have to go back and look up what's special about them because I don't remember what it is. (I'm in tech services, not marketing.)
 
Re: New QSC amp ????

John Roberts said:
or what industry is really driving the switching device development (IMO not audio, maybe solar power or electric cars? While electric cars are low volume too... :).

JR
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Back when tripath was around I think they were targeting DSL applications. I'm not sure if that pushes the limits on current or voltage. Solar and wind might be the biggest consumer of power inverters? But I would think some smart grid ideas might also use some high power inverters.
 
Re: New QSC amp ????

drew gandy said:
Back when tripath was around I think they were targeting DSL applications. I'm not sure if that pushes the limits on current or voltage. Solar and wind might be the biggest consumer of power inverters? But I would think some smart grid ideas might also use some high power inverters.
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Tripath came in to Meridian and gave us a presentation. IIRC they were interested in selling modules to manufacturers to use in audio power amps. I was not very impressed by their response to what I thought were pretty basic power amp design questions. I think there was a college professor behind the basic Tripath invention, and some business types invested in his idea to be the next "game changer", but stuff happens. I don't think the professor was there for that particular MS dog and pony show.

I'm just guessing, electric cars, windmill convertors, something other than pro audio is driving device technology. Universal switching power supplies can handle 240V x 2.8 x +20% volts so that enough volts to make some serious audio power, but the uni-switchers are not high current for typical consumer goods so we need the volts and amps to make serious output power with single devices. Perhaps UPS for large computer installations but i don't know what battery voltage they size those for.

They do some crazy high power stuff where the major power grids meet. I think they convert both sides to DC to avoid the pesky phase matching issues, for power transfers between major grids, but that's silly low volume stuff so just of academic interest. The military may buy a few for rail guns or pulse weapons.

JR
 
Re: New QSC amp ????

Bob Lee said:
The PLD and CXD lines are 4-channel class D amps with built-in DSP and a set of processing presets (such as voicing, crossover, and protection for specific loudspeaker models, as well as various bi- and tri-amp configurations).

Power amps have long been bridegable (i.e., channels put in series) to boost output voltage capability. These amp channels can also be paralleled for boosting output current--something which typically couldn't be done with linear power amp stages without disconnecting the feedback loop on one of them.

The proprietary thing is the MOSFET output devices, and I'll have to go back and look up what's special about them because I don't remember what it is. (I'm in tech services, not marketing.)
Click to expand...

Bob, welcome to SoundForums.net. You've been missed.

Tim Mc
 
Re: New QSC amp ????

Bob Lee said:
The PLD and CXD lines are 4-channel class D amps with built-in DSP and a set of processing presets (such as voicing, crossover, and protection for specific loudspeaker models, as well as various bi- and tri-amp configurations).

Power amps have long been bridegable (i.e., channels put in series) to boost output voltage capability. These amp channels can also be paralleled for boosting output current--something which typically couldn't be done with linear power amp stages without disconnecting the feedback loop on one of them.

The proprietary thing is the MOSFET output devices, and I'll have to go back and look up what's special about them because I don't remember what it is. (I'm in tech services, not marketing.)
Click to expand...

Hi Bob,

if that is the case (current summing instead of voltage summing) then how come for the CXD you only show 70V specs for 4 channel mode?

I often need one large 70V amp and one small one so I thought this would be awesome to sum 3 channels and keep the last one separate, but it doesn't look like we can do that (or can we?)

Jason
 
Re: New QSC amp ????

Jason Lavoie said:
Hi Bob,

if that is the case (current summing instead of voltage summing) then how come for the CXD you only show 70V specs for 4 channel mode?
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I look forward to Bob's answer but I wouldn't make a full leap that the output is a current source. More likely there is some compliance in the output filter that facilitates load sharing, and perhaps reduced negative feedback all the way down to DC. I suspect there may still be issues driving two channels in parallel from different input sources. Something they probably manage cyberneticlly.
I often need one large 70V amp and one small one so I thought this would be awesome to sum 3 channels and keep the last one separate, but it doesn't look like we can do that (or can we?)

Jason
Click to expand...
Why not? If the total power limit is PS current you can parse that current any way you want.

Of course wait for Bob's confirmation.

JR
 
Re: New QSC amp ????

Actually the channel combining is pretty flexible. You can actually have the first three channels combined in parallel and the last channel independant. Then, you can put the last channel into either 70 or 100V mode. I think that the 70/100V modes are setup so that it makes it easy for an integrator to configure things... like instead of having to set up limiters and what not, you can just go to the right mode and it does all that for you under the hood. So I guess in that respect it is different than some other 70/100V amps where it truly was a "mode" that the amp had to go into -- and would usually require all channels to be that way.

Also on the power device... in order to get good clean audio performance and tight integration of power silicon, plus the right voltage swings etc, QSC had to go with custom silicon.
 
Re: New QSC amp ????

Matt Skogmo said:
Actually the channel combining is pretty flexible. You can actually have the first three channels combined in parallel and the last channel independant. Then, you can put the last channel into either 70 or 100V mode. I think that the 70/100V modes are setup so that it makes it easy for an integrator to configure things... like instead of having to set up limiters and what not, you can just go to the right mode and it does all that for you under the hood. So I guess in that respect it is different than some other 70/100V amps where it truly was a "mode" that the amp had to go into -- and would usually require all channels to be that way.

Also on the power device... in order to get good clean audio performance and tight integration of power silicon, plus the right voltage swings etc, QSC had to go with custom silicon.
Click to expand...

Hi Matt, thanks for chiming in. Should we assume you work for or represent QSC?

I am rather curious about the custom silicon. It is a major investment for a professional audio company to develop full custom silicon.

The evolution of high power class D amps seems to track with device technology. The combination of both high voltage and high current (with low on resistance of course) in single devices seems to be the hard part and cutting edge for the technology. Of course integrating all the supporting glue circuitry and DSP into a chip or ship set will reduce manufacturing cost.

I understand if you don't want to share proprietary details.


JR
 
Re: New QSC amp ????

John Roberts said:
I look forward to Bob's answer but I wouldn't make a full leap that the output is a current source. More likely there is some compliance in the output filter that facilitates load sharing, and perhaps reduced negative feedback all the way down to DC. I suspect there may still be issues driving two channels in parallel from different input sources. Something they probably manage cyberneticlly.
Click to expand...


Paralleled channels get the same PWM modulator feed to their respective output device pairs, and they all draw from the same PS rails. This allows the outputs to be parallel combined since there is no danger of one output backfeeding the other because of even slight mistracking.
 
Re: New QSC amp ????

Any more details on DSP signal path.. I cant seem to find a big enough pdf to see exactly what the routing scheme is..

Interested in some compression capabilities...

Thanks.
 
Re: New QSC amp ????

John Roberts said:
Hi Matt, thanks for chiming in. Should we assume you work for or represent QSC?
Click to expand...

Matt is director of R&D for the Power Group at QSC. He's giving you info straight from the source.

If he gets more established here he should set up a sig.
 
Re: New QSC amp ????

John Roberts said:
Hi Matt, thanks for chiming in. Should we assume you work for or represent QSC?

I am rather curious about the custom silicon. It is a major investment for a professional audio company to develop full custom silicon.

The evolution of high power class D amps seems to track with device technology. The combination of both high voltage and high current (with low on resistance of course) in single devices seems to be the hard part and cutting edge for the technology. Of course integrating all the supporting glue circuitry and DSP into a chip or ship set will reduce manufacturing cost.

I understand if you don't want to share proprietary details.


JR
Click to expand...

Yes, I am a colleague of Bob's at QSC.

As the thread has mentioned, there are some big name players in the industry who have worked with major IC manufacturers to develop modulator/drive technologies -- but from our perspective, that was quite expensive and the result wasn't going to be worth the investment. When we targeted custom silicon, we looked at the whole product needs. What needed to be done to create a platform of amplifiers that would be able to support the channel combining without majorly crazy and difficult small signal technology, to be able to support the specific needs of the integrator community, and support the needs of the portable pa/touring community. In many cases the requirements were at odds with each other. In the end, developing custom power silicon was the way to go. By creating our own silicon, we could develop a package that incorporated all of the needs. I know I am being a bit obtuse, but so it goes with custom stuff.

From a technical point, each custom module has 6 power semiconductors... each module can electrically and thermally handle more than 1250W at 8 ohms.

Matt
 
Re: New QSC amp ????

I was disappointed to learn yesterday that QSC is reserving the use of the FIR filter for QSC speakers only. I won't be able to use them for Level 1 processing of my Fulcrum Acoustics speakers. I am hoping they change their minds as these would be a great cost effective solution.
 
Re: New QSC amp ????

Matt Skogmo said:
Yes, I am a colleague of Bob's at QSC.

As the thread has mentioned, there are some big name players in the industry who have worked with major IC manufacturers to develop modulator/drive technologies -- but from our perspective, that was quite expensive and the result wasn't going to be worth the investment.
Click to expand...
While I have been out of the trenches for about a decade I am pretty familiar with the history of class D amps for a few decades before that.
When we targeted custom silicon, we looked at the whole product needs. What needed to be done to create a platform of amplifiers that would be able to support the channel combining without majorly crazy and difficult small signal technology, to be able to support the specific needs of the integrator community, and support the needs of the portable pa/touring community. In many cases the requirements were at odds with each other. In the end, developing custom power silicon was the way to go.
Click to expand...
In my judgement the low level front end could probably be handled by off the shelf DSP platforms. I guess nowadays you can just about do semi-custom DSP using quasi standard building blocks from a foundry library. (I'm starting to see features show up in microprocessors that they are licensing from Arm Holdings or somebody like that).

The output side is where IMO the heavy lifting is required and there is probably some utility in considering different voltage/power points. FWIW I use a small 1+W class D IC about the size of a hungry wood tick in a battery powered design, and it gets unhappy with much more than 6V supply. Now that's silly low power and for now you guys need to be pimping kW not W.
By creating our own silicon, we could develop a package that incorporated all of the needs. I know I am being a bit obtuse, but so it goes with custom stuff.

From a technical point, each custom module has 6 power semiconductors... each module can electrically and thermally handle more than 1250W at 8 ohms.

Matt
Click to expand...
Interesting... I recall one program we tried years ago back at my old day job to get one of the major switching device manufacturers to just put 4 of their existing devices into a single package with common substrate. There are are obvious and non-obvious benefits from that. They blew it and the thermal resistance (junction to case) of the combined package was so high the part wasn't unable to make serious power. Hopefully the industry has gotten better at packaging since then (15-20 years ago).

The magic number 6 devices per module raises more question than answers in my mind, but I really do not need to know every detail.

Thanks for the info.

JR
 
Re: New QSC amp ????

Bob Lee said:
Paralleled channels get the same PWM modulator feed to their respective output device pairs, and they all draw from the same PS rails. This allows the outputs to be parallel combined since there is no danger of one output backfeeding the other because of even slight mistracking.
Click to expand...

I probably don't need to get off in the weeds with you about techie minutiae but, in an ideal world feeding power switching pairs with the same PWM input drive "should" result in identical output. In the real world there can be very small timing differences at the output due to sundry device switching speeds. If these switching outputs were hard wired to each other, fun could ensue.

Since each amp power section requires it's own output filter, and the amps (probably) don't get connected to each other until the very output (after the filters), the inductance of two output filters in series between the two switching stages probably keeps the current from the very small timing differences well under control.

Next issue is how negative feedback from after the output filter is handled for combined amp stages. But this is all low power feedback signals so manageable.

I like the concept, good luck.

JR

PS I bet it fits nicely inside your powered speakers. Tell the guys that want access to your FIR filters that they should just buy QSC powered speakers. :)
 
Re: New QSC amp ????

Jason Raboin said:
I was disappointed to learn yesterday that QSC is reserving the use of the FIR filter for QSC speakers only. I won't be able to use them for Level 1 processing of my Fulcrum Acoustics speakers. I am hoping they change their minds as these would be a great cost effective solution.
Click to expand...

+1

Although on the surface this may be a strategy to try to sell more speakers, in my mind it will just mean that when I want an amp to power Fulcrum speakers I'll buy cheaper amps..
I'm a QSC fanboy, but I won't buy an amp that I know is capable of the task I want it to perform (FIR) and then set it up to do a lesser task (IIR) regardless of the price. either my current customer doesn't care (so, no DSP at all) or they care a lot (I'll find a way to get FIR presets implemented)

Jason
 
Re: New QSC amp ????

Jason Lavoie said:
+1

Although on the surface this may be a strategy to try to sell more speakers, in my mind it will just mean that when I want an amp to power Fulcrum speakers I'll buy cheaper amps..
I'm a QSC fanboy, but I won't buy an amp that I know is capable of the task I want it to perform (FIR) and then set it up to do a lesser task (IIR) regardless of the price. either my current customer doesn't care (so, no DSP at all) or they care a lot (I'll find a way to get FIR presets implemented)

Jason
Click to expand...

QSC makes non powered speakers? that I didn't know... yes I am being honest... well I can only think of the Wideline rig.
 
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