ElectroVoice CPS8.5 8-channel Class 'D' amplifier

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#4
Well, I think that I'm beginning to zero in (from other sources) on some of what I was trying to figure out... For instance, I've discovered that the fans are expected to be running at idle, since this amp actually runs hotter at idle than under load. Is that true?

I have only had the amp in service for a couple of days. It's being used in a Home Theater environment, and has been placed in a rack full of QSC PLX3042s. I currently have it at the top of 7 of those. This amp is driving 8 x 8Ohm nominal, loudspeakers (diysoundgroup.com's Volt-6, a 6.5" woofer, coaxial with a mid/high-frequency compression driver...) I would think this would be a fairly easy load for this amplifier.

I had been lead to expect that the unit's fan-noise would be an issue, so, before placing into service, I swapped out the original fans for a lower sone fan model. And, since all the QSC fans are back to front, I figured I better try reversing the fan flow, which I did. I noticed that, even with no load, the fans were coming on, and the unit was getting warm. That worried me a little bit, but I guess that what I mentioned up above accounts for this, yes? The unit does not appear to be overheating, but I guess it is running warmer than I expected it to.

Another thing, that I just noticed last night, is that the unit has a bit of a buzz. While I don't have any before/after comparative behavior regarding the fan swap, I definitely remember that there was no buzz in the amp when it was sitting on the carpet, turned on, with nothing plugged in to it. So that brings me to another couple of questions: Should there be any buzzing coming from the amp? And, would you expect this amp to behave differently, with respect to buzzing, when it has sources and loads plugged in, versus just being turned on with no connections?

It is my intent to move this unit to the bottom of the equipment rack, restore its front-to-back fan direction, and try again. While I have the unit out, I intend to check it for buzzing (with everything unplugged).

So, to summarize:
  • CPS8.5 in HT service driving 8 Volt-6s as surrounds/atmos.
  • Unit is fairly warm, and fans run, at idle.
  • Unit has a buzz, now that it is in service, that I don't remember when I turned it on prior to installation. This buzz is not unlike the transformer buzz one might have experienced in older amp designs.

And, now, all my questions are:

  1. Has anyone performed a lower-sone fan-swap on these amps?
  2. Has anyone reversed the fan direction?
  3. Will the unit shut itself off in the event of overheating?
  4. How hot should I expect this unit to get?
  5. Does this model ever exhibit a buzz?
  6. Would you expect a difference in behavior, with respect to buzzing, when the unit is unplugged from all sources and loads, vs when everything is plugged in?

Thanks.

- s.west
 
#5
@ Swest.


To tell you the truth, I also was surprised that this amplifier heats at NO load, and in idle. while no load is connected.

The hot air was measured around 40C minimum, and it may go up to 50C. so that's normal!

This amplifier is a Class-d amplifier, and because of the very low DT, it heats that much.


and Yes the amplifier will SHUTDOWN in case of over-heating, you can install the IRIS-NET cards + software and monitor it, I had all my amplifiers installed with IRIS-NET.

Regarding the buzz, I cannot remember I had any amplifier with such problem.

Hope that answers the questions.
 
#6
@Cresnet

Very helpful. thanks for those numbers, and the shutdown confirmation.

What's 'DT'?

What's the $$ for adding the IRIS-NET card?

I'll keep you posted as to the unit's behavior when I pull it from the rack. While I have it out, in addition to restoring the fan direction (since I'm going to put this at the bottom of the stack, the direction will be less of an issue) I am going to explore the buzz a little further, and make sure it behaves the same loaded and un-loaded...

Thanks, again.

- s.west

p.s. There are a number of things on this amp that are just, well, backward, when compared to, at least, my QSCs. I've had such good luck with the QSCs that they are my gold standard.

  • Front-mounted fan... why in the world would you mount a noise-making device in the front of your amp? Even considering its 'Pro'-amp heritage, I don't get why you would do that. I haven't looked extensively, but I can't think of a single amp with the fans in the front.
  • The input jacks have the XLR wired as 'ground, + -', instead of '+, -, ground'.
  • The output jacks are wired, '+,-,+,-,+,-,+,-' instead of '+,-,-,+,+,-,-,+'
 
#7
In my installation, all of the EV amplifiers are stacked on top of each others, ran under heavy use for a few hours.

Never had any over-heating issues, even when the internal temperature reached 80C.

I really didn't like that amplifier from EV due the HEAT issues, otherwise it sounds just like AB amplifier.

DT = dead time


Regards
 
#8
Roger that. It is a little counter-intuitive (the fact that it's Class D, and runs warm).

Thanks for that other Temp number, that further relieves me of any worry about the low-noise fans I installed.

Also, thanks for the comment about sound quality. I'm glad to hear your experience.

Ok, that's it for now. I'll report later, after I've rearranged my rack, and had a chance to listen for the buzz with the amp disconnected...

- s.west
 
#9
By the way, here's a link to a video where I'm demonstrating the buzz. Sorry for the bad focus. I was 'focused' on getting the sound.

You will hear all the other amps/PDUs powering up, and then the CPS8.5 light will come on, and then you'll hear the startup buzz... that will fade somewhat, and then you'll hear the steady buzz. Also, you won't hear the fans, as they haven't started spinning yet.

- s.west
 
#10
swest said:
By the way, here's a link to a video where I'm demonstrating the buzz. Sorry for the bad focus. I was 'focused' on getting the sound.

You will hear all the other amps/PDUs powering up, and then the CPS8.5 light will come on, and then you'll hear the startup buzz... that will fade somewhat, and then you'll hear the steady buzz. Also, you won't hear the fans, as they haven't started spinning yet.

- s.west
Click to expand...

Really cant tell exactly if I heard it clearly, but I heard something like (nnnmmm) when the CPS turns on, is that it?

Any speakers connected to the Amplifier?
 
#11
That video was taken when everything was still in the rack and hooked up.

I have since rearranged the rack, moving the CPS from the top of the stack to the bottom. While I had the CPS out, and on the floor, with nothing but a power cord plugged in, I powered it up and experienced the same buzz. The thing is, I just don't remember hearing that back on day 1, before I had placed the unit into service.

So, anyway, before I put it back into the rack, I reoriented the fans so that they are now pushing the air front->back (per the design). This won't be a problem now, since, again, this amp is now at the bottom of the amplifier stack, and won't be breathing in anyone's hot exhaust.

Apart from this buzzing, I really have been needing to do something to cover up all the lights on all the amps in the rack, because they're pretty distracting... blinking all the time during movies. So, I think I will end up with some sort of decorative cover over the lower half of the equipment rack (where the amps reside). I will place it just far enough away so that the QSCs are not starved for exhaust space out the front, and I will make it as sonically opaque as possible. Hopefully, this action, along with the fact that now that the CPS is near the floor, there is a subwoofer that sits right in front of it, will adequately muffle the buzz.

No matter what, I'm going to alert the company where I bought the CPS that I have experienced this problem (there's a 30-day return period), so that if I am unsuccessful at masking the noise, I can take it back. They had a second copy of this amp, so I'm going to ask them to plug it in, power it up, and check it for any buzz, in case I need to swap with them.

I'll let you know how it goes.

Thanks, again.

- s.west
 
#13
theAnonymous1 said:
If there's a bright side to the heat issue it's that lower DT gives better sound quality.
Click to expand...

This is the second time that this term, DT, has been used. Cresnet clarified the acronym's definition for me as, "Dead Time".

As my father would have said, "I don't understand all I know about Class D amplifiers."

Is there a summary of the operation of Class D amps that includes the significance of this term? Or, can you, or someone else on here, tell me what the meaning and significance of DT is?

Thanks.

- s.west
 
#14
Here's a small quote from this page...

Class-D Amplifiers

Timing is critical in all this process: any error as delays or rise-time of the MOSFETs will ultimately affect efficiency and audio quality. So all the involved components must be high-speed. Dead-time also affects performance, and it must be minimised. At the same time, the dead-time must be sufficiently long to ensure that under no circumstance both MOSFETs are on at the same time. Typical values are 5 to 100ns.

The dead-time is a critical factor for distortion performance. For lowest distortion, the dead-time must be as small as possible, but this risks 'shoot-through' currents, where both MOSFETs are on simultaneously. This not only increases distortion and dissipation dramatically, but will quickly destroy the output devices. If the dead-time is too great, the response of the output stage no longer follows the true PWM signal generated in the modulator, so again distortion is increased. In this case, dissipation is not affected.
Click to expand...

Basically you have to trade higher dead-time for lower losses, or lower dead-time for higher losses. No free lunch. 😉
 
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#16
Well, buzzing aside, the fact is that it runs so hot, and the fans' speed is so high, that I'll never be able to mask the sound... I've tried everything.

Alas, this will have to go back.

Too bad. I really liked the thought of providing my surrounds and atmos speakers with so much power.

I guess I'll have to settle for my QSC CX168. It's quiet, runs fairly cool, and appears to have minimally adequate power.

- s.west
 
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