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CX750M Gray Label - Loud under load


c00lkatz
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I have a new CX750M (just bought a few weeks ago, gray label) that is getting loud under gaming loads. I had an RTX2060 KO installed up until yesterday, and didn't notice the noise much. Just installed an RTX3080 XC3 Ultra last night, and everything is working fine except the PSU is getting insanely loud. It's way louder than all of my other fans (2 x 120 intake, 1 x 120 & 1 x 140 exhaust, 3700X [stock] with stock fan). I thought it was my GPU at first, since it's the only thing I changed, but after going fan-by-fan in the system looking for what was causing all the noise (and setting custom fan profiles for everything), it's the PSU.

 

Is it normal for this PSU to be this loud? I know the 3080 is a beast, but I wasn't expecting this. According to HWInfo, my GPU is at about 315-325W max under load, and my Cyberpower UPS is reporting a total of 525-540W (with other things plugged into the battery backup side as well, so not all the PC). My CPU package power is reporting around 86W. So I'm probably around 450W or so out of a 750W unit.

 

Should I RMA?

 

EDIT: Case is a Corsair 275R, PSU is mounted fan down towards the bottom vent, ambient temps are around 24-25*C or so and my "system 1 temp" as per my mobo (Gigabyte B450 Aorus M) is reporting 30-32*C idle and 51-52*C under load after about 10-20 minutes of gaming.

 

EDIT 2: SOLVED - just bought an RM850x and it's totally silent - don't use a CX750M with a 3080 if you're worried about noise!

Edited by c00lkatz
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EDIT: Case is a Corsair 275R, PSU is mounted fan down towards the bottom vent, ambient temps are around 24-25*C or so and my "system 1 temp" as per my mobo (Gigabyte B450 Aorus M) is reporting 30-32*C idle and 51-52*C under load after about 10-20 minutes of gaming.

 

Flip the PSU around so the fan is pointing up.

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Flip the PSU around so the fan is pointing up.

 

Thanks Jonny, I will try that. Just for my own reference, what is the benefit of doing this? To put the fan facing towards the inside of the case to help reduce noise? I was always under the impression that fan down was better if your case has a vent for it (which it does, along with a filter), as it will be drawing in cooler outside air rather than warmer case ambient air. The PC is sitting on a solid surface (not sitting on carpet or something like that), and the case feet are pretty tall. It is sitting about waist high on a ledge next to my TV (it's my HTPC - not my main system listed in my "system specs" here). However, there is a vent on the PSU shroud to accommodate the PSU being mounted with fan up, so I will definitely try it.

 

Just to be clear, I don't doubt you at all, and will definitely try it (I've been reading your reviews for years, you're the first reviewer I look for when PSU hunting, you have helped me pick many a PSU - thank you!), but just want to understand the reasoning behind your suggestion so I know when to do this in the future.

 

Thanks again!

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Thanks Jonny, I will try that. Just for my own reference, what is the benefit of doing this? To put the fan facing towards the inside of the case to help reduce noise? I was always under the impression that fan down was better if your case has a vent for it (which it does, along with a filter), as it will be drawing in cooler outside air rather than warmer case ambient air. The PC is sitting on a solid surface (not sitting on carpet or something like that), and the case feet are pretty tall. It is sitting about waist high on a ledge next to my TV (it's my HTPC - not my main system listed in my "system specs" here). However, there is a vent on the PSU shroud to accommodate the PSU being mounted with fan up, so I will definitely try it.

 

Just to be clear, I don't doubt you at all, and will definitely try it (I've been reading your reviews for years, you're the first reviewer I look for when PSU hunting, you have helped me pick many a PSU - thank you!), but just want to understand the reasoning behind your suggestion so I know when to do this in the future.

 

Thanks again!

 

 

The thermistors for the fan control are on the PCB. Fan down, some heat rises into the PCB and can trigger the fan.

 

THAT SAID, the CX750M is NOT engineered for low noise. A Bronze PSU generates more of it's own heat than a higher efficiency unit.

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The thermistors for the fan control are on the PCB. Fan down, some heat rises into the PCB and can trigger the fan.

 

THAT SAID, the CX750M is NOT engineered for low noise. A Bronze PSU generates more of it's own heat than a higher efficiency unit.

 

Ah, ok makes sense, I will give it a whirl. Yeah, normally I wouldn't buy a bronze rated PSU for such a high end card, but impulse buys and all. I was lucky enough to get into the notification queue early for the 3080, and pulled the trigger. Normally, I would have gone with a gold rated PSU regardless, but the prices have sky-rocketed. I bought this CX750M for a whopping $105 - my EVGA 750 G3 in my main rig cost $120 only a year ago! An equivalent gold rated PSU now-a-days is going for around $150. I may just bite the bullet and get an RM850x, try to return this CX750M. It was adequate with the old RTX2060, but seems the 3080 is heating it up quite a bit. It still works fine (running 2 individual PCI-e cables to the card), but it's just too dang loud!

 

Thanks again for your help!

Edited by c00lkatz
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Well... If you're in the U.S., don't expect those prices to drop any time soon. Over the last year, PSU prices have been impacted by Trump's 25% China tariff. And even if Biden gets into office, that's not likely to get reversed.. at least any time soon.

 

And while some "final assembly" can be done in Taiwan or Vietnam to avoid tariffs, labor rates are 10 to 15% higher than in China and the supply chain for almost all of the parts have to come from China, so you have shipping costs from China to the "middle destination" on top of that. It's just a lose-lose.

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Bit the bullet and swapped out the CX750M for an RM850x - MASSIVE improvement! Can't hear the PSU at all now, and after 30 minutes of load there was just the slightest bit of warm air moving out of the PSU, compared to the CX which was blasting heat out of the PSU. Problem solved!

 

I also replaced my stock 3700X Wraith cooler and front 2x120mm SP120 fans with a Corsair H100i RGB Platinum - another MASSIVE improvement! The PC is totally silent now, can't hear it at all above my speakers while gaming, while before the PC was super loud. Temps on my CPU before the 3080 (with the 2060) were in the low 60s to mid 70s while gaming, but after the 3080 swap, they skyrocketed to mid 80s (extra heat dump from the GPU overpowering the CPU cooler I imagine). Now I'm in the mid 50s with the occassional spike to the mid 60s. The CPU was also throttling back to around 4050MHz due to heat, now it's sitting around 4250-4350Mhz again.

 

Overall super satisfied now. New H100i cooler and RM850x PSU made a huge difference with the 3080!

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