CS800x - quieter fan and input sensitivity

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CS800x - quieter fan and input sensitivity

Post by DaleMurray » Sun Sep 06, 2020 11:09 am

I just picked up a pristine CS800X to power subs in my home audio system.

The amp works great but that fan is making me nuts; I can hear it clear as day even when music is playing.

I would like to replace it with a quieter fan but it being 115v really limits options, I think.
I would prefer to find a quieter AC fan but can add a 12v power supply and fan instead.

Input sensitivity.
I have yet to review the schematic, but I would like to make the input a bit more sensitive. I initially thought I would have to turn the gain down, but I actually must set them to 10 with my sub out of the preamp set to max. I even decreased the signal level to my main L & R output to balance the sound.

I totally forgot about consumer -v- professional line levels.

* please note, this is only driving two 12" 4ohm drivers in my living room. Its unlikely I will ever use more than 150 watts of output, 200 would be absolute max, thus I doubt it will ever get very hot. After a few hours yesterday the only heat was at the transformer.

** Yes, this is overkill for my use but it was 1/3 the price of other amps I was looking at. (ADCOM GFA555, NAD 2200, Carver, Crown, Etc)

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Re: CS800x - quieter fan and input sensitivity

Post by Enzo » Tue Sep 08, 2020 9:13 pm

There are TONS of 120v fans, and I don't recall 12v fans being any more quiet than others. You may not stress the amp yourself, but someday someone else may inherit it, and they will have no idea you installed a weaker fan, and THEY may have heat issues.

Fans come in dimensions, 3" or 4" or whatever. (Or 80mm, 100mm etc) And don't forget the thickness, If the amp needs a slim fan and you buy a 1" model, it won't fit.

Mouser has a large selection, as do other suppliers. Fan data sheets have a noise figure, and an airflow figure. Some are quieter but also move less air. You really don't want to cheat on air.

And make sure to note airflow direction before you tear into it.

Now, maybe your fan is just noisier than it should be. Fan bearings can dry out and get noisy. A typical fan has a round sticker covering the hub on the frame side, not on the fan blade itself. Peel back that sticker and add a drop of light pol to the end of the axle you will see there.

Also, the fan has two speeds, it could be stuck in HIGH. On the main board, there are three thermostats. Two are mounted atop power transistors, and the third in between the rows of transistors. That third one is the one for the fan. With the amp unplugged, check to see if the contacts of that thermostat are closed. They should be open.

Also, there is a small board inside with a couple fuses in one corner and right in the center is a 400 ohm 15 or 20 watt resistor. WHile the amp is running, measure AC voltage across that 400 ohm resistor. Should not be about zero. If you getzero, it is stuck on high. If you get a goodly sum of volts, it is working.

You can contact customer service at Peavey to see if they have a bulletin to convert the amp to consumer input levels, I don't recall one myself.

You could get an inexpensive EQ unit between the amp and the signal source, and leave it flat, but either goose all the sliders up a couple decibels, or leave them centered and turn up the level control on the EQ.

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Re: CS800x - quieter fan and input sensitivity

Post by DaleMurray » Tue Sep 08, 2020 10:26 pm

Thanks for the reply.

Some fans have different blade shapes, counts, etc, that can affect noise and CFM. Over the years I have purchased various 12v fans designed to be quieter while retaining CFM. I have never looked for such features in 120v fans. Since I initially wrote this post a few days ago (it took several days before it was actually approved) I did a bit of searching and there are options available.

The fan is definitely not stuck on high, I connected it to mains power and it was much faster.

The original fan has a large central hub with stubby flat blades and all metal construction. It makes sense they would use such a fan, noise is of little concern when powering a PA system, durability and reliability are of primary concern.

Turns out I already had a 120mm 120v fan on hand that is much quieter than the fan that came with my unit. Its glass fiber reinforced nylon construction with longer swept blades and a smaller central hub allowing more air to pass. I already swapped out the fan and it is much quieter.

I have the original fan completely intact. If I ever sell the amp the fan will be included.

Now that the fan is quieter I need to address mechanical noise coming from the transformer. First I'll check all the hardware to make sure nothing is slightly loose and vibrating.

As for line level input, I can look into that a bit on my own.
My gripe about the input levels is quite foolish, honestly. I simply had to pull down the output to my L&R amp by 1.5db as measured by my calibrated mic.

What is nice, I bought this cheap enough that if I screw it up horribly I will not be terribly upset. It would suck but its not like I spent several hundred on it.

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Re: CS800x - quieter fan and input sensitivity

Post by Dookie » Thu Sep 10, 2020 7:25 pm

How are you feeding the Inputs? XLR Balanced inputs or 1/4 inch unbalanced inputs?

2 things to consider.

If your going in with Unbalanced inputs there is a 6 db drop in input sensitivity. I believe it is +4dbu at 4 ohms for rated output per channel with Balanced inputs so unbalanced would be in the neighborhood of +10dbu for full rated output.

2nd thing is the XLR inputs on the CS800X are not the Standard wired inputs.
Normal XLR in is Pin 1 ground, Pin 2 Positive, Pin 3 inverted input.

The CS800X has Pin 1 ground, Pin 2 inverted, and Pin 3 Positive input. Pins 2 and 3 are reversed compared to the standard pin setup used. The issue with this is the CS800X has Quais Balanced inputs. Pins 2 and 1 are connected together with a circuit. If you put the standard XLR input into them then Pin 2 and 1 are grounded together and it gives you a loss in input sensitivity and sound quality. If you use the XLR inputs be sure to use a cable that puts ground to pin 1, neg to pin 2 and positive to pin 3. ( a pin 2 and 3 reversal can is available in places too ) This will work much better. If you put a PL2 balancing Transformer can in the back in the PL island then the inputs are True balanced inputs so the input cable can have the standard pin out and work.

When I used CS800X amps for years I always had a cable handy that reversed Pin 2 and 3 just for this reason.


As a side note I used a CS800X to power my Magnepan speakers for a few years. Like you I got tired of the fan noise. I built a enclosed box and lined it with egg create foam kind of stuff. I turned the amp so you'd be looking at the left side of it and the front of the amp was on the right side. I put a hole in each side for air flow. There is a transformer on the right front side of the amp with a few vent slots in it. It is normal for this to get quite hot. I left some room for venting there. I had the egg create so it made the air only flow from the input side to the output side with the holes in the box. I had thought about a box with its own fan on the back and again controlled airflow so it had to go from the back of the amp to the front. Never go around to it though. I agree its a noisy fan for high fi use. :(


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Re: CS800x - quieter fan and input sensitivity

Post by DaleMurray » Fri Sep 11, 2020 7:59 am

I am using unbalanced input.

As for the noise, I have a couple options:
Move the amp from my rack to the floor under the couch; that should my is a bit quieter. My one reservation is due to cat fur; I fear it getting inside the amp. I may have a solution for the fur, too. I have some foam filter material I've used for servers in nasty environments to minimize crud getting inside them.

The foam filter material is about 1/4" thick and allows air to pass through with minimal resistance. A couple layers of that should make it safe from fur and may have the added benefit of reducing some of the noise coming out of the tunnel.

I really appreciate the thoughtful response.

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