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Reviews Categories | Power Supplies | MFJ-4125 Help

Reviews Summary for MFJ-4125
MFJ-4125 Reviews: 73 Average rating: 4.2/5 MSRP: $100.
Description: MFJ-4125 13.8 volts 25 amp switching power supply
Product is in production.
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WB0FDJ Rating: 4/5 Jul 4, 2013 08:09 Send this review to a friend
Ok, now it's quiet!  Time owned: more than 12 months
Update: I got over being lazy and did the fan mod, putting a 100 ohm resistor inline on the red power lead to the fan. The noise went from very loud to "whisper quiet" while sitting in front of me on the operating position and it still seems to move enough air. I plan to use this for my QRP and low watt rigs. Still recommend it for it's outstanding low RF noise, size and cost. Hey it's MFJ, the first thing you do when you buy their stuff is warm up the soldering iron!
VE3LFS Rating: 4/5 May 26, 2013 16:41 Send this review to a friend
Nice unit.  Time owned: 0 to 3 months
Agreed with most other reviews here. The unit works good and causes no RFI on any HF bands that I could see. Only things I would change is the power connectors on the front seems silly to me. And the fan is on all the time and it is a bit loud. But a simple mod should be able to fix that so I can't complain.
K1TWH Rating: 4/5 May 13, 2013 13:56 Send this review to a friend
No Hash, solid 13.8VDC  Time owned: more than 12 months
OK, the fan is noisy. I placed a 60 ohm 1W resistor in series, and the supply stays cool and the fan noise is very tolerable. No HF hash from 160 through 6M. Can't hear a single birdie, so I really didn't mind doing the mod on the fan. I dislike the main terminals being on the front panel, so between the terminals and the fan noise this supply slipped from '5' down to '4'. Tom Howey WB1FPA
KG4RUL Rating: 5/5 Mar 9, 2013 11:38 Send this review to a friend
No Problems at all  Time owned: more than 12 months
I have purchased eleven of these power supplies over the last few years, in the "P" version with the PowerPoles. No problems in any of the applications they are being used in: powering the all-band radio in my GoBox; powering an all-band radio at our EOC; powering radios in Go-Kits for American Red Cross Shelters; my bench supply. The fan is about as noisy as the ones in some of my desktop computers or the linear Kenwood suppply that I use with a TS2000(X).
AK4ZF Rating: 5/5 Mar 9, 2013 09:17 Send this review to a friend
Nice Power Supply  Time owned: 0 to 3 months
Some folks complain of the fan noise but it doesn't bother me at all. I have heard computers with more noise than this unit produces. I like the size and weight of it and it seems to put out all the power I need. I'd recommend it.
WB0FDJ Rating: 4/5 Nov 3, 2012 10:11 Send this review to a friend
Wake the dead....  Time owned: more than 12 months
Great supply. No hash that I can find. Small. The fan, advertised as "whisper quiet", can probably be heard in the next county. I put on a carpeted floor, under the desk and I can still hear it with the headphones on. Might do a mod but until then it's a backup. That said it otherwise does what it's supposed to do.
KW4H Rating: 3/5 Apr 29, 2012 07:19 Send this review to a friend
Incredibly noisy  Time owned: more than 12 months
I've had a MFJ-4125 for several years, and use it on the bench in the garage for testing gear, as a backup supply for the shack, or for portable use. It puts out clean DC power without any noticeable RF hash, but this supply is definitely NOT worth the "5" rating that some folks have given it. At best, this supply is a "3" rating (which means it's "OK"). The reason for the "3" rating is the truly outrageous amount of noise the fans in this little box put out. I don't object to the noise when it's in the garage or when out in the field, but it will eventually drive you nuts in the shack. MFJ has obviously sold a lot of these and they do perform well as a supply -- just be prepared for the noise!
VE7IG Rating: 5/5 Feb 12, 2012 22:33 Send this review to a friend
Excellent switching PS.  Time owned: 6 to 12 months
I have two of these now. One is the standard 4125 and the other is the 4125P with the power pole jacks. Both are completely rf-noisless, small and lightweight for travelling and as I use a headset I don't hear any fan noise. I have tried other switching power supplies and they were always too noisy for HF use. These are quiet on all the HF bands.
QRPNEW Rating: 5/5 Mar 29, 2011 04:27 Send this review to a friend
Noisy Fan  Time owned: 3 to 6 months
This power supply produces no noticeable RFI, which is great. It is also very energy efficient in standby.

The down side is that the fan is very noisy. It is by far the loudest fan in the shack. The only other fan that is noisier is the linear amplifiers blower.

The fan noise is very noticeable and its even louder than my tower PC which has a heavy duty 1200 watt supply in it.

If you can live with the noise its a great supply.

The only thing that would have made it even better is the ability to trim the voltage a bit higher to allow for voltage drop from things such as protective diodes.

I was pleased with the general wiring and quality of this MFJ product. Certainly a quality product which is made in Taiwan rather than a sweat shop in China with poor quality. The casing holes lined up and seemed to have good quality threads rather than the usual poorly drilled and aligned holes like on other MFJ products.

Anyway thanks MFJ for a well designed decent product that has quality and is well constructed. If anyone knows of a power supply from MFJ that has a silent fan please let me know. I am back to using my linear power supply since i cant stand the fan noise. I will use it as a backup and maybe mount it somewhere that will hide the noise.


K0FTB Rating: 5/5 Jan 9, 2011 20:12 Send this review to a friend
Good but noisy  Time owned: 0 to 3 months
Most of the time my xcvr is just on for listening so I installed a minimum modification fan switch to my MFJ-4125 power supply. There is a sunken 110/220 Volt select slide switch on the rear that I certainly do not need and I just happen to have a direct replacement in the junk box with a handle on it. I use it as a fan on-off switch to reduce dust build-up inside. The old switch is wrapped with tape to prevent shorting and is tucked down below in a very convenient space that was just the right size and location. I also added a 100 Ohm resistor in series to the fan that really quiets it down so I now have the best of both worlds. If one does not have the correct slide switch, the wires can removed from the original switch, permanently shorted together, taped and tucked inside. Then the original switch can be used to control the fan but will not be as easy to use as one with a handle. Of course a thermal control is the best option and would not be that much of an extra cost at the factory which I would gladly pay.
73 K0FTB
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