Russ R New to CJ just bought a MF2500A not here yet

[Rrroberts44]

Hello all,
Been into audio for 50+ years. Started young with Klipschorns and Yamaha CR2020 then CR3020. Then Yamaha separates CX1/MX1, Aragon 8008BB/Aurum pre, Pass Labs X250/X1 preamp then XP20/ X250.5 then some Mac stuff bought and sold many amps/ preamps and then retired and decided to downsize. Had a Schiit Freya plus for a while recently, Then a Mac pre C47 and the MC152 amp which didn't give me the full sound I expected. Did my research on older CJ stuff and found the MF2500A amp to go with my Lyngdorf DPA-1 preamp and Aerial 10T''s. Anyway there were others along the way but I do hope the MF2500A will give me the smooth listenable sound I and searching for. It will be here on Sat. so I will see...Thanks for reading my rant and will post my thoughts after it arrives. Russ

[admin]

Welcome to CJO, great to have you with us.

Sounds like you have a lot of experience with many different kinds of gear over a long time. I am very interested in what you will think of the MF2500's. It's a great amp and I am sure you will enjoy the sound. Again, welcome to CJO and congrats on the purchase. Let us know what you think when you get the unit set up and have a little time to put some listening time on it.

[AnotherJohnson]

Good luck with the search for the sound. I’ve enjoyed several of the CJ solid state amps over the years. The MF2500A is very capable. It’s always fun to try new things.

[Rrroberts44]

Hello all,

Well I did receive the MF2500A and fired it up yesterday. It would seem to fulfil all the expectations I have for it and sounds as good as all have said. There unfortunately is an issue with the amp. It looks as new as can be. It produces a hum when turned on that is quite audible when in the listening position. The hum does not come in thru the speakers at all only from the amp itself. I looked thru the forum some and did see a post when someone suggested that the rubber feet harden with age and putting additional isolation under them helps. I do have some isolation pads made of 2 rubber layers with cork between them and placed those under each corner. I would say this did lower the sound maybe 20% but it is still audible enough to be troublesome. The hum seems to be a vibration against the amp and the wood platform in my audio rack. I did call CJ to talk about this but it was after hours Fri Pac vs east coast time issue but will talk to them on Mon. I think it could be some type of transformer hum issue. I tried a different outlet inc. an extension cord several outlets apart on another circuit but no go. Tried a ground isolation plug to float the ground again to good. My audio rack has two 20 amp separate circuits adjacent to each other and I have swapped them around as well and no change. Tried different interconnect cables, unplugging everything but speaker cables, diff. speaker cables etc and no change. Again the sound out of the speakers is not affected and the amp sounds just fine....any ideas?
Thx in advance
Russ

[AnotherJohnson]

If it is mechanical hum from the amp, it’s a vibrating transformer.

Unplug it. Let it sit for an hour to allow the caps to discharge.

Take off the top and tighten the screws that hold the transformer in place.

It is possible that the insulation or glue has failed. If tightening the screws doesn’t help, you may need to have it rebuilt or replaced.

[admin]

Agree, this sounds like a transformer vibrating.

[Rrroberts44]

Thanks guys that is what I thought as well...I will discharge the amp with a wait period and cross fingers and hope it just needs tightening...

[roberto]

Hola, unplug i5 from the mains AC...then retighten all 4 screws. This will bring the hum down. I have another trick to bring down the buzzing hum from the amp. Get two pine wood logs, use only this wood due to the ability that the pine wood has to absorb the vibration. The size of the logs should be 2 X 2 X 13 inches. Position the logs under the amp in a such way that they do not touch the feet of the amp, and place one at the left side and the other to the right side, touching only the chassis of the amp. This tweak is very cheap and really works. Please tell us your findings.

Happy listening!