If it's a ground loop hum there is a pretty easy fix. To test if it's a ground loop hum, put a cheater plug on the amp's plug and see if the hum goes away.
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I used to own a 2500, and I personally wouldn't advocate modding it - it was a great piece to begin with. Incidentally, that hum is probably a ground loop - CJ amps, especially the MF series, are highly susceptible. You can probably kill the hum by using a "cheater" plug to lift the ground. I used one on my amp and the hum disappeared completely - and I continued to use the amp for several years with no ill-effect.
I put WBT RCA jacks and binding posts on my CJ 350. No A-B possible of course but I thought it gave a worthwhile improvement. I would change the RCAs at least; they are not CJs strong point. There are several RCAs cheaper than WBT which are still worthwhile upgrades. I second installing an iec plug.
Thanks for the replies. I read a review of the amp on Steroephile and the reviewer addressed the hum with a Shakti Stone. What the heck is that?
"........One note I should make here: when I first connected the amp, it did hum a little. I checked all of my connections and everything was tight. Instead of experimenting with cheater plugs, which I dont like to use, I put a Shakti Stone on top of the amp, center towards the rear. The hum went right away and all of my listening was done without a trace of hum."
I have already contacted CJ and I am waiting for their response. Anyone have an idea of how much the upgrade to the "A" model costs? I wonder if it's worth it. Should it be given the "once over" by CJ without the "A" upgrade because it is ten years old?
Thanks for your advice.
Thanks for the responses. I am surprised that the Shatki Stone is considered snake oil, since the reviewer on Steroephile used it.....makes me wonder about the reviewer.
Chuck, I talked to the seller of the amp and he said he had both the MF 2500 and MF 2500A versions at one point, but sold the MF 2500A because it seemed to lose the musicality that he enjoyed in the non A version. He told me this after i already bought it, so there is not the concern his recommendation was colored by his wanting to sell the non A version. Can you tell me your experience when you upgraded? What speakers were you using at the time?
I was using Thiel 3.6's at the time along with a premier 16lsII pre-amp. The amp became more detailed and faster while retaining the typical cj 2500 sound. It did require about 20-25 hours of burn in. The non A version smoothed over the details of the music seemingly masking it. I like to hear everything in the performance something my current system does very well(Cary SLI-80F1 / Focal Be monitors).
In the end it depends on what you are trying to improve or what you don't like about the amp.