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. |
I have heard of the hum problem with that particular amp, and I believe that it can be fixed. Are you aware that there was an "A" revision also? You should call Conrad Johnson and inquire. That is a great amp. I auditioned it once for a couple of hours, and thought it was extremely musical. |
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. |
Have an iec plug installed and use a better aftermarket power cord. It can also be upgraded to a 2500a by CJ with using better quality caps.
You can also install audiophile grade fuses for better sound. |
Upgrade it to a 2500A if it isn't an A already. The "A" mod improves the amps speed and detail. You have to send it to cj to get the work done but it is well worth it and while it is there they can go through it.
Chuck |
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.
Jeff |
Bad power supply caps cause a slight buzz with older amps thru the speakers. fYI |
A "Shakti Stone" is the modern version of snake oil. The plug will cost a fraction of what you'll pay for the stone, and be far more likely to work. |
When I had mine upgraded it cost $500 plus shipping there and back; well worth it.
Chuck |
I'm seriously anti hum...I've been a serial "ground floater" for years (including pro audio live sound...although with electric bands the musicians may be mildly electrocuted) and even found a NOS "PS Audio Humbuster III" which really knocks out mechanical transformer hum. |
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. |
Is the hum coming from the speakers or the amp? The transformer in the 2500 does have a propensity to hum.If you placed the stone on top of the amp it is probably dampening the cover which in certain circumstances can amplify the hum.
Chuck |
I'm late to this thread, but own both an MF 2500A, & a MF2250 ("non-A"). No hums with either. They're both very musical-sounding amps. I can't tell that the MF2500A sounds "better" than the non-A MF2250, except for the increase in power. And as I recall it's several hundred $$ for the upgrade.... |
