MF-2200 repair

[AudioDon]

Hi,
I've owned an MF-2200 for a long time, it was my first CJ. It's always had a pretty loud hum through the speakers. I took it a part to do a cap upgrade and decided I didn't have the money to spend on this unit, and so it sat for a few years. I'm now trying to get back at it. I tried some Mundorf Mlytics in the past and the leads didn't work on the board. I needed snap in style. I ended up replacing the Power supply caps with Solen Fast caps which I understand could be very similar to the SCR that were there originally. I powered it up and it's still got the pretty nasty hum that it's always had. Maybe it's just louder with the speaker next to my ear. I was also just using an iphone connected to the main inputs. There's also a pretty loud thump when turning it on or off. I've always avoided replacing the small caps on the board (.5uf 100V) as I was told that "CJ uses good caps". When I was in the unit doing the PS caps I noticed that one of the small caps was leaking, it just wasn't noticeable. Upon closer inspection I see that most of the smaller caps are swollen in diameter. They appear to have been .5" in diameter originally and now they're 5/8", and the ends are stained.

I could use a recommendation for a replacement for the .5uf caps. and there's not a lot out there that's affordable. Mundorfs are $50 each, MultiCap RTX are $25 each. Mulitply x 10 and it's closing in on the value of the amp. I can get a Metalized Polypropylene MultiCap PPMFX for about $10 each. It's either a .47uF or .68uF -200V. Do you think these would work or should I try and find a different Film/foil ? The RTX are Polystrene and tin, probably closer to the original. I thought I would replace the caps and see if the hum is still there.

Any ideas for the power-on thump? I thought about replacing the Orange drop on the power switch, but I'm having trouble finding a suitable replacement.

I appreciate any and all help.
Thanks, Don

[admin]

Any chance that hum is 60hz? If so, it could be a ground loop.

[AnotherJohnson]

It sounds like the MF 2200 needs some serious love ... spa time at a first rate repair shop. It may need more than recapping, but it does appear that recapping is probably a first step.

Frankly, if it were mine, I’d sell it for parts “as is.” I just don’t think it will be worth the cost of repairs.

But ... if I really wanted to save it for sentimental reasons, I’d send it to Tom Brucker at HiTech Service in Nashville. He might be able to get it going again for a few hundred bucks by using “good” parts, but not OEM spec parts.

If you send it to CJ, they may be able to bring it back close to original specs, but my guess is that it would cost more than half of what the unit would be worth after the repair.

[AnotherJohnson]

Any chance that hum is 60hz? If so, it could be a ground loop.

The power on thump is not hum.

It is a sign of further problems... I’ve had this with old Krell solid state gear.

[admin]

Any chance that hum is 60hz? If so, it could be a ground loop.

The power on thump is not hum.

It is a sign of further problems... I’ve had this with old Krell solid state gear.

Agreed, the thump is definitely not ground loop. But he mentions the hum has always been there so it's not something that has developed. That would make a ground loop issue more likely as a cause (for the hum at least).

[Joe Appierto]

I've owned two CJ tubed amps and one solid state integrated and in each case I had a ground loop that I was only able to eliminate using cheater plugs and/or an isolation transformer. I know cheater plugs are frowned upon but they did work for me.

[AnotherJohnson]

I've owned two CJ tubed amps and one solid state integrated and in each case I had a ground loop that I was only able to eliminate using cheater plugs and/or an isolation transformer. I know cheater plugs are frowned upon but they did work for me.

That generally says more about house wiring than the gear.

I assume that by cheater plug you are referring to a 3 prong into two prong adapter.

Back before three prong was expected and before the two prong blades were made different sizes, the owners manuals all recommended that, if there was noise, to flip the plug.

I think this issue of house wiring is probably often in play.

[Joe Appierto]

It could have been or is a wiring problem. It's been the case though in different places I've lived and the hum was present but the common denominator seems to be the incoming cable line. Disconnecting the cable which is plugged into the various systems I've had eliminated the hum. The isolation transformer has done the trick in my current place and the three into two cheater plug is no longer needed.

It may have been the review of the PV-10A by Corey Greenberg that I read but somewhere I had seen that inverting its two prong plug did result in a difference when I had that as my preamp. One orientation was a bit quieter than the other.

[AudioDon]

Hi all,

Sorry I haven't responded sooner. I was waiting for a notification of responses.

Let's see, I'm just going to respond to all of the questions but not in sequence.

There is a thump and a hum. Both of them have always been there but they've both increased in volume. I do have it connected to a cheater plug but I'll try flipping it. I've never heard that. I'll try a different plug as well. I might have been on the circuit with the fridge.

I agree that it's out of my realm of ability for repair. I'll check out Hi tech service, but as much as these things weigh, shipping usually costs close to $150. I'll check with Bill Thalmann as well. I can't afford to send it to CJ. I actually sent an email to them asking for a schematic but haven't heard back.
I'm going to ask a friend who's a local tech, maybe he'll come out of retirement for a friend

I'd rather spend $2-$300 on this then trying to find something else used with unknown problems

Thanks

[admin]

As mentioned above, the thump is definitely not a ground loop. However, for under $10 you can rule out the ground loop as the source of the hum.

https://www.amazon.com/JacobsParts-AFIL ... 594&sr=8-9

Having one of these is a nice tool in the audiophiles toolbox. If it removes the hum, you know it's a ground loop and you can work on removing it from the system.

[AudioDon]

Thanks, I just ordered one. Only $8 with tax and shipping.

Does anyone have a suggestion for a cap to replace the white .5uF 100V? Something similar to what CJ used originally?

[admin]

I've replaced caps in my equipment using solen. You can buy it directly from their site (shipping is from Canada) and many of their caps are available on parts-express for faster shipping.

https://solen.ca/product-category/capacitors/

[roberto]

Hola Chicos,

I am just going to chime a little bit. The question is, why Conrad Johnson sounds right? Because they use the best parts available. These parts are pricy, and if you are going to replaced some caps, buy quality caps, don't look for cheap ones with the same value...look for the best price for the same quality caps...please don't get me wrong, I only try to address the wonderful world of good parts. These parts make to sing very nicely.

Happy listening!

[AnotherJohnson]

The basic problem is that, “it just sounds right” was a fast moving target in the era of the MF2200.

To me, today, the MF2200 no longer sounds right. In SS, the MF2550 and MF2275 both run rings around it.

The used market for the MF2200 is not strong. It is a good starting point for a CJ based system ... until you can move up.

A lot of these 20+ year old CJ components look to me like a game of musical chairs. Eventually someone will be stuck when their sample can no longer be repaired to original specifications. It might still be pretty, and worth curating on some level. But that’s a different hobby compared to finding audio Nirvana.