MV60 transformer hum

[4thtimeaudiophile]

I am getting some "mechanical" hum from the transformers in my MV60 power amp. I have the identical issue with my MV45. I resolved it, sort of, by removing the cage on the MV45 and running it with the tubes exposed. Since the MV45 is my "backup" power amp, it does not get used regularly. But the MV60 is my everyday amp. I can live with it since it is not hum in the speakers. The MV60 is very quiet electrically. I was just wondering if anyone had any ideas about a quick fix to quiet it down a bit

[admin]

Have you tried tightening down the transformer screws? Not too much, just a little. If that doesn't fix it, the transformer may need to be replaced to get rid of the hum.

[Truth71]

Sometimes I’ve had that as a result of DC voltage on the line.
There are a plethora of devices/designs available to filter that out. In addition to equipment designed for that purpose, many “power conditioners” have that capability .

[admin]

Sometimes I’ve had that as a result of DC voltage on the line.
There are a plethora of devices/designs available to filter that out. In addition to equipment designed for that purpose, many “power conditioners” have that capability .

If you think it's truly a main power line issue, I would try to take the MV60 to another house and see if it is still happening. It would be a cheaper experiment than buying expensive power management solutions just to see if that is the problem.

[roberto]

Hola Truth71,

Admin said to tighten the four screws that secures the cage of the transformer. It is a very good advice. The power transformer is made with a lot of metal sheets. Sometimes hum is due to these metal sheets that vibrate with the 60Hz of the AC line frequency. Retighten the screws will make to have almost dead noise vibration. These metal sheets are bonded with a special lacquer and due to time, the lacquer adhesive property is lost. I will not harm if you apply enough force to have a well tighten screws.

I hope this will solve the unwanted hum.

Happy listening!

[4thtimeaudiophile]

Thanks for the good advice. I will work on tightening the screws. I just hope that the transformers are not beginning to delaminate.

[roberto]

P4thtimeaudiophile,

I am confident that it will work. Please keep us posted how it went.

Roberto.

[4thtimeaudiophile]

I removed the tube cage and the hum went away. I re-installed it and tightened it down good. There is just a bit of hum but you have to really listen for it. Thanks to everyone's input, I have a lot more insight into these types of problems.

[admin]

If you think the tube cage is somehow involved and but you don't want to have it removed, you can try putting some thin plastic washers tween the cage and the screws. It would decouple the cage from the body and it should cost less than a dollar to try it.

[4thtimeaudiophile]

Good idea with the plastic washers. I know that I have something like that. They could be teflon or delrin. There are other materials that I could try. My concern is that it may cause an alignment problem with the two allen head screws that connect the cage to the front panel on the left side.

[admin]

Try to get those really thin soft ones that compress. I'm not sure what exact material they are made from but I know they have ones which are very thing so hopefully don't present an alignment problem.

[Big Dog RJ]

On the MV60/SE, the trannies are housed separately under a metal cover, like nearly all of CJ's newest amplifiers. Every vintage amplifier of CJ and a few of the Classic series had their trannies exposed, hence they weren't housed separately under a fully enclosed metal cover.

So, in the case of the MV60, those trannies aren't exposed... tightening the screws is not as easy as one thinks! You have to open that cover and that can only be opened from the inside... it's a bit tricky. This is not the tube cage cover I'm referring to.

Another note: CJ installed these full metal covers solely for one purpose, and that was to minimise transformer hum!
If your MV60 is humming, and you could hear this even through that protective metal cover then there's another issue.

With both the versions I had, the last one being the MV60SE fitted with KT120's, was very quiet! Although there was one minor quirk... when shutting down the MV60SE, it would cause a dull "thump" from the speakers, even after the preamp was in Mute. CJ advised me at the time that this was normal...high voltages suddenly getting shut down. However, it never happened with any other CJ amps that I've had, only with the MV60/se, must be a special thump!

Like I said, the metal cover separately housing the trannies was used to quieten things down... so if you can still hear a hum, that needs to be looked at. I would not tolerate Any hum! Not even if it's very slight...

Just my 50cts worth.
Cheers, RJ

[4thtimeaudiophile]

I have never removed the rear transformer cover on the MV60 as there really never was a need to. Even though I have a mid-range hearing loss, being a discriminating listener has taken me in the direction of listening for nuances (except for my wife's voice, which is not a nuance). At my last job, we dealt with buzzing E-I solenoids at times, which truly was an annoyance. Although I like to dive into problems, I can work at minimizing the mechanical hum. If there is a small amount there, I can tolerate that. I am truly grateful for the ideas and suggestions that I have received from the fine folks here in this forum.

[Big Dog RJ]

Ok mate, no worries. Sounds like you've managed to figure it out, just as long as it doesn't interfere with the music! That's the main thing.
BTW, do you happen to get that dull thump when shutting the MV60 off? Or maybe this was a case only with the MV60SE version... I don't know. It's a funny thing though and only happens on the MV60 series. I think it also happened on the MF2550SE that I had, similar dull thump when shutting off.

Must be some Fairies in my head causing those dull thumps...
Cheeers mate,
RJ

[4thtimeaudiophile]

I am not sure if I am hearing the dull thump as you describe it. I am hearing something as the power supply fades into oblivion. Whatever it is, I don't seem to be bothered by it. Like most of us, at some point in our years of listening, we have heard much worse come out of our amps. This is not limited to, but it includes bad source material and awful coloration from preamps.

[Redver]

Hi Big Dog RJ please excuse me contacting you this way, I need help with my Conrad Johnson MV60SE, something has blown, burnt underneath, is there a circuit diagram so I can identify the component/s. I am up near Newcastle NSW and only got the amp last year hardly listened to it and it’s failed on one Chanel. Kind regards, Nick

[4thtimeaudiophile]

I may have a schematic for this. Otherwise, there may be one available here on this forum. I will see what I can find out. You have the "SE" version. So, there is a slight difference between your amp and mine. I quick suggestion, if you have not done so already, is to take the bottom cover off. Then, look for any apparent physical evidence.
Best regards

[Redver]

Hi 4th time, My electrical friend has the amp, he said it looks like there is a burnt component, I’m going to his house tomorrow and will take photos. I’m interested to see inside. I do hope you find a schematic for the amp, much appreciated.

I’ll post here any findings. Thanks everyone.

Regards, Nick

[roberto]

Hola
Pics will tell us more sometimes than words. If something is burned, usually is the bias resistors of the power tubes. Also the location of it tells that you have right there a faulty power tube.
Please keep us updated.

[Big Dog RJ]

Hi Big Dog RJ please excuse me contacting you this way, I need help with my Conrad Johnson MV60SE, something has blown, burnt underneath, is there a circuit diagram so I can identify the component/s. I am up near Newcastle NSW and only got the amp last year hardly listened to it and it’s failed on one Chanel. Kind regards, Nick

G'day Nick, so you're up in Newcastle. That's a nice area in NSW. Apart from the NC Knights, I reckon the Melb Storm are a better outfit! Ha, there goes my NRL madness...

The MV60SE is not a complicated amp / design and any skilled electronics tech will be able to help out. If for some reason he can't figure out the problem or fix it, there's always David up in QLD who can very easily sort it out. David is the CJ importer for Aus and is always available to help out, just a phone call away. Since he's up state though and sometimes shipping the unit out of state that far doesn't appeal to many, they end up sending their gear to my long term trusted techie who's in Melb.

In any case, since the amp is now being looked at by your local tech, I'm sure he'll find the issue sooner or later. Could be a resistor or two from perhaps a failed Output tube or fuses or something like that... who knows but it's definitely not difficult to assess. Also, once it's sorted out just make sure all the fuses are of correct value/ type and the two large ceramic plate fuses are of correct value and type.

***This is most important because these large plate ceramic fuses are the ones that protect the Output trannies from the event of an Output tube failure***

These large ceramic type fuses are quite pricey, around $50 -$60 each... so they're not regular type fuses. So make sure all that is in order and the correct type of Output tubes have been installed in your SE version. Once that's sorted out, make sure you properly bias each Output tube according to spec and the MV60SE should be good to go!

Let us know how it goes and what the problem was. Always a learning curve.
Cheers, RJ