Ampex MX 10 Hum

[bwb011]

I have a noise problem with my Ampex MX 10 that is driving me absolutely nuts. I had been using my MX 10 for years with no issue, until a channel died a few months ago. I decided to take the preamp to a very highly regarded tech here in LA and since he gave it back to me ($$$$$ later) it has been making a loud 60 cycle hum plus some other noise. Everything else about my studio is exactly the same, I've isolated all the variables, and I cannot get rid of the hum. At the tech's shop the preamp is quiet so it's looking like after his work the preamp is now sensitive to some sort of power issue at my studio that it wasn't sensitive to before.

I'm so upset I spent soooo much money and my preamp is less useable than it was before. Does anybody here have any kind of guidance?

I attached a short clip of the sound the preamp makes in case that's helpful. Any insight would be really appreciated! Thanks!

 

[vintagelove]

I have a noise problem with my Ampex MX 10 that is driving me absolutely nuts. I had been using my MX 10 for years with no issue, until a channel died a few months ago. I decided to take the preamp to a very highly regarded tech here in LA and since he gave it back to me ($$$$$ later) it has been making a loud 60 cycle hum plus some other noise. Everything else about my studio is exactly the same, I've isolated all the variables, and I cannot get rid of the hum. At the tech's shop the preamp is quiet so it's looking like after his work the preamp is now sensitive to some sort of power issue at my studio that it wasn't sensitive to before.

I'm so upset I spent soooo much money and my preamp is less useable than it was before. Does anybody here have any kind of guidance?

I attached a short clip of the sound the preamp makes in case that's helpful. Any insight would be really appreciated! Thanks!

Hello, the first step is to find out what he did to it (assuming you’ve made him aware of the problem already).

Was it shipped? Fed ex’s tech department is well known for what they do to amps…

 

[bwb011]

Thanks for your feedback. I dropped off and picked up the unit. No Fed Ex involved here but I definitely believe they are no friend of tube preamps haha. After I heard the preamp making noise in my studio I brought it back to him and he couldn’t replicate the issue.

He added two triad a67j transformers to the outputs and wired for balanced output. Replaced 4 can capacitors and 5 axial electrolytic caps. Added IEC connector.

 

[scott2000]

I brought it back to him and he couldn’t replicate the issue.

Have you tripled checked something hasn't happened on your end? It's not unheard of for things to come loose in cables, power strips deciding to get wonky, etc....

 

[vintagelove]

Thanks for your feedback. I dropped off and picked up the unit. No Fed Ex involved here but I definitely believe they are no friend of tube preamps haha. After I heard the preamp making noise in my studio I brought it back to him and he couldn’t replicate the issue.

He added two triad a67j transformers to the outputs and wired for balanced output. Replaced 4 can capacitors and 5 axial electrolytic caps. Added IEC connector.

Was it a 2 prong cable previously?

 

[Bo Deadly]

He added two triad a67j transformers to the outputs and wired for balanced output. Replaced 4 can capacitors and 5 axial electrolytic caps. Added IEC connector.

Was it previously 2 prong? Temporarily try an earth ground cheater plug adapter:

It could be that something you have plugged into it now has a an earth ground path that it didn't have before and you're picking up some ground noise from that for some reason.

Otherwise, standard procedure for diagnosing noise issues is to unplug everything but the power cable and the output to a high quality differential input like a modern USB audio interface that will allow you to listen, terminate the inputs with 100 ohms or so and then listen. If the hum goes away, clearly the origin of the noise is external (although the problem could easily still be internal with respect to how connections are wired). If the hum does not go away, the problem is definitely internal and you'll need a more specific plan. Or it could be that the hum is reduced in which case you have multiple problems which would not be unheard of with an old piece of gear like that. Also note if hum changes when adjusting levels.

 

[mrtnasty]

I noticed a hum / buzz on my Mx-10 (with no mics plugged in) on channel A but not B. I noticed there was a ceramic 0.05 uf cap that had was pushed near the rectifier diodes on channel A, and it was very sensitive to interference. I pushed it away from the diodes and the buzz reduced. I plan to replace the cap, as I believe it has gone bad. Maybe this info will help with your buzz problem too.