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Update on my Coincident Dynamo 34SE

Hi everyone,

A while back many of you gave me guidance on some hum issues I had with my new Coincident Dynamo. I ended up sending it back to Coincident for service. They said the filter caps were the problem and replaced them. I got it back today, plugged it in, and….the hum started up right away. It is not only just as bad, now it's equally bad in both channels (it was worse in the right channel before). I have to imagine that the techs listened to the amp after changing the filter caps, so perhaps this level of noise is normal?

I'm somewhat new to single ended tube amps, and I know that there is some hum associated with them. However, I can hear the hum from 20 feet away. It makes headphone listening impossible. It's also not going to work for near field listening at my work desk. From about 8 feet away in my listening chair, the hum is audible during very quiet passages and between songs. I guess it's just not meant to be...

I guess this falls under the "live and learn" category.

Scott
smrex13
smrex13 OP
423 posts
 
Another clue - the buzz is now stronger in the right channel. I swapped the tubes from right to left and it continues to be stronger in the right channel. Damn, this is frustrating…I will try it at a friend's house or at work and let you know how it goes.

Thanks,
Scott
mapman's avatar
mapman
15,679 posts
 
Have you tried running a different pair of ICs in from the source as a test?
smrex13 OP
423 posts
 
Yes, I've used multiple ICs. I've also tried just headphones plugged in with no sources/ICs connected, and the hum is exactly the same.
mapman's avatar
mapman
15,679 posts
 
perhaps before a roadtrip to see if a change of location helps....

What does Coincident have to say about it at this point?

Assuming all was well when they shipped it as was indicated, there is still possibility it was damaged again in some way while in transit.

Or there is something about the ground still currently that is causing a problem.

Or something in your source device perhaps? Have you tried an alternate source device for comparison? With different ICs?

Always gotta switch everything possible in and out for comparison in order to isolate a problem best.

It is three prong plug right? Did you try the cheater?

No sense testing anything with things disconnected really. It only matters when all parts are connected. Plus you avoid potential to cause more problems running devices in isolation that might not be designed to do so.
smrex13 OP
423 posts
 
Coincident says it's bizarre and that it was working well when it left their shop. I told them I'd try it in another system at another location to see what happens.

No matter what I try (different sources, different ICs, different outlets, different rooms, headphones, speakers, etc.) the hum is exactly the same in all cases.

Frustrating!
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