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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

Showing 5 responses by smrex13

smrex13 OP
645 posts
 
As far as I have been able to determine, the buzz is exactly the same regardless of where I plug it in, what's plugged into it, and whether it's through headphones or speakers. When I start it up there's no buzz for the first few seconds, and then the buzz begins. It sounds like the coils in a toaster oven heating up, for lack of a better description, but it stays constant for as long as the amp is on. I have tried two sets of tubes in it as well.

Any more thoughts?

Thanks,
Scott
smrex13 OP
645 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.
smrex13 OP
645 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
smrex13 OP
645 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!
smrex13 OP
645 posts
 
Thanks for all the suggestions and feedback. I'll try to answer most of the questions here. I haven't had the chance to listen to it in a friends system yet.

1. Yes, I send the tubes with it for the repair.

2. The level of the hum does not change when the volume control is moved.

3. The Emotiva DC Offset strip did not make any difference.

4. Yes, it buzzes with no sources plugged into it.

5. I have another SE tube amp (Musical Paradise) that has no hum issues when in the system.

6. Yes, the hum can be heard both at the amp and at the speakers.

7. I'm going to try to hook it up today in various places in the apartment with just headphones to see if I get the same hum everywhere.

8. I can't tell whether the hum is coming from the power or output transformers.

I'll experiment a little more tonight…

Thanks again,
Scott
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