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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
dmarkov
29 posts
 
May I suggest you physically move the amp away from any transformers that can interfere with each other.
Also make sure it is indeed the amp. But start with moving various components away from each other, far away if needed, see if it changes the hum level. You can place the nuce and pretty later.
There are 2 thing: noise and hum. Hum is the 60 hz AC hum (50 hz in Europe). Is it hum or noise you have? I could help out more but I have some questions.
almarg's avatar
almarg
8,673 posts
 
Sorry to hear of these troubles, Scott. Some questions:

1)When you sent the amp to Coincident, did you send the tubes with it, or might they have tested it with their own tubes? If the latter, based on my experience with other amps a possible cause or contributor to the problem might be heater-to-cathode leakage in a tube, especially the 6SL7's.

2)Did the Emotiva DC offset remover which Mikirob suggested in your previous thread on this problem make any difference?

3)In your previous thread you indicated that hum was being emitted both directly from the amp and via the speakers. Is that still the case?

4)If hum is still being emitted directly from the amp, can you tell whether it is the power transformer or the output transformers that are humming?

5)Is the hum through the speakers present when nothing is connected to the inputs of the amp?

6)Does the hum through the speakers vary as you change the volume control setting?

Regards,
-- Al
seikosha
205 posts
 
Really feel bad for you that it's still giving you issues. The only thing I would add that Almmarg didn't already cover is that if it's possible, try it out at a friends house just to make sure it's not something inherent to your location.

Good luck!
mapman's avatar
mapman
15,679 posts
 
Grounding problem of some sort?
mapman's avatar
mapman
15,679 posts
 
People go down a unique path with tube amps including SETs.

I would hope the vendor is proactive and goes out of their way to help resolve issues. Given the financial investment in a somewhat rare and esoteric technology, customers should not have to rely on public forums for answers.

Customer support is always key for any large investment, but even more so when the technology is more unique and might require special knowledge and expertise to deal with it effectively.

Something worth keeping in mind as one chooses their path through this sometimes complex world of hifi sound and tachnology.

I suspect Coincident will be a good provider and do whatever they can to help resolve the problem. Keep us posted. I am very interested in how different companies I am less familiar with handle customer service.
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