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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
mapman's avatar
mapman
15,679 posts
 
Once its determined if teh ground is a problem or not, the next regression test would be to change one tube at a time and listen for differences. Of course, one must have spare tubes to do that. I always keep at least one spare tube around for each in use in my system so that when teh time comes (and it inevitable will with tubes) to regression test for tube related issues, it can be done.
mapman's avatar
mapman
15,679 posts
 
Also check to see if there are any nearby electric devices that generate EM fields. ANy power consuming appliances or devices nearby or on the same circuit with large power transformers, like airconditioners, refrigerators, etc. are prime suspects. Also flourescent lighting and dimmers are often sources of noise.

If any such devices that might be the casue are identified, then look for ways to both physically and electronically isolate your hifi from those external sources of noise.
roxy54's avatar
roxy54
2,651 posts
 
Smrex13,
Al and everyone else have made great suggestions and I have nothing to add, as I don't have the expertise anyway. I did notice though that you said in your OP that you thought that hum was part of the SET experience. I would say don't lose heart yet, because that has not been true for me. My SET is quieter than my previous solid state amp.
Good luck in solving the problem.
smrex13 OP
423 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
rebbi
1,319 posts
 
Scott,
I know this is cold comfort, but like Roxy54, I have a SET amp - same one, the Audio Note Kits Kit 1) and it's dead quiet, no hum at all. So you certainly should not be getting any hum with this amp, at least not because it's single ended.
I know first hand that problem solving can be tricky and frustrating but you'll figure it out and, as Coincident's customer service is said to be first rate, I've no doubt they'll stand behind you.
FWIW, I had a nasty ground hum for years in my analogue side that I was certain must be due to a problem with my Bottlehead Seduction phono preamp, which I also built from a kit. Turns out that the problem was a broken ground wire in the tonearm cable of my turntable. Local service tech fixed it and tightened up the tonearm and now the hum is completely gone. So, try to be both patient and persistent!
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