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, I love my Dynamo. This is not normal, and I'm pretty sure Israel wouldn't let that amp get back to you without it being right. I don't know what is wrong, but something is certainly wrong. I suggest if you have a friend who has a compatible system, you plug the dynamo into his rig and see what it does. I had bad hum problems with mine that were ground loop related. Once I got that resolved, I had no issues. This is just weird.
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.
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?

-- Al
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!
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.
Are source and amp plugged into teh same wall outlet or known to be on the same electrical circuit in the house?

COnencting components to different outlets/circuits is a common cause of ground related hum regardless of amp type.

if so, try plugging source and amp into same outlet and listen for any difference.

Or as Seikosha suggested, as a test, try a different location and check for any difference. Could be different circuit/room in teh house or another location altogether.
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.
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.
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.
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,
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!
" Yes, it buzzes with no sources plugged into it."

Same noise as with source plugged in (hum) or different (buz).

Buz with no input attached is not uncommon and could be normal.

Hum is not normal should not be considered part of the experience in any case, SET or otherwise.

If not the same noise, could still be a ground related issue when source attached. Are source and amp definitely on the same circuit currently? Both plugged into same outlet would mean yes. OTherwise, even if different outlets in same room, they still may not be.
Concur with Brownsfan. Sorry the Emotiva didn't work for you. I'm sure you will get this resolved. Something weird is truly going on. Good luck and keep us posted. I'm positive Israel Blume will do his utmost to help. Best.
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?

Is the hum just out of the woofer? If so...it is most likely a grounding or ground loop issue. Put a cheater plug on the amp and see what happens. A buzzing tranny is most likely mechanical only and has no impact on noise coming out of the speaker.
Bill (Grannyring), I'm doubtful that it's a ground loop issue given that exactly the same symptoms occur when nothing is connected to the amp's inputs as when a component is driving those inputs. But it can't hurt to try a cheater plug to defeat the AC safety ground, and see what happens.

On the other hand, though, it seems conceivable to me that these symptoms might result with some designs BECAUSE there is no safety ground, due to a wiring problem in the house (or in this case, the apartment building). And also if the zero ohm connection that should exist at the breaker panel between AC safety ground and AC neutral is a significantly higher impedance, due to corrosion, looseness, etc.

Therefore I second Seikosha's suggestion of trying the amp at a friend's house, if possible. Or at least checking the outlets with a multimeter or an outlet tester. Post back, Scott, if you'd like further details on how to do that.

I'm assuming, btw, that the outlets are 3-prong types. Let us know if that is not the case.

Finally, regarding what appears to be a suggestion above to try the amp with no speakers or headphones connected: As most are aware a tube amp having output transformers should not be operated without a load. Otherwise there is a risk of damage or degraded long-term reliability to the output transformers and/or the output tubes, as a result of "inductive kickback." Although it is unlikely (but not totally impossible) for that to be a problem if no signal is being put through the amp.

Best regards,
-- Al
I have had problems like that a couple of times. One I traced to faulty RCA plugs.
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.

Have you tried running a different pair of ICs in from the source as a test?
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.
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.
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.

I spoke with my friend who is a tech.
The Coincdence amps use the Excellent Star grounding scheme
Which grounds at several avenues. This IMO is a excellent way to go.
If there still is a hum then another item in the chain needs the ground to be lifted . With the ground lift box from emotiva try plugging that into other equipment.Possibly just plug the amplifier in
Seperately. Since it only has one volume pot for a pre . If using a preeamp
Then hook up through rca and turn volume to full on the Dynamo and just back off slightly ,
plug both in same circuit. I run dual isolated circuits from the breaker box
With Audiophile Copper,Gold sockets. Please remember unless you are using a Regenerator which is the best - New power, then any factories in your area as well as noise from lights frig can sometimes dirty a signal
Bleed into the house circuit.