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extracampine

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  1. I've not frequented this site as much recently and am therefore a little out of the loop - but why was the name changed from Computeraudiophile to Audiophilestyle? I think I prefer the former as it is a clearer description of the site.
  2. Still trying to work out if this is tongue in cheek or not....?
  3. Yes, you really needed a fairly silent environment to pick up the hum (with no ambient noise in the background). I had worried about there being too much noise at the Lampizator testing lab and had mentioned this to them in my first email. But that is how I (and likely others) like the listening room - silent! From some of the comments, I'm surprised that this isn't a more recognised issue. It's not that I have super-sensitive hearing or that my room is an anechoic chamber or anything!
  4. A final update for anyone that is interested or experiencing a similar problem. I ended up returning the DAC to the manufacturer (Lampizator) a second time. This time they replaced the transformer with the one they are using in their newer DACs. I had thought that the noise was coming from the choke (what I had initially thought was a EI transformer), so was somewhat skeptical that replacing the toroidal transformer would make a difference. So on unpacking, inserting the tubes and making the various connections at the rear, with trepidation I pressed the power switch. And....BOOM the DAC blew up!! Just kidding...THERE WAS NO HUM!!! Hallelujah! Or, more accurately, there was a very low level of hum which is in keeping with the other audio components and not audible once a foot or two away from the DAC. So after a (fairly) long road, this problem has been solved. Thanks to all for the advice given
  5. OK, I had it checked by a local electrical engineer - he seemed to think that the level of transformer hum was within manufacturers tolerances.
  6. Conducted a further experiment. I plugged the DAC in in a music shop some 35 minutes drive away to see if it would still hum whilst on a different part of the grid - and it did. So it would seem to be less likely that it is something else in my house, or the power supply to my house, which is causing the problem.
  7. Interesting! Did you try plugging the amp in somewhere else, other than at your house? I tried it at my work too and the hum remained the same - thus reducing the possibility of something like what you had experienced, I think.
  8. I tried measuring the mains DC with the meter set to a range of 600V DC, but it didn't measure anything.
  9. I have the Sinometer 830B - this one: http://jbryant.eu/pages/DMM.htm I think it has a DC range of 600V, to the left of "OFF" if I am not mistaken?
  10. OK One and a half - I looked back at the post you mentioned. Here are my findings: Black probe to earth, red probe to active: 246V Black probe to earth, red probe to neutral: nothing registered on my multimeter - 0.00V (however the lowest "setting" for AC V is 200V) Black probe to neutral, red probe to active: 246-247V You initially said that it should read 230V. Does this therefore seem quite high?
  11. Yes, I gathered that this was normal and within the acceptable range as far as the transformers are concerned. One and a half - what other measurements would be helpful here?
  12. OK, further to the above - I tested the mains voltage at an outlet in my house with a multimeter and it was reading both 245 and 246 volts.
  13. Thanks for this reply Bob. I don't think I can feel a vibration when touching the case. Although I say that I can hear the hum/buzz from a distance, it is still relatively quiet. Regarding the over-voltage, I am going to use a multimeter to check the mains voltage in the house in the next day or two. You are correct re the tubes - 1 rectifier tube and 4 DHP tubes. I will make sure it is off in future when poking around inside I doubt that it could have been static - the shock was a little too pronounced, and it happened twice. Item B (the transformer/choke) is bolted to the base of the case via 2 of the 4 available bolt points. I will look further into this with a plastic rod as you suggest. Yes, the fact that my Classe amp hums (though to a lesser extent) and my linear PSU (now to a lesser extent also - I think it used to be worse) makes me wonder about my mains. I still plan to measure this as mentioned above, and try the DAC a bit further afield.
  14. Thanks for the ongoing insights here - though some of the technical discussion is a little above my head I have 4 further small findings that might help in the quest to remove the hum; 1. I took the case off (again) to see if the rod that holds the transformer needs tightening or loosening. What I found before getting to that however, was that the casing seems to be contributing to the noise. With the case removed, the noise is definitely less. It is still audible, though perhaps heading towards the level that would not be noticeable from the listening spot. I had tried removing the case before and don't remember a particular reduction in noise, but there you go. So I got some thin rubber pads and tried to insert them in-between the front panel and side casing. Once the screws were again tightened, this did not seem to improve the noise. Flexing or moving the top casing also seems to affect the noise somewhat, though inserting anything in-between this and the base is quite tricky. Either way I did not have the impression that inserting further bits of rubber would likely affect the noise, given my findings with the rubber at the front. 2. Trying again to isolate the area that the hum is coming from, I think it is coming from a different component to what I had expected. I had thought that the noise was coming from the main transformer (a big round thing which I have labelled 'A'), though it appears to be coming from somewhere nearby. The exact culprit is difficult to determine, though I'm wondering if it is coming from the component highlighted in my photo below (which I have labelled 'B'). I'm not sure what this component is but am wondering if it is also a kind of transformer? 3. I noticed that one of the bolts/pillars holding the PCB to the casing appears to have current running through it (if that is the right term) - when I touched it, I felt a small shock. I can't remember if my other hand was touching the casing or not. I also don't know if this is normal/expected or not. The unit was powered on at the time. Maybe I was stupid to be prodding around inside with the power on. I don't know if the other 4 bolts are the same (I didn't fancy testing)! I have highlighted this bolt in the picture below also. 4. I took the DAC to my workplace and plugged it in there. Same hum. It is however only about 3 miles away as the crow flies - don't know if this is relevant or not. Thanks again for the help here.
  15. Don - thanks for the specific suggestion Yes I will look into that. Won't such a transformer dampen dynamics and limit peak draw? Peter - you're saying that measuring DC offset on the mains using a multimeter is not a viable option? Perhaps a more powerful oscilloscope is required for such measurements? I did not try the power amp or HDPLEX on their own, no - I'm mainly concerned about the DAC as that has the most prominent hum. And no, I have not yet tried the DAC elsewhere - what I did do was send it back to the manufacturers (in Poland) where there was no hum found. What I will do in the next few days is try the DAC elsewhere in the UK, first at my work and if it still hums there (it is only 5 minutes drive away) then I will try it further away (e.g. a music shop 30 minutes drive away). If it does turn out to be silent at work I will be pleased as it will be a clue as to the problem!
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