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Old 24th June 2012, 01:45 AM   #1
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Default help

im hoping someone out there is a tech and my have some insite on a problem i have..
my perreaux r200i started to develop a static hum in the left channel (with no input just power supply and speakers connected..changing power supply and power points,location house etc didnt help..so sent it back to perreaux where they tested heard the problem..but then it went away so they replaced some components just in case (what they thought would have been causing the problem) bench tested ok then sent it back..after a day or so i can hear the noise again not as loud as it was before but still there...
now what i have noticed is the channel with the noise is about 7deg hotter than the chan without the noise at the heatsinks... also the transformer on that side is quite audiable even in standby mode (has dual mono)
any suggestions?
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Old 24th June 2012, 07:42 AM   #2
AndrewT is online now AndrewT  Scotland
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Give it away rather than worry about it.
That will make you feel good.
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Old 24th June 2012, 07:52 AM   #3
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geee thanks
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Old 27th June 2012, 06:12 AM   #4
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Default Perreaux-ken?

Your observations suggest a remaining intermittent fault but locating this is not going to be a simple excercise for the non-tech. To begin, you need to measure currents as guesses and impressions of the problem are not likely to help.

Since Perreaux gear is not common, you need to locate and post a schematic so we can suggest likely fault areas. Even so, the likely fault may not be that obvious, regarding 7Deg. temperature difference. This should be verified by a difference in quiescent (idle) current which you should be able to measure as a mV level voltage drop across any of the large source resistors associated with the output Mosfets. I'm guessing this is class AB, not A, as a noisy transformer would not be unusual at high standing class A currents.

Assuming you have no problems finding these power source resistors, it should be a straightforward test to see whether the small temp. difference is actually relevant.
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Old 27th June 2012, 07:57 AM   #5
MarianB is offline MarianB  Romania
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If there are noises in the transformer of that channel then maybe the foult could be in it, so if possible disconect both of the transformers from the board and power them up to compare theyr idle function, voltages; hum/buz ( if any ) temperature after an nour or so of working without any load; and if both the transformers acts about the same than to be sure you could swab them ( if possible ) that way if the foulty channel acts the same with the known working transformer then the problem must be on the board of the power amplifier. An schematic would help.
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Old 28th June 2012, 11:18 AM   #6
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do they test graphs show anything.. one was done befor i got from the factory.. the other done now... IMG_1850 | Flickr - Photo Sharing!
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Old 28th June 2012, 01:19 PM   #7
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Quote:
Originally Posted by boomtheroom View Post
do they test graphs show anything.....
Only that the right channel is slightly improved now at the bass-mid audio end which could be caused by any any number of mods, even new or different spec. electrolytic caps. In any event, distortion < 0.002% is exemplary for a commercial hi-fi amplifier. Most struggle to get <0.02%. However, this tells you nothing about intermittent faults.

The suggestion by MarianB is the most obvious test to find whether the fault lies in a transformer or its wiring but diagnostics require some activity and skills from you as we can't run tests from here. Without a schematic, there is no chance of guessing what is there to consider, so we would have to rely on you.

It seems you are not considering running your own tests on the amplifier or digging around inside so the best advice I can suggest is that as you are uniquely close to the manufacturer, that you go back again and say that you aren't happy with the product. Perhaps this is mains borne noise. If you want to get serious, you can data log the noise with some modern multimeters even and this will show a pattern, perhaps a daily one that coincides with a local power user who is emitting noise on the line or as RF. I would not expect Perreaux to be careless in EMC protection but you never know about product susceptibility until you are faced with specific tests as manufacturers now are.

Now some questions:
  1. How long after turn-on does the hum take to return?
  2. does the noise begin immediately after power-up?
  3. how long after the repair (hours use) before the hum returned?
  4. do the hum and mechanical buzz coincide?
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Old 29th June 2012, 09:40 AM   #8
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1 = always there
2= always there
3 = straight away
4 yes
however they noise it the same as before it went away for repair but only say a1/4 the loudness
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Old 29th June 2012, 09:50 AM   #9
MarianB is offline MarianB  Romania
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I doubt it's just a coincidence that the transformer noise coincide with the amp hum, so i restate my sugestion to check the transformer in cause, disconect both of the transformers to have a good comparison template, and compare everything from the noise of each of them to idle working temperature, idle voltages, same load voltage dropout and so on, only when you make sure both the transformers are in good working condition you can turn your attention to the amplifier board.
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Old 29th June 2012, 09:52 AM   #10
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its only one speaker as well....
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