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  Reply # 1261264 17-Mar-2015 20:07
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Things I would try are:

Shield it, dollar shops have metal sticky tape that you can line the wood with. Make sure it gets a connection to the earthed metal plate.

Put some more caps across the power supply, without seeing the design its hard to know what they have used. You could also add some inductors inline with the power between the bridge rectifier and the smoothing caps.

Power one part of the system at a time off an isolation transformer and see if that helps. Usually can get them dirt cheap on trademe. Friend who was deploying projectors that only worked properly on VGA for some reason had to get some to remove the flickering mess that a ground loop caused.




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  Reply # 1261376 18-Mar-2015 00:17
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networkn:
sir1963:
networkn: Hi There!

I am looking for someone pretty experienced but reasonably cost effective  to help me troubleshoot a buzz I can hear in a home made headphone amp I have been trying to complete for far too long. 

It's been difficult to do this over the provided forums with the supplier, as I have very little free time right and would rather spend it listening to than fixing this AMP. 

If you know someone who may be able to assist. Please let me know. It's AC mains Powered.

Cheers



Quick guesses.
1. Earth loop
2. Not enough filtering of the DC rails
3. Poor Earthing 




I am pretty sure I don't have enough experience to work with information that non specific. All the Voltages are within the margin of error as were the resistances and other than the buzz it sounds wonderful, so I am unsure how to troubleshoot further. 


You are doing well to get any troubleshooting advice considering we still don't have access to a circuit diagram.





 
 
 
 




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  Reply # 1261477 18-Mar-2015 10:20
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You are doing well to get any troubleshooting advice considering we still don't have access to a circuit diagram.


Yup, sorry, I have been trying to get permission to post the circuit, but they haven't replied so I'll assume they aren't that worried about it. Hopefully this is what you need: 






With my laymans understanding of the whole thing, because the Buzz seems limited to one audio channel, could it be an issue with the headphone jack or the red/white input jacks?

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  Reply # 1261502 18-Mar-2015 11:03
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networkn: With my laymans understanding of the whole thing, because the Buzz seems limited to one audio channel, could it be an issue with the headphone jack or the red/white input jacks?

This is the first time you say it is limited to only one channel.  The issue is likely on the input jack of that channel, or the cable to the input jack.  But could also be the valve socket.




You can never have enough Volvos!


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  Reply # 1261506 18-Mar-2015 11:08
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Or proximity of the AC cables to the input wiring or the connections between the tubes. How about some decent pictures of the construction.




Richard rich.ms



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  Reply # 1261550 18-Mar-2015 11:56
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Niel:
networkn: With my laymans understanding of the whole thing, because the Buzz seems limited to one audio channel, could it be an issue with the headphone jack or the red/white input jacks?

This is the first time you say it is limited to only one channel.  The issue is likely on the input jack of that channel, or the cable to the input jack.  But could also be the valve socket.


So is there any way to further isolate without starting to unsolder everything?

I presume this issue must be something that still allows the voltages and resistance checks to come back normal? Is that usual?



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  Reply # 1261574 18-Mar-2015 12:26
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Have you swapped the tubes around to see if the problem follows them?




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  Reply # 1261576 18-Mar-2015 12:28
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richms: Have you swapped the tubes around to see if the problem follows them?


 

The tubes are different sizes and wouldn't fit elsewhere and I don't have spares to try unfortunately. 

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  Reply # 1261921 18-Mar-2015 19:46
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networkn:
richms: Have you swapped the tubes around to see if the problem follows them?



The tubes are different sizes and wouldn't fit elsewhere and I don't have spares to try unfortunately. 


This is a stereo amp isn't it? So surely it should then have a total of 4 valves in 2 pairs of 2. So you should be able to swap them round.

But seriously the death of zen headphone amp will deliver better sound quality. http://sound.westhost.com/project70.htm The only advantage of a valve amp is being able to say "I own a valve amp". The exception being guitar amps.







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  Reply # 1262206 19-Mar-2015 10:38
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Aredwood:
networkn:
richms: Have you swapped the tubes around to see if the problem follows them?



The tubes are different sizes and wouldn't fit elsewhere and I don't have spares to try unfortunately. 


This is a stereo amp isn't it? So surely it should then have a total of 4 valves in 2 pairs of 2. So you should be able to swap them round.

But seriously the death of zen headphone amp will deliver better sound quality. http://sound.westhost.com/project70.htm The only advantage of a valve amp is being able to say "I own a valve amp". The exception being guitar amps.


It has two valves, neither are the same. I am not really interested in abandoning the many hundreds I have spent on this to start another project. 

I disagree with the valve amp comments generally. I have both solid state and valve amps and other than this buzzing noise which I believe is something relatively straight forward to someone with more experience and technical knowledge, this AMP is by far my favourite. 

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  Reply # 1262424 19-Mar-2015 14:03
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There are tubes with 2 sets of whatever in them. Even some with way more.

I tried an amp with that and there was crosstalk and Intermodulation between the 2 sides. Apparently that is what gives different tubes their "character".

Still should be able to swap halves of the tube around and see if it follows. There is 50hz ac sitting in them on the heater so buzz from that is quite common. Also without filtering that supply it will nicely couple other noise to a wire beside it running to the grid for amplification.




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  Reply # 1263534 19-Mar-2015 16:31
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richms: There are tubes with 2 sets of whatever in them. Even some with way more.

I tried an amp with that and there was crosstalk and Intermodulation between the 2 sides. Apparently that is what gives different tubes their "character".

Still should be able to swap halves of the tube around and see if it follows. There is 50hz ac sitting in them on the heater so buzz from that is quite common. Also without filtering that supply it will nicely couple other noise to a wire beside it running to the grid for amplification.


Are you saying I should be able to turn the tube 180 degrees and insert it and see if the noise moves to the other channel? (Should I do both, or just one at a time).

I still don't really get what you mean about the filtered power supply, as I have mentioned many times, there are HUNDREDS of these around without the buzz (Otherwise people wouldn't buy them) and so it's something specific to MY Amp and as I've followed the build instructions to the letter, as best I am able, I am still left
with troubleshooting the issue. Filtering is working around the problem which doesn't normally exist on this device. 

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  Reply # 1263569 19-Mar-2015 17:11
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Each valve has 2 channels.  You can't physically turn the valves around, but you can swap wires on the valve so that a different half of the valve is used for a different audio channel to see if it is an issue on one of the halves of that valve.  Based on your comments/questions, I'd strongly recommend you get someone that knows what he is doing to work on it.




You can never have enough Volvos!


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  Reply # 1263599 19-Mar-2015 17:48
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Niel: Each valve has 2 channels.  You can't physically turn the valves around, but you can swap wires on the valve so that a different half of the valve is used for a different audio channel to see if it is an issue on one of the halves of that valve.  Based on your comments/questions, I'd strongly recommend you get someone that knows what he is doing to work on it.


Yeah, those voltages can bite !

When you get the buzz, does the sound drop out, or is it overlaid, and the audio drops in volume ?

Does the buzz change in volume when the volume control is moved ?

Since i's intermittent, I would really doublw check your eacrthing in the circuit. All those earthing points as disignated with the 3 stacked dashes must be clean and solid, especially if they are connected to any metal bits. And preferably joined at a single point, or at least joined with a good chunk o wire.




My thoughts are no longer my own and is probably representative of our media-controlled government




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  Reply # 1263604 19-Mar-2015 17:58
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Niel: Each valve has 2 channels.  You can't physically turn the valves around, but you can swap wires on the valve so that a different half of the valve is used for a different audio channel to see if it is an issue on one of the halves of that valve.  Based on your comments/questions, I'd strongly recommend you get someone that knows what he is doing to work on it.


That was actually the purpose of starting this thread. I would be happy to send you the assembly manual and pictures of the unit in case you were willing/interested in assisting?


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