dicky
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Post by dicky on Jul 14, 2014 18:33:02 GMT
I just realised I never got back into this thread with the outcome of this noise issue!
Anyhoo, the source of noise turned out to be a combination of 2 things - a dodgy phono didn't help but the main culprit was my amplifier; a Panda . The Panda has been replaced by the Ember and the combination is almost silent - just the faintest of hiss that is barely audible. The Panda noise was quite different and definitely a mains hum rather than a hiss.
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Rabbit
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Post by Rabbit on Jul 14, 2014 19:38:28 GMT
Exactly what I got with my Panda Dicky. Gave up on it way back because of that. It showed more on the HD650 whereas the AKG's weren't anything like as bad. Likewise, my Ember is dead silent and I don't even seem to get phone noises either!!
My Panda has long gone now. I enjoyed its power and warm sound but couldn't put up with constant hum, no matter how low it was. Curiously, I only got it in one side. It was always like that.
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dicky
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Post by dicky on Jul 14, 2014 20:18:51 GMT
I have 2 Pandas and they both have the same problem on only one channel. I have kept them, though as they were the first thing I assembled.
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Rabbit
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Post by Rabbit on Jul 14, 2014 20:38:33 GMT
It screams 'design fault' Dicky.
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dicky
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Post by dicky on Jul 15, 2014 6:58:15 GMT
It does; and when I built the second unit I re-routed the wiring as practically as I could - but the resulting hum was almost identical. To be fair though, you'd have to be listening at deafening volume to hear the hum over the 'silences'.
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dicky
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Post by dicky on Jul 15, 2014 7:00:26 GMT
In fact, one of these days I might yank the transformer out and put it into an external box.
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solderdude
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Post by solderdude on Jul 15, 2014 7:08:55 GMT
I suspect its a layout problem.
What MIGHT bring a solution is feeding it with a regulated DC instead of AC, BUT the AC detection of the speaker protection circuit must be altered.
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dicky
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Post by dicky on Jul 15, 2014 7:12:03 GMT
Hmmm, sounds like a lot of effort for possibly no gain. I'll keep them as paperweights.
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Rabbit
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Panda amp
Jul 15, 2014 9:30:28 GMT
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Post by Rabbit on Jul 15, 2014 9:30:28 GMT
Hmmm, sounds like a lot of effort for possibly no gain. I'll keep them as paperweights. Mine left just before I moved. It had been stored away for over a year so I got rid of it.
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juke
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Post by juke on Jul 16, 2014 21:48:25 GMT
I brought my Panda out of storage after reading this. I had a LOT of help from Frans at the time and I seem to remember that he thought my attenuator might be part of the problem. I looked inside and it has an Alps Blue volume control, which I don't normally use. Anyway, it is very quiet with no input, from fully down to almost maximum. It has 75 ohm output resistors and it also handled my HE-6 phones quite well.
Two downsides, the Alps has become scratchy and would need replaced, and when I attached my newly upgraded iRiver, power off, it hummed and reacted to touch. It did the same with the iPhone. Switched on, they were fine.
Syd
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solderdude
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Post by solderdude on Jul 17, 2014 5:09:02 GMT
some hum with powered off devices is quite normal.
I have never encountered a scratchy blue velvet pot though. Is it also scratchy with no input signals ?
All pots become scratchy when there is some DC on the input. That can be cured by using coupling caps.
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juke
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Post by juke on Jul 17, 2014 10:01:14 GMT
Sorted Frans. I found that the Alps was a little loose, though the case with matching inset knob was actually disguising this. I've fitted a spacer between the Alps' body and the case and tightened it up. No scratches, so very pleased. I rechecked for noise and this Panda is silent up to about 85% of travel when some hum becomes discernible but low. This was without music playing and would never be heard with music and the chances of anyone having the volume up that high would have to be nil. Glad I mentioned it!
Would it be worth fitting coupling caps as a matter of course on HAs?
Syd
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solderdude
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Post by solderdude on Jul 17, 2014 10:18:44 GMT
The Panda amp is fully DC coupled so all DC on the input will be amplified. For that reason the output circuit has a DC detection circuit that switches off the amp above a certain DC level (think around 1Volt) Of course if the source has some DC on it the volpot may 'scratch' a bit and the amp will switch off when the volume control is above a certain point. In that case fitting input caps will be beneficial.
The panda was obviously designed to work from DC up so would only fit caps if you have a source that does give off some DC.
The value of those caps will be determined by the resistance of the volpot. I reckon it will be between 10k and 50k somewhere (it's mentioned on the volpot)
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juke
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Post by juke on Jul 17, 2014 11:03:10 GMT
It is 50k Frans, but I think it's OK as is. I still have to find out how my AK HA blew the Superlux but that's not for this thread!
I'm not aware of any of my inputs having DC.
Syd
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solderdude
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Post by solderdude on Jul 17, 2014 14:22:36 GMT
for 50k 2.2uF or 3.3uF coupling caps will be O.K. in case someone needs them.
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