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Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum |
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#251 |
Banned
Join Date: Nov 2005
Location: McKinney, TX
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#252 |
diyAudio Member
Join Date: Sep 2009
Location: UAE
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One of the other thread which Andy posted in 2007, he mentioned about hum due to unbalanced filament supply when 26 tubes put in series. Can someone explain this? I use series filament and sometimes experiencing slight high frequency hum which I believe due to the same reason. I experimented with different filament voltage and current variations where I noticed that the 26 inducing hum when the current goes below certain limit.
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#253 |
diyAudio Member
Join Date: Sep 2003
Location: London
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Hi,
I've stopped putting tubes in series - separate filament supplies for each tube. Don't know if hum was the problem, but I just made the decision to use one supply per tube. I just use a big cap and a LM1084 so the filament supply is pretty simple, apart from the sheer bulk of it including the heatsink. andy |
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#254 | |
diyAudio Member
Join Date: Sep 2009
Location: UAE
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Quote:
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#255 | |
diyAudio Member
Join Date: Apr 2006
Location: Holland
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Quote:
Further, connecting the filaments in series makes a beautiful antenna for strayfields.
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jaap |
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#256 |
diyAudio Member
Join Date: Sep 2003
Location: London
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Hi coolzero,
you say you have "voltage sources following simple current source". I'm not quite sure I understand you here. If you mean "I have a voltage source following a current source" that makes no sense - the Ronan Reg type circuit has voltage reg first then current source as last in the chain before the filaments. Current source should be last, even a common mode choke seems to make no improvement after the current source, though curiously it improves things after a voltage reg. But you may mean "first I tried a current source, then I tried a voltage reg and they both hummed". I can't diagnose your problem, but I can only say my setup doesn't hum. I use a LM1084. And I use a seperate power supply - the transformer is in another box, and so is the HT including the choke - only DC goes to the signal chassis. And each filament has a separate transformer. I have loads of small 6v transformers which I use for filaments. And another thing - these filament transformers can pick up hum if they are close to chokes and mains transformers even in the remote PSU box. The whole filament supply from beginning to end has to be kept away from any magnetic fields. andy |
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#257 |
diyAudio Member
Join Date: Sep 2009
Location: UAE
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#258 | |
diyAudio Member
Join Date: Sep 2009
Location: UAE
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Quote:
Sorry for the confusion in my explanation. It is somewhat similar to Ronan's with voltage regulator first and current regulator after that. It was not two of those separably I have used. I used a transformer with dual secondary windings of each 5V/1A. Everywhere I read about this, people mentioned that this works like a charm but for me it was a hummingbird in side my 26 pre ![]() Later I found those SMPS and used one for the filament but then came this slight high frequency hum from one channel I believe becuase of not enough current floating across the series filaments. One other thing I noticed was that, when 26 filaments put on series one of the filament slightly brighter than other and there is a slight delay always when those are lighten up. One fires up a second or two later than the other. There was no change of this behaviour even the different tubes were used. Something funny. ![]() |
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#259 |
diyAudio Member
Join Date: Apr 2006
Location: Holland
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hi, without knowing your exact build it's guessing what went wrong. This artice holds all information you need for building a hum free amplifier. I'll upload some data in a couple of hours so you can compare yours.
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jaap |
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#260 | |
diyAudio Member
Join Date: Sep 2009
Location: UAE
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Quote:
I started with Jim's 26 pre and modified it to the present level with help of Kevin and many other in this forum. I have posted the schematic and the details in this same thread before. Initially I followed all Jim's advices mentioned in his site but with less luck. Even Jim had mentioned that he had hum issue with his 26 preamp which he couldn't get rid of. What I have now is far better than the original design in terms of hum and sound quality. I checked and re-checked many time of grounding, filtering, shielding and all the other possible hum inducing mishaps hence pretty sure that the slight high frequency hum I am getting time to time in my audio path is not related to any of those usual suspects. ![]() |
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