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In the Forum: Analog Playback
In the Thread: The last phonocorrector: “End of Life" Phonostage
Post Subject: Distributed boltPosted by N-set on: 11/22/2011
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 Romy the Cat wrote:
I think that you did not exactly my version but made some modifications;
I do not know/remember what they were. 

CCS heating of the tubes based on LT337A, 2x0.47u+470K at the output,my filtering is a bit bulkier at HT. I think all that is +/-  irrelevant.
 Romy the Cat wrote:

The major think that I see at your picture is that your main grounding point is too far from where I accustom to have it. In my view the  main grounding point, the location where everything need to come together, including the negative from filament and contact o chasses is  the spot where you phono cable enter the box. Right next to RCA jack you need to have a big bolt driven into chasses and to this bolt everything needs to go. When you do ground bypassing and trace the source of your hum then you need to bypass everything in the respect to this bolt.

1) Yes, indeed the chassis to GND plane bolt you see in the upper right corner; the RCA inputs are about 2-3cm above that bolt,
at the other side

2) The gounding of the tube stages, ouputs and the "+" of the heater is some 20cm away from the chassis bolt, so the communication between the chassis bolt and the stage GND's is via my massive Cu plate; the grounding of the "-" HT is some 5cm from the stages, again communicating via the massive Cu plate; it's all +/- clearly visible in the pic above; so I think have a sort of a distributed bolt, with much bigger cross-section and much lower self inductance and resistence than the usual steel bolt...or am I strongly halucinating???

3) The grounding of the stages it is done not with bolts, like in your case, but with 10mmx1.5mm tinned Cu strip (a silverish thing in circes in the above pic), hard-bolted to the GND plane and protected with shellack (thanks Paul);
I think this GND-ing is in principle quite similar to what I could inferr from your pictures:IIRC you have 4 small bolts grounding the tube stages to your Cu plate and one big input bolt where the input (cart loading) resistors are grounded to the plate; where you ground your chassis I do not know.

4) I did try breaking my actual Cu plate-to-chassis bond and looking for another grounding point between the
GND points of the stages (those tinned Cu strips) and the chassis; no result; same ham; I also tried to look for another GND-ing of "-" HT; again no result; I tried shorting all other parts of my GND with each oter and with the chassis; again no result

5) In lieu of a better explanation I ass-u-me the ham I have is an electrostatic free air pickup, mostly from the nearby PS, ass my ham:
      i) decreases when the PS box is completely closed
      ii) depends on a relative orienation between the PS and signal boxes; there is an orienation where it disappears
         completely with the unshielded signal box; in this oreination the PS transformers are shielded from signal by a 3mm
         grounded alu mounting plane within the PS box              
      iii) gently fades away when the unit is switched off, suggesting electrostatic rather than magnetic nature
      iv) moving a hand close to the signal part (esp. the input and the output 470k resistors) increases the ham, without changing it's nature
 
Maybe I'w wrong but at this moment I have neither a better explanation nor a possibility to re-route the phono, so I'm force to proceed with what I have. The next step are MC trannies.
 Romy the Cat wrote:

I do not insist that this is how it always needs to be done. I am not an experience equipment builder – you have much more experience and knowledge.

Please...I think all the above only certifies my mediocrity...
Cheers,
n-set

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