GoodSoundClub - Romy the Cat's Audio Site - It is not about power supply.

11-20-2011

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Romy the Cat

Boston, MA
Posts 10,156
Joined on 05-28-2004

Post #:	151
Post ID:	17393
Reply to:	17392

I think your game is not over.

Hmmmm. Nset I will tell you something that will disturb you but it is what it is. If you did not use transformers and your phono was noisy and shielding did help it to be not noisy then you do not a proper grounding in your phonstage. The non- shielded phonstage might have some minor noise but it will be upper range noise and shielding, or putting it into an enclosure, will help. If you have num then it has nothing to do with shielding but only grounding. If your shielding helped against num then it was not because shielding but because you inadvertently change something in grounding. It is my believe and it is my experience that a phonstage with properly implemented grounds (from perspective of hum) does not need any shielding or even enclosure for this meter. Yes, shielding of cause will help but to a VERY minor scale (for hum) and only if you are willing to place it right next to aggressive polluters (like TT motors etc…)

The Cat, not Sir.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

11-20-2011

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	152
Post ID:	17395
Reply to:	17393

More ham

I see the point, thanks a lot for your comments. Playing with the phono I've somehow come to a conlusion (possibly wrong)
that my ham is an electrostatic air pick-up from the PS. During the operation both PS and signal boxes are very close
together and the hum depends on the relative orientation of the two and gently fades away when switched off.
I must say though I have not done your trick with shorting the stages (only shorted the input) as it's difficult with this
design: 2nd stage is fixed bias, DC coupled to 3rd. I did pay a lot of attention to the ground, so actually cannot
imagine having a ground loop anywhere (I guess this is what you are referring to as improper grounding?).

However, if I lift the ground I get a horrible pick-up, which I think is in turn magnetic (it desappears instantly
when I switch the phono off). THis is actually something that worries me and perhaps indicates that
you may be right: why lifting the ground leads to such a drastic change?

Cheers,
N-set

Cheers,
Jarek
STACORE

11-20-2011

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Paul S
San Diego, California, USA
Posts 2,657
Joined on 10-12-2006

Post #:	153
Post ID:	17397
Reply to:	17395

Route(s) to Ground

The ideal "star" grounding plan is seldom realized in practice, for lots of reasons. For one thing, it takes serious concentration to really think it through. As I have said many times, it is often useful to have a "bleeder" on the chassis, and this works better if it runs uninterrupted to a dedicated ground rod rather than via the mains neutral or ground. Again, neutral and ground share a bus at the main (service) box, in any case, and often before that in a sub-panel, or even in outlet or junction boxes, even though this is not good for hi-fi (nor is it safe...).

The phono [pre]amp exacerbates both parasitic and self noise both just because it boosts a small signal so well. Sure, any EMF can harbor and/or effectively generate noise that gets picked up by the gain circuitry, in addition to generic EMI and RF. Likewise, current may be "stacked" internally due to varying ground potential, especially between gain stages, not to mention the loops we always figure out the hard way.

Lastly, not saying it is this way for you, but I have also been quite peeved when replacing a special $$$ tranny with someting "less special" cured the hum immediately!

Best regards,
Paul S

11-21-2011

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	154
Post ID:	17404
Reply to:	17397

Grounding arrangement

The grounding I have employed is a mixture of a "local star" and GND plane (I've obviously copied it from the Cat).
I did pay a lot of attention not to have loops. Here is my grounding scheme. I wonder if there are any obvious errors?

There is a switch breaking lifting the GND plane from the chassis. If I lift it I get a horrible pickup, I think magnetic
100Hz from the PS (the hum disappears instantly when switching all off).
The connection between the signal and the PS box is via a shield (braid) on the umbilical.
Then at PS, the chassis is connected to the GND
pin of the IEC power inlet (for the time of experimentation I connect to the power ground).

Actually, connecting the scope across 470k output resistors (at the RCA's) the pick up with the phono switched off
is of the same amplitude as the ham with the phono switched on (but for eample the pick up on the 2M grid is negligable).

Cheers,
N-set

Cheers,
Jarek
STACORE

11-22-2011

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Paul S
San Diego, California, USA
Posts 2,657
Joined on 10-12-2006

Post #:	155
Post ID:	17405
Reply to:	17404

Ground Thoughts

Is the "ground plane" in this case literally a sheet of copper that you run all the grounds to? If so, this may be overkill on the one hand and an antenna/noise magnet/generator on the other hand, and/or it may well make for ground loops. It is usually sufficient to have a ground "bus" that is not connected to the chassis, and this goes out on the neutral wire. Parts should not directly touch the copper sheet or the chassis; stand them off mechanically and electrically. The chassis and your IC shields can use the "dedicated" ground. The "house" ground is lifted at the chassis/not used for the phono stage. You are using shielded IC, right? Bleed the shields from the upstream end only (and leave the downstream end loose; do not ground shields at both ends...).

Good luck.

Best regards,
Paul

11-22-2011

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Romy the Cat

Boston, MA
Posts 10,156
Joined on 05-28-2004

Post #:	157
Post ID:	17408
Reply to:	17404

Where is the Bolt?

N-set, it is difficult to say anything without seeing the circuit. I think that you did not exactly my version but made some modifications; I do not know/remember what they were. 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. 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. But how I described I bolt all my 4 phonostages and I never had any problems with noise, I presume that something I did right.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

11-22-2011

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Romy the Cat

Boston, MA
Posts 10,156
Joined on 05-28-2004

Post #:	158
Post ID:	17409
Reply to:	17406

Gas tubes in the phonostage

AlexBerger wrote:
Hello Romy,

What brand of 0A2 do you use in your phonostage?
I used RCA, but after 1.5 years of work it began to spark when phonostage is switched on.
I tried Siemens, Mazda and now Sylvania 0A2.
Siemens has "disco sound", without mids, just metallic highs and punchy bass.
Mazda has strong sweet coloration with accent to upper mid and week bass.
Sylvania sounds good, actually more interesting than RCA did. But vocal doesn't sound smooth enough.
Maybe it needs some break-in time?

Alex,

They all are good questions

I have published a short survey: “150V Gas Tubes survival guide.” at:

http://www.GoodSoundClub.com/TreeItem.aspx?PostID=2792

where I did explore hot the gas tube impact sound. However, that was in context of Melquiades amplifier, where the gas tubes drive bias – MUCH more sensitive element then anode supply in my view. Regardless if it was more sensitive or not I think the topological difference would make my experience with Melquiades’ use of gas tube not applicable to use of gas tubes in my phonostage.

I never made any tube roiling in the PS of phonostage, I should but I did not. I put in there Telefunkens and did not try anything else, the Telefunkens were not my the best choice with Melquiades, but since Telefunken tube are very reliable and I have no easy access to phonostage’s PS I figured that Telefunken will be a reasonable choice if I am not going to see those tubes for very long time, preferably never again.

Telefunken most likely made by Siemens, or versa versa, so it is possible that your Siemens and my Telefunken are the same tubes rebranded. Sylvania are very very good tubes, I always like them, in fact I use special Sylvania 12AX7 in the second stage of my “End of the life phonostage”. My the most beloved 150V gas tube is Amperex. They have not flat shields like all other tube but many small holes in the shield that make them to look very different and they do sound in my estimation much bettered. But again, it was in Melquiades, who knows how they will sound in phonostage.

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

11-22-2011

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	160
Post ID:	17411
Reply to:	17405

GND plane

Paul S wrote:
Is the "ground plane" in this case literally a sheet of copper that you run all the grounds to? If so, this may be overkill on the one hand and an antenna/noise magnet/generator on the other hand, and/or it may well make for ground loops.

Oh, this is a very controversial statement Paul! The 2D sheet of thick copper (or in my case actually semi-3D as the Cu is 1.5mm thick)
has vanishing inductance and resistence. Thus it's antena action is zero so is it's resistance in any "ground loop". Thus no loop.
Think that various induced currents have a much more space to distrubute themselves properly. I have zero experience with RF,
but, the common knowledge there says a 2D sheet provides an ultimate ground.

Paul S wrote:
It is usually sufficient to have a ground "bus" that is not connected to the chassis, and this goes out on the neutral wire. Parts should not directly touch the copper sheet or the chassis; stand them off mechanically and electrically. The chassis and your IC shields can use the "dedicated" ground. The "house" ground is lifted at the chassis/not used for the phono stage.

Again, bus is semi 1D, it has higher self inductance than a plane and so it's antena action is stronger. Yes, all the parts are lifted from the GND plane/chassis. I use house earth for the safety of experimentation-I don't want to electrocute myself before I finish the phono.

Cheers,

Nset

Cheers,
Jarek
STACORE

11-22-2011

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Romy the Cat

Boston, MA
Posts 10,156
Joined on 05-28-2004

Post #:	161
Post ID:	17412
Reply to:	17410

That crazy 7025.

AlexBerger wrote:
I think I should to give some break-in time to Sylvania 0a2.
50 hours is enough?

Previously I used in my EAR the next set of tubes ECC83: 1-Amperex (red print), 2-Amperex (red print), 3-Sylvania 7025 (yellow print).
When I built "End of Live", I used tube set exactly lake you do: 1-Telefunken (smooth plate), 2-Sylvania 7025 (yellow print), 3-Telefunken (smooth plate).
(But my Sylvania 7025 is not specialty strong...)
Now I changed Sylvania 7025 to Amperex (red print). IMHO the sound is steel natural and well balanced but more refined.

I do not know about the break-in of gas tubes.

My Sylvania 7025 for whatever reason has twice (!!!) transconductance then my input and out tubes. My tube tester is well celebrated and the Telefunken 12AX7 that I use are well within the normal operational limits. The 7025 max out the tube tester and I need to switch the load in order to any sensible reading. I have no idea why it behaved this way but I like sound less when replaced that “crazy 7025” with good Telefunken 12AX7. I do have some Amperex and I might try them another day if I develop more interest to play with tube rolling.

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

11-22-2011

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	162
Post ID:	17413
Reply to:	17408

Distributed bolt

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

Cheers,
Jarek
STACORE

11-22-2011

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Romy the Cat

Boston, MA
Posts 10,156
Joined on 05-28-2004

Post #:	164
Post ID:	17415
Reply to:	17414

Amperex "Bugle Boy".

AlexBerger wrote:
I tried Amperex ECC83 "Bugle Boy". They sounded bad in the EAR RIAA. I like more modern Amperex ECC83, Holland made with orange-red prints.

Yes, the Amperex "Bugle Boy" are horrible tubes. They have huge publicity among audio people (surprise?) but in really they are very bad. I remember around 10 years back, what I use Lamm ML2 with 12AX7 in input I bought in Paris a box of 180 Amperex "Bugle Boy" from the guy who did not exactly knew the price. I think I paid $500 or something like this. They were the meanest sounding 12AX7 I ever heard and they were new. Thankfully I was able to get rid of them under the new-matched BS and to my surprised the guy who bought them where extremely happy. It is true that one person waste is another person treasury…. For Amperex I never even look at anything with Bugle Boy. The Non Bugle Boy Amperex are MUCH better tubes.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

11-23-2011

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	167
Post ID:	17421
Reply to:	17413

More findings

I did one thing: I swapped the phase of one of my PS transformers (the heater one).
My PS transformers are placed parallel side-by-side and super close to each other.
Very wise, but I had no choice. I tried to wire the primaries
out of phase to have some cancellation, but what one can expect from a person who notoriously confuses left and right?
I had done it wrong. Swaping the primary reduced 2x the emitted garbage (as certified by a search coil and a scope)
More importantly, it also gives me finally no hum at my desired orientation of the boxes with the signal box open.
(but at certain other orientations I still get an audible ham). The drawback is that the trannies seem to
be noisier a bit.

Interesting thing happens when I lift the ground. A terrible magnetic pick-up brum appears as usually and I have
no clue why. But it is
sometimes enough to rotate the box by a very small angle to shut it down completely...

All this seems to point to my PS as the source of the garbage. And this is the "reward" for my heroic fight,
huge oversized tarnies with tripple screens, box sectioning, grounding of all metal parts,expensive SiC diodes, etc, etc!!!
My case does not properly magnetically shield--front and back pannels are thin alu, only top, bottom and sides are steel.
The RF noise is also there (the hiss increases when I move PS very close, I also saw a 30kHz pollution
correlated to a glitch in the HT switching).
Either my implementation is shit (most probable) or perhaps all that soft switching SiC's is just a pile of BS.
I'll get a 10km umbilical to put all this misery in another city.

Cheers,
N-set

Cheers,
Jarek
STACORE

11-23-2011

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Paul S
San Diego, California, USA
Posts 2,657
Joined on 10-12-2006

Post #:	168
Post ID:	17422
Reply to:	17421

EMF and "Split" "Grounds"

If you can do it, try isolating both cases/chasses from your "ground plane(s)". Use one inclusive "ground plane" for both the PS and the gain/RIAA sections, and ground this "ground plane" to the house "neutral" wire. Do NOT connect any shielding to the "ground plane". Then ground the cases/chasses, all internal shields, the IC shields, TT/motor, arm and step-up ground lugs to a special, dedicated ground rod (not the house neutral or ground!). This special ground rod is the "bleeder" I keep referring to. Make sure any un-used inputs or outputs are covered/shielded. If you have noise from the bridge, consider using the (Fairchild?) "Stealth" diodes; they are VERY quiet. I posted about these in my K&K thread.

Maybe the above will work to quiet your rig. The big, strong trannies throw big, strong "fields", however, and they do tend to make their own problems. Surely you have the trannies on isolation pads of some kind, with fasteners tightened "just so", to quell vibration, and tranny axes at right angles when they are adjacent?

I don't remember now if you said your step-up tranny is in the phono stage case/chassis. It might be quieter if the step-up tranny is in its own shielded case that is grounded to the special, dedicated ground rod. Certainly, it should not be connected to the house neutral or ground wires.

Good luck.

Best regards,
Paul

11-24-2011

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	169
Post ID:	17423
Reply to:	17422

Grounding, tarnnies and diodes

Paul S wrote:
If you can do it, try isolating both cases/chasses from your "ground plane(s)". Use one inclusive "ground plane" for both the PS and the gain/RIAA sections, and ground this "ground plane" to the house "neutral" wire. Do NOT connect any shielding to the "ground plane". Then ground the cases/chasses, all internal shields, the IC shields, TT/motor, arm and step-up ground lugs to a special, dedicated ground rod (not the house neutral or ground!). This special ground rod is the "bleeder" I keep referring to.

Paul, thanks for a valuable input!
Unfortunately I'm unable to do it--apartment on a 6th floor...city center... Sad

I plan to disconect
from the house neutral at all once I'm sure the equipment will not kill me. But the hum I have
is 99% an air pickup, not the hum enetering from the grounds.

Paul S wrote:
If you have noise from the bridge, consider using the (Fairchild?) "Stealth" diodes; they are VERY quiet. I posted about these in my K&K thread.

What are they? I use those en vogue Cree SiC's. When I have time and motivation I'll experiment with adding
a 10nF C accross the diodes to soften the tranny kick-back...in principle this antique technique should be
redundant with SiC's...so the advertising slogans say.

Paul S wrote:
Maybe the above will work to quiet your rig. The big, strong trannies throw big, strong "fields", however, and they do tend to make their own problems. Surely you have the trannies on isolation pads of some kind, with fasteners tightened "just so", to quell vibration, and tranny axes at right angles when they are adjacent?

...and here we eneter a minefiled. Tha tranies are adjacent but the axes are parallel....I had no other choice
to place them. I'm considering an attempt to individually pot them in a steel tomb.
Size matters, the theory says oversized tranny=lower magnetic fields=lower emission
(at least due to the fields generated by the currents in the secondary; this is what one
usually can easily control when ordering trannies; making transf. winders oversize the primary is a lost battle).
The vibration I get is probably due shitty made windings. The isolation for the chassis is tip-top (thick silicone,
nylon tight screws, alu base, etc).

Cheers,
N-set

Cheers,
Jarek
STACORE

11-24-2011

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Paul S
San Diego, California, USA
Posts 2,657
Joined on 10-12-2006

Post #:	170
Post ID:	17425
Reply to:	17423

Again with the "Neutral" Explanation...

N-Set, why would you disconnect from the house neutral, unless you are using battery power??? This "neutral" is the "ground" leg of your circuit! The house neutral wire is typically white, and the house ground wire is typically green. The "extra", green, house "ground" wire is intended to be a safety leg, to ground any stray current or shorts. The problem for us is, the house "ground" is typically too noisy for audio, and it effectively winds up working more like an antenna than a real ground. Also, impedance, etc. tend to vary between the house neutral and ground, creating a reactive "noise generator".

I am not sure what I would do with all your shielding if I could not bleed/ground it separately (from the circuitry). Apartments and condos are typically the worst case scenerios, as far as ground noise. If you can trace your circuits back to a real, mechanical gound, try to find a quiet, separate, "un-broken" line to ground for your shields. It might be a quiet neutral leg of an un-used circuit that makes a "home run", such as a dedicated appliance circuit. This is sub-optimal, but it should help.

To damp mechanical vibration it actually sometimes helps to loosen very tight screws to a "critical" tightness.

BTW, are you telling me that a Gauss meter reads higher near a smaller transformer (vs, a larger one)?

Best regards,
Paul S

11-24-2011

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	171
Post ID:	17427
Reply to:	17425

Grounding and trannies

Paul S wrote:
N-Set, why would you disconnect from the house neutral, unless you are using battery power??? This "neutral" is the "ground" leg of your circuit! The house neutral wire is typically white, and the house ground wire is typically green. The "extra", green, house "ground" wire is intended to be a safety leg, to ground any stray current or shorts. The problem for us is, the house "ground" is typically too noisy for audio, and it effectively winds up working more like an antenna than a real ground. Also, impedance, etc. tend to vary between the house neutral and ground, creating a reactive "noise generator".

Of course I meant "ground" Big Smile

sorry

Paul S wrote:

I am not sure what I would do with all your shielding if I could not bleed/ground it separately (from the circuitry). Apartments and condos are typically the worst case scenerios, as far as ground noise. If you can trace your circuits back to a real, mechanical gound, try to find a quiet, separate, "un-broken" line to ground for your shields. It might be a quiet neutral leg of an un-used circuit that makes a "home run", such as a dedicated appliance circuit. This is sub-optimal, but it should help.

At the moment the most stable and quite hum-wise (no idea if this extrapolates to other noise etc) configuration is signal ground tied to the case.
Lifting this connection (the signal ground--the big Cu plate--floating) in some circumstances catches a horrible magnetic brumm from the PS.

Paul S wrote:

To damp mechanical vibration it actually sometimes helps to loosen very tight screws to a "critical" tightness.

These are windings unfortunately buzzing, but it's not so bad, from 0.5m one hardly hears anything. I will try to dampen the PS case with a heavy rubber.

Paul S wrote:

BTW, are you telling me that a Gauss meter reads higher near a smaller transformer (vs, a larger one)?

This is more complex than that. Everything depends on how the tranny is loaded and wound on the primary.
What I meant is an oversized transformer. For example if it's oversized regarding the nominal secondary current (e.g. you tell your winders to wind a tranny for 3x the current you expect to draw from it) then the magnetic field produced by the actual currents will be lower--the winders use some tables which always assume the highest possible fields to get max out of a given core. If you draw 3x less current, your field strength will be also lower as compared to e.g. a small tranny designed exactly for that current. If you in turn manage to get the primary overwound by e.g. putting 50% more turns than known design tables say (which always assume max B for a given steel), you reduce the field contribution from the primary as well (your B drops those 50%).
This all concerns magnetic fields. Then there are electrostatic fields from the windings, but that's a different story.
Sorry for not offering a clearer explanation...
Cheers,
Nset

Cheers,
Jarek
STACORE

11-26-2011

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N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	172
Post ID:	17430
Reply to:	17427

Ignorance is bliss...

I've spent two more nights examining and fighting my ham (I'm vegetarian and I want my phono to be so as well).

1) I did Romy's excercise with shorting the stages via a 0.47u cap to GND. Shorting the plate of V2/grid of V3 resulted
in the biggest reduction of ham (around 8-10x); shorting V1 plate or V2 grid produced moderate reduction of 3x-4x;
shorting V3 (plate to cathode) and the output produced no result. So the largest pick up seems to be at the second stage.
Small changes of wiring around there gave no result.

2) The ugliest discovery and most probably the source of ham: if ignorance is a bliss, don't look into your power supply operation!
Below is an example how ugly my operation is:

This is the current in the secondary of the HT transformer (red trace; taken at the resitor in series with the input choke)
and a signal from a 100mH RF
search coil placed close to the transformer (blue trace). A very very ugly current waveform, with large oscillation, caused
by the big 20H input choke. I'll probably try snubbers a la Morgan Jones to tame this oscillation.

The blue spikes (produced by the inductance of the transformer at the zero crossing of the voltage, when the rectifiers switch)
is with high probability what couples to my interference-sensitive signal layout (it's fucked up, sorry to admitt that,
I wanted to avoid steel bolts and being unable to solder to 1.5mm Cu plate directly I had to rise the components
too much off the ground plane, creating areas which catch whatever is in the air; it's not compact enough).
As I understand it I can't really do anything to kill the spikes, only shield them and try to kill the oscillation.
My only way is to shield heavily the signal box and place the PS box 10km away.

Cheers,
Shit-set

Cheers,
Jarek
STACORE

11-26-2011

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Paul S
San Diego, California, USA
Posts 2,657
Joined on 10-12-2006

Post #:	173
Post ID:	17431
Reply to:	17430

Shakey DIY Basics

How do I hate DIY? Let me count the ways...

Is there some reason you cannot make through-holes to facilitate soldering leads to your copper sheet? Use a hot iron (800 F) and plenty of aggressive flux to pre-tin the holes... Stand parts on short leads or use little blobs of removeable Si caulk (like GE marine grade). Do not let parts (other than ground leads...) touch that copper sheet... Cross various wires at right angles, as much as possible... Solder relevant parts directly to each other and to tube pins whenever possible. I don't remember from the pictures if your box has a steel bottom under the copper "ground plane", but it should. I also don't remember how you mounted the tube sockets; but it has to involve some parts floating well away from your copper sheet, in any case (not that this in itself should be a problem...).

Again, no way to over-stress this: Divorce all shielding - including the 6-sided box - from the copper sheet/ground plane... Drain the only the shields (including the boxes), to a (grounded) water pipe if you have to, anything with lower resistance than a "field discharge" via the circuit ground/house neutral...

I have used plenty of low-level gain stages without hum, despite parts that float well away from the "ground plane" (in my case, IC board or ground bus). A decent steel box with proper grounding, and covering un-used inputs and outputs, should be proof against external problems. AGAIN, physically and electrically isolate the copper sheets from the boxes! The sorts of problems you are talking about rather suggest an inside job...

Consider a DACT or Tent PS...

Best regards,
Paul S

11-26-2011

Post does not mapped to Knowledge Tree

N-set
Gdansk, Poland
Posts 617
Joined on 01-07-2006

Post #:	174
Post ID:	17432
Reply to:	17431

Poor photographer

Paul S wrote:

How do I hate DIY? Let me count the ways...

I hate it just as much!
Paul, thanks, but most of what you are talking about has been already
addressed and described. Perhaps not very visible from
my pictures but I'm a very poor photographer.
I'm 99% sure my problem has to do with coupling to my PS
and I don't want neither Tent nor DACT PS
nor any other. The filtering that I have is very powerfull, the HT supply has only
0.5V ripple at the first cap (LT only 0.2V). But this power comes at a price.
This is theis trade off that I'm investigating now.

Cheers,
N-set

PS If you find a gun which can directly solder to a 1.5mm Cu plate I'll sacrifice an ox.

Cheers,
Jarek
STACORE

11-26-2011

Post does not mapped to Knowledge Tree

Paul S
San Diego, California, USA
Posts 2,657
Joined on 10-12-2006

Post #:	175
Post ID:	17434
Reply to:	17432

Spare the Oxen...

Like you, I would not eat it, anyway...

Maybe try through holes, good flux, pencil torch to pre-solder? I use a torch to completely coat my Cu "bus bars" with solder. Then, no (ok, very little...) Cu oxides, and no problems attaching anything (also pre-soldered) down the road.

Of course you know that separating the cases and shields from the copper sheet will probably work if the cases/shield are actually drained separately; but it will not work if the shields just "float" or if the neutral and ground are co-mingled before ground, proper (which they usually are, especially in apartments)...

Many/Giant Parts, beware the Evil Capacitance...

Time to listen to Music!

Best regards,
Paul S

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