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11-22-2011

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Romy the Cat

Boston, MA
Posts 10,159
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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AlexBerger
Israel, Beer Sheva
Posts 20
Joined on 04-19-2010

Post #:	163
Post ID:	17414
Reply to:	17412

Amperex ECC83

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.

11-22-2011

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Romy the Cat

Boston, MA
Posts 10,159
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

11-22-2011

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AlexBerger
Israel, Beer Sheva
Posts 20
Joined on 04-19-2010

Post #:	165
Post ID:	17416
Reply to:	17415

ECC83 Amperex picture

This is my ECC83 Amperex picture.

11-22-2011

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Paul S
San Diego, California, USA
Posts 2,658
Joined on 10-12-2006

Post #:	166
Post ID:	17417
Reply to:	17411

More "Ground" vs. "Neutral"

What we call the electrical "ground" or "earth" end of a circuit is the house "neutral" as far as the power company and your house wiring are concerned. By all means, use that, apropos. The "bleeder" is not in the circuit, and it is the "dedicated ground". There are no safety issues with this, and if care is taken to keep the circuit, per se, off the dedicated ground, the noise is gone.

Best regards,
Paul S

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 2,658
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 2,658
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

Post does not mapped to Knowledge Tree

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

Post does not mapped to Knowledge Tree

Paul S
San Diego, California, USA
Posts 2,658
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

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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 2,658
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

11-28-2011

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

Post #:	176
Post ID:	17439
Reply to:	17430

Is SiC sick?

Ok, I think I've finally vivisected my ham--it's connected to the rectifier switching (at least some part is).
Below is the waveform of the loaded HT secondary (red trace) and the signal from a search coil
catching the leakage flux close to the transformer core (with LT everything very much the same):

HT_secondary+coil_loaded.bmp

Well, I remember seeing much nicer switching....of voltages
well above 1kV and with a bridge of huge MV tubes...SiC's, loaded with my big input chokes, hold the voltage for a considerable
period at switching!! A rough estimate from the above trace is 0.8ms! (when unloaded it's much shorter
0.2ms perhaps, and the spikes are proportionaly smaller) and is the same for the LT too--perhaps this a property of a choke-loaded SiC?
Interesting if this has ever been examined as 99% of commercial supplies are either switching or cap-input.
One should have in mind that all those marvelous features of SiC's we've been fed with by manufacturers'
propaganda, have been measured in labs, under precise "test conditions" etc
and here we have a real life situation.

What happens is that the core integrates the voltage (the resulting flux is an integral of the applied voltage), so in the death zones
the flux starts to rise linearly with time, producing the spikes. A closer examination indeed shows that the
blue spikes above start exactly at the beginning of the death zone and peak exactly at the right end of it.
Integral of a constant is a linear function in time.
Now, this flux happily leaks out of the transformers due to a one inevitable compromise.
I've specified my PS transformers to be isolating type with the secondary and primary beeing on different legs
of the C-core. This minimizes capacitive coupling to the line but the price to pay is of course a high
leakage flux. I've put Cu leakage bands around all the transformers and chokes; transformers in the shooting direction
are blocked with a Cu plate (very efficient indeed) not to shoot on the input chokes but still the flux leaks
out in other directiuons.

BTW, one sees a gentle core saturation as a result of me being lazy to persuade the winders to overwind the primary
some 20%. But this saturation is harmless compared to the death zones.

I believe this is this HT flux which somehow couples to my signal circuit. Below is a trace of my output ham with
the search coil signal from the HT transformer:

Channel2hum+HTcoil.bmp

I think the correlation is not entirely by chance (interestingly the ham is anticorrelated with LT flux).
Reducing the ham with box orienation seems to confirm it.

The ways out of spikes:

1) DIY-style grotesque way:change SiC's to tubes, esp. TV dampers...and burn 2x the power of the rest of
the circuit i their heaters.
2) try to close trannies in steel coffins, thick steel, 1mm at least; this would be my choice; the efficiency is unknown
and can be low at the 50Hz fundamental of the spikes but should increase greatly with harmonics;

The ugly choke ringing observed earlier I ignore at this moment as at the first caps behind the chokes
I have an almost perfect 100Hz sine; if I have a harch fatiguing sound then I try snubbers.

Cheers,
Ham-set

PS Those flux peaks are also most probably (co)responsible for the mechanical noise of the transformers.

Cheers,
Jarek
STACORE

11-28-2011

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Romy the Cat

Boston, MA
Posts 10,159
Joined on 05-28-2004

Post #:	177
Post ID:	17440
Reply to:	17439

Possible, so what?

Ham-set,

I think you are digging a hole in a wrong place. Regardless of any SiC alleged or actual problems I absolutely assure that the ham you have has absolutely nothing to do with type of the diodes you use but only come from grounding, shielding and interference. I tend to agree that “something” is not so clean with SiC diodes. If you remember I made my old version of Milq with regular super-fast switching and then went for high-voltage SiC Schottky. I do remember that when I measured how they return period to zero right before the choke I saw some anomalies. I did not give to them too much credit and I did not remember that it had any influence neither to Sound nor to noise. I do not remember details already, it was a few year back and I do not do all of this shit anymore. I do remember that I was persuaded by the manufacturer’s propaganda and their reasons did make sense to me at that time. On my side I was only concerned only to set the chokes in the critical inductance and let them to squash anything before them. Right or wrong, I kind of do not want to think about it again and I am very glad that the hated by me soldering episode of my life is over. Anyhow, I still under impression that with all your desire to go into the DIY details you are dealing with regular ground loops.

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

11-29-2011

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

Post #:	178
Post ID:	17442
Reply to:	17440

If you dont want to hear the bell...

...you either damp it or not kick it at all.
The symptoms suggest that what kicks my bell is my PS-rotating it changes the hum from strong to no audible.
I don't have a desire to go into DIY details but I have no better ideas at the moment on where the hum comes from.
I'd love to believe that there is a loop somewhere.
I've done all your procedures with shorting all the grounds and shorting the stages.
Shorting the grounds gave absolutely nothing and I cannot imagine where the fuck I should have a loop???
Shorting the stages kills the hum when I short the plate of the second stage (not the grid, but exactly the plate).
So my loudest bell is the output of V2/input of V3. I tried to find any loops round there, changing wiring, changing Holco to Dale
etc but no result (the hum has less HF and is more regular with Dale). What am I left with? Shield and proceed?

Cheers,
N-set

Cheers,
Jarek
STACORE

11-29-2011

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Romy the Cat

Boston, MA
Posts 10,159
Joined on 05-28-2004

Post #:	179
Post ID:	17443
Reply to:	17442

Seek and you’ll find.

N-set wrote:
... I cannot imagine where the fuck I should have a loop???

And you are not alone. Any single person who is chasing noise in phonostage ask himself the same question. I assure you that sun of later you will find it and it will be much simpler then you think.

N-set wrote:
... Shorting the stages kills the hum when I short the plate of the second stage (not the grid, but exactly the plate).

Did you try just for test to increase the caps value that short the plate to ground? Will it amount and the character of the noise change?

N-set wrote:
... What am I left with? Shield and proceed?

If I were you then I would use elimination techniques. Get rid of the output buffer and see if the noise still there. Replace the air caps in feedback with mike or alike and see if noise is there. The air caps are in a way antenna and they suck anything from air. My experience with similar problems suggest that it is good to take you mind away from it and do something else. Then is time you return back to the project and you will suddenly come to you…

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

11-29-2011

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AlexBerger
Israel, Beer Sheva
Posts 20
Joined on 04-19-2010

Post #:	180
Post ID:	17444
Reply to:	17442

Filament

What about filament?
Is the filament ground connected to the common ground?
Is the filament ripple is small?

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