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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old 21st September 2019, 01:39 PM   #29021
orjan is offline orjan  Sweden
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Quote:
Originally Posted by PMA View Post
This is interesting as it shows where it starts clipping (the spectral view).
Hi PMA

Do you have the waveform saved so you can show the severity of clipping for the measurement?

Would it be possible with a metric on clipping, perhaps power from spectrum weighted with increasing frequency. Then multiplied with "blocking" time. Problem might be at wich powerlevel.

/örjan

Last edited by orjan; 21st September 2019 at 01:42 PM.
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Old 21st September 2019, 02:42 PM   #29022
PMA is offline PMA  Europe
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Yes I have. Give me some time, please. Clipping occurs in last 4 columns. Other transitions are digital/soundcard issues during on/off. Fast digital scope is much better to catch on-off transients. I have it as well.
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Old 21st September 2019, 05:12 PM   #29023
gpauk is offline gpauk  Scotland
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And once again, many thanks Pavel - thanks for the dose of sanity, and all the work on getting real, reproducible, meaningful and useful results. Excellent stuff.
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Old 21st September 2019, 05:32 PM   #29024
PMA is offline PMA  Europe
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Thank you for your kind words gpauk, at least I may have a feeling that the effort is not useless.
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Old 21st September 2019, 05:33 PM   #29025
jneutron is offline jneutron  United States
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Also my thanks for the time taken.

My next test will involve the measure of proximity effect on an inductor. To wit, it will be to look at the third harmonic distortion created by proximity effect.

The inductor will be air core copper not sure what gauge copper yet.. at least two layers, larger diameter wire will have more than two layers. I will co-wind a second copper wire, a much smaller gauge the will nest in the interstitial spaces between the larger wire. I will wind it with an ID of probably 2.05 inches, as I have a 5 inch long piece of aluminum 2 inch OD that will be destined to be placed inside the coil for eddy loss measurements static as well as during oscillatory motion.

The intent is to drive the large gauge at frequency, compare the tap coil voltage to the drive voltage on the large coil.

The tap coil will measure only the time dependent flux in the coil set. The difference between the two will show the dc resistance of the primary coil as well as any additional losses, for example external eddy losses as well as the wire losses.

Since proximity effect is rate of change related, the expectation is that there will be a third harmonic distortion of the primary coil current because the resistance increases when the current crowds during high current slew rates.

The hypothesis: using a co-wound two coil inductor, the use of the tap coil voltage pickup coil to cancel all magnetic field induced reactances will show a third harmonic signal due to proximity effect. I will tie the two coils at the drive side of the pair, the large wire will return to the amp ground, and the pickup coil will be used to monitor the difference voltage with respect to ground.

When complete, the coil will be sent to someone else who has equipment available to further test. Received the next two 8 inchers...I'm chilling on that for the moment, I still need to try the chem detach of the spider from the frame..using an exacto is killing the spider as it is too well attached to the frame. Either local heat of the frame, or chemistry will be tried. I've also been looking at .025 thick steel, and am thinking of making a laminated plate for the visiton magnet assembly, as well as some method of attaching the basket to the faceplate so that I can remove and replace it. Given how strongly the faceplate sticks to the magnet, I think I could probably get away with no epoxy at that interface. I would need some kind of non ferrous adapter over the ferrite that the basket can be tie to, and it will need an adjustment to align the voice coil. If I make my own faceplate, I can also increase the ID a bit if the co-wound coil increases the vc thickness.

jn

ps. or, you guys could tell me to get lost, and go back to discussing tinfoil hats and zombie lizards...
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Last edited by jneutron; 21st September 2019 at 05:43 PM.
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Old 21st September 2019, 08:10 PM   #29026
simon7000 is offline simon7000  United States
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Max,

Managed to have a bandsaw I was cleaning fall over on me Tuesday. Nothing serious as it was small one at 280 lbs. So sort of a slow rest of the week.

Next week will remove the wheels, extend the base and then attach wheels that will leave it lower off the ground.
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Old 21st September 2019, 10:08 PM   #29027
benb is offline benb  United States
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John Curl's Blowtorch preamplifier part III
Quote:
Originally Posted by jneutron View Post
Also my thanks for the time taken.

My next test will involve the measure of proximity effect on an inductor. To wit, it will be to look at the third harmonic distortion created by proximity effect.
The proximity effect of WHAT? Something being in proximity to the coil?
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Old 21st September 2019, 10:09 PM   #29028
jneutron is offline jneutron  United States
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Originally Posted by jneutron View Post
The tap coil will measure only the time dependent flux in the coil set. The difference between the two will show the dc resistance of the primary coil as well as any additional losses, for example external eddy losses as well as the wire losses.
Edit: stated incorrectly...

The primary driven coil will show all inductance and all resistances.

The resistance seen will be a sum of the DC resistance of the wire modulated by proximity effect, and the losses caused by any phenomena that is spoken to via magnetic flux. For example, eddy losses in a conductive object brought into the field will be seen by the driven coil as well as the tap coil. Proximity losses in the driven wire will NOT be seen by the tap coil, just by the driven coil.

By subtracting the two, the difference should be the IR losses in the driven coil. This is where I expect to see any proximity effect.

(note, the only caveat to that is, proximity effect will cause the effective radius of the centroids to increase...I am hoping that by putting the tap wire in the interstitial spaces, it will not be too susceptible to the centroid drift..)hmmm. I bet if I put a third tap coil on the outside of the coilset, I might be able to purposely make it more susceptible to centroid drift...have to think about that.

Ed, thankfully you are still up and around. What were you cleaning it with, a backhoe??

Quote:
Originally Posted by benb View Post
The proximity effect of WHAT? Something being in proximity to the coil?
No. Proximity effect causes the current within an inductor's turns to shift to one side of the wire. It is essentially the same thing as skin effect, but in a round conductor not close to anything, skinning occurs symmetrically. In a multi turn inductor, the rate of change of the magfield caused by the lots of turns will cause the current to tend to one side of the conductor. This can sometimes be seen on a frequency scan of an inductor, for example the ones in my gallery. An air coil inductor will show as flat up to some frequency, then it will start to decrease as the current starts to shift. When that happens, you can see the resistance also start to increase.

Sometimes this is called skin effect..large inductors run at high frequencies will dissipate more because less of the conductor is actually involved in the transport of current. The correct term is proximity effect, but it is used interchangeably with skin effect. No big deal..

In a gapped toroid for example, when the windings get close to the gap, they will tend to dissipate more because the field lines are seriously "bent" by the gap. Sullivan from Dartmouth College had some good writeups on that, as well as some good write-ups on skin and proximity.

jn
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Old 22nd September 2019, 12:15 AM   #29029
john curl is offline john curl  United States
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Personally, I am all for talking about: 'Spooky action from distant objects'. This is what intrigues me most these days.
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Old 22nd September 2019, 12:21 AM   #29030
simon7000 is offline simon7000  United States
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An oily rag. There is now a "Model B" which has a larger base. Both upper and lower doors were open.

If I were crazier I would do a test to see how much force would tip it. I suspect it is less than a decent sized piece of wood around 20 pounds off the table.
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