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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old 11th September 2019, 12:02 AM   #28871
jneutron is offline jneutron  United States
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Quote:
Originally Posted by keantoken View Post
You take the pole plate, which is the steel plate that is on the other side of the flux gap from the pole piece. You split it from ID to OD the same way a lock washer (AKA split washer) is split.
Bingo.

Jn

Quote:
Originally Posted by mountainman bob View Post
I think there's a pic @ POST #28706

tried to move the pic but can't seem to do it on my phone.
I didn't post a pic. But I can draw one up tomorrow, if I have time.

Both the alum and brass are ID and OD correct, but still too thick. I can't believe my bottle of super glue dried up.. I have the facing mandrel made, but can't glue the rings in place to cut the thickness.

I"m still going to measure tomorrow bare, alum, and brass. But I'll still have to recalc the resistance for the thicker rings. If I can finish that during lunch, I'll be happy.

The copper is going slow...it's a square plate, and I can't hold it properly in a 3 jaw chuck. Which of course means, I need a 4 jaw.. Point and click with credit card, here I come..
I was pricing 2.75 inch diameter copper rod..holy mackerel, that stuff is expensive!! I need about 2 inches of that, and about 4 inches of 3 inch diameter magnetic steel.
Jn

Quote:
Originally Posted by TNT View Post
Nice metal work there jn!!

//
Thanks. I have an advantage in that I have an absolutely excellent machinist I work with, he is a tremendous resource to answer all my really stupid questions. And there are a lot of those..
Jn
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Old 11th September 2019, 06:49 AM   #28872
tvi is offline tvi  Australia
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The Alpine patent uses other means to the same end see first pic.

closer to what you are doing

US5357587 Distortion reduction in loudspeakers
GRODINSKY ROBERT M; CORNWELL DAVID G

In FIG. 1B, which is a rear view of a loudspeaker magnetic structure, the paths of the AC signal induced eddy currents in bottom plate 12 and pole piece 13 are illustrated. For a given polarity of AC signal in voice coil 14, the dashed line 24 shows the direction of eddy current flow in pole piece 13. Dashed line 25 represents eddy current flow in bottom plate 12 that is electrically coupled from pole piece 13. For the same polarity AC signal, the eddy currents that traverse the outer paths illustrated by dashed lines 26 and 27 in bottom plate 12 rotate in a reverse direction from those illustrated by the dashed lines 24 and 25. The difference reflects the reversal that occurs as flux travelling up the pole piece changes direction as it returns through the top plate 11, the magnet 10 and the bottom plate 12 as shown in FIG. 1A. Because the voice coil 14 surrounds the pole piece 13, the AC flux and the resulting eddy currents are highly concentrated. In the prior art, the pole piece is both electrically and magnetically connected to the bottom plate, which allows the concentrated eddy currents to couple into the bottom plate where they oppose and partially cancel the reverse rotating eddy currents induced by the returning flux. The result is distortion in the form of smear due to the phase differences between eddy currents in the top plate 11, which is not electrically connected to the pole piece, and eddy currents in the bottom plate, which is electrically connected to the pole piece. The resultant electrical fields from these eddy currents in both top and bottom plates induce rotating dielectric currents in the magnet, which adds distortion.

In FIG. 3, a more complex pole piece structure is illustrated. This structure further reduces eddy current distortion with an insulated pole extension 48, which also helps to linearize the magnetic flux in the vicinity of the voice coil and to reduce variations in the voice coil inductance. In this version, the bottom plate 42 is in contact with the second pole piece section 45 which is insulated from first pole piece section 43 by thin insulating washer 46. Another thin insulating washer 47 insulates pole extension 48 from first pole piece section 43. Slots 41 and 49 are formed in first pole piece section 43 and pole extension 48, respectively, for further reducing distortion by altering the eddy current flow patterns to reduce the coupling of the energy therein to other magnetic circuit elements. The slots also increase the eddy current path lengths which increases the resistance of these paths.
-------------------------------


have a few more...
Attached Images
File Type: png alpine.png (28.5 KB, 306 views)
File Type: png US5357587.png (37.7 KB, 305 views)
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Old 11th September 2019, 08:40 AM   #28873
Bonsai is offline Bonsai  Europe
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Originally Posted by Evenharmonics View Post
That would be the least of my worries on personal info disclosure.

Good one!
How about "victim card fanatic"?


@In the aforementioned conventional speaker, the ring-shaped iron plate 73 and the iron yoke 77 are used as component parts of the magnetic circuit. Therefore, the magnetic field of the voice coil 76 produced by applying voice current (alternating current) thereto develops eddy currents in the ring-shaped plate 73 and the yoke 77 which define the magnetic gap 79. These eddy currents are the primary cause of sound distortion.

"The very low inductance of the voice coil 76 increases to a high value when it is placed close to the ring-shaped iron plate 73 and the iron yoke 77. Therefore, the impedance increases from the intermediate-frequency to high-frequency ranges, which leads to reduced sound conversion efficiency. At the same time, phase rotation increases due to impedance, which causes a distortion in the output sound phase."

I might be jumping the gun, but is this perhaps an explanation as to why current drive lowers distortion?


@tvi so the slit is just down thee side of the pole piece per the drawing?
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Old 11th September 2019, 09:44 AM   #28874
tvi is offline tvi  Australia
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Yep but each of the 3 sections are electrically insulated.

The slot would be covered by jps52117931 which i can only find in Japanese, I think its Sony?

Grodinsky & Cornwell have another patent where they slot the ferrite magnets
US5070530
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File Type: png JPS52117931.png (34.5 KB, 283 views)
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Old 11th September 2019, 10:25 AM   #28875
gpapag is offline gpapag  Greece
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John Curl's Blowtorch preamplifier part III
Quote:
Originally Posted by Bonsai View Post
I might be jumping the gun,
IMO they exaggerate. For their case, they should provide measurements for the three effects

Quote:
These eddy currents are the primary cause of sound distortion.
Quote:
Therefore, the impedance increases from the intermediate-frequency to high-frequency ranges, which leads to reduced sound conversion efficiency.
Quote:
At the same time, phase rotation increases due to impedance, which causes a distortion in the output sound phase."
I hope JN will provide measurements before and after slitting the pole and front plate (in a dedicated thread)

George
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Old 11th September 2019, 10:30 AM   #28876
jneutron is offline jneutron  United States
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Thanks again, great stuff.

But nobody slits the front plate. I would have thought that the front plate as a shorted turn would have been obvious.

Jn

I was thinking... If I had some spare D-205TI drivers, I would just take the diaphragm assembly out of the magnet structure, put the assembly on the bandsaw, and cut from the edge to the center of the pole piece. That would eliminate the need for insulating the front plate from the magnet and would cut down the pole piece and magnet shorted turn currents.

Cleaning the gap would not be too easy, but certainly doable.

Then, use some JB weld to fill in the kerf all the way around. That way, dust can't get into the gap.

Unfortunately, I have 6 of these puppies in service, no spare magent structures, and only two replacement diaphragms, one of which I am using for this test.

jn
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Old 11th September 2019, 01:48 PM   #28877
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by tvi View Post
The Alpine patent uses other means to the same end see first pic.

The resultant electrical fields from these eddy currents in both top and bottom plates induce rotating dielectric currents in the magnet, which adds distortion.

The slots also increase the eddy current path lengths which increases the resistance of these paths.
-------------------------------
have a few more...
Seems I mentioned this as a question #28866 with no response.

"yes, thx. Any eddy currents involved.... before or after slit cut?"

What affect would it have?

THx-RNMarsh

In other words, increased impedance from the cut(s) will reduce the effectiveness of the "short".

No? Yes? Maybe?

THx-RNMarsh
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Old 11th September 2019, 03:43 PM   #28878
DPH is offline DPH  United States
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Quote:
Originally Posted by jneutron View Post
Then, use some JB weld to fill in the kerf all the way around. That way, dust can't get into the gap.

Unfortunately, I have 6 of these puppies in service, no spare magent structures, and only two replacement diaphragms, one of which I am using for this test.

jn
JB weld uses iron filings as a reinforcement, so maybe choose a different epoxy.
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Old 11th September 2019, 04:07 PM   #28879
jneutron is offline jneutron  United States
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Quote:
Originally Posted by DPH View Post
JB weld uses iron filings as a reinforcement, so maybe choose a different epoxy.
I'll check a tube at home with a magnet, I thought it was non magnetic as well as non conductive.

John
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Old 11th September 2019, 04:31 PM   #28880
DPH is offline DPH  United States
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JB weld makes a few different compositions under their brand, but their "classic" dark grey stuff is both conductive and magnetic from the filings. Not extremely so, but enough to matter when you need something truly non-conductive/non-magnetic. It's bitten me before on some prototypes at work, where I grabbed the tubes out of convenience. For most things, it's a great product.
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