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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old 6th December 2018, 02:00 PM   #11091
jneutron is offline jneutron  United States
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Quote:
Originally Posted by Max Headroom View Post

FFT - YouTube

Dan.
Fun to watch.

In the clock world, it is called sympathetic vibration. Put two grandfather clocks against the same wall, and eventually they will synchronize.

When troubleshooting a grandfather or grandmother clock, one of the first things to look for is, when it stops, where are the weights? Many times, the case sways ever so gently to the pendulum, and when the weight frequency of oscillation gets close to the pendulums natural frequency, weight sway will take energy from the pendulum. As a clock nears servicing time, the escape wheel/pallet assembly is not receiving enough energy to sustain through that energy loss. Sometimes, just locking the case to the wall near the top is sufficient to get a few more years of operation. If the problem is due to lack of oil, those few more years will make the repair more extensive as the steel pivots will wear a channel in the brass plate.

Some scientists recently did a paper on this sympathetic vibration. Of course, the clock world has known about it for several hundred years.

Jn
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Last edited by jneutron; 6th December 2018 at 02:04 PM.
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Old 6th December 2018, 02:06 PM   #11092
Jakob2 is offline Jakob2  Germany
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@DPH,

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Originally Posted by DPH View Post
Jakob, as I wrote just above, this is going to be a case where unless someone here does the measurements, and covers the bases needed by using a suite of precision low frequency and RF instruments in a shielded room (plus all the replications, resetting of the test setup to make sure it's not aerials injecting into the measurement, etc., etc.)<snip>
I agree; actually that somebody could repeat the measurement (noise source and sine combined via power mixer), was what i hoped for (as stated before).

That something is always disputable is just normal, no perfect experiment thinkable; i thought it is interesting as the result of that measurement is not compatible with the statement that the device is just an ordinary resistor (small value) .

@ jneutron,

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Originally Posted by jneutron View Post
Without seeing the setup, we can't know if "direct" is the baseline. at 100 dB down, even wiring physical layout can have an effect.
Sure; "baseline" with respect to the measurement equipment would be result of the calibration procedure along with the uncertainty and so a measured internal connection between generator section and analyzer section.

Experimentwise "baseline" is imo what he described as the external connection between generator section and analyzer section via coaxial cable without devices and then with devices installed.

Agreed that the implementation of the devices and comparison conditions are crucial and that it would be much better to have some pics of the "fixture/installation" .

Quote:
For LOTO, we will check the meter against a known source of the correct voltage, then test the entity we want to look at, and then re-test the meter on a known source. That way we know that the meter works both before and after we checked the widgit. Otherwise, safety can be compromised.
Same procedure we follow.
Btw, i remember a discussion about the Meyer/Moran experiment over at hydrogenaud.io, where i mentioned that measuring the test equipment before and during the experiment (all the more in that case of a long term experiment) is very important - even dared to mention a lab notebook - i was strongly attacked for "rasing the bar to high" and being only interested in discrediting "blind tests" .....

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Here, we have no way of knowing if the 1dB is test error, measurement setup, room air conditioning, whatever.. They don't mention going back to "baseline".
Again agreed, but the lab lists the measurement limits and uncertainty for their equipment on the website

Overall it could be that the actual lab report contained a lot more pages, but that it would be too much for the magazine to print the full report.

Quote:
We agree, one result can actually be meaningless if it doesn't repeat.

I suspect that the lossy part they noticed and spoke of is probably what's going on. But again, without any details, nobody can validate..

jn
Sure.

@gpauk,

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Originally Posted by gpauk View Post
My experience of test labs is that the technicians follow recipes for standard measurements - but step off the script, or need understanding of the process - well, good luck!
As said before, it could be.
Otoh in this case the situation is a bit different, as the quy who did the measurements is actually the owner of the lab, seem to know (from what iīve read from him) what he is talking about, has some examples of carefully done stuff.

There surely is a slight impression of a nerd factor in there but also surely he isnīt just an ordinary technician being lost due to lack of understanding.

But as said before, itīs just speculation/assumption.....
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Old 6th December 2018, 02:22 PM   #11093
scottjoplin is offline scottjoplin  Wales
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A resistor with some inductance, is that in dispute?
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Old 6th December 2018, 02:24 PM   #11094
Indiglo is offline Indiglo  Australia
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Quote:
Originally Posted by jneutron View Post
Thanks, very interesting.
Note that the inductance slope of the pickup coil runs opposite to that of the primary driver. When the drive goes out of it's gap, inductance goes down but the pickup goes in deeper, getting higher inductance.

All those switches and choices, too complex for me.
It might tailor the sound I guess, so the owner could play.
My scheme is to try to eliminate the bad stuff by magnetic and pickup design, not to try to do this acceleration or velocity calculation stuff.

Jn
Okay, Im starting to understand what your're trying to achieve.
Just thinking out aloud, multiband vehicle mobile phone antenna's use printed inductors (akin to RF striplines) on plastic, the plastic being quite thin could almost wrap around the existing voice coil.
You could print the inductor in any shape you like, i guess the limitation is would this generate enough inductance ?
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Old 6th December 2018, 02:29 PM   #11095
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by Max Headroom View Post
One experiment that did show remarkable effect was when listening to pink noise through loudspeakers.
Except in this case the pink noise was the signal.
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Old 6th December 2018, 02:35 PM   #11096
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by scottjoplin View Post
Me too YouTube
I had a lady friend who was in a small amateur ensemble and she told me how strange the scoring was for stuff like this.
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Old 6th December 2018, 03:06 PM   #11097
jneutron is offline jneutron  United States
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Originally Posted by Jakob2 View Post
@ jneutron,


Experimentwise "baseline" is imo what he described as the external connection between generator section and analyzer section via coaxial cable without devices and then with devices installed.
Yes, that can confirm the equipment capability. But as we know, many times the exact setup, cables, connectors, can impact the end result, especially down near the mud.

One guy here is trying to get good readings with a nano-voltmeter...he has found the learning curve is quite steep.

One question...why are they comparing a resistive device to a wire??? Wouldn't it be better to compare a resistive device with a resistor? We already know that a resistor is different from a wire..


Agreed that the implementation of the devices and comparison conditions are crucial and that it would be much better to have some pics of the "fixture/installation" .
Quote:
Originally Posted by Jakob2 View Post
even dared to mention a lab notebook - i was strongly attacked for "rasing the bar to high"
How dare you. What were you thinking??


Quote:
Originally Posted by Jakob2 View Post
Again agreed, but the lab lists the measurement limits and uncertainty for their equipment on the website
sigh...

Quote:
Originally Posted by Jakob2 View Post
nerd factor....
What's that??? I've never heard of that before, especially in reference to me...

jn
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Old 6th December 2018, 03:14 PM   #11098
jneutron is offline jneutron  United States
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Originally Posted by Indiglo View Post
Okay, Im starting to understand what your're trying to achieve.
Just thinking out aloud, multiband vehicle mobile phone antenna's use printed inductors (akin to RF striplines) on plastic, the plastic being quite thin could almost wrap around the existing voice coil.
You could print the inductor in any shape you like, i guess the limitation is would this generate enough inductance ?
Absolutely..The print can be finer than the vc wire, it can be matched to number of turns.

I recall mentioning that in a thread, not sure where, perhaps months ago. I've seen many Kapton based flexible circuits out there. The problem is, I'm not sure how easy it would be to print on a cylinder, a simple print would require a significant number of connections in there in order to wrap around the coil. If the turns do not wrap around the center pole, it will not be sensitive to the variation of inductance the actual vc sees.

I had spoken about printed loops on the vc former, but the intent back then was to monitor the gap flux or lack thereof. My newer scheme automatically compensates for the variation in vc inductance through the entire vc travel range, the old concept only measured the flux falloff and would require significant DSP to understand how to predistort as it would still require calculation of position and then a lookup table/polynomial fit to apply the compensation distortion. My newer concept will not adjust to flux falloff if the coil leaves the gap.

jn
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Last edited by jneutron; 6th December 2018 at 03:33 PM.
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Old 6th December 2018, 03:23 PM   #11099
hitsware is offline hitsware
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Quote:
Originally Posted by jneutron View Post
Fun to watch.

In the clock world, it is called sympathetic vibration.
Jn
Same with a group of these :

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Old 6th December 2018, 03:30 PM   #11100
jneutron is offline jneutron  United States
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No, sorry.(they talk to each other. many times, they say bad things about your driving skills, your taste in clothing, your choice in music...) but don't say that out loud in the car, they tend to gang up.

And they do it just like baby Groot in the final scene of GOTG 1 (the talking amongst themselves I mean..)

jn
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Last edited by jneutron; 6th December 2018 at 03:33 PM.
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