Author Topic: EEVblog #1104 - Omicron Labs Bode 100 Teardown  (Read 32847 times)

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Offline rx8pilot

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #175 on: October 04, 2018, 03:10:21 am »
And for the graphics.....
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Offline DualTriode

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #176 on: October 04, 2018, 05:06:38 pm »
Wolfgang,

Such pride?

Been there done that.

The VAC T60006-L2030-W514-03- core appears to be an exact match for size and color for the core in the real B-Wit injection transformer.

See Reply #79 for a photo.

See Reply #96 for a plot (identical to the real deal)

It all fits into a cute little Hammond box just like the real deal.

DT
 

Offline rx8pilot

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #177 on: October 04, 2018, 06:33:19 pm »
Wolfgang,

Such pride?

Been there done that.

Now, now.....
The write up by Wolfgang is really nice....and seeing some of the initial efforts is very interesting.

The VAC T60006-L2030-W514-03- core appears to be an exact match for size and color for the core in the real B-Wit injection transformer.

See Reply #79 for a photo.


This is exactly why I already have one on my bench....I put it in my next Mouser order. Good work, thank you.

See Reply #96 for a plot (identical to the real deal)


Do you have this plot scaled by chance? The db/div and deg/div are rather course in the range of interest. Not too critical, but the conversation has been splitting hairs and the precision of your plots are bigger than a hair  :-DD.



Back to one of the earlier questions.....
Why does the response need to be so flat and phase perfect when the calibration of the VNA can null out the transformer response?
Are nude virgins actually helping here?
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Offline Wolfgang

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #178 on: October 04, 2018, 06:39:26 pm »
Wolfgang,

Such pride?

Been there done that.

The VAC T60006-L2030-W514-03- core appears to be an exact match for size and color for the core in the real B-Wit injection transformer.

See Reply #79 for a photo.

See Reply #96 for a plot (identical to the real deal)

It all fits into a cute little Hammond box just like the real deal.

DT

Hi,

I disagree that it is the same core.

The datasheet of your part is here:

https://www.vacuumschmelze.de/fileadmin/Medienbiliothek_2010/Produkte/Kerne_und_Bauelemente/Anwendungen/Kerne/Kerne_SKDs_Kunststoff/W514.pdf

the core in my B-WIT100 (I disassembled it today to check) has a diameter of 42mm.

Maybe they changed the core during production, I dont know.

The internals of the box I did not like so much. Its all antistatic mats and glue, the fuse is soldered and insulated by shrink-wrap, only one side is fused, ...
Not a convincing expression of quality, for 500€, I would say. So the real deal is not exactly a good deal.

To make my own was a challenge and a prank. I do know its not rocket science, and it was just a fun thing. See last photo on my "injection Transformers" page.
 

Offline Wolfgang

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #179 on: October 04, 2018, 07:02:26 pm »
Hi,

the reason why you should not rely on nude virgins but rather have a good injection transformer is measurement accuracy. It is correct (it was the prime argument of the Texas instruments people in their Bode papers) that the transformer can be normalized out, but:

- the problems occur at the band corners, where the S21 of the transformer deviates from 1 a lot (e.g., 10dB for the B-WIT100 at 1Hz).
  Lets say we are at the low frequency range (there its most prominent) for now.
- your injection amplitude is now 10dB down, say, i.e. your measurement noise goes up
- If you try to increase drive level, you will soon run into core saturation problems creating harmonics and all other kinds of dirt effects.
  The lower the frequency gets, the more pronounced this problem is. Dont forget that allowable DC-AC current to avoid saturation is in the range of 10mA.

- At the high frequency edge stray inductances and interwinding capacitances could make your measurements problematic, because the parasitic elements are
  normally not very well known.

So, transformer imperfections can be calibrated out, but at the cost of less dynamic range.

I think what we got here is about the max that can be expected from a single-transformer design.
When you look at the market, they have special transformers for the low end (Ridley, Picotest, Omicron, ...) with heavy cores. Their high-end behaviour is bad, however. The small cores do it just the other way. It only depends what you need.

Techniques that could work (I never tried, just saw some literature) are stacked transformers, each for its own frequency band, ...)
To make this is extremely tricky, involves extended alignment and compensation and you can be glad to get a factor of 10 in frequency range over normal cores.
 

Offline ogden

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #180 on: October 04, 2018, 07:13:21 pm »
- the problems occur at the band corners, where the S21 of the transformer deviates from 1 a lot (e.g., 10dB for the B-WIT100 at 1Hz).

Are you really not sure about your DC supply stability below 1Hz? Or even 100Hz?  :-//
 

Offline Wolfgang

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #181 on: October 04, 2018, 07:21:16 pm »
Hi,

what I hear the problems at low frequencies are a peculiarity of the PFC (power factor correction) people. Dr. Ridley has a video about this; they attack a PFC regulator by imposing strong sub-Hz disturbances and then check if the PFC IC still works. For normal linear PSUs, LF instability is not likely to occur because most PSU at least are good enough to suppress rectified line ripple, around 100Hz in Europe. Switching regulators with several regulating loops working parallel are a different matter. There testing LF also makes sense.
 
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Offline DualTriode

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #182 on: October 04, 2018, 07:56:27 pm »
Apologies,

Back on June 7th I opened the B-WIT-100 and measured the core inside and went to Mouser to see if I could find the part. I just looked up the part that I ordered and used to make the Home Roll transformer is this one: https://www.mouser.com/datasheet/2/599/W424-237924.pdf . In error I posted the wrong part number in Reply #79.
 
The photo and plot are the correct items.

In terms of plots with a finer scale what I posted is what you get from the Bode 100 software. The Bode 100 and software does record precise data points that will split fine red hair.

All the conversation about gain and phase at the tails of the plots I believe is mostly arm waving. The Bode 100 or for that matter any VNA will do Thru calibration and correct for a moderate degree of Phase and Gain variation.

Again I am sorry for posting by mistake the incorrect part number, this is the part in the photo and tested and appears to be very close to the B-WIT-100 core.

https://www.mouser.com/datasheet/2/599/W424-237924.pdf


Thanks DT
 

Offline Wolfgang

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #183 on: October 04, 2018, 08:22:14 pm »
Dont worry, many ways lead to Rome.

One should not forget that the cores have tolerances of a few 10 percent up and down. The difference between the homebrew curves and the B-WIT100 are probably less than the average variation between different B-WIT100 units.
The core you used has an average Al of 109, the one I used has one of 94. The mouser part number you gave has no plastic trough filling around it as mine and the one used in the B-WIT100. I know that only german readers can identify this difference. So maybe you got yourself a similar, but not the same part.

I am not completely in agreement with the idea that the Bode 100 will kill *all* problems. For PFC, there are probably better (sub 1Hz) machines, and for ultra-high frequency switchers you probably need another lineup of injectors. I have no big trust in banana wired setups at 50MHz. Another field where I have not worked myself in sufficiently yet is the measurement of really small impedances like PDNs on digital boards.

At the moment I am testing the E5061B-3L5 and the Bode 100 in parallel and the agreement at low frequencies is good (10MHz). Above that I would believe the E5061B-3L5 a lot more (upper limit is 3GHz). But - no final results here yet.
 

Offline rx8pilot

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #184 on: October 04, 2018, 08:28:35 pm »
@Wolfgang HA! :-DD

Funny.....
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Offline ogden

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #185 on: October 04, 2018, 09:18:03 pm »
what I hear the problems at low frequencies are a peculiarity of the PFC (power factor correction) people. Dr. Ridley has a video about this; they attack a PFC regulator by imposing strong sub-Hz disturbances and then check if the PFC IC still works.

Oh, PFC people. They are supposedly rich, right? ;) - I would say that sub-1Hz job is not easy for transformer. To cover low frequency range down to DC one could try isolation amplifier based "injection transformer"
 

Offline Wolfgang

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #186 on: October 04, 2018, 09:29:53 pm »
... the video shows a transformer that has a few 100g (Dr. Ridley *weighs* them as a criteria for quality) and then he weighs all the others (and concludes that they are too light for the hard job). Irony apart, of course you could always throw some kilograms of iron and copper at any LF problem it will work. It wont be cheap, however, and an independently powered solid-state injector could be a better option. There are quite some on the market.

Whatever you see at Ridley, Omicron, Picotest or Keysight is made to make their own products shine. Independent thinking is key to not fall into a vendors honeypot. The matter is tricky, there are many pitfalls, and a lot of info is not very well communicated. Lots of work to do !
« Last Edit: October 06, 2018, 01:58:39 am by Wolfgang »
 

Offline rx8pilot

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #187 on: October 04, 2018, 09:44:17 pm »
When Ridley got out the scale, I almost fell out of my chair.

All I really care about is how it performs in real life - it was really unexpected from a person with his pedigree and credentials. That type of sales pitch really degrades his own line of products for me.

And yes, for the really low frequencies - a solid state solution is a clear winner in performance at that expense of complexity.

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Offline Wolfgang

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #188 on: October 04, 2018, 09:50:47 pm »
The Omicron people have their own videos where their products shine and Ridleys dont (no surprise, the focus on bandwidth and flatness, where the big super-LF stuff flunks out in the 10kHz range). There is no such thing like a single size that fits all. Check what you really need, try all yourself and let the salesmen talk as much as they may.
« Last Edit: October 04, 2018, 10:33:10 pm by Wolfgang »
 

Online Bud

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #189 on: October 04, 2018, 10:53:15 pm »
Why does the response need to be so flat and phase perfect when the calibration of the VNA can null out the transformer response?

In general you want errors to be as small as possible to reduce dependency on stability of calibration, because of time or temperature changes,etc.
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Online Bud

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #190 on: October 04, 2018, 10:57:48 pm »
@Wolfgang HA! :-DD

Funny.....

You can bet someone is about to get offended and , given the placement of the transformer symbol, ask what do you mean by "injection"  :-X
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Offline DualTriode

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #191 on: October 04, 2018, 11:12:50 pm »
One size does not fit all.

The high permeability cores saturate easily with only a handful of ma’s current. This one I used a much lower permeability core and tested inductance with up to 100ma with no sign of saturation. The lower permeability also results in less LF performance. (tested with Rhode HN8118 LCR meter)

This injection transformer is intended to be in series with the power supply and test audio amplifier PSRR.

I have misplaced the APx555 output plot.

DT
 

Offline Wolfgang

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #192 on: October 04, 2018, 11:38:44 pm »
@Wolfgang HA! :-DD

Funny.....

You can bet someone is about to get offended and , given the placement of the transformer symbol, ask what do you mean by "injection"  :-X

IMHO, its a harmless prank, and the words came from the master of all this forum himself, Dave.
The picture is a classic Amadeo Modigliani, and no obvious sexuality is shown.
This is art, not porn.  :-+ Smut is in the eye of the beholder (Tom Lehrer).
 

Offline Wolfgang

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #193 on: October 04, 2018, 11:44:00 pm »
The plot would say more with a proper scale (1dB/div) for gain.

The problem with high-mu cores saturating with small DC currents is well known.

Two ways out exist:
- lower mu, with worse LF response as a consequence
- dont change core, but let no DC go thru it by using a huge blocking cap.

There is some Keysight literature about how to do this.

What is the frequency range you would like to cover ?
 

Offline DualTriode

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #194 on: October 05, 2018, 12:33:38 am »
No Problem.

This transformer demonstrates that one size does not fit all.
 
It is installed at the output of a DC power supply.

The frequency range is from below 10hz to mid Mhz range.

This transformer will test Amplifier and Power Supply Rejection Ratio.

DT
 

Offline Wolfgang

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #195 on: October 05, 2018, 12:39:07 am »
Hi,

just a hint: you could do it in two sweeps, with the LF part covered by a fat transformer (Omicron, Ridley, Homebrew by stacked cores, ...)
and a normal transformer for the higher frequency part.

Just a question: Why are you testing up to a few MHz ? Are you afraid of amp instabilities of RFI problems ?

Do you want to try a core that withstands a lot of DC current or by the Keysight method with a DC block cap so the transformer always runs in AC mode ?

How many amps does your supply current have ?
 

Offline DualTriode

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #196 on: October 05, 2018, 02:38:01 am »
Hello,

I want to keep this as simple as possible and only add complexity as needed. Audio Precision uses a Jensen JT-123-BLCF transformer for this application in their technote 106 (you need to sign in at the AP.com site to download the technote). https://www.ap.com/download/technote-106-measuring-psrr-power-supply-rejection-ratio-2/?wpdmdl=5795

I am looking for a transformer that will withstand maybe 200ma or 300ma, so far 50ma is enough. I have used this transformer with a 12B4A audio tube amp tube circuit biased to ~ 35ma. The 12B4A will oscillate if you give it a chance.

Why test to a few Mhz? Afraid? No. Yes I am looking for wider bandwidth than the Jensen transformer. I do want to take a look for RF and possibly other oddities even oscillation. Mostly it is fun to look.

I am not opposed to the Keysight method. Perhaps you can supply a reference. I do have Keysight instruments on the bench and Keysight books on the shelf.

Thanks DT

 

Offline Wolfgang

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #197 on: October 05, 2018, 10:33:03 am »
Hello,

I want to keep this as simple as possible and only add complexity as needed. Audio Precision uses a Jensen JT-123-BLCF transformer for this application in their technote 106 (you need to sign in at the AP.com site to download the technote). https://www.ap.com/download/technote-106-measuring-psrr-power-supply-rejection-ratio-2/?wpdmdl=5795

I am looking for a transformer that will withstand maybe 200ma or 300ma, so far 50ma is enough. I have used this transformer with a 12B4A audio tube amp tube circuit biased to ~ 35ma. The 12B4A will oscillate if you give it a chance.

Why test to a few Mhz? Afraid? No. Yes I am looking for wider bandwidth than the Jensen transformer. I do want to take a look for RF and possibly other oddities even oscillation. Mostly it is fun to look.

I am not opposed to the Keysight method. Perhaps you can supply a reference. I do have Keysight instruments on the bench and Keysight books on the shelf.

Thanks DT



Some comments to that:

- Your Jensen transformer covers the audio range only, and one winding (of 4) has 20 Ohms already. I have missed a DC current tolerance spec in the datasheet.
- it could well be that even a moderate DC current of a few 10 mA drives it into saturation so much that the inductance goes down a lot.
- What you might need is an output transformer for tube class A linears. They are used to DC bias.
- Info about some Keyside tricks can be found here:
http://literature.cdn.keysight.com/litweb/pdf/5990-5902EN.pdf

hope that helps because 10Hz to a few MHz with up to 300mA DC - thats a challenge.

  Wolfgang

 

Offline MilkmanCDN

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #198 on: October 18, 2018, 11:53:18 pm »
@DualTriode,

Thanks for updating the correct BWIT transformer part number.   In my haste I ordered 3x of the wrong one and was wondering why I could only get 30 turns around the transformer, instead of 40.    Looks like the correct transformer is a little larger.   It's all making sense now.   New order placed.
 

Offline Relaxe

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Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #199 on: October 23, 2018, 08:40:25 pm »
Thanks for your work Wolfgang!

Can you tell us the part # of the Hammond Box?
I want to duplicate this here...
 


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