Any thoughts about "True Phantom"?

[abbey road d enfer]

But it is very important for mikes with a output transformer.  I would never connect this phantom power supply to a 414, U87 and similar.

Any DC current delivered would be constrained by the common-mode impedance. According to specs, it's about 200 kiloohms (or 2 Megs??). As long as the system operates within its linear limits, the worst-case (i.e. with one pin shorted to ground) differential DC current would be about 250 uA, not enough to do any harm to the transformer, nor magnetizing it significantly.

 

[Gus]

the circuit(s) design deserves more discussion.

 

[abbey road d enfer]

the circuit(s) design deserves more discussion.

Does it really? The patent is pretty clear.
I have been very critical in the past towards the FetHead, that seems to be spiced with too much fairy dust, and it may be the case here too, but the principle is sound.

 

[Gus]

I was thinking more along the lines of
Two well matched(better than .1%) 1/2 watt 6.8K resistors
vs
A circuit that has more parts.

Are there power up power down failure issues?

Does it make a difference that can be heard?
I don't trust reviews, videos and recordings on the web I use them as a starting point.

Plus will the user have to remove the phantom resistors in preamps that have them for the full effect of the circuit. Phantom power can be switched out at the phantom resistors power supply node so they are always in circuit.

 

[mhelin]

Found this schematic with component values by accident in Youtube.

 

[RuudNL]

Do you have a link to the video?

 

[mhelin]

Do you have a link to the video?

https://youtu.be/VWWIbEf0268

 

[gyraf]

If that circuit is real, I see a whole range of error modes that can bring up voltages to a point (63V DC anyone?) that is really not healthy for many P48-based mics.

I see potential of many smoked output electrolytics in e.g. Neumann TLM and Schoeps-type microphones.

Nobody, Nobody expecs to see over 52V there..

/Jakob E.

 

[Gus]

I simmed the figure 4b circuit. I did not sim the one from the youtube video yet.

I might build one for fun to see how it interacts with different phantom powered microphones circuits.

 

[MediaWorksOKC]

Yo!

It's my understanding that Joost Kist and Triton are separate entities and that Triton has licensed the design. His AES paper is attached below. I'll delete if inappropriate to post. I had some correspondence with him years ago about this.

He said a chip is "in development" to be available at low cost at some point in the future, for some time now... tick-tock. Maybe 3 years since I first looked at his design.

I hear a positive difference in the resulting sound from the design that doesn't correlate to the minor improvements of a few percentage points here or there. It's real. Just sounds more natural. To me.

I would never pay 500 dollars but would happily buy quantities of a 5 dollar chip.

Chris

 

[RuudNL]

Of course, theoretically it might be an improvement.
But personally I am not really worried about second harmonics at -107 dB (people even like tube microphones for the second harmonic content they produce!) and certainly not about -139 dB third harmonics...
And I am not over excited about the 0.06 dB higher output.
I wish the makers all kinds of luck, but I am afraid that this won't change the world.

 

[analogguru]

I don't know why but I am unable to see anything remarkable new compared to the current-source-design A52 from AKG from the late 60's:

 

[Gus]

It is a little different to the AKG
I simmed a circuit based on fig 4B in the following link
http://www.sumobrain.com/patents/wipo/Phantom-power-supply-microphone/WO2016171551A1.pdf
I used  resistors values I calculated that should work for a range of microphone currents about .2 to 10mA

repeating what has been posted in this thread in a little different way

The 6.8K resistors ARE NOT connected directly together at the 48VDC supply
The middle opamp  in the patent adjusts the voltage to current sources that are "feeding" the individual 6.8K phantom resistors the opamp senses the voltages by  resistors. The output of the current sources are  collectors and they have high resistance.

 

[Joost Kist]

Dear fellow recording engeniers,
Because I am the designer of the True Phantom®, I like to comment on the suggestion that the AKG N66E is simmular and prior to the True Phantom. This is not the case. It is a regular 48 Volt phantom power that creates a load of 6K8 Ohm to the microphone. The True Phantom creats not such a load. The distortion of the microphone is consequently lower:
at 100 mVRMS      standard: 0,00095%= -100,4 dB  True:    0,00058 = -104,7 dB
at 200 mVRMS                            0,0039%  = -  88,1 dB                    0,0024    = -  92,3 dB
at 300 mVRMS                            0,016%    = -  75,5 dB                    0,0104    = -  79,6 dB   

For further information see the independent measurement report of the Audio Precision employee Dan Foley
http://www.aes.org/tmpFiles/elib/20200617/19821.pdf 

Kind regards,

Joost Kist

 

[RuudNL]

OK, but 300 mV RMS is an extremely high level for a microphone signal.
So in that case you gain 0,0056% distortion?...

 

[analogguru]

....I like to comment on the suggestion that the AKG N66E is simmular and prior to the True Phantom.......

Hmmm..... has there been such a claim about the AKG N66E and I missed it ?

 

[abbey road d enfer]

Hmmm..... has there been such a claim about the AKG N66E and I missed it ?

Well, your post seemed to imply something along this line. 
I may have misunderstood, but it seems I'm not alone in that case.
Actually, there is nothing in common between the N66 and the True Phantom, except they are both P48 supplies.
The N66 is constant-current at 3.2mA, which can be a problem with a mic that draws less than 1mA, such as U87.
Thrue Phantom is definitely constant-voltage, which also can be a problem with mics that rely on the voltage drop in the 6.8k resistors to provide the intended voltages to the circuit, such as Schoeps.

 

[analogguru]

Well, your post seemed to imply something along this line. 
I may have misunderstood, but it seems I'm not alone in that case.
Actually, there is nothing in common between the N66 and the True Phantom, except they are both P48 supplies.
The N66 is constant-current at 3.2mA, which can be a problem with a mic that draws less than 1mA, such as U87.
......

Interesting.... but...., sorry, I was not talking about the N66E, I was talking  about the AKG A52 ....

But I had a look at the schematic of the N66E now and no, there is not a single A52 inside.... the circuit consists of a constant voltage source fed through some 6k8 resistor to the microphones.

 

[abbey road d enfer]

Interesting.... but...., sorry, I was not talking about the N66E, I was talking  about the AKG A52 ....

Correct. My comment was pertinent to the A52.

 

[analogguru]

..... My comment was pertinent to the A52.

.....
Thrue Phantom is definitely constant-voltage, .....

Hmmm.... sorry, but I am unable to spot a constant voltage (source) [seen at the microphone] as there are - referring to the schematic posted above - these two 6k8 resistors which transform every voltage into a current.... even when the supply voltage is variable it stays a (variable) current source - at least this is what I have learned in school....

And the "inventors" don't claim anything different:
[quote author=True Phantom ®]
Another approach to supplying 48-volt phantom powering is to utilize a voltage-controlled current
source in series with 6K8 resistors. In Figure 1, the 48 volt power supply is now replaced by two 48-volt regulated current sources.
[/quote]
BTW, the maximum current (shortcut) though a 6k8 resistor at 48V is ~ 7,1 mA, at 62V it is 9,1 mA.  Therefore the maximum current variation can only be 25 %.

Now let's have a look at the claims for the A52:
[quote author=AKG]
..... the A-52 provides the following outstanding features:
• Safely and effectively accommodates dc-supply inputs ranging from +7 .5 volts minimum to +60 volts maximum.
• Automatically adjusts itself to power a 12-volt microphone only with any dc input from +7 .5 to just below +50 volts .
• Automatically adjusts itself to power a 12-volt or 48-volt microphone with any dc input from +50 to +60 volts.
• Acts as a regulator with any dc input above +13 volts; the dc source itself need not be inherently well regulated.
• Provides additional filtering; the dc source may have some what higher ripple than a passive-divider network permits.
• Works with microphone-input transformers having untapped and center-tapped (but floating) primaries.
.....
[/quote]
and:
[quote author=AKG]
.....
A52 guarantees in addition, due to its high A.C. resistance (approx 2. megaohm), a hum or unbalance damping of 100dB.

This damping is sometimes required, since a potential difference may occur between the preamplifier (by way of the microphone stand) and the ground point, should the microphone not be properly setup.  This could - provided the source impedance is low - on the one hand superpose on the D.C. supply voltage of the phantom and, on the other, made weaker by way of the balanced attenuation, take its effect directly at the amplifier input.
.....
[/quote]

And this was my statement concerning the A52:

I don't know why, but I am unable to see anything remarkable new compared to the current-source-design A52 from AKG from the late 60's:

So where are the remarkable properties of the "true" phantom ® (of the opera) which makes it superior over the A52?
An "improvement of 0,0056% distortion" or "0.06 dB higher output" ?
Come on....

The Ri of the current source is the same as of the A52:
[quote author=True Phantom ®]
.....
The major benefit of this design (= True Phantom ®) is that the load of the emitter followers is now not 6810 Ω in parallel with 1000 Ω (mic preamp input impedance), but 2.00681 MΩ in parallel with 1000 Ω. (the Ri of the current source is 2MΩ) Per Equation 1, the load impedance as “seen”by condense microphone emitter follower is now 999.5 ohms.
.....
[/quote]
So......