FET Mic with dedicated power supply.

[abbey road d enfer]

Don't forget my KM84 s too ... the original P48V mike  8)

I don't remember which one of the 87 or the 47FET had issues with low phantom voltage, like ceasing to work. What is the behaviour of the 84 in that respect?

The issue(s) are leaky/noisy input caps AND leaky/noisy protection diodes AND wonky P48V AND wonky drivers ....

In da 21st century, there's no reason why a MOTU Traveler shouldn't be faultless in all this and cost no more ... except for incompetence 

One would expect they have fixed these issues for the MkIII...and created new ones

 

[Pip]

Abby Roads comment "most mics work quite well with reduced voltage, not mentioning those that are specified for 9-52V" while absolutely true the mics will work they suffer a compromised operational reality at lower voltages. Also a lot of mics dont work right at less then P48V. One example I am well aware of is the Neumann KM88i. I am lucky enough to have one and it will not work right at all with any less Phantom Standard than P48V. There are other such mics out there that hate anything less and are compromised.

I learned this over 20 years ago when I built my first mic pre based on the Burr Brown INA103 instrumentation amplifier which used a PSU that put out a bipolar voltage +/- 24VDC so I used the plus rail for the phantom.  Sounds awesome but some mics work with it and some mics don't. Still have it and it still works.

http://recordinghacks.com/microphones/Neumann/KM-88
http://recordinghacks.com/pdf/neumann/KM88-manual-english-1984.pdf 
http://www.ti.com/lit/ds/symlink/ina103.pdf

 

[abbey road d enfer]

Abby Roads comment "most mics work quite well with reduced voltage, not mentioning those that are specified for 9-52V" while absolutely true the mics will work they suffer a compromised operational reality at lower voltages. Also a lot of mics dont work right at less then P48V. One example I am well aware of is the Neumann KM88i. I am lucky enough to have one and it will not work right at all with any less Phantom Standard than P48V. There are other such mics out there that hate anything less and are compromised.

That is true, my comment to Ricardo acknowledges it, but in this respect, I think that statistically Neumann are the odd ones.
My first encounters with phantom-powered mics were  the AKG451 and the Primo-branded siblings of Nakamichi. They would operate with 15V power without any distinctive sign of misbehaviour.

It seems many designers chose to base their circuits on 12v operation, which would give them flexibility to adapt to the then-concurrent T12 powering.
That checks with MTG, AKG and even Sony with the C37 operating at 9v, so they would have alternative battery powering, much more convenient than that of the first issues of U87.
Apparently, all these designers have rather well dealt with this self-impose constraint.

Ricardo has not been very voacl about this, but I believe he would have a lot to say about the Calrec mics that had a peculiar powering scheme, with a separate DC conductor an unbalanced output, or the 7.5v-power 700 series.

Neumann's approach was apparently based on a strict implementation of P48, not anticipating the variants (P12, P24...) that eventually became the 9-52v system that is prevalent today.
As a result, when Radio France asked Neumann a P12 version of the U87, named U497, they had to completely redesign the circuit, for something that became the core of the U89.

BTW, 48V was not so much based on a technical argument than on the fact that 48v was the standard voltage for signalling systems in German broadcast facilities, probably a sequel of telephony. The fact that they turned it into a standard is testimony to the strength of government-owned  media in Deutschland.

 

[ricardo]

Don't forget my KM84 s too ... the original P48V mike  8)

I don't remember which one of the 87 or the 47FET had issues with low phantom voltage, like ceasing to work. What is the behaviour of the 84 in that respect?

KM84 has a very simple circuit.  IIRC just a FET driving a transformer so used very little current.  It used the phantom power to polarize the capsule.  If phantom was less than 48V, the sensitivity of the mike would be less.  But the simple source follower still worked though with lesser headroom.

Later circuits were more complicated and more affected by less than the 48V +/-4 spec.

The most common Calrec mikes (later 1000 & 2000 series) used this scheme too but included a Class B output stage (Class A until 130dB spl) so they only lost sensitivity but not headroom.

That's one reason for the early DIN P48V spec that specified IIRC less than 2mA current draw.  Only a little mike maker in Hebden Bridge followed this religiously.  All the Germans, even Neumann who invented P48V, abandoned this.

The other reason I didn't steal .. I mean improve on ... the Schoeps design was cos it took 5mA which was well outside the circa 1980 DIN spec.  ;D

The issue(s) are leaky/noisy input caps AND leaky/noisy protection diodes AND wonky P48V AND wonky drivers ....

In da 21st century, there's no reason why a MOTU Traveler shouldn't be faultless in all this and cost no more ... except for incompetence 

One would expect they have fixed these issues for the MkIII...and created new ones

MOTU are one of those companies that source out all R&D so there's no continuity & improvement or even sensible Tech Support.

Certainly, Mk2 Travelers are MUCH more unreliable than Mk1s

 

[ricardo]

Ricardo has not been very vocal about this, but I believe he would have a lot to say about the Calrec mics that had a peculiar powering scheme, with a separate DC conductor an unbalanced output, or the 7.5v-power 700 series.

This was the 600 series (the 700 series was a commercial flop cos expensive) which was meant for hobbyist unbalanced inputs.

This included the Sony PCM-F1 which had nice but unbalanced mike inputs.

We dealt with RFI etc up to 20m by having a lot of output and some careful attention to earthing.  But these efforts were often foiled by poor design of the recorders.

Among the cassette recorders, some Sonys, Hitachis, TEACs & Akais worked very well with 20m unbalanced to Calrec 652s.

At the top end, many small record companies used these with PCM-F1s to make some excellent recordings.
_____________________________

I wish P12V (or better still, P15V +/- 3) had taken off.  It would be easy for mixer makers from the 1980s on to provide good phantom.

The common 'P12V' don't actually meet the proper spec.  ... even Sound Devices 

They are really crappy P48V circuits, 6k8 resistors with less than 48V.  True P12V should use 680R resistors as in the CMC5 schematic.

This is important cos the resistors limit the power you can draw so if you have less volts, you need to up the current ie smaller resistors.

 

[Sredna]

Sorry for the hijack, but does someone know where to get a schematic for the Calrec 700-series?
I have two CB 7Ds which I try to wrap my head around for the possibility to use them with 48V/balanced.

Regarding higher current than phantom power admits, check the CAD solution for their Equitek mics.
They use two internal NiCad batteries to be able to use more current demanding Bi-Fet-ICs.

 

[0dbfs]

Any pro's/con's to increasing phantom supply voltage from 48VDC to 120VDC in a DIY situation or perhaps making your DIY phantom supplies switchable from 48V to 120V to accommodate mic's designed for a 120V phantom supply on a traditional 3 wire XLR system?

Intent would not be to power tubes, rather provide low current 0V, 60V, 120V for typical capsule pattern switching and lower voltages dropped accordingly to power FET's/etc.. Instead of DC-DC converters in the mic's..

I guess it would be easy enough to make a standalone 120V phantom box with a nominal number of XLR I/O's and if you're rolling your own pre's you could make it switchable so that you could also easily use regular 48V mic's...

If we were to redesign a secondary phantom spec what might the resulting parameters look like?

Cheers!
-jb

 

[abbey road d enfer]

Regarding higher current than phantom power admits, check the CAD solution for their Equitek mics.
They use two internal NiCad batteries to be able to use more current demanding Bi-Fet-ICs.

Actually, the circuitry of the E300 draws less than 7mA, which is well within the 10mA limit of the norm. The justification for batteries is not the current draw. That's just one of the possible solutions. Actually, the batteries are an easy and convenient way to provide the dual-rail supply.
With the batteries, the total current draw is a tad over 8mA, leaving about 1 or 2 mA for charging them.
I would be somewhat concerned if I had to rely on NiCad batteries for remote recording; it is notorious that they tend to degrade enormously after a few years and lose their capacity. I see that now they are fitted with NiMH.

 

[Sredna]

Thanks for this information!

The official explanation from CAD for using batteries was to provide extra current for large signals, but maybe that was
just  sales talk...

The NiCads in my E-300 are still good, but Im only using the mic with  phantom power.

 

[abbey road d enfer]

Any pro's/con's to increasing phantom supply voltage from 48VDC to 120VDC in a DIY situation or perhaps making your DIY phantom supplies switchable from 48V to 120V

You may want to do that at your own risks, but for a manufacturer it's entering into the arcane world of certification. Anything above 48Vdc is considered lethal. 

to accommodate mic's designed for a 120V phantom supply on a traditional 3 wire XLR system?

AFAIK, there are no commercial 120V phantom mics. B&K and dpa high-voltage mics use separate conductors for power and polarization.
BTW, the output is not balanced; it rather relies on the concept of remote ground-sensing, which requires a particular arrangement of the preamp for working.

Intent would not be to power tubes, rather provide low current 0V, 60V, 120V for typical capsule pattern switching and lower voltages dropped accordingly to power FET's/etc.. Instead of DC-DC converters in the mic's.. 

  Actually, DC/DC converters draw a fraction of mA. At 10mA max, phantom power is unconcerned with voltage drop, as opposed to tube mics, where the heater voltage may suffer from long cables.

 

[abbey road d enfer]

Thanks for this information!

The official explanation from CAD for using batteries was to provide extra current for large signals, but maybe that was
just  sales talk...

It is actually correct for high SPL applications and flimsy phantom power.

 

[Andy Peters]

Thanks for this information!

The official explanation from CAD for using batteries was to provide extra current for large signals, but maybe that was
just  sales talk...

It is actually correct for high SPL applications and flimsy phantom power.

And the mics handle high SPL quite well. I have three of the E-100s. They see most use on guitar amps. One of my pals who is also in the He Man E-100 Lovers Club would use one on a kick drum which did not have a hole in its resonant head, and that worked like a champ.

 

[Pip]

Sorry for the hijack, but does someone know where to get a schematic for the Calrec 700-series?
I have two CB 7Ds which I try to wrap my head around for the possibility to use them with 48V/balanced.

Regarding higher current than phantom power admits, check the CAD solution for their Equitek mics.
They use two internal NiCad batteries to be able to use more current demanding Bi-Fet-ICs.

Yes this is true! It had to do with constant current delivered to a dual-rail power topology. I actually met the man who developed this for CAD (which by the way is a part of the Astatic mic group) and it at the time was a real leap of design initiative and American made mic manufacturing. Sadly I think a lot of people didn't pay attention and then CAD did not really market the products that well.

The hijack is fine but check other places here The Lab section as a suggestion.

As too the CAD reference. This thread is getting very nicely long so please, read back a few pages before you add to it, there is a lot of really good stuff including:

http://groupdiy.com/index.php?topic=61037.msg773296#msg773296

http://groupdiy.com/index.php?topic=61037.msg774204#msg774204

 

[ricardo]

Sorry for the hijack, but does someone know where to get a schematic for the Calrec 700-series?
I have two CB 7Ds which I try to wrap my head around for the possibility to use them with 48V/balanced.

Sorry.  It was 30+ yrs ago.

To convert to P48V, I would strip out the electronics and use a Schoeps variant like Zap's

DIYgenericNonElectret.pdf in his Yahoo MicBuilders files.  You have to join.

This only gives 35V Vp.  If you want the full output, you need to use an oscillator which could be the Schoeps oscillator or a simple Hartley oscillator with Cockroft-Walton multiplier as on the 700 series.  The multiplier is the secret to low noise, low current Vp in both the 700 series and the Schoeps.  The little potcore does the Hartley in the CB7D

Apart from that, the only bits worth salvaging are the FET, if it is a metal can Mullard BFW11, and the 2 little blue bead 1G resistors that you can just see on the left in the last 3 PCBs on

http://saturn-sound.com/images%20-%20microphones/calrec%20pcb's.jpg

These appear only on the later models.

You might get a schematic off Ashley at saturn-sound.com but don't hold your breathe waiting.

 

[SSLtech]

The B&K 130V approach definitely results in some great sound transducer technology. The proof is in the pudding.

Actually, no.
the proof is NEVER in the pudding, and anyone who says this misquotes the original saying, and misses an important distinction...

The correct quote is:

"The proof of the pudding is in the eating"

 

[CJ]

that makes sense,


https://www.youtube.com/watch?v=Ma78qWiEgnk

 

[Sredna]

Thanks a bunch Ricardo! 

 

[bockaudio]

KM84 has a very simple circuit.  IIRC just a FET driving a transformer so used very little current.  It used the phantom power to polarize the capsule.  If phantom was less than 48V, the sensitivity of the mike would be less.  But the simple source follower still worked though with lesser headroom.

KM84 is not a source follower (thankfully!).
Most modern xfmrless do seem to be complex source followers.

 

[bockaudio]

I was thrown by the idea of using the Schoeps xfmrless for the "dedicated psu fet mic experiment". I know "everyone" uses it etc. I rarely see it implemented correctly, with precise matching of xistors, resulting in undue loss of bass (at least). My opinion of that circuit is that it was designed for a very specific capsule set, not as a universal platform for any mic capsule to be experimented with, which is how it seems to be treated. 
Even the Hohendahl improved Schoeps was unremarkable (to me).
I would stick to a simple circuit, and would not rule out transformers. You can do a class A fake balanced out (like Neumann does today, I recommend it).  Really, You're going to have to do xfmr and xfmrless versions eventually anyway, they both have their advantages (depending upon what's being recorded) and if you really want to know if the dedicated psu is a source or cause of greatness or boredom  you must explore all permutations (otherwise you would only know if the dedicated psu matters on insert tested mic circuit here.
I would also advise against the Mackie being involved, it is a really destructive device for all things microphone. Yes I have used it for exactly this kind of test and yes there were results.
Also with your dedicated supply please pay attention to the details here. Use unregulated or shunt reg, and a big core xfmr.  No series reg or switching.
Start with a pair of matched Large D capsules before embarking on the smalls.
Then I am really curious about the results.

 

[Pip]

So to a schematic jumping off point what about this: