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"Ghosts in the Machine"

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"Ghosts in the Machine"

Postby ef37a » Tue Nov 24, 2020 9:00 am

For the last few days I have been comparing some microphones (and checking polarity, see *)
My reference microphone has been the Sontronics STC-2 the best mic I own. The interface used was the NI KA6 Mk1.

I became aware that the STC needed more gain to equal a cheap BM-800 ldc and further investigation showed that the 0, -10dB switch made no difference to the level. There was no evidence of noise or distortion from either mic.

To clinch the matter I replaced the BM with one of my AKG P150s. That was virtually equal i sensitivity to the Sontronics. Something is wrong here! The 150 has a quoted sensitivity of 12mV/Pa whereas the STC is 20mV/Pa. I was about to send an email to Sontronics when I thought I had better make another check, this time with my A&H zed 10 mixer.

Blows me down! The sont' was way more sensitive and the dB switch behaved as expected, waffle at ~0vu dropped to -10vu. So, check the spook juice!

The results were not quite as I expected. The voltage entering the STC-2 was 36.48V for the KA6 and for the Zed 39.62V, not a vast difference and by my calculations the current drawn was 2.11mA KA and 2.53 for the mixer. Again a minimal difference but obviously just enough to depress the sensitivity of the STC -2 mic.

I did know that the phantom power capability of the bus powered KA6 was below standard spec but had never had a problem with it. The AI only produces 44.1V off load and with the minimal drain of the Sontronics the right hand, unloaded channel drops to 43.6V. Again, not good but adequate in most circumstances?

I shall email Sontronics with my findings and see if they can shed any light. Meantime I have ordered a USB powered phantom power box!

*It appears that the otherwise super VFM Behringer XM8500 is opposite polarity to every other mic I have? Some other's findings would be welcomed.

Dave.
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Re: "Ghosts in the Machine"

Postby Arpangel » Tue Nov 24, 2020 9:42 am

Dave, just for the record, my friend Mike got given a Behringer mic, he noticed that it was out of phase, reverse polarity, not sure if they are all wired like this? or if these are just mistakes.
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Re: "Ghosts in the Machine"

Postby ef37a » Tue Nov 24, 2020 9:51 am

Arpangel wrote:Dave, just for the record, my friend Mike got given a Behringer mic, he noticed that it was out of phase, reverse polarity, not sure if they are all wired like this? or if these are just mistakes.

Since I am pretty sure they are built by robots I suspect a 'byte' in the wrong place and they are all the same.

Since they are never likely to be used as a stereo pair I doubt the polarity flip will make itself heard at all often. After all, a pair of mics on stage are almost invariably the same model?

Could make a mixture on a drum kit "interesting" though? !!

Dave.
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Re: "Ghosts in the Machine"

Postby Arpangel » Tue Nov 24, 2020 10:10 am

ef37a wrote:
Arpangel wrote:Dave, just for the record, my friend Mike got given a Behringer mic, he noticed that it was out of phase, reverse polarity, not sure if they are all wired like this? or if these are just mistakes.

Since I am pretty sure they are built by robots I suspect a 'byte' in the wrong place and they are all the same.

Since they are never likely to be used as a stereo pair I doubt the polarity flip will make itself heard at all often. After all, a pair of mics on stage are almost invariably the same model?

Could make a mixture on a drum kit "interesting" though? !!

Dave.

:D

Yes, Mike had one of these...

http://www.muzines.co.uk/articles/the-box/2822

When using multi-mic arrays it was a very useful piece of kit for showing phase, stereo field.
I’ve got one built into my mic-pre.
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Re: "Ghosts in the Machine"

Postby Hugh Robjohns » Tue Nov 24, 2020 11:52 am

The Box was an ingenious engineering solution in the early 1980s to make a low-cost single-quadrant vectorscope alternative -- back in the days when a proper audio vectorscope really did need most of the gubbins of a full oscilloscope!

But the world has moved on. A lot.

The Box is still available and now costs an astonishing £450... and it just does the one job, fairly poorly by modern standards.

Alternatively, you can by a TC Clarity M that does a proper four-quadrant vectorscope, as well as Loudness Radar, spectral analysis, calibrated level metering and more besides, all in a very elegant and user-friendly package... for just £230...

Nostalgia is a lovely thing, but common sense, practically, and fiscal sense easily win the day!
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Re: "Ghosts in the Machine"

Postby Arpangel » Tue Nov 24, 2020 11:58 am

Hugh Robjohns wrote:The Box was an ingenious engineering solution in the early 1980s to make a low-cost single-quadrant vectorscope alternative -- back in the days when a proper audio vectorscope really did need most of the gubbins of a full oscilloscope!

But the world has moved on. A lot.

The Box is still available and now costs an astonishing £450... and it just does the one job, fairly poorly by modern standards.

Alternatively, you can by a TC Clarity M that does a proper four-quadrant vectorscope, as well as Loudness Radar, spectral analysis, calibrated level metering and more besides, all in a very elegant and user-friendly package... for just £230...

Nostalgia is a lovely thing, but common sense, practically, and fiscal sense easily win the day!

The TC is a better option, for sure, I didn’t even know that "The Box" was still being made, I ended up with mine simply because Mike fitted it into my pre-amp.
The Box had a poor start, it was over-priced, and the designer refused to compromise on it's looks, which I think held it back.
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Re: "Ghosts in the Machine"

Postby ef37a » Tue Nov 24, 2020 12:16 pm

TALK about wandering OT!
i started on about a microphone's sensitivity to a slightly low phantom power voltage and now we are into vectorscopes and bloody test gear cosmetics!

Heh!

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Re: "Ghosts in the Machine"

Postby Arpangel » Tue Nov 24, 2020 12:24 pm

ef37a wrote:TALK about wandering OT!
i started on about a microphone's sensitivity to a slightly low phantom power voltage and now we are into vectorscopes and bloody test gear cosmetics!

Heh!

Dave.

Sorry Dave... :blush:
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Re: "Ghosts in the Machine"

Postby zenguitar » Tue Nov 24, 2020 12:29 pm

And when they are looking at the phantom power, they could fit a midi in/out, it only costs pennies.

:silent:

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Re: "Ghosts in the Machine"

Postby Hugh Robjohns » Tue Nov 24, 2020 12:39 pm

:bouncy:
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Re: "Ghosts in the Machine"

Postby ef37a » Tue Nov 24, 2020 12:40 pm

zenguitar wrote:And when they are looking at the phantom power, they could fit a midi in/out, it only costs pennies.

:silent:

Andy :beamup:

Are you talking about the KA6 Andy? If so it already has it and blindingly low latency it gives as well!

That is the Achilles' heel of the interface, 4 ins, 4 outs, MIDI and S/PDIF and it pulls 480 mA from the USB bus so spook juice had to be curtailed a bit. i did try doubling up USB ports but the limit is designed in. I wonder how the Mkll fares? I had hoped they would make it USB 3.0 with an optional 5V rat for 2.0.
While I am waffling, I reckon NI should make a 4 mic jobby with 6 line ins and ADAT, MIDI (of course!) and keep their wood burner drivers and low latency. Get that out close to £300, sell sheds.

Dave.
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Re: "Ghosts in the Machine"

Postby zenguitar » Tue Nov 24, 2020 1:42 pm

Sorry Dave, I couldn't resist.

:thumbup:

Andy :beamup:
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Re: "Ghosts in the Machine"

Postby ef37a » Tue Nov 24, 2020 5:11 pm

Update:
Dug out a "bTsky" phantom power box* I bought years ago to get a cap mic into a Teac A3440. Improves things into the KA6, definitely a tad more level at 0 than at -10 but not as obvious as with the mixer. The supply to the mic is 38.8V whereas the mixer gives 39.6V.
Not a lot more but obviously the mic needs around 40V for optimum sensitivity.

*Don't buy one, not bad build quality but run from an 18V AC rat and so just a peak voltage doubler and delivers only 46V off load. Quiet mind. Going to have it apart now and if the caps are rated for it hit it with a few more volts.

Dave.
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Re: "Ghosts in the Machine"

Postby ef37a » Tue Nov 24, 2020 5:42 pm

Holy voltage doublers Batman! The box has an HT of 85V which ultimately feeds a TIP 122
Dartlington transistor. But the daft buggers have used a FORTY SEVEN volt Zener!

Did not account for the base emitter drop. I reckon if I put a couple of 1n somethings in series with that Zener I can get 48V +. (caps are all rated at 100V and 105C as well! )

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Re: "Ghosts in the Machine"

Postby blinddrew » Tue Nov 24, 2020 5:45 pm

"The dilithium crystals cannae tek it cap'n!"
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