EEVblog - 2014-05-15
Doug Ford, former head designer at Rode Microphones explains 48V phantom powering of microphones and how it works. There is a ton of stuff here: Electrostatic and electromagnetic noise, differential amplifiers, common mode noise, transformer magnetisation current, JFET differential driver circuits, balanced impedances, phase splitters, miller capacitance and how it matters, and he explains how the Schoeps amplifier topology works. Forum here: http://www.eevblog.com/forum/blog/eevblog-616-how-microphone-phantom-powering-works/ All the videos in this series with Doug: http://www.youtube.com/playlist?list=PLvOlSehNtuHv98KUcud260yJBRQngBKiw EEVblog Main Web Site: http://www.eevblog.com EEVblog Amazon Store: http://astore.amazon.com/eevblogstore-20 Donations: http://www.eevblog.com/donations/ Projects: http://www.eevblog.com/projects/ Electronics Info Wiki: http://www.eevblog.com/wiki/
Having Doug on the show has been a great addition to the eevblog ever since the start when you were blowing up cheap-ass multimeters together :-) I think the microphone series is very worthwhile because i knew quite little about it before. Keep it up Dave & Doug!!
I love watching this series. As an audio engineer, it feels good to have a chance to go over the basics again! Also great to introduce newbies to audio engineering and electronics. Cheers for the uploads Dave.
Thanks for getting Doug to do this series. This is my favorite so far because I have always wondered how phantom power works.
Microphone design has proven to be a really deep and rich subject, even at a "basic" level!
The learning never stops. Wished I took up sound engineering when I was in college. Thanks Dave for the series. Think you've hit another goldmine.
I remember when this was published, it all was Greek to me, and probably I half-watched it. Now, because of the EEVblog, and other inspirations like Fran and so many, many who stopped doing videos long ago, for some reason today this series was in my feed and it was like a revelation! Wait a minute - I can do these things, now! I can build it! I have the technology! Thank you Dave!
These videos are brilliant and exceptionally helpful. Doug's passion for his craft really shines through. Id love to see more of these videos. Get him back in the lab!
Even though I'm a mechanical engineer (well, almost) and know close to nothing about electronics (hope to change that), I still enjoy watching this series. It's entertaining to see how a person who knows a lot explains it in a witty way.
This series is awesome!! It would be great to have a mic preamp specialist (Neve, API, etc) and other music electronic specialists to explain gear, circuits, and debunk myths
Great series. Keep those mic videos coming :)
Ahh....now it all makes sense. So all the Elvis moves on stage were involuntary electric shocks! :)
Made me think of Elvis too when the engineer acted out that scenario!
Find those videos very interesting! Thank you a lot Doug and Dave!
"Let's have a look at balanced topology amplifier" What a cliffhanger !!! More than 5years later still waiting for this one !
Great series of video by the way, it's at least 3rd time i watch them all and each time i watch again i still learn few new things. "that's... brilliant"
Any plane to have Doug Ford back ?
this is such a great series
Thanx again guys! I love learning about the innards of my every day tools. :-)
I must say I'm not really inito microphones, but I actually like this series. That's because Doug gives so detailed information, real-world examples and really covers a broad spectrum. I'd like to see a series on ADCsDACs/OpAmps/other building blocks of electronics. Any chance Dave will produce some hour-long FUNdamentals friday videos in a similar fashion?
Great Series, I hope you get the next/last part uploaded soon.
I want to see a balanced topology microphone!
brilliant idea to invite head designers from different companies.
I guess that this is also how the twisted pair cables work in an internet LAN cable by also using the instrumentation amp or some similar principle? I pity those who nag that the topic(video) is boring as their own field of knowledge is short and they can't see connections to different things. Thanks Dave! I did not give any interest in mics before but I see that it benefits greatly in my general knowledge :)
I think there is lots of good stuff in here besides micophones too, plenty of circuit detail that can apply to many things.
@EEVblog yah the whole twisted pair - i always do that anyway for protos... it just looks cooler. i really didnt know it was 'better' (for some things). but after this video - yah, totally makes sense.
@EEVblog There sure is. I'm working on analog synth stuff lately and this series is giving me lots of ideas
Ethernet, ironically, uses transformers. At the frequencies that ethernet runs at they're cheap and small. And the isolation is pretty nice to have. They look a lot like a black DIP chip on a NIC.
@Kevmatic22 Yup, and there are two transformers on one end and they are now even in tiny IC package or even integrated to the LAN sockets. Check hanrun HR911105A for example
What a tease ending as always... just about to get into some more details and BAMM!!! Nothing!!! :-|) Thanks for sharing as always. Way neat video and looks like a series I'm going to have to watch now that I'm looking into expanding up to 192kHz monitoring without aliasing with a 384kHz SB G6 USB sound card. Wondering what other ways there are to monitor into the ultrasonic range more effectively? Definitely have more than Bat's, Rat's and Mole's around us.
Man i love this series!
won my subscription on the first video I've seen! love how you describe things.
I am an audio Engeneer student, This stuff is awesome!
I think this is the most engrossing video you have done yet Dave. You should get guests on more often. The years Doug has put in really show in the passionate way he talks about microphone design.
Please show more things like this!
I hope dough got a good few pints for this, very good series so far!
Great explanation. Great people.
I loves Doug's little jabs at the audiophile market.
@KX36 DAC had their feature mostly integrated, and pretty much "FIXED" ...Why measure the supply? a filtered supply is mostly adequate,and a 10 ohm ground terminator on both input and output. I've build a thumbdrive size USB DAC a few months back with this configuration NUF2101M>CP2114>WM8523>NJM2703>LME49726 for my KOSS headphones. but the key to good audio is still "Equalizer" and good studio recording. IMO
"mostly adequate" is the key phrase here. Even though the last few bits in a 20-24bit DAC are usually made irrelevant by the system noise as well as the noise in the original audio signal and that in the recording hardware, it generally doesn't matter because you probably can't hear the difference anyway. Just like audiophiles hearing the difference between an expensive gold plated phono cable and a normal one is usually psychological. Mentioning the rail voltage was just an example to show just how small a voltage the LSB of 24bit is and how it can be dwarfed by system noise.
@BlueFoxTV audiophool
One who spends mass amounts of cash on ridiculous Audio components and accessories. They truly believe they can tell a difference, and come up with elaborate excuses to justify these purchases.
agree, but there is an area lower down, so to speak, where some might not really appreciate the difference between various systems and their abilities to bring out the qualities of, say, an orchestral recording properly, because of peaks and troughs in the response. It certainly is a very large area to cover though and some devices with their gold plated components and what have you, costing many hundreds of pounds do make one cringe!
its kinda hilarious to see someone talking about 192khz but shunning high end DACs
I'm at 8:38 and trying to figure out how the source impedance for the S (assuming source on bottom, drain on top for this JFET) is lower than the source impedance on the drain. We're talking about from GND and VCC, right? I'm definitely missing something here.
EDIT: The only thing I can figure so far is that this is actually a common-source JFET amplifier with the capacitor shunting the low-side resistor there to ground. Or, arguably he mentions there is more capacitance gate to source than gate to drain(later). That could definitely unbalance it, guess I assumed it wasn't that big of a difference at the frequencies we're at. And he seemed to act like it wasn't the same thing because they were separated by time he got to it.
When this first came out I couldn't watch it, I just couldn't follow along. I still can't really, but I understand some of what is being said. Here's hoping that in a few more years I'll learn enough to really appreciate this!
Watch it twice! Once for actually hearing what they're saying, and the second time enable the automatic english subtitles. I laughed so hard, my wife came to check if I was alright :-)
Youtube subtitles of aussie accents are always a hoot!
very funny with captions, sounded like an attempt at a disguised illicit phone call between two people into some very weird activities.
"...not being stressed by any DC magnetize Asian..."
That is just sooo wrong, YouTube! :-)
"...the two round ass secretary which we then..."
Dave, what on earth were you two talking about? :-D
Does the circuit at 9:50 have some name by which I can google it? There's one thing that I can not understand about it. Okay, we have the collector voltage fixed, good. To be able to work in the linear region, transistors need some voltage headroom between collector and emitter (determined by base bias voltage). Well, by looking at the circuit, one can deduce that this is provided by voltage drop on the base resistors, so collector-to-emitter headroom voltage becomes
Vce = Ibase*Rbase + Vbe
From this, it is natural to expect that when the AC amplitude of the input (base) voltage exceeds this value, we must hit the collector voltage (fixed by zener diode) and the waveform should become distorted. I.e., it seems that the maximum input/drive amplitude is set with base resistor and transistor beta.
But SPICE simulation shows that this is not the case! When the input voltage amplitude exceeds base resistor drop, the DC offset at emitter magically shifts to accomodate any AC amplitude, and the real limit is
V_ac_max = Vphantom/2
And no limiting at all (until the signal hits the rails, of course)! How this is possible?
Moreover, it can be seen that when AC input exceeds the above mentioned limit (Vbe determined by base resistor), the voltage on a zener diode actually dips to accomodate the peaks. So, in a sense, AC amplitude limit is actually defined by base resistor voltage drop if we want to have stable power to our curcuit, but not in an expected way.
Actually, this can be fixed by adding a separate zener diode for the base resistors. I.e., if we disconnect base resistors from the collectors and connect them to a separate zener diode having a greater voltage than the collector zener diode, we'll fix the common mode voltage at one level and collector voltage at the other, providing defined headroom for a signal and stable supply voltage at collectors.
Can you build some prototipes to show how it works?
It could be more like the regular stile of this channel.
¡¡¡Beauty!!!
9:48 Aren't pins 2 & 3 touching, effectively shorting out the microphone?
Wow that guy knows so much about microphones. Like he must be the guy that everybody consults on microphones.
He worked as a designer for them at rode for ages, so he is supposed to :)
How can the Schoeps-type preamp voltage swing capability be increased? I have a Chinese copy which clips if the singer goes anywhere closer than 2ft from the mic! Can the output transistor collector-emitter voltages be increased by increasing the value of the base-collector biasing resistors?
Transformers may be bandwidth limited but don't they still have enough bandwidth for the audio range?
The wanker transformer market. Priceless! Great video.
"Nobody likes transformers these days" - yeah thanks to Michael Bay!
18:00 Could someone explain? Why "typically electrolitics" and not film caps for signal path? Is it still about costs and good enough or there is something about ECAP characteristics suitable for this application?
This guy should teach engineering somewhere
I really really enjoyed this.
Thumbs Up!
Great Series.
If I use a 48v mic wireless mic transmitter for my condenser mic to audio interface, would it deplete the quality of my mic... is it also liable to pick up unwanted sounds?
Joe Khoury
1 second ago
I'm a DJ, and run into videographers wanting to connect into my mixer. I don't have issues doing it. The problem occurs when they connect to the back of my speaker. It either lowers my output, or basically shuts off the speaker. I believe it may have something to do with phantom power perhaps? Is that something somebody here can explain. I don't have an audio receiver, but is there a setting to turn off phantom power?
Whoa this video is a real eyeopener for me. Great Vid!
Now it make sense !!
I have Behringer c1-u USB microphone, which has quit low volume output.
Is there any way to get phantom power into it ??? or make it output more volume ???
Not really. Yours is a USB mic, not an analog mic. It solely draws power from the USB port for a fixed-gain preamp and built-in ADC. Most likely you have a driver or software issue. It is faintly possible that your USB host cannot source enough current for the preamp (in which case, try a powered USB hub).
edit: apparently a common problem with that mic. Poor design.
Did you try to adjust the recording level in the Windows Volume Control
panel? right click on the speaker icon in the task bar then select "recording devices" and go to your mike properties.
Thanks guys. I know USB doesn't have phantom power, just wanted to know is there any alternative way to get it louder.
@DolganoFF Ya I increased the volume level and thats how i have been working with that mic. But still I feel thats not an efficient way to get a good volume.
@vaidhya nathan If you still have gain left in the mic adjustment parameters, crank it up! And if nothing helps, well, you'll have to get another microphone I guess...
I didn't understand about 90% of this but I still thought it was great
Dave Cooper - 2014-05-15
Fantastic having an explaination of microphones directed at engineers rather than musicians. I would love some more on amplifier circuits in the same way.