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Күн бұрын

Part 5 - Doug Ford explains the design of Electret Microphone circuits, and all the associated traps:
Transconductance, correct biasing, and temperature effects, leaky JFETS, non-linear clipping & headroom, current noise and voltage noise, and pseudo bias resistors.
Also, the non-intuitive concept of higher resistance = less noise, and how this applies to electret biasing.
And what is a soggy circuit board and why is it important?
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Пікірлер: 79

@hubercats 2 жыл бұрын

Hi Dave - Thanks very much for taking the time to share your expertise through your numerous videos. In a correspondence with Alan (w2aew), I believe he mentioned that you have done work in the area of underwater acoustics. I spent about 45 years working on underwater acoustic signal processing algorithms. Now that I’m (mostly) retired, I’m trying to learn more about the hardware side of underwater acoustics. Recently I’ve been trying to come up with a 40 dB gain preamp for a hydrophone as related to some student mentoring I’m involved in and I’ve been focusing in on designs that employ JFET front ends. I’m curious to know if you’ve produced any videos that may be helpful to me. Thanks again! - Jim

@tshddx 10 жыл бұрын

This series is fantastic. Thanks.

@dpneber 4 жыл бұрын

Part 5? Didn't see that until the video was over. Part 1 here I come! Thank you, both!

@enginerdy 10 жыл бұрын

Thanks Dave, Doug, This series is absolutely amazing! I would love to see more in depth / master-class type stuff on your channel. I'm learning some really useful stuff here.

@motokokusanagi1147 10 жыл бұрын

Great series, Dave! Even though you say Mail Bag is everyone's favorite, practical electronics lectures are far more interesting and useful. That's why your channel is one of my favorite ones. I missed fundamentals videos so much)

@kludgeaudio 10 жыл бұрын

The microphones that don't have leak resistors don't use a normal JFET, they use what the friendly people at Toshiba call a FET-IC. They have parasitic diodes fabricated on the surface of the transistor in order to provide a leak resistor as well as a source bias resistor. Sadly this does not improve linearity or noise performance, but it sure is cheap to make!

@kevinbeckenham3872 6 жыл бұрын

Doug Ford is a brilliant presenter and lecture; I look forward seeing Doug becoming a T.V presenter of a science program one day on T.V, can't wait for that to happen.

@jj74qformerlyjailbreak3 Жыл бұрын

Had to be about 1 year ago I forced myself through this video. ATT I did t understand any of it. Now with a full year of research I can design my own circuit, test it and implement it into another circuit. For those just now playing along at home. Keep it up. In the beginning it’s like learning a new language. Kinda cool.

@VidarrKerr 5 ай бұрын

That is good to know. I was about to give up after one of the other videos in this series. Sometimes I have no idea what they are talking about, like this: What is a biased "gig omish" resistor? 3:06 I understand what it does, I just don't know what it is. Thanks.

@jj74qformerlyjailbreak3 5 ай бұрын

@@VidarrKerr Sometimes a circuit or an IC input needs a specific voltage, or current too turn on or activate another element within the circuit. We can accomplish solving the specific voltage or current for said circuit with simple Ohm's Law calculation and voltage dividers to reflect the needed voltage or current. I know it's a lot to wrap your head around. What I e found is keep up with it. Most circuits can be solved with simple equations, long as you understand math and or physics. Remember what electric goes into a circuit can be calculated by Kirchhoff's Voltage Laws or loop rule. Hope this helps.

@jj74qformerlyjailbreak3 5 ай бұрын

@@VidarrKerr R&D Academy channel really helped me with understanding KVL and Ohm's Law. Bob is a great teacher.

@jj74qformerlyjailbreak3 5 ай бұрын

@@VidarrKerr oh "GigaOhmish" describes one magnitude above MegaOhm resistors. They are actually quite rare in my experience as I've never ran into a GigaOhm resistor in the wild. For audio circuits you shouldn't run into anything with such high resistance.

@SabrinaVideo 3 жыл бұрын

09:24 This part is GOLD IN MY EYES. This microphones series are marvellous.

@AntonioBarba_TheKaneB 10 жыл бұрын

Doug is *really* good at teaching, keep goin on!

@joostjepek 5 жыл бұрын

Hi Dave, I did a rerun off some your vid's, kinda missed this one.. But this set is one of your best guest appearances !! So informative an clear on info! Fun to see the interaction of you both...

@bain5872 10 жыл бұрын

Very informative. Enjoyed it greatly Dave. I'm surprised they aren't more views than they are on this. Thanks for sharing these series of vids.

@luistorh 5 жыл бұрын

Thanks! I found the part of choosing the bias resistor for the JFET in cases of low supply very useful! Good advices!

@EvelienSnel 10 жыл бұрын

This explains exactly why the microphone in the cheap-ass headset I bought does not want to work with my semi-professional mixer. It gives me no output voltage and when measured, it likes to draw a fixed current of about 200 µA, no matter what voltage I apply. (Well, I'm glad I did not go higher than 10 V.) Looks like I've got to build myself a small pre-amp. No, I am not going to sing :) I just want to be able to talk to the musicians over the monitor channel in case of emergency.

@TheHeraldOfChange 4 жыл бұрын

Would love to see you guys extend this series with a discussion on Piezo Electric Oscillators as microphones, especially since many people are using them for acoustic guitar pickups.

@OtusAsio 10 жыл бұрын

I like this very much...even if I will never build a microphone, it gives me knowledge about electronics...Thank`s

@gixerags750 2 ай бұрын

You guys have been sniffing too much quality rack .. Was fun to watch.

@MrTridac 10 жыл бұрын

I love the way you guys chat together. Hilarious :D

@eyescreamcake 3 жыл бұрын

I hate it haha. But it's very informative so I suffer through it.

@vasileceteras 10 жыл бұрын

Those cheap mics can be modded (or at least some of them) to get access to the source pin and use the fet in common drain connection (repeater). Look up "Linkwitz Mod"

@gulassuppe4065 10 жыл бұрын

Nice job Dave! Your vids are always educational and very entertaining!

@ConorFenlon 5 жыл бұрын

This is absolute gold. Thank you so much!

@bio1573 7 жыл бұрын

This is just awesome, great teachers both of them. Thank you very much.

@declanallan885 2 жыл бұрын

thanks guys, this content is amazing!

@ratdude747 10 жыл бұрын

Ah, now I see why a microphone project I attempted last fall failed... those bias currents.

@kabandajamir9844 Жыл бұрын

So nice and real thanks

@jahester09 10 жыл бұрын

Please show more things like this!

@wa57s577 3 ай бұрын

I don't get the jfet circuit. Wouldn't the microphone deliver a small AC signal to the gate that certainly is in cutoff region or does it also have a permanent bias voltage because of the charge?

@2326TOM 9 жыл бұрын

Thank you Doug

@gert_kruger 8 жыл бұрын

Just a comment on the dimensions, its not -45dB/Pa, dB is the logarithm of the ratio of two units, in this case -45dB where 0dB=1V/1Pa. Thus adding the /Pa again after dB is wrong...Just nitpicking, still thumbs up!

@gustavlicht9620 3 жыл бұрын

If you have current modulation per pressure, then why not use a transimpendance amplifier?

@mokopa 6 жыл бұрын

...and now I know what the experts know bout electret mikes. Came here to have a question answered, left with answers to questions I'm yet to ask.

@Likeaudio 3 жыл бұрын

Amazing

@Impedancenetwork 6 жыл бұрын

Nice! I just took an Analog electronics, electronics and circuit analysis class. I had to design an electret microphone amplifier for a project . It was interesting to see how a professional would have designed it. You should do more of these professional designer guest appearances.

@gregkrobinson 10 жыл бұрын

The electrets without gate resistors remind me of grid-leak biased vacuum tubes - unstable as hell!

@guitarrelic 10 жыл бұрын

Really very interesting.

@elye3701 8 жыл бұрын

At 6:35, you brought out a device. How well does that work? Can I have the circuit diagram of that device? Please?

@Kevinjimtheone 10 жыл бұрын

Do you know of any digital microphones within the range of 10Hz (20Hz at most) to 10KHz (the upper limit is not important to me)?

@compactc9 10 жыл бұрын

I had to add this, but on the part that computer audio inputs have, Apple doesn't supply a voltage on their audio in, so you have to use a powered mic. Not sure why though...

@Monkeh616 10 жыл бұрын

To sell you a more expensive mic.. Why would they let you use any old cheap mic when they can charge you for any old cheap mic with a cheap power supply?

@WingmanSR 10 жыл бұрын

Monkeh616 Yup... Exactly why Apple's anti-consumer antics don't earn a single cent from me.

@metaforest 10 жыл бұрын

This is because Apple is supplying a line-in NOT a Mic-in. Apple's reasoning here is that it is better to provide a good 1 Vpp line-in for input quality, than a crappy mic-in that sounds like shite no matter what you plug into it. Apple is using a different standard that gets better results.

@AstAMoore 10 жыл бұрын

Not true. Apple’s laptops, desktops, and mobile devices all provide a few volts of DC on their audio inputs. You can plug in (virtually) any electret mic into virtually any Apple device (with a TRRS jack).

@Monkeh616 10 жыл бұрын

Ast A. Moore 'virtually any'.. except all the ones spanning the 10 year range I own personally. I can't speak for the current models, but not one Apple machine I have personally owned or interacted with supplies power for an electret mic.

@jessesmith8552 4 жыл бұрын

i just built a pcb and i got my mic to work but im getting a bit of a low hum or feed back in the back ground it was really loud then i started to an some resistors to the input of the pcb and it smoothed out but i still cant figure out how to get ride of it so i can use the mic to make music idk if i should change quality of wire from the mic to pcb or from pcb to xlr out put or if i need to add something balance out the pcb some how

@jessesmith8552 4 жыл бұрын

im using all 5% resistor seems like i should be in better condition then i have another pcb i was working on i bailed on it i had it working where you could here my voice but as i spoke i got back ground rumble totally different than the one im working on now and it was odd if i left the mic alone but on it was quiet but as i talked it would get more feed back and more so i got sick of playing around and went back to the other design i was working i just need some one t ling me up with the front half of a circuit so a 34mm capsule will work and im using 2n5457 jfet

@BarriosGroupie 10 жыл бұрын

Who uses Jfets, when Mosfets are so cheap nowadays? Doug Ford is quite an electronics guru: search the web for his article "the secret world of oscilloscope probes"

@peterpv0001 10 жыл бұрын

The choice for a JFET has nothing to do with the price (vs a MOSFET) but all to do with noise, MOSFETS are notoriously more noisy than JFETs and bipolar transistors, they have significantly more 1/f noise, i.e. low frequency noise which will be in the audio band ;-)

@ianc4901 10 жыл бұрын

Some strange sound compression weirdness going on (or is it noise gate ?) that's very distracting, it feels like my ears are shutting off every time it goes quiet.

@EEVblog 10 жыл бұрын

I ran this one through The Levelator, which usually does a pretty good job. I might not have noticed any issues, because I edited this one in my temporary (see twitter photo) computer setup, and the room acoustics are terrible.

@MWNewey 10 жыл бұрын

EEVblog I noticed it in a cheap caravan, in France.

@ppaolosan 2 жыл бұрын

da dove viene quest'uomo?

@RafaGmod 10 жыл бұрын

Genial, simplesmente!

@eddyfontaineyoutu100 10 жыл бұрын

Outstanding ! :-)

@Justsquareenough 6 жыл бұрын

for the life of me I don't understand why the gain goes down as the bias resistor goes down, increasing Vds. I've simulated as such but still don't understand the why. anyone?

@baroque_engineer 6 жыл бұрын

See, the FET inside is essentially a current source. Now note that we're speaking of VOLTAGE gain, and output voltage will be, of course, Vout = Id * Rd, where Id is a drain current (which is dependent on a transconductance, which is constant) and Rd is a bias resistor. So now you see - the lower the resistor, the lower the output voltage...

@baroque_engineer 6 жыл бұрын

Well, more correctly, the output voltage will be Vout = Vbias - (Id * Rd), but this does not change the principle. :)