OPA Based Alice Microphones: Cardioid and Figure 8

Turn a $20 BM 800 microphone into a world class Cardioid or Figure 8 microphone. This video is part of an Instructable for building an "OPA-Alice" microphone. It uses a Texas Instruments OPA1642 dual operational amplifier for the impedance convertor and internal electronics for both a TSB2555B Cardioid capsule based microphone and a dual TSB165 capsule back to back microphone with a figure 8 response pattern. The instructable is here: www.instructables.com/OPA-Bas...
00:00 Intro
00:45 About the OPA1642 www.ti.com/product/OPA1642-Q1
01:10 How the Circuit Works
03:54 Build the PCB
06:18 Cleaning the PCB
07:30 Disassemble the Donor Body
09:35 The Mic Build: Cardioid - XLR Prep
10:31 Capsule Gluing
11:16 Microphone Assembly
11:54 Saddle and Capsule Mounting with Rubber Grommets
13:04 The Mic Build: Figure 8

[@Xenogenocide]

Pulled the trigger today, decided to buy the PCBs and components. I'll wire up a mic for me, my brother (who frequently records vocals) and keep some parts spare (incase I botch it up). Thanks for the instructable Jules! This is legendary!

[@TheSlyMouse]

Love your build videos. The schematic walk-through was appreciated and helped me learn a bit. I hope you keep posting!

[@psi4262]

You’re genius man thanks 🙏🏻

[@SoundSleuth]

lol your welcome

[@genghisbunny]

Thanks for your work Jules. I've bought the boards and am now checking which components are already in my spares bin before going shopping for the rest. Really appreciate your willingness to share your design with the open hardware community like this.

[@dj4mc]

You are welcome!

[@xef6]

Thank you for this great build video. It clearly outlines the steps necessary to DIY. The careful explanation of the circuit is greatly appreciated. Great work🎵

[@SoundSleuth]

Thank you! Really appreciate the feedback

[@petercornell2002]

Excellent video, thanks Jules

[@SoundSleuth]

Thanks Peter!

[@juliancarreno101]

Excellent! I love it!

[@SoundSleuth]

Thank you!

[@raymota4515]

Excellent.

[@restoband7338]

thank you so much for this!

[@NBryanBlack]

Just curious as to why you have the capsules in series to make the figure-8 vs. in parallel. (or if it would make any difference one way or the other.) Thanks! Great instructable and KZbin video!

[@SoundSleuth]

Thank you! I put them in series as that made more sense to me. It drops the capsule capacitance in half but that isn't an issue. If they are not matched, putting them in parallel could cause differences in signal outputs. That was my thought process...

[@nicholasmarrs2779]

Thank you! I bought and built the true condenser version (LOVE IT!) and now I'm hooked! I was wondering if you could point me in the direction to learn more? I'd really like to actually understand the circuitry instead of just putting things where they go. All of my searching only ever takes me to you or mic-parts. Any recommendations would be a huge help!

[@SoundSleuth]

There is some good stuff from the Application Notes for Analog Devices and Texas Instruments Operational Amplifiers. I am working on a book for this as there is a dearth of information that isn't 40 years old as well.

[@voiceovervandeen]

You might find some JLI Electronics capsules harder to come by for a while as DIY Perks channel has just dropped a video of a DIY mic, he used a USB sound-card though so I've pointed people to your channel if they need mic plans for use with a proper external interface.

[@dj4mc]

Thank you. I'll have to go check it out.

[@voiceovervandeen]

@@dj4mc He's a massive channel & from what he said he's open to suggestions by e-mail for improvements to his circuit design, so he could be a great ally for growth if you can get some sort of a collab with him for an interface version :-)

[@dj4mc]

@@voiceovervandeen Already reached out, hope he replies.

[@Ryezn5057]

Love the builds. Out of curiosity what interfaces do you use?

[@SoundSleuth]

I have a Scarlett 18/20 gen3 and for Field/portable use a ZoomF6

[@ollyk22]

What difference in the overall experience would we get with an M+S recording technique instead of mic for voice and mic for guitar? Can the latter work well?

[@antoninherve1259]

Hi it's a really nice video but do you have the Gerber of the pcb ?

[@cdeltv8025]

Hi! Do you need an extra board for a 34mm condenser mic like a k47?

[@jayroldtabuzo9479]

any alternative in that opamp ? can i use opa2134?

[@shubhambobhate4941]

OPA134/164s are hard to come by where I'm from. Can OP177s, NE5532s or LM358s fill their roles adequately?

[@teddy3k3]

anyone know where i can get 2 mic saddle in an XY position?

[@Xenogenocide]

Hi, I love the design of this PCB, it's very simple and easy enough so that the average Joe like myself can put one together, and best of all the end product sounds comparable to a decent £200 - £500 condenser microphone. What are the advantages to using this OPA based circuit instead of other Alice mic PCB designs (for example, Homero Leal's Pimped Alice circuit)???

[@dj4mc]

The main benefit is parts availability long term. It also has higher output prior to clipping. The Opamp portion has about 120db dynamic range with the phantom power supply we are using. Im in process of gettign a test setup going and will update the instructable with my results.

[@Xenogenocide]

@@dj4mc Thanks for the quick reply Jules. Your work and documentation is fantastic. From the video, the mics sound very clear and crisp. I can't wait to try this circuit out for myself for a future project. I'm probably going to sound dumb asking this too but here goes: Is it possible to use this with a 34mm capsule?

[@genghisbunny]

@@Xenogenocide capsule size can vary a lot, as long as it fits in your mic body you should be fine.

[@AbdoZaInsert]

Thanks for the great video. Only thing I'm having trouble with is finding the electrical components, any Idea where can I get them all in one package ?

[@dj4mc]

You can get the capsules and PCB fully populated here: www.jlielectronics.com/diy-accessories/opa-alice-single-channel/

[@AbdoZaInsert]

@@dj4mc Thanks for the fast reply ! I already have the capsules, for the PCBs I honestly would like to get the raw materials and order the PCB from PCBWay and solder them my self to exercise on soldering. I found some parts on the xls file you shared but most of other ones couldn't be found. So if there's any certain website you know of that'll provide the components in pcs I would extremely appreciate it !

[@ZipZash]

Nice video, I'm am not to experienced with auido interfaces or XLR. Is it possible to just wire it to a 3.5mm headphone jack and plug it into a computer? Or is it not that simple and I need an audio interface or special adapter?

[@YLSQUID]

You won't be able to provide phantom power from a computer 3.5 headphone jack, and thus will not be able to polarize the capsule to make it work. There are very cheap audio interfaces like the Behringer Um2 (

[@audiofreq]

This is great! What power board did you use for this? Dc dc hex?

[@SoundSleuth]

Those two capsules are electret condensers. No bias needed.

[@audiofreq]

Ahhhhh! I ended up buying the Alice Single and DC DC from JLI. Great work! And Thank You! @@SoundSleuth

[@buzzysmurf2999]

Hello. I've soldered almost every thing but the resistors, I got lost because you haven't mentioned which one to use & where, I tried to read the paper circuit but tbh I couldn't understand it that much ( Positioning). Can you please give me a heads up or a link to exact positions using the PCB board "R1,R2 - R10" signs, and their polarity side ? Sorry for the inconvenience and thank you in advance.

[@SoundSleuth]

There are pretty detailed pictures here. Resistors are not polarized so you are good there. www.instructables.com/OPA-Based-Alice-Microphones-a-Cardioid-and-a-Figur/

[@devampatel1265]

Hi Love the video but Can you tell me how i should change the circuit diagram to connect the mic to a usb port instead of an XLR port?

[@SoundSleuth]

You would have to add a lot of electronics to do that. This one is pure analog, meant for a mic pre or USB interface with XLR input.

[@devampatel1265]

@@SoundSleuth Hi thank you so much for replying btw! context is, i had a condenser microphone whose circuit board got fried for some reason, so im tryna build myself a new circuit for it. the output it took was a USB-B which had +VCC, Drain+, Drain-, and GND the 3 pin XLR connection you showed is =12v,Gnd and Drain(-) So i need to figure out how do i get the drain +

[@SoundSleuth]

@@devampatel1265 USB has +5V Gnd and: Data "+" Data "-" Look at this video for a USB based one kzbin.info/www/bejne/gqC0pmaOja6Ur8U

[@justinlee8328]

Do the large 47uF electrolytic capacitors coupling both of the signal paths not harm the tone? Could you connect the output of the op amps to ground through 10M resistors, which would allow you to use small 0.1uF film capacitors for a corner frequency of 0.16Hz?

[@SoundSleuth]

The 47uF do not affect the tone. My testing of this shows extremely low THD. The opamp outputs are about 6VDC thus need the coupling caps. Which actually couple the signals into the phantom voltage at the XLR connector. The output impedance of the circuit needs to be low to drive the input to the mic preamp or recorder.

[@konstantinNeo]

Hello. Thank you for your hard work. What device do I require to connect this diy microphone to my pc through the XLR connector? (a budget version preferably)

[@SoundSleuth]

This is probably the least expensive way to do this: www.amazon.com/Behringer-UMC22-BEHRINGER-audio-interface/dp/B00FFIGZF6

[@konstantinNeo]

@@SoundSleuth Thank you very much. Do I have to enable the 48v phantom power? I went with the OPA Alice single channel + JLI-2555BXZ3-GP capsule. I am affraind I might burn it so I ask.

[@SoundSleuth]

@@konstantinNeo see this: www.jlielectronics.com/content/FET-LessREV2.pdf

[@konstantinNeo]

@@SoundSleuth Thank you. The schematic is very useful and pretty simple. I meant in the audio interface UMC22, what should be the position for the 48v phantom power switch on the back. On or OFF?

[@SoundSleuth]

@@konstantinNeo On. That is what powers the circuit.

[@AnalogDude_]

Do you have information on how to add a line input on "high end" camera that have a stereo micro input. These camera's tend to have a optional breakout box with XLR inputs, but are easily around 600€/piece. I wonder how they source power for this breakout box as there are multiple switches on for options it. Both Sony as Panasonic do this. The producer isn't keen to provide a schematic to their gear so you're be abled to build it yourself and threaten to void you warranty. Cool, video.

[@SoundSleuth]

Ill look into it as a project. Problem is more size constraints and getting it to fit on the camera rig.

[@AnalogDude_]

@@SoundSleuth Wha, i don't see that as a constraint to fit on the camera, but rather than it works and prevent spending 600€ for a box! I just hooked the camera on to the scope, using a DIY 3.5 mm stereo to 3.5 mono jack using shielded singled stranded cable, i measure a bit more than 2.0V coming from the stereo microphone input, seemingly while recording that channel was disabled and only picking something up on the other channel. Would be cool if i was be able to record my gear by taping directly in to it. although my euro rack gear is 10Vpp, i do have module to converts it to line level.

[@AnalogDude_]

@@SoundSleuth I have soldered a "electret" mic i had laying around to cable previously mentioned and it works. I measured a 1Vpp while speaking in to the microphone on a distant from the camera. Not sure if it's automatically disabling the internal microphone. Sony Alpha camera.

[@SoundSleuth]

@@AnalogDude_ this is one of my solutions. www.instructables.com/Camera-Mount-ORTF-Stereo-Microphone/

[@AnalogDude_]

@@SoundSleuth Someone mentions a "Neutrik" NTE x.x audio transformer could help.

[@DiyintheGhetto]

Hello for a none audio duy like my self. But I'm a 100% DIY that builds pretty much anything would love to know how to hook ones of a xlr microphone up without having to pay a lot of money that is on a budget. What would i need to build my own little setup And run a microphone like this? I forgot one thing yet i would be using this on a pc as well for recording audio. By the way awesome build man makes me want to now build one of theses. Thank you for sharing with us this build.

[@SoundSleuth]

Thanks! This is XLR based. If you are asking about the interface side, those are sadly much easier/cheaper to buy than to build.

[@matthewcote107]

I built one of your MS mics a few years ago and its output has become very noisy and low in level. Mine is pre-OPA. I can't find any broken connections or shorts. Would it be practical to replace its two circuit boards with one of the dual-channel boards from JLI? Would the substitution be fairly straightforward?

[@SoundSleuth]

Yes. The dual board works great for this I’m actually about to release an Instructable on this and have JLI carry a kit

[@matthewcote107]

@@SoundSleuth Perfect! Thanks for such a prompt reply. Please sign me up for any way I can serve as guinea pig or proof that it works. I'll order the board and await the next Hollywood blockbuster so I can get my mic back in action. I really miss having an MS mic! I just bought a Zoom F3, so I'm eager to use it with a renewed MS mic to capture the sounds of the spring peepers finally emerging in northern New England.

[@SoundSleuth]

@@matthewcote107 email me [e-mail] I'll fill you in on my ms mic thoughts

[@audiofreq]

Is there a HF de emphasis in this circuit?

[@SoundSleuth]

Nope. The circuit is very flat to about a Megahertz and about 40dB lower distortion than an equivalent FET circuit. You can EQ in post should you like.

[@audiofreq]

Ahhhh ok, was curious. The capsule I paired with it is very bright. I might just buy a different capsule. I will try out the TSC-2 next :). Thanks!@@SoundSleuth

[@jervi_sir]

m totally newbie, is it possible to turn this into usb powered and jack output, instead of XLR ?

[@shubhambobhate4941]

DIYPerks has a great video on this subject. Check it out.

[@s.b.l.u6114]

Does an OPA mic sound good on an OPA preamp installed in the channel?

[@SoundSleuth]

It sounds good on any mic preamp. All audio interfaces and modern consoles use IC mic preamps. THAT corp or SSM2019’s. If you want a little vintage or added THD use a tube or transformer input mic preamp.

[@s.b.l.u6114]

@@SoundSleuth I have a mixer with OPA amplifiers on almost all channels. And I was wondering whether it wouldn't blow up in my face when I connected Serena

[@SoundSleuth]

@@s.b.l.u6114 It absolutely won’t.

[@TheRealPekpyT]

Is it better than AKG P120?

[@SoundSleuth]

Yes

[@fastunovaudio]

Please tell me, can I use this circuit (or the OPA Alice Dual SMD v1.0 board) with the Primo EM264Y Cardioid electret capsule?

[@SoundSleuth]

No, the Primos and many others have a built in FET. This wont work for that. However, you are not the first to ask this. I am planning on updating the circuit for use with a capsule with FET. It will be a PIP to Phantom Power circuit using the same Operational Amplifier.

[@fastunovaudio]

@@SoundSleuth Thanks for the answer, everything is clear! I am insanely glad that you are working on a preamp for Primo. This is very cool news. I'm looking forward to the release as I dream of using Primo capsules for my parabolic reflectors in combination with your cool developments! I would like to thank you separately for the fees that appeared in the DIY accessories section. For those who are not friends with soldering, this is just a breath of fresh air. I ordered two sets (OPA Alice - Single Channel+DC-DC Hex Inverter PCB) two assemblies of two cardioid microphones. I'm looking forward to the delivery))))

[@SoundSleuth]

@@fastunovaudio Thanks, this is exactly why I put time into this.

[@chrisislocox24]

what is the 1g ohm resistor for, is there not enough impedance through the positive op amp terminal?

[@SoundSleuth]

It provides a load to the Opamp input and combined with the capsule capacitance provides a cutoff frequency of 3-15 hz depending on the capsule. This is similar to FET and Tube circuits. My real change is to use a low distortion low noise Opamp instead of the FET or Tube

[@chrisislocox24]

@@SoundSleuth I appreciate it!! HPF at the input? Thank you I have had trouble understanding this part in the Alice circuit!

[@crancarenotafish]

Are the actual PCB tested? I'm going crazy trying to find the problem. Voltages are all wrong. Desolder OPA1642 then all voltages are good. I tested for solder bridges on in and I have none.

[@SoundSleuth]

Yes. I have built many of these as have others. What voltages are you getting and where? Email me [e-mail]

[@crancarenotafish]

I just emailed you, thanks so much for quick response.@@SoundSleuth

[@RecehDIY]

question so the capsule itself powered by a 6 volt bias from divider, am i right?

[@SoundSleuth]

The capsule has no internal FET or electronics. The voltage divider is to get the opamp biased so that it can run on a single supply voltage vs split rails (+/-)

[@RecehDIY]

@@SoundSleuth last question sir, is it possible to do this project on a USB based microphone w/o boost the 5 volt supply?

[@SoundSleuth]

@@RecehDIY five volts is too love for the opamp This will run on about 6.5 to 35 Volts

[@RecehDIY]

@@SoundSleuth a very lasy question sir, can i use 1meg resistor instead a gig? or, is there any minimum requirement for bias resistor? it's hard to find a resistor that big in my area

[@SoundSleuth]

@@RecehDIY No, a 1Meg is too small for this. Digikey and Mouser both carry them Digiky: www.digikey.com/en/products/detail/stackpole-electronics-inc/HVA12JA1G00/6195865 Mouser: www.mouser.com/ProductDetail/TE-Connectivity-Holsworthy/RGP0207CHK1G0?qs=sGAEpiMZZMsPqMdJzcrNwlDepD%252BlwznyoKugq%252BfXem0%3D

[@NoNeNoNeNoNe134]

do we need to use any specific wires?

[@SoundSleuth]

No, just use decent 22 or 24 gauge stranded wire.

[@NoNeNoNeNoNe134]

@@SoundSleuth I built this microphone however it buzzes when I touch microphone... Help will be greatly appreciated...

[@SoundSleuth]

@@NoNeNoNeNoNe134 Check this out: www.jlielectronics.com/content/TroubleshootingOPA-Alice%20MicRev1.pdf

[@runnningonempty]

How much for a completed board? or four?

[@SoundSleuth]

I'm not selling them as of now. We are working on a fully populated surface mount version that will be available. Will keep the channel posted.

[@runnningonempty]

@@SoundSleuth Great,I hope it wont be too long,I am after single cardioid rk12 capable boards. or stock large used mxl diaphragms

[@MsLanderX]

They are out!!! www.jlielectronics.com/diy-accessories/