DIY Tube Mic project

[thor.zmt]

This "datasheet" is a bad joke!

I found somewhat more useful information:





So basically we can expect -2dB @ 20Hz & 20khz and 1.2V across the primary at 60Hz give ~1% THD, so 0.6V max. @ 30Hz. So in 10:1 mode maximum 30Hz output at 30Hz & 1% THD = 60mV.

Recommended load in 10:1 stepdown is 500R or higher.

Thomann has recently discontinued these transformers, the price was really good.

Banzai has it at 20 Euro

And I think it would be worthwhile for a first build, including for @Emmathom to make this SELA S12 Clone with the NTE10/3.

It would literally be a stereotypical early tube mike. My recommendation based on Sim's for a bit more tube current, and easy to build, using 12V/1A DC (plug top SMPS?) to power:



As HT supply either this DIY Kit or something build on Veroboard to the published circuit should work well:

https://threeneurons.wordpress.com/nixie-power-supply/hv-supply-kit/

The kit is available on e-Bay for 16 Bux, which beats a smack in the gob:

HV Power Supply - 12V In, 45 to 350V Out - 5.5W Nixie, Old Radio - US Seller

E.g. this, which can be made with all through hole parts:





With the suggested 90V HT the tube will draw around 3.5mA and total gain with the Transformer accounted for will be in the region of -3dB, so it's not a very "LOUD" microphone.

A bit of extra gain is to be had by replacing the 10K Anode load resistor with E352 (3.5mA/100V) Current Regulator Diode, e.g.:

Mouser - Semitec E-352 Current Regulator Diode (currently outstock preorder)



I think together with being able to use a basic 12V SMPS as overall power (or even a USB-C battery pack with a USB-C PD trigger PCB set for 12V), the small DC-DC boost converter a very easy DIY project emerges with both an option for a transformer less and transformer based option, that is a very realistic proposition.

Attached is also the .tsc file (as zip archive) that was used in the simulation - just download free Tina-TI and open the TSC file....

Thor

 

[thor.zmt]

I found somewhat more useful information:

Even more, in GDIY of all places:

https://groupdiy.com/threads/tiny-n...icrophone-output-10-1-for-tube-and-fet.63432/

I measured response and it's linear from 20Hz to the sky

Found info on the inductance too, around 80H.

For that a 1uF/100V MKP from Wima looks like a good coupling cap, or Nichicon 1uF/100V ES "Muse" Bipolar, it will give a bit of a resonance at 20Hz (2-3dB boost).

So, other than small core and thus not recommended for Kick Drum (I'd use an AKG D12 or 112 for Rock anyway) it seems the NTE10/3 is a great find. Mouser has stock and sells the under 15 Colonial Bux.

Mouser - Neutrik NTE10/3

Thor

 

[Emmathom]

Ok... now we come with a very different schematic...
and the need to get a NTE10/3 : why not after all if adds "something" compare to BSS84... ?

We now heat with 6v positive (still under 175mA ~ 180mA) > I still would use my SMPS 12v • 1,3A filtered by RC (30Ω*180mA for ex.)

You sim. says 90v under 3,5mA : excuse me if I insist but I'd like to use one of my different Tr in stock. I think I got a 2*24v • 12VA or 16VA (I must check) but anyway I've got for sure a 2*18v • 12VA which means 330mA / 36v and 150mA doubled. I think I can use this last one in worst case to generate B+ 90v DC since the current draw is low (3,5mA) and will not cause a significant voltage drop. 72*1,414 = 101,8v > still have a few volts for a good RC...

Other suject : the Quad is finished this afternoon : great sounding (I posted in the dedicated thread)

 

[thor.zmt]

Ok... now we come with a very different schematic...

Yes, remember that I listed the rather expensive transformer as a reason against doing a traditional tube Mic?

With the NTE10/3 very affordable and good, we can go back to a simple tube microphone.

and the need to get a NTE10/3 : why not after all if adds "something" compare to BSS84... ?

It is more "classic"....

We now heat with 6v positive (still under 175mA ~ 180mA) > I still would use my SMPS 12v • 1,3A filtered by RC (30Ω*180mA for ex.)

Please note that I propose the LM317 to allow an easy adjustment of the heater voltage, from (say) 5V to 6.6V. You can still use the SMPS.

You sim. says 90v under 3,5mA : excuse me if I insist but I'd like to use one of my different Tr in stock. I think I got a 2*24v • 12VA or 16VA (I must check) but anyway I've got for sure a 2*18v • 12VA which means 330mA / 36v and 150mA doubled. I think I can use this last one in worst case to generate B+ 90v DC since the current draw is low (3,5mA) and will not cause a significant voltage drop. 72*1,414 = 101,8v > still have a few volts for a good RC...

Absolutely. At the same time I wanted to show a different way to get the HT.

If you buy the HT module from E-Bay, the NTE10/3 and the rest it is probably possible to make a really nice tube mike for under 100 Euro, including a donor BM-700 in the budget.

I think it could get a lot more peeps into building such a microphone.

Other suject : the Quad is finished this afternoon : great sounding (I posted in the dedicated thread)

Congratuations!

Thor

 

[Emmathom]

Please note that I propose the LM317 to allow an easy adjustment of the heater voltage, from (say) 5V to 6.6V. You can still use the SMPS.

... yeah and maybe with a LM317 too : what will be more "silent" ? RC or regulator ? I thought heating had to be at 6v, not 5 or 7...

Absolutely. At the same time I wanted to show a different way to get the HT.

Yes I understand and agree 100% to use "new" technologies (or topologies) that are often smarter, less consumption, smaller, etc... but I have stock I must use and when it's possible...

If you buy the HT module from E-Bay, the NTE10/3 and the rest it is probably possible to make a really nice tube mike for under 100 Euro, including a donor BM-700 in the budget.

I've got a small LDC donor body on Ali. It's small, like a toy but it will do to test things. Nothing stops me after that to move the parts in another body more fitted (and prettier)

I think it could get a lot more pepes into building such a microphone.

Google Transl. doesn't know what is a "pepe" you mean people ? (a pepe in ancient french (around WW2) meant a nice little young woman > "des jolies pépés à la plage"

Congratuations!

Thanx to you !!! +++++

Thor

 

[rock soderstrom]

For that a 1uF/100V MKP from Wima looks like a good coupling cap, or Nichicon 1uF/100V ES "Muse" Bipolar, it will give a bit of a resonance at 20Hz (2-3dB boost).

ERO MKT1813 1uF/100V is pretty small and does nothing wrong to the sound IMO.

If you buy the HT module from E-Bay, the NTE10/3 and the rest it is probably possible to make a really nice tube mike for under 100 Euro, including a donor BM-700 in the budget.

I prefer for low budget projects used t.bone bodies. SC450 is pretty good and offers plenty of space for the tube and the rest. SC440 and SC450 USB are usable as well, the USB connector is a bit pain in the butt. I modified them to a fixed cable solution with hot glue ;-), not everybody liked this, bit I build it for a young band and the do not care.


Overview of some t.bone bodies:

https://groupdiy.com/threads/inside...tting-party-for-mic-diyer.81965/#post-1058087

low or better now budget solution for former USB mics:

https://groupdiy.com/threads/mic-body-modification-from-usb-to-xlr.86838/post-1138244

 

[thor.zmt]

... yeah and maybe with a LM317 too : what will be more "silent" ? RC or regulator ? I thought heating had to be at 6v, not 5 or 7...

Well, you can run a tube with lower heater voltage than standard.

It means there less rlectron mobility, cathode emissions and you thus must use the tube at a fraction of the rated current.

Bell labs did a massive test series for the repeater amplifiers in undersea telephone cables - low heater voltage and low anode current reduced noise and allowed extremely long tube life.

Seeing the 6AK5 is rated at 10mA @ 6.3V, I think 5.5V will be fine with low current.

Yes I understand and agree 100% to use "new" technologies (or topologies) that are often smarter, less consumption, smaller, etc... but I have stock I must use and when it's possible...

Of course, however even you might find building up the DC-DC converter on veroboard cheap, light and highly effective.

Because it can help towards future projects, where you need HT and being able to have a small (circuit) module that makes 5W worth of HT from 12V up to quite high voltages makes a lot of things easier.

google Transl. doesn't know what is a "pepe" you mean people ?

Peeps - indeed slang for people.

Thor

 

[Emmathom]

ERO MKT1813 1uF/100V is pretty small and does nothing wrong to the sound IMO.

Yep . And I have choice between a MKP10 1uF (at bit big but should fit) and a russian PIO 470nF (big too) but I'm ok for that ERO (that I see in many tube mics DIY)

I prefer for low budget projects used t.bone bodies. SC450 is pretty good and offers plenty of space for the tube and the rest. SC440 and SC450 USB are usable as well, the USB connector is a bit pain in the butt. I modified them to a fixed cable solution with hot glue ;-), not everybody liked this, bit I build it for a young band and the do not care.

Yes a SC450 or 440 at second hand is a good option > + there's is some components to recover !
But does the headbasket fit this project ? Is it "acceptable" in terms of sound ?
Other possibilities (picts attached > the Eagletone comes with a HT PSU > to use at least the chassis and some comp.)
These mics are all sold 50€ - 80€ max.

And Yes ! I intend to stick the cable out of the mic since it needs its dedicated PSU (so no compatibility needed with other PSU's ) and the less connectors the better

BTW I was well inspirated to order 5 pin XLR and 4 pairs audio cable since now we have moved from 4 wires to 5 between PSU & mic !

Thanx for your participation @rock soderstrom

 

[Emmathom]

Seeing the 6AK5 is rated at 10mA @ 6.3V, I think 5.5V will be fine with low current.

10mA ? You mean HT or heater ? because datasheet says 175mA @ 6v

Of course, however even you might find building up the DC-DC converter on veroboard cheap, light and highly effective.

Because it can help towards future projects, where you need HT and being able to have a small (circuit) module that makes 5W worth of HT from 12V up to quite high voltages makes a lot of things easier.

Yes, good thinking

 

[Emmathom]

My choice (Thomann) : Sommer Cable Quantum Highflex Multipair 4
4 pairs shieded of good quality cable / 3,85€ per meter (not expensive for this quality)
Exists also with 2 pairs...

Will order 4m or 5m and fix it in the mic...

 

[rock soderstrom]

My choice (Thomann) : Sommer Cable Quantum Highflex Multipair 4
4 pairs shieded of good quality cable / 3,85€ per meter (not expensive for this quality)
Exists also with 2 pairs...

I usually take this Sommer cable. You do not need the 7 cores but there are 2 x 0.50 mm² for the heater, big plus. Price is the same.
https://www.thomann.de/gb/sommer_ca...PR0yxStGBzO5GN2MQ9FGRiaC714x49exoC_tAQAvD_BwE

 

[rock soderstrom]

But does the headbasket fit this project ?

Yes, I think so. Most of the cheap capsules are kind of K67 clones anyway, so this headbasket is a good fit. I had no problems, but it is DIY, you can take whatever you want.

The original T12 was a Lollipop style headbasket with a Neumann M7 capsule.

 

[Emmathom]

I usually take this Sommer cable. You do not need the 7 cores but there are 2 x 0.50 mm² for the heater, big plus. Price is the same.
https://www.thomann.de/gb/sommer_ca...PR0yxStGBzO5GN2MQ9FGRiaC714x49exoC_tAQAvD_BwE

Yes this one is a standard tube supply mic cable...

But 6v*175mA = 1,05w > don't you think 0,28mm2 (I'll use 2*0,14mm for +6v & 2*0,14mm for ground) won't ne sufficient ? I guess yes...

 

[rock soderstrom]

But 6v*175mA = 1,05w > don't you think 0,28mm2 (I'll use 2*0,14mm for +6v & 2*0,14mm for ground) won't ne sufficient ? I guess yes...

Yes, this will probably also work, the voltage drop will be slightly higher. I would still use the 7 core. Very good cable, easy to work with and is also used successfully with very high-quality microphones.

A standard cable in the good sense of the word!

 

[thor.zmt]

10mA ? You mean HT or heater ? because datasheet says 175mA @ 6v

10mA operation, 20mA max cathode current with a nominal heater. Reduce heater voltage, you get less emission and thus less current. Seeing we run 3.5mA cathode current...

Thor

 

[Emmathom]

About the NTE10/3 :
buying "basic" components for testing is ok but then we don't know what to do with them if we need to upgrade the project.

Would there be another candidate instead of the NTE10/3?
Certainly a little more expensive one, I suppose, but perhaps "stronger" to work with high pressure levels ?

I just ask : maybe this neutrik is sufficient...

Another point is the possibility for switching between cardio & omni : maybe a small relay inside the mic driven by 5v ? (6v of the heater in fact)

 

[rock soderstrom]

About the NTE10/3 :
buying "basic" components for testing is ok but then we don't know what to do with them if we need to upgrade the project.

You can always upgrade to bigger and more expensive transformer if you want to.

Here are some options:

member @igs at https://utmindustry.com/

http://www.3uaudio.com/chanpin1.asp?dh=2

member @Moby at https://www.mobytransformers.com/

Would there be another candidate instead of the NTE10/3?
Certainly a little more expensive one, I suppose, but perhaps "stronger" to work with high pressure levels ?

check the links above, any 6:1 to 10:1 mic transformer is a possible candidate.
I think it's important to gain a lot of experience with your first project and a mic based on the SELA T12 is well suited for this. The result will be good and will then also provide as a good comparison reference for further projects.

I just ask : maybe this neutrik is sufficient...

There is always a better, no question, but with the Neutrik you get surprisingly far in this circuit. Check it out!

 

[thor.zmt]

About the NTE10/3 :
buying "basic" components for testing is ok but then we don't know what to do with them if we need to upgrade the project.

After doing some reading I think it's a good choice unless you want a Mike for kick drum.

It small core will start to distort progressively as frequency falls, this will for example give more warmth and power to vocals.

And let's bf honest, of all the peeps in the biz brandishing original Neumann or more rate tube mikes, most use them on vocals.

So I'm kinda, well, we want a vocal mike with "good colour" and this simple circuit and transformer seems suitable.

Build something else with different parts for the next Mike project. Mikes ard like Girls, non is perfect, but there are so many you want anyway...

Make it a dedicated Vocal and Acoustic Geeturr mike. Perfect for audiophile "Gurl with Geeturr" and Roland on the Dru.s music.

I'd skip pattern switching, you mainly use cardioid for vocals or acoustic Geeturr.

Would there be another candidate instead of the NTE10/3?

Sure, but my alternative design was transformerless for a reason. And would handle a lot of SPL. To get a transformer to handle this would mean big, heavy and expensive.

I just ask : maybe this neutrik is sufficient...

Ask Rod for some sound sample's.

Another point is the possibility for switching between cardio & omni : maybe a small relay inside the mic driven by 5v ? (6v of the heater in fact)

Nah, I'd do the first ground-up mike without pattern switching.

Later versions you can use for example my transformerless design and vary the bias to the second diaphragm, was it the C12 who did?

Thor

 

[Emmathom]

Ok guys, thx for your answers.
Let's go on with NTE10/3 & cardio only

 

[Tubetec]

A pencil mic version might be do-able with a submini and a suitable donor body/capsule.

Building a mic dedicated to close micing quieter sound sources for small money
sounds like a really good plan .

If the HT module and LT regulator could be incorporated in the mic itself it could further reduce the cable complexity ,
a simple two core screen could carry the audio and 12v could come in on the usual DC power connector .

Battery supplied 12v might be another interesting option ,