DIY Tube Mic project

[thor.zmt]

So shouldn't it be wired reversed ?

Of course.

Thor

 

[thor.zmt]

Yes I get a "nice" 50Hz hum but I tried without the mic body > will put it on and come back
I think it will be better but not perfect > what should I do to get rid of this hum ? I got no scope to measure AC in the HV nor in the heater voltage...

First, is the hum mainly 50Hz or 100Hz?

Second, I think you need to tie together mic case and Mic Gnd hard in the Mic and then leave the case as "GND" and use a telescoping shield (shield not connect hard on PSU Box side 100R//100nF to case)

I was think about this shielded 5 wires cable : maybe use two cables tied together > one XLR "classic" shielded cable + one (not shielded and outside the XLR cable) with 2 wires just for heater & HV... but anyway the ground will be common !

Heater and Audio ground on the same wire means you will get DC offset.

As Audio out is via transformer this not critical.

The audio pair should be twisted.

You can probably get away using the shield as ground.

So XLR 5 plug with star quad microphone cable could be used I think. CANARE L-4E6S comes to mind.

Thor

 

[Emmathom]

First, is the hum mainly 50Hz or 100Hz?

50Hz (seen in my DAW)

Second, I think you need to tie together mic case and Mic Gnd hard in the Mic and then leave the case as "GND" and use a telescoping shield (shield not connect hard on PSU Box side 100R//100nF to case)

Sorry Thor but even with Google translate I can't get what you mean : could you please tell me clearly what to do, like unplug this on mic side, plug that on PSU side ? (attached the cable how it is wired now > I follow @rock soderstrom and put ground & PE at 2 diff. locations in the PSU enclosure)

You can probably get away using the shield as ground.
So XLR 5 plug with star quad microphone cable could be used I think. CANARE L-4E6S comes to mind.

Thor

I indeed use a 5 wires + shield cable and I think it makes no diff. to tie ground (let's say "minus" or 0v) and shield together...

 

[Emmathom]

I had the (good ?) idea of "housing" the transformer in modeling clay (the one for children) > I think it's good for damping and this also holds the cable which is thin in the wide opening of the old connector USB.
Since I decided not to use a connector at mic side (why would do I do so ?) I also use a XLR "plastic screwer" to hold the cable out of the mic : not bad to my taste

 

[Emmathom]

First audio test...
* enough level out (I compare with other mics / speaking at 20cm fom mic and input gain set at 50% on my audio card)
* pretty full sound (from 20Hz to 16kHz on my voice)
* no noise or hum (but a kind of light rumble between 10Hz to 100Hz but I suppose it's the ambiant noises of my room because I test it in my house just to ear)

It's really cool !
Thanks to @thor.zmt and @rock soderstrom !!!

I must add that it's a (very) low budget K87 style capsule from Ali that I use for tests... despite this I find the sound pretty well balanced

 

[Emmathom]

size matters...

 

[thor.zmt]

size matters...

That's one big Bone(er).

"Is that a microphone in your pocket or are you THAT happy to see me?" she said.

Thor

 

[thor.zmt]

Sorry Thor but even with Google translate I can't get what you mean

Microphone Case = Audio Ground = Shield

All "tied together" (lined) at the microphone.

I indeed use a 5 wires + shield cable and I think it makes no diff. to tie ground (let's say "minus" or 0v) and shield together...

Shield and GND lined at the Mic.

In the PSU Box, 10R/100nF to link shield to GND.

Thor

 

[Emmathom]

That's one big Bone(er).

"Is that a microphone in your pocket or are you THAT happy to see me?" she said.

Thor

The PSU box is 20cm long x 11cm large x 6cm height

 

[rock soderstrom]

It's really cool !

How did you solve the USB connector problem? Did you drill out the old USB port?

 

[rock soderstrom]

In the PSU Box, 10R/100nF to link shield to GND.

What's the advantage of the 10R/100nF over a direct connection to ground?

 

[Emmathom]

View attachment 130431
How did you solve the USB connector problem? Did you drill out the old USB port?

The USB connector goes off by simpling pushing it (a bit hard) from inside to outside.
I used an XLR cable tie sleeve: it's just the outer size of the tube and I attached it simply with electrician tape. I tried to heat the plastic sleeve so that it covered the outlet tube but I couldn't do it because the plastic is too hard. Inside the tube is filled with modeling clay. With care, this should hold in place...

 

[Emmathom]

I just replace the cheap Ali by another Ali which I find greater in terms of fidelity... but I'm asking myself if it's not a bit bright.
How be sure ? I could record a pink noise from my speakers but they have to be calibrated (they are supposed to be) and watch the curve in my DAW...

If there's a bump 5kHz - 8kHz is there a solution inside the mic (in the cicrcuit so) to damp this ?

 

[Emmathom]

What's the advantage of the 10R/100nF over a direct connection to ground?

I think that it isolates PE from electronic ground unless the current flows with a sufficient current to pass thru the R.
Everything is ok ? ground is not connected to PE. A problem appears with current passing into ground ? ground connects to PE thru R10 Ω. 100nF cap is to filter (but lets AC pass thru in case of leak)
but @thor.zmt would explain this much better...

 

[thor.zmt]

What's the advantage of the 10R/100nF over a direct connection to ground?

No loops.

Thor

 

[Emmathom]

Microphone Case = Audio Ground = Shield

All "tied together" (lined) at the microphone.

That's done

In the PSU Box, 10R/100nF to link shield to GND.

Thor

That's not what I did...
I connected (cable from mic arriving in PSU) :
1) ground wire (one of the five) with shied to ground PSU and ground PSU connected to chassis
2) PE connected to chassis thru 10Ω + 100nF
have you looked at my schem ?

 

[Emmathom]

Well it seems that this project does not get the interest of much diyer's aroud there... since nobody comments or ask for further infos...

I don't mind

I love this simple but efficient design, not expensive, and great souding mic !

Anyway, there's no names of Neumann - AKG - Telefunken - Manley - and so in this thread but a nice little DIY project, discreet but efficient

Thanks again @thor.zmt you're definitely a good designer +++

 

[micolas]

Well it seems that this project does not get the interest of much diyer's aroud there... since nobody comments or ask for further infos...

I don't mind

I love this simple but efficient design, not expensive, and great souding mic !

Anyway, there's no names of Neumann - AKG - Telefunken - Manley - and so in this thread but a nice little DIY project, discreet but efficient

Thanks again @thor.zmt you're definitely a good designer +++

Congratulations to both!
To you and @thor.zmt
You worked hard, with passion, on this project, in the true spirit of DIY.

 

[MidnightArrakis]

Sorry guys, I really don't understand the hype around tube mic designs. A lot of additional electronic components, high current consumption and expensive transformers with one outcome: Heat, noise and distortion

Some people just like the physical shape of the glass envelope of vacuum-tubes, along with the soft, warm glow that emanates from within them!!! What's there -- NOT -- to love about vacuum-tubes.....despite all of their inefficiencies???

 

[MidnightArrakis]

Like the Hong Kong guy who's GF had a black baby 9 Month after the USS Hancock made a port call in '66 said: "Sum Ting Wong!"

Is all "loose metal" tied to Audio ground, nothing but audio ground and nothing else?

Thor

[Is all "loose metal" tied to Audio ground, nothing but audio ground and nothing else?] -- .....So help you God!!!

/