24v Phantom on Schoeps CMC?

[Studiogearlover]

Thank you so much..i will study/ read through this...

Umm... Let me see if i can (try to) clear things up a bit for you.

1) http://sound.whsites.net/project96.htm

Specifically Figure 2 - http://sound.whsites.net/p96-f2.gif

And see the attachment below as well.

 

[Studiogearlover]

Due to the configuration of the output stage, the Schoeps circuit needs to be phantom powered. If you want to power a mic from a battery but not phantom-powered, you need another arrangement.
Now you need to define more clearly your project. What is the mic going to be connected to? Balanced or unbalanced inputs? What cable length? What SPL?

oooh...okay...so I've got it completely wrong....

Basically, got a pcb on the Schopes design (ish)...got a capsule (not Schopes but could work). The pcb is designed similarly as below. I thought if I change a few components accordingly, could work with a 9 V battery cnsidering tha capsule is an electret capsule require approx 3V, / 0.003A.

I could be completely wrong tho..i thought it could work as it is a very simple circuit?

and I was hoping to use XLR balanced connector...

attached a schemtic I had in mind...

thank you for your help, I value your opinion and advise !

 

[RPC360]

The output stage on this design depends on phantom power passing through the transistors. You'd have to rearrange the emitter followers and capacitor couple their output for this to work off a single 9V supply.

 

[Khron]

Electret capsule + Schoeps circuit = "Alice" mic (lower half of the image below).

http://audioimprov.com/AudioImprov/Mics/Entries/2015/4/23_Basic_FET_Microphone_Circuits_files/alice%20mic%20cirucuit.jpg

Although the small capsules (ie. 1/4" ones) with the built-in JFET, with a bit of care, could have the "Linkwitz mod" applied (ie. where you separate the pad that goes to the case, so you have a part where the internal JFET source is, and a part that goes to the casing).

http://www.linkwitzlab.com/images/graphics/microph1.gif

Taken from http://www.linkwitzlab.com/sys_test.htm

That being said, what's this microphone (circuit) supposed to plug into?

Basically, got a pcb on the Schopes design (ish)...got a capsule (not Schopes but could work). The pcb is designed similarly as below. I thought if I change a few components accordingly, could work with a 9 V battery cnsidering tha capsule is an electret capsule require approx 3V, / 0.003A.

I could be completely wrong tho..i thought it could work as it is a very simple circuit?

and I was hoping to use XLR balanced connector...

attached a schemtic I had in mind...

thank you for your help, I value your opinion and advise !

 

[Studiogearlover]

hey...thanks! But my schematic is very similar to the one on the link, and again, there is the 6.8K resistor...the one questioned...so this design simply can not be powered with 9V? mmm....

Electret capsule + Schoeps circuit = "Alice" mic (lower half of the image below).

http://audioimprov.com/AudioImprov/Mics/Entries/2015/4/23_Basic_FET_Microphone_Circuits_files/alice%20mic%20cirucuit.jpg

Although the small capsules (ie. 1/4" ones) with the built-in JFET, with a bit of care, could have the "Linkwitz mod" applied (ie. where you separate the pad that goes to the case, so you have a part where the internal JFET source is, and a part that goes to the casing).

http://www.linkwitzlab.com/images/graphics/microph1.gif

Taken from http://www.linkwitzlab.com/sys_test.htm


That being said, what's this microphone (circuit) supposed to plug into?


into a mic preamp...XLR.... just like any other electret or condenser mic...?

 

[Khron]

It's only a coincidence that that particular resistor just happens to have the same value (6.8k) as the accepted standard for the phantom-power feed that's inside most microphone preamps today.

That resistor-zener regulator is there to provide a fixed voltage for the JFET impedance-converter (ie. a set of fixed / controlled operating conditions). Even if you provide 9v across that zener, without the phantom-power feed, the audio signal will only go as far as the bases of the two PNP transistors there.

Most solid-state condenser mics are designed to accept the 48v phantom power coming from the preamp (see my earlier links).

While it's true that there are some condenser mics that can be powered with batteries (some shotgun mics come to mind), those are usually designed for "field use" anyway (where preamps that provide phantom-power may not be available) and is highly unlikely they use the Schoeps-style circuit, plus they most definitely(?) have some form of DC-DC converter inside, to turn the battery voltage (thinking of a 1.5V AA here) into a more appropriate value for the circuitry.

Although speaking of which, you still haven't answered my "intended application scenario" question.

hey...thanks! But my schematic is very similar to the one on the link, and again, there is the 6.8K resistor...the one questioned...so this design simply can not be powered with 9V? mmm....

 

[Studiogearlover]

It's only a coincidence that that particular resistor just happens to have the same value (6.8k) as the accepted standard for the phantom-power feed that's inside most microphone preamps today.

That resistor-zener regulator is there to provide a fixed voltage for the JFET impedance-converter (ie. a set of fixed / controlled operating conditions). Even if you provide 9v across that zener, without the phantom-power feed, the audio signal will only go as far as the bases of the two PNP transistors there.

Most solid-state condenser mics are designed to accept the 48v phantom power coming from the preamp (see my earlier links).

While it's true that there are some condenser mics that can be powered with batteries (some shotgun mics come to mind), those are usually designed for "field use" anyway (where preamps that provide phantom-power may not be available) and is highly unlikely they use the Schoeps-style circuit, plus they most definitely(?) have some form of DC-DC converter inside, to turn the battery voltage (thinking of a 1.5V AA here) into a more appropriate value for the circuitry.

Although speaking of which, you still haven't answered my "intended application scenario" question.

hey! Thank you ...now it is clear. I was hoping to use this with an analog mixer (no phantom power) ...for any purpose really i think might be an easier solution then to just do the "usual" DIY design and get a phantom power for 48V and raise the resistor values accordingly to get a voltage of 3V around the capsule...


thanks again for your help!

 

[Khron]

I stand to be corrected, but that "3v on the capsule" is, at best, some rule-of-thumb type value. It's a pretty safe bet the JFET inside that is rated for at least 20v (drain-to-source) anyway. What electret capsule is that, by the way?

A few years ago i hacked together a mic with a Linkwitz-modded Panasonic WM-61A and a Schoeps-circuit (ending up, in essence, with an Alice circuit). I just opened it up and measured, and i read about 6.2v between the drain and the source (ie. between the "inside" ends of the 2.2k resistors). I seem to have used a 9v or 9.1v zener, and after the RC filter on the power rail, end up with 8.8v applied on the "top" end of the drain resistor.

That being said, i might have screwed up the capsule itself when i heated up the heatshrink around it (to hold it to the end of a hollow steel tube) - it was intended to be a measurement mic, but came back from calibration with a really wonky response  ;D

 

[abbey road d enfer]

hey! Thank you ...now it is clear. I was hoping to use this with an analog mixer (no phantom power) ...for any purpose really i think might be an easier solution then to just do the "usual" DIY design and get a phantom power for 48V and raise the resistor values accordingly to get a voltage of 3V around the capsule...

Indeed there are many possibilities for a battery-powered microphone, which would be much more efficient than stepping up to 48V and stepping down to the 3-10V required for proper operation of the capsule.
There is one solution that involves only two components, one resistor and one capacitor; the output would be unbalanced, but perfectly usable for short (about 5 meters) cable runs.
With one more R and one more C, it would be impedance-balanced, which would make it suitable for somewhat longer cable runs.

 

[Studiogearlover]

Indeed there are many possibilities for a battery-powered microphone, which would be much more efficient than stepping up to 48V and stepping down to the 3-10V required for proper operation of the capsule.
There is one solution that involves only two components, one resistor and one capacitor; the output would be unbalanced, but perfectly usable for short (about 5 meters) cable runs.
With one more R and one more C, it would be impedance-balanced, which would make it suitable for somewhat longer cable runs.

ooookay....thank you...but what do you mean by one more R and one more C?  i have ordered two pcbs...one for fun to just try out what this would do/ sound if I follow the circuit but changing the voltages according to the capsule..


btw the capsule is a Russian mke 271 LOMO... to me if we do have the zener's 6.2V and the right caps and res's...why this circuit would not work with the 3V capsule considering that let;s say I use a Toshiba MOS FET SK 30 A GR, and any of the same valuse for 2N5087 or a Siemens BC307 ( checking the pin outs)... i think the PCB is designed for the Tosh and the Motorola's PNPs...


I am just throwing my 5 cents here...i love these discussions...opinions...and results...if any..

greetings to you all from Budapest!

chers

 

[Khron]

http://sound.whsites.net/articles/balanced-2.htm

[Then see attached schematic with highlights]

ooookay....thank you...but what do you mean by one more R and one more C? 

 

[enricoribbon]

Hello there,
I just opened a new thread about building a battery powered preamp to use with modded KC cables + MK2 capsules.

https://groupdiy.com/threads/shoeps-cmc-style-preamp-on-9v-battery-portable-pcm-recorder.78857/

Please don't hesitate to pass by ;-)
Cheers!