problem understanding with DC converter 60v schoeps CMC5.

[mudevilo]

Hello everyone.
I have a problem understanding the schematic of the Schoeps CMC5 preamp...
excuse my ignorance!!
But I don't understand how we get 60v of bias for the capsule from 6.1v as shown in the diagram?
I did a simulation with LTspice which absolutely does not give me 60v voltage...
if someone could explain it to me?
Thank you to all of you.

 

[Khron]

In the physical circuit, those two inductors are usually placed side-by-side, so there is some magnetic coupling going on. Perhaps you need to add that in your simulation?

https://en.wikipedia.org/wiki/Inductor#Energy_stored_in_an_inductor
Hartley oscillator - Wikipedia
(although i could be wrong about the exact type of oscillator this is, i'm no magnetics expert)

 

[rogs]

You can think of the concept in two parts...
• A Hartley oscillator, typically running an ultrasonic frequency.
See here for some details: https://www.electronics-tutorials.ws/oscillator/hartley.html

• A voltage multiplier, which takes the oscillator output signal, and then 'multiplies' and rectifies it to obtain the higher DC voltage required.
See here for some concept notes: https://www.electronics-tutorials.ws/blog/voltage-multiplier-circuit.html

 

[mudevilo]

In the physical circuit, those two inductors are usually placed side-by-side, so there is some magnetic coupling going on. Perhaps you need to add that in your simulation?

https://en.wikipedia.org/wiki/Inductor#Energy_stored_in_an_inductor
Hartley oscillator - Wikipedia
(although i could be wrong about the exact type of oscillator this is, i'm no magnetics expert)

Ok this is a common mode choke if I understand ?

 

[mudevilo]

You can think of the concept in two parts...
• A Hartley oscillator, typically running an ultrasonic frequency.
See here for some details: https://www.electronics-tutorials.ws/oscillator/hartley.html

• A voltage multiplier, which takes the oscillator output signal, and then 'multiplies' and rectifies it to obtain the higher DC voltage required.
See here for some concept notes: https://www.electronics-tutorials.ws/blog/voltage-multiplier-circuit.html

thank you for this documentation...
I will read this carefully.

 

[Khron]

Ok this is a common mode choke if I understand ?

Not necessarily; common-mode chokes are two totally separate windings on the same core, meant to filter out signals present on both lines.

https://en.wikipedia.org/wiki/Choke_(electronics)#Common-mode_choke

 

[jp8]

In the physical circuit, those two inductors are usually placed side-by-side, so there is some magnetic coupling going on. Perhaps you need to add that in your simulation?

https://en.wikipedia.org/wiki/Inductor#Energy_stored_in_an_inductor
Hartley oscillator - Wikipedia
(although i could be wrong about the exact type of oscillator this is, i'm no magnetics expert)

A while ago, I simulated a similar circuit of the MXL770/990. With a coupling factor of k=0.1, I got approximately 48V on the multiplier output. Output voltage varies with different k values, i.e. distance between the coils.

Jan

 

[rogs]

If you have room, you might like to consider an alternative arrangement for a DC voltage multiplier which doesn't use inductors at all?
So there is no 'iffyness' that can come from the polarity and orientation of Hartley oscilllator inductors.
It's based on circuits in this artlcle from the 1980s : https://gyraf.dk/schematics/Voltage_multipliers_with_CMOS_gates.pdf
I use it for my OPIC mics. (See the bottom half of this PDF: https://www.jp137.com/lts/OPIC.41.pdf )
It's used in the Alice OPAs mics from Jules Rykenbusch as well ... and Rode use the same concept to derive polarisation volatges in some of their LDC mics (eg.NT1).

 

[mudevilo]

thank you once again to all of you, never one of my questions remained unanswered. But I need to improve!!!

 

[mudevilo]

A while ago, I simulated a similar circuit of the MXL770/990. With a coupling factor of k=0.1, I got approximately 48V on the multiplier output. Output voltage varies with different k values, i.e. distance between the coils.

Jan

In the case of CMC5, what are the values of Dr1 and Dr2? they are not indicated...
Are these values critical or not?

 

[Khron]

In the case of CMC5, what are the values of Dr1 and Dr2? they are not indicated...
Are these values critical or not?

To some extent, they are. Although in chinese copies of this circuit, most often Dr1 is about 150uH while Dr2 is 68uH.

https://audioimprov.com/AudioImprov/Mics/Entries/2013/2/4_MXL_990_Zener_Swap.html