gen china mic mod remove dc-dc converter

[patosandia]

can someone guide me on how to remove the dc-dc converter on chinese schoeps circuit mics?

 

[Matador]

Do you know why?  Which microphone?

It's pretty simple:  there should be a tap for phantom power through two resistors.  You break the connection coming from the DC-DC and tie it to this point (which leads to the capsule through a high value resistor and a filter cap).

If you also want to turn off the DC-DC you can pull one of the coils or the Zener.

 

[gemini86]

I've attached a pic of the generic chinese mic circuit. (MXL, NADY, etc schoeps circuits)

 

[Matador]

1) Remove R100:  this will de-power the DC-DC convertor.

2) Lift up the side of R120 that comes from D1.

3) The junction of D5 and D6 (that goes up to C30/R90) contains the phantom voltage.  Tie this point over to R120 that is raised.  This will couple it to the capsule to power it.

 

[mabell313]

How much different is the sound with the dc-dc converter removed? Better? Some before and after sound clips would be great.

 

[Gus]

Think about the other things that change when you remove the DC to DC section.  To do it correctly you will need test gear.

 

[Matador]

Think about the other things that change when you remove the DC to DC section.  To do it correctly you will need test gear.

Aye, this is what prompted my "Why do you want to do this?" question.  Sensitivity will drop by about 6dB at the minimum.

As much as I hate MXL's implementation of the Shoeps circuit, the DC converter section isn't where I would start making changes.

 

[Gus]

I was thinking more about the jfet bias and output transistor operating point changes due the increase in voltage due to the removal of the converter section.

 

[mabell313]

Aye, this is what prompted my "Why do you want to do this?" question.  Sensitivity will drop by about 6dB at the minimum.

As much as I hate MXL's implementation of the Shoeps circuit, the DC converter section isn't where I would start making changes.
[/quote]


Exactly what I was thinking. There are so many other areas that need to be addressed with that style of mic. An upgrade to the capacitors would most likely give a greater change to the sound.(for the better!) The Shoeps-style circuit is a simple circuit allowing it to be manipulated in a myriad of ways. MXL mics have very crappy capacitors in them. Polarized signal caps? Not good! Look for some of the other circuit upgrades for this style of mic/circuit. Perhaps a capsule upgrade? All of the afore mentioned mods will most likely yield greater results than messing with the DC-DC converter.

To go off of what Gus is saying, the operating range of the JFET/BJT's will change. More changes will have to be implemented to the circuit to get it back in a useable range. Resistor values will have to calculated for the new circuit voltage. Plus, there will be no type of "regulation" to the voltage. This will cause the voltage to sag. This is all WAY more than needs to be done with this circuit. Stick with some of the more typical mods.(go with what ya know) If you would like to do a mod a little outside of the box, match up the whole output circuit. Remember, this is not a tube amp. A little imbalance is not good. It will not generate 2nd harmonics like a tube driver/phase inverter circuit. As with anything, there is a point of diminishing returns.