Polystyrene Outer Foil Orientation between mic capsule and FET

[Dr nEon]

Hi guys!

I'm about to mod a pair of Tbone SC100 ii's which are basically the same as the MXL603 - based on the classic Schoeps circuit.  The stock coupling cap between mic capsule and FET is currently a ceramic.  I'm replacing this with polystyrene, as many other folks have done.

However, I see no discussion anywhere on which is the optimum way to connect the polystyrene, in this particular instance.  I've searched around the net, and found no answer.  Typically, in coupling positions , the outer foil goes to the lower impedance side, but in this circuit I can't get my head around whether the outer foil should be on the capsule side, or the FET side.  Since it's at the most sensitive end of the mic circuit, I imagine the correct orientation will have a beneficial effect.

Presumably, the same rule of thumb will apply across many of the mic mods which people have been doing, so hopefully one of you gurus can put me right on this!

Many thanks in advance!

nEon.

 

[RuudNL]

I think the answer is simple: there IS no lower impedance side!
As long as the capacitor is well screened (which will be the case inside the microphone body), I don't think it will make any difference.

 

[Dr nEon]

RuudNL..

Great, thanks for  the answer!  Looking again at the schematic, that does make sense! 

Upon opening the mic, I've also discovered another potential cap improvement, which is the 100pF cap on the -10dB pad switch.  It currently uses a ceramic disc c0g type - probably OK as is,  but since I have some polystyrenes in that value, too, I will replace that cap,  as well.  Maybe I'll do one just one mic, from the pair,  and see how the c0g disc compares to polystyrene when the pads are switched in..

Many thanks for putting my mind to rest!

Cheers
nEon.

 

[JohnRoberts]

+1 both ends are high z.

Don't expect an audible difference from replacing a COG (NPO) cap.

JR

 

[Dr nEon]

Thanks John!

Great to have two solid answers on the outer foil issue, in this application! Might save other modders some time... cut out the worrying, and get on with it!   

Re the 100pF cap..  My curiosity was more about the fact it's a ceramic disc. Whether that aspect could be bettered, though I do understand that c0g/np0 has a better reputation re microphonics etc.. 

I also have some 100pF c0g/np0  multilayer ceramics.  Do you think there's any argument for swapping a disc out for a multilayer, in this position in a mic circuit? 

Many thanks in advance,

nEon

 

[JohnRoberts]

It's all about the dielectric, many different flavors of ceramic.

NPO/COG have excellent linearity (voltage coefficient) for low distortion.

JR

 

[Dr nEon]

OK John, thanks!

Maybe I'll just leave that one alone, then!  If it ain't broke...

Cheers for your help,

nEon.