Superlux S502 MK2 test, teardown and improvements

[Emmathom]

I have studied the circuit board a little bit. Nothing special, standard Schoeps CMC5 from 1973. But the component selection is nasty. JFET is MMBF5486, the output transistors are BC860C. All of them noisy as hell..
The oscillator circuits do not have the same frequency, they are shifted by about 23kHz. And now the first problem: After a while the beat frequency gets smaller and smaller. I saw 19kHz in the spectrum with nearly 1mV level! Maybe most of us do not detect this, but my grandchildren would...
Time to take the solder iron

Hum... thank you for these investigations... Please let us know your mods and the results !
That's incredible because even after a 2 hours recording I didn't notice any change in the sound : will investigate on my own too...
Regards

 

[ubxf]

Does the Superlux S241 have the same capsule?

 

[Emmathom]

Does the Superlux S241 have the same capsule?

Now that is "the" question I asked myself (about the sound quality - the capsule is different) with the secret hope that the answer would be yes and that therefore the S241 would be a small cardio SDC with an very good quality/price ratio...

So same for the E524/D ??? Reviews on Thomann are positive...
I guess that on stage, where you don't want to bring your $$$$ mic, a E524/D would do the job on a conga pair (for ex.)

 

[jp8]

The oscillator circuits do not have the same frequency, they are shifted by about 23kHz. And now the first problem: After a while the beat frequency gets smaller and smaller. I saw 19kHz in the spectrum with nearly 1mV level! Maybe most of us do not detect this, but my grandchildren would...
Time to take the solder iron

Both amplifier sections share the same GND, so I cannot think of a reason why two separate Upol generators would be required. What could be the rationale?

I guess what you'll be trying is to remove one oscillator and feed the Upol from one generator to both capsules?

Jan

 

[bremusound]

Maybe the intention for dedicated DCDC converters is the ability to compensate differences in capsule sensitivity.

 

[jp8]

Does the Superlux S241 have the same capsule?

I was wondering that too. I don't know about the internals, but the S241 body diameter is bigger than the 20mm of the Schoeps/S502 mics. The S241 could

Jan

 

[jp8]

Maybe the intention for dedicated DCDC converters is the ability to compensate differences in capsule sensitivity.

Good point, but on the pictures, I don't see any adjustable devices that could be attributed to such a feature.

FYI, in my SDC builds, I use a CMOS pol voltage generator and always with adjustable supply voltage, so you can adjust for gain differences and make matched pairs of mics.

Jan

 

[bremusound]

There is a pot for each Vpol generator, they go above 80V if you want… the pots are on the „other“ side of the pcb

 

[jp8]

There is a pot for each Vpol generator, they go above 80V if you want… the pots are on the „other“ side of the pcb

Ah, my bad, I only watched the first picture. The trim pots are on the second picture. Anyway, the question remains how Superlux adjusts them: for same Upol left and right (the easy way), or same audio output level using calibrated sound sources on both capsules (the better, but more expensive way).

A single oscillator with a single balancing pot would be preferred, I guess. Probably also cheaper to build.

Jan

 

[MicUlli]

Ah, my bad, I only watched the first picture. The trim pots are on the second picture. Anyway, the question remains how Superlux adjusts them: for same Upol left and right (the easy way), or same audio output level using calibrated sound sources on both capsules (the better, but more expensive way).

A single oscillator with a single balancing pot would be preferred, I guess. Probably also cheaper to build.

Jan

I fully agree. One of the oscillators should be put to death. Same pol voltage for both sides. And the 6V-lines of both channel should be connected together too. This would enable single channel operation (of course doubtful)

 

[LevinGuitar]

I've made a few mods (but find the post about them) : replaicing the coupling cap (680pF I guess)

Haven't read all thread, but if the membrane and backplate have separate connections from ground you have a way to avoid the imput cap at all (and best cap is no cap as have been told here )

 

[Emmathom]

Haven't read all thread, but if the membrane and backplate have separate connections from ground you have a way to avoid the imput cap at all (and best cap is no cap as have been told here )

Would be great so... yes the best component is the one you can do without.

I guess that after @MicUlli reports about his mods I will open mine too and do all it must be done in one shot. But I keep in mind to remove (eventually) the coupling capsule cap.

 

[mhelin]

Does the Superlux S241 have the same capsule?

S502mkII has smaller diameter, about 20mm, and thus smaller about 18mm capsule whereas the S502 original and SS241 have about 22mm dia and 20mm capsule or thereabouts. In addition the S502mkII capsule has the odd ring and propably won't fit any body of about that size (Rode NT5 or t.bone SC140).

 

[jp8]

In addition the S502mkII capsule has the odd ring and propably won't fit any body of about that size (Rode NT5 or t.bone SC140).

That ring is the 2nd capsule contact? So the backplate and membrane are isolated from the capsule body?

I don't mind 3D printing a nosecone for such an interface. I always make my own nose cones to preserve the stock PCBA as a reference. All I'd like to know are the thread dimensions and I'll take care of the internals. That's least of a problem for me. Actually the fun part of it.

Jan

 

[MicUlli]

Teardown is complete. Here is the circuit for the left channel. For simulation i added some components from phantom power supply...
The right channel marks all components with the postfix 'a', all components are identical.