Superlux S502 MK2 test, teardown and improvements

[Emmathom]

I have a question regarding the wire colours in the S502 1st version. What relationship exists between the XLR pins 1..5 and the colours?
In the S502 MKII the relationship is as follows:

XLR pin 1: black, GND
XLR pin 2: red, +phase L
XLR pin 3: yellow, -phase L
XLR pin 4: blue, +phase R
XLR pin 5: white, -phase R

Thanks in advance for clarification
MicUlli

Hi @MicUlli sure I will have a look in the weekend...
PCB stuff is going foward ?
Regards

 

[micro1_de]

Hi @MicUlli sure I will have a look in the weekend...
PCB stuff is going foward ?
Regards

In my opinion it is the same.

Reiner

 

[MicUlli]

Hi @MicUlli sure I will have a look in the weekend...
PCB stuff is going foward ?
Regards

Yes, thanks
Boards arrive next week. I ordered 5 pieces in order to get confident with the design. Test next weekend

 

[MicUlli]

In my opinion it is the same.

Reiner

Thanks a lot Reiner,
as i can see it looks different for the S502 1st version:

XLR pin 1: black, GND
XLR pin 2: white, +phase L
XLR pin 3: red, -phase L
XLR pin 4: yellow, +phase R
XLR pin 5: blue, -phase R

It is important for correctly soldering the wires for the different versions

 

[micro1_de]

Thanks a lot Reiner,
as i can see it looks different for the S502 1st version:

XLR pin 1: black, GND
XLR pin 2: white, +phase L
XLR pin 3: red, -phase L
XLR pin 4: yellow, +phase R
XLR pin 5: blue, -phase R

It is important for correctly soldering the wires for the different versions

Ah, thanks!!

 

[Clem777]

That's exactly what I read on Thomann customers' reviews... interferences with MkII and none with MkI... But I guess it comes from the circuitry, not the capsules, so @MicUlli 's board should solve that

Thanks, finger crossed

 

[Emmathom]

Thanks, finger crossed

Look also to my post #179

 

[Clem777]

Hi @Clem777 I've read in Thomann users reviews that a guy exchanged the original Y cable for a "pro snake stereo Y" https://www.thomann.de/fr/pro_snake_splitkabel_stereomono_xlr.htm and then this high sensibility to interferences disappeared... (or you make your own Y adaptator with good quality cable and Neutrik connectors > that's what I will do)

Do other MKII owners encounter the same problem?

Thanks, I had saw this review. I tested all the xlr-5/3 Y cables I have including the pro snake, a Neumann from the RSM191, and cables assembled by trusty local professionals. I guess my MkII is from a bad batch.

 

[olafmatt]

I have been using a S502MkII for a while now for recording ambience for film (TV actually). RFI pickup seems to be higher than on other mics indeed.

As part of the tripod mount I use a short "pigtail" cable made from thin star-quad mic cable (see pic). On the mic end of the cable the XLR plug has a wire link between pin 1 and the connector shell. This seems to help a little with RFI.
The real problem seems to be the location of the RF filter caps (those 22n caps to ground). They connect to ground on the PCB which then has about 5cm of wire to the XLR connector which connects pin 1 to the mic housing. Maybe soldering 22n caps directly onto the XLR connector and then shortest wire to mic housing would help. The way they are located now they only prevent oscillator hash leaving the mic, but not so much RFI getting into the mic.

And speaking about wires, I always wondered whether it wouldn't make sense to modify the two wires coming from the mic capsules. There is enough space behind the capsule mount (in the angled part of the main mic body) to put the JFET, ferrite bead and 1G resistor right there and then run four wires into the main mic body.

 

[Emmathom]

The real problem seems to be the location of the RF filter caps (those 22n caps to ground). They connect to ground on the PCB which then has about 5cm of wire to the XLR connector which connects pin 1 to the mic housing. Maybe soldering 22n caps directly onto the XLR connector and then shortest wire to mic housing would help. The way they are located now they only prevent oscillator hash leaving the mic, but not so much RFI getting into the mic.

Yeah, you should try this mod. if you feel easy with it ! If you do, please let us know (and add picts)

And speaking about wires, I always wondered whether it wouldn't make sense to modify the two wires coming from the mic capsules. There is enough space behind the capsule mount (in the angled part of the main mic body) to put the JFET, ferrite bead and 1G resistor right there and then run four wires into the main mic body.

That would surely be productive too ! There's space behind the "interface" on which the capsule screws on.

I (we !) hope that the @MicUlli circuit will not suffer from the same defect...

 

[jp8]

I have been using a S502MkII for a while now for recording ambience for film (TV actually). RFI pickup seems to be higher than on other mics indeed.

As part of the tripod mount I use a short "pigtail" cable made from thin star-quad mic cable (see pic). On the mic end of the cable the XLR plug has a wire link between pin 1 and the connector shell. This seems to help a little with RFI.
The real problem seems to be the location of the RF filter caps (those 22n caps to ground). They connect to ground on the PCB which then has about 5cm of wire to the XLR connector which connects pin 1 to the mic housing. Maybe soldering 22n caps directly onto the XLR connector and then shortest wire to mic housing would help. The way they are located now they only prevent oscillator hash leaving the mic, but not so much RFI getting into the mic.

Nothing wrong with trying to place the 22nF caps on the XLR, but I tried that on a MXL603 as a test. Verfied the result with my RF jammer and had negligible effect. But in other mics, the 22nF did suppress RFI to some extent, though a dedicated filter for cell phone frequencies directly mounted on the XLR insert should work better.

And speaking about wires, I always wondered whether it wouldn't make sense to modify the two wires coming from the mic capsules.

Capsule wires could pick up RFI, but the mic should be a near perfect Faraday cage. Shouldn't be an issue. They could vibrate, modulating the capacitance to the mic body and act just like a condenser capsule. And static wire capacitance would attenuate the signal. But the wires are only 40mm, halfway running through a 2mm hole from capsule to body, so I wouldn't expect significant movement to be possible. And I expect the static capacitance to be less than 1pF, which is much smaller than the capsule capacitance. Hence, little attenuation. So all in all, I would not expect any improvement when moving the JFET closer to the capsule. As a manufacturer, you would only add assembly costs.

Jan

 

[olafmatt]

And static wire capacitance would attenuate the signal.

Yes, its the wire capacitance I was thinking about but also the fact that the high impedance part of the circuit sits as SMD on a normal PCB with the signal from the capsule even going through a via from the bottom of the PCB before it reaches the JFET gate. - Older through-hole Schoeps mics had the gate of the JFET soldered directly to the connector pin on the capsule mount. And the modern SMD versions seem to have some sort of "guard ring" with solder mask removed around the high impedance area.

I record only outdoors with the mic, so moisture resistance is important. Didn't have any obvious problems so far, but somehow trust this mic less than my MKH mics when weather gets bad. So its more about peace of mind and not any immediately measurable improved performance.

 

[pmfalcman]

But the wires are only 40mm, halfway running through a 2mm hole from capsule to body, so I wouldn't expect significant movement to be possible. And I expect the static capacitance to be less than 1pF, which is much smaller than the capsule capacitance. Hence, little attenuation. So all in all, I would not expect any improvement when moving the JFET closer to the capsule.

What about twisting the capsule to PCB wires together?
Like in a twisted pair.
Commonly seen in old equipment, nowadays somehow abandoned practice.
Would it help in any measurable way to reject interferences of any kind? Or, again, at these distances it is pointless?
Would help minimising said microphonic vibrations maybe?

 

[jp8]

Yes, its the wire capacitance I was thinking about but also the fact that the high impedance part of the circuit sits as SMD on a normal PCB with the signal from the capsule even going through a via from the bottom of the PCB before it reaches the JFET gate. - Older through-hole Schoeps mics had the gate of the JFET soldered directly to the connector pin on the capsule mount. And the modern SMD versions seem to have some sort of "guard ring" with solder mask removed around the high impedance area.

I record only outdoors with the mic, so moisture resistance is important. Didn't have any obvious problems so far, but somehow trust this mic less than my MKH mics when weather gets bad. So its more about peace of mind and not any immediately measurable improved performance.

Ah, yes, sure! Moisture protection is less than ideal on the S502 PCBA. You'll need to apply one or more protection methods, such as PTFE Turret, guard ring, conformal coating, slits and removal of soldermask.

Jan

 

[jp8]

What about twisting the capsule to PCB wires together?
Like in a twisted pair.
Commonly seen in old equipment, nowadays somehow abandoned practice.
Would it help in any measurable way to reject interferences of any kind? Or, again, at these distances it is pointless?
Would help minimising said microphonic vibrations maybe?

Try it...

And try to prove microphonics from the cable and distinguish that from microphonics from e.g. capacitors on the PCBA. Challenging, I think.

Jan

 

[pmfalcman]

Try it...

I gather it means: "No measurable or distinguishable effect", in Dutch
Thanks Jan.

 

[jp8]

measurable

Haha!

Seriously: theoretically that wire-related microphony is possible. And I wish I knew how to prove it, or that is a non-problem in reality. Does anyone know if this has ever been investigated?

W.r.t. capacitor microphony: I have a test PCB in the mail that I want to use for comparative measurements. Long, narrow PCB, with caps mounted at one end, which I polarize through a resistor. And the other end clamped in a vice. I suspend it over a 5" broadband speaker, then measure resulting voltage via a JFET buffer. I've done this with stripboard and it works!

Jan

 

[Clem777]

I have been using a S502MkII for a while now for recording ambience for film (TV actually). RFI pickup seems to be higher than on other mics indeed.

As part of the tripod mount I use a short "pigtail" cable made from thin star-quad mic cable (see pic). On the mic end of the cable the XLR plug has a wire link between pin 1 and the connector shell. This seems to help a little with RFI.
The real problem seems to be the location of the RF filter caps (those 22n caps to ground). They connect to ground on the PCB which then has about 5cm of wire to the XLR connector which connects pin 1 to the mic housing. Maybe soldering 22n caps directly onto the XLR connector and then shortest wire to mic housing would help. The way they are located now they only prevent oscillator hash leaving the mic, but not so much RFI getting into the mic.

And speaking about wires, I always wondered whether it wouldn't make sense to modify the two wires coming from the mic capsules. There is enough space behind the capsule mount (in the angled part of the main mic body) to put the JFET, ferrite bead and 1G resistor right there and then run four wires into the main mic body.

Thanks, I'll try the short pigtail with pin 1 wired to the connector shell

 

[MicUlli]

Yeah, you should try this mod. if you feel easy with it ! If you do, please let us know (and add picts)

That would surely be productive too ! There's space behind the "interface" on which the capsule screws on.

I (we !) hope that the @MicUlli circuit will not suffer from the same defect...

Regarding some RFI problems reported by several people (affected S502 MKII and NOT S502 1st version) there may be an issue with the housing.
If you remove the 2 screws on the bottom side you will find 2 plastic space holders which bridge the gaps between top and bottom of the housing. These gaps can act as slot antennas to the inner part of the housing...
This issue can be repaired easily. Cut 2 pieces of kitchen aluminium foil and wrap them into the space holders at their inner side. After screwing the housing together top and bottom should have no interruption of the Faraday cage
PLS take this advice with a grain of salt. I am not able to execute EMC measurements at home...

 

[Emmathom]

Regarding some RFI problems reported by several people (affected S502 MKII and NOT S502 1st version) there may be an issue with the housing.
If you remove the 2 screws on the bottom side you will find 2 plastic space holders which bridge the gaps between top and bottom of the housing. These gaps can act as slot antennas to the inner part of the housing...
This issue can be repaired easily. Cut 2 pieces of kitchen aluminium foil and wrap them into the space holders at their inner side. After screwing the housing together top and bottom should have no interruption of the Faraday cage
PLS take this advice with a grain of salt. I am not able to execute EMC measurements at home...

If you do so, please show us some picts of how you manage that... (because Google Translate is often not very accurate...)