Help to balanced MB Quart Phone 85

[musicman59]

Can somebody help me with some instructions on this one?
I am trying to recable a pair of MB Quart Phone 85. Currently they have the stock cable which is a single entry to the left cup.
The cable has 3 wires. Left and right positive and a common negative.
As you can see in the pictures the negative wire goes to the negative pole of the left driver and from there the blue wire carry the negative signal to the right cup going thorugh the headband.
The left positive goes to the positive pole of the left speaker. Soldered to the positive pole of the left speaker is a small yellow electronic component. It has the inscription “n47”. To the other leg of this electronic component is soldered the right wire from the cable as well as the red wire going to the positive pole of the right cup passing through the headband also.

Does anybody know what is that yellow electronic component with the “n47” and what is it for?
If I want to modify the headphones to dual entry and balanced would I need the yellow component in place? Do I need 2? One for each side? or if I leave it as a single entry should I replace the 2 wires going to the right cup and with what kind?

Thanks for your help.

 

[-=Germania=-]

Do you have a multimeter with a "connection" buzzer? - looks like a volume symbol.
I would check with the poles of the 1/4 plug which wire is really which

Tip - Left
Middle - Right
Bottom - Ground

Which amp do you have? One with a single 4 pin - or two three pin?

Nate (n_maher) gives some clarification in this thread.
http://www.head-fi.org/forums/f6/xlr...or-pin-374555/


The yellow thing seems to be a small bipolar ceramic cap which has the value of 470pF (pico farad) or 0.00047uF. If it was me, I would find a nicer film cap with great bang/buck to replace it with since ceramics should not really be used in the signal path to get the best possible sound. However, I can't find a single nice one that small! You might be able to forgo it - a quick test would work.

If you want a one-stop shop of where you can get everything you need on the cheap ... I highly reccomend Redco.com . You can get the XLR's there, sleeving, heat shrink, solder, and some quad microphone cable. My suggestion would be Mogami or Gotham.
You need to get your own iron though.

Hope that answers your questions!

 

[musicman59]

Yes, I have amultimeter with buzzer.
My amplifier is a Rudistor RP010B with 2 3pin balanced outputs.
I already have the XLR connectors. I bought a pair of Vampire Wire cryo trated. I was thinking in using also a quad cryo trated Vampire Wire.

What kind of confuse me about the ceramic cap is the one leg goes to the positive of the Right channel and the other leg to the positive of the Left channel. Do you know why?

 

[musicman59]

Looks like the mistery is clarified. I wrote German Maestro (formely MB Quart) looking for information about that little capacitor. Here is what they answered:
"The small electronical part is a condenser with value of 47nF. This condenser isn't used original. It seems that someone has modified this headphone but I can't identify the reason. The condenser in this configuration has the result that the mode on higher frequencies will switch to MONO.
So I would recommend to conect the new cable without this condenser.

 

[ericj]

They're lying - or they just don't know. My QP85 has the same capacitor. I think it's way less than 47nf, but i haven't taken it out and measured it.

As for making it balanced, why don't you just remove the original wiring completely, cut a bit of plastic to fit in the D-shaped openings in both slabs, and install mini-jacks just like the original PMB 85?

Then you can have one double-entry cable for single-ended and a couple xlr-to-mini cables for balanced.

 

[bjarnetv]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif As for making it balanced, why don't you just remove the original wiring completely, cut a bit of plastic to fit in the D-shaped openings in both slabs, and install mini-jacks just like the original PMB 85? Then you can have one double-entry cable for single-ended and a couple xlr-to-mini cables for balanced.

unless he finds some really low profile 2,5mm jacks i wouldnt recommend this.
at least i found this setup quite annoying when i had it on my pmb100.

why not just reterminate it with an xlr connector, then make an xlr to jack adapter in case you should need it?

 

[ericj]

Quote:

Originally Posted by bjarnetv /img/forum/go_quote.gif unless he finds some really low profile 2,5mm jacks i wouldnt recommend this. at least i found this setup quite annoying when i had it on my pmb100.

I believe the 2.5mm configuration stock on my pmb100 is switchcraft TR2A:

http://www.switchcraft.com/products/jack-113.html
http://www.switchcraft.com/products/jack-141.html

The matching plugs come in regular and locking, and you can get them with handles anodized black or red.

I used the non-locking plugs on my pmb100 and i don't find the configuration to be particularly annoying.

 

[bjarnetv]

mine stuck out to much, so i couldnt use them while resting my head against something.
it also put a lot of weight at the back of the phones, so i had to adjust the fit every time i moved.

 

[ericj]

I can see how that could get annoying.

I have some kobicon 3.5mm jacks that i bet would fit in the pmb-100 slabs, allowing the use of high-quality right-angle plugs, but my concerns with my pmb-100 are more that it sounds odd and i haven't got it tuned right yet. I have the version with fewer holes in the magnets, and no factory damping other than the fabric glued to either side of the driver - which i've removed.

Tried adding heavy felt similar to what's in the other version in the body of the slab, and it was utterly awful.

took that out, stuck thin black dense felt to the front grille around the driver, and it was better, but too much.

I guess the next step is to try a less-dense felt on the front grille?

 

[musicman59]

I am not fan of connectors so the least I can have the better for me.
Really the dual netry is not a problem.
What I am trying to figure out is what's the purpose of the capacitor. I just can not undrestand why is connected to the positive wire of both channels.

I wonder what can happen is I remove it for the signal path.

I cannot just reteminate the cans becuase the stock cable is just 3 lines where the negative is common for both channels and to balanced them you need 4 wires.

 

[musicman59]

Based on ericj comment I sent another email to German Maestro to confirm about the capacitor (or as they say "condenser"). I got 2 responses. here they are:
"[FONT="Garamond][size=small]I was reading the old Bill of Material of this headphone and there is no condenser listed. Unfortunatelly I cannot find any schematic of this headphone any longer because it is more than 20 years old. In discussion with our lab we cannot see any sense for this condenser. Maybe the performance of the hardware 20 years ago has made the usage of this condenser necessary.
We still use drivers like this in our actual headphones without this condenser and they work fine. So it can nothing happen to the driver if you use them in balanced configuration.
I will hear and measure an actual headphone model modified with such a condenser and will keep you informed about the possible changes[/size][/FONT]."

And then he followed up with:
"[FONT="Garamond][size=small]I tried this configuration with the condenser on our actual headphones using different headphone systems (35, 100 and 300 ohms) and different values for the condenser. The result is always the same: hearable Effect = 0.
Also when this configuration with the condenser was original, they makes no sense. So don't worry and recable the headphone in balanced mode. Nobody will miss the condenser by hearing[/size][/FONT]."

I orderd a SPC Vampire Wire Quad cable so i will go ahead with the job and report later.

 

[ericj]

I agree that the little capacitor probably doesn't make a difference that anyone can hear. I've always wondered what the heck it's for, and I guess i may never know.