TRRS to TRS adapter
HiFiMAN HM-901 in balanced mode used with the balanced phone TRRS plug.
This topic will DIY adapter for convert that balanced phone to 3.5mm single ended in compact size.
The main problem >>> I can't find the high quality female TRRS jack.(at July 2013)
Now they are TRS Oyaide and TRS Rean(Neutrik) jack.(that I think they are good enough)
I choose to modify the Rean(Neutrik) because its body shorter...can total put into Viablue body.
But in some conditions.
- the metal plug has a gap between them with the position at very centrical.
- the plug's body made from plastic with the position at very centrical.
>>> no any part of the S...sleeve can contact with the TRS jack.
For this reason I will insert the fourth pin for contact with S...sleeve.
In the picture, The largest area is above the left signal pin.(blue arrows)
This area is the safety zone that can insert the fourth pin.
>>> not damage or cantact with another pins.
When look at the outer of normal jack.
I will make a hole at blue arrow.(in a line above the left signal pin)
The fourth pin I get it from the first Rean(Neutrik) that I had opened it to survey the internal structure.
One jack has 2 long pins and 1 short pin.
Thus pin 1 , 2 , 3 and the fourth pin come from the same material for the same sound quality.
Prepare for solding.
Mark the length of the Viablue body.
Cut and bend all legs of the Rean(Neutrik) jack.
Cut the ground leg of the Viablue plug.
Measure the lenght again.
*** the left signal pin of Viablue touch to the base of Rean(Neutrik) jack.
This is the shortest length that I can do.
Solder the Rean(Neutrik) jack to the Viablue plug.
Solder the fourth pin to the Rean(Neutrik) body.
***Solder at the end only.
Leave the body and the head of the fourth pin free.
The fourth pin act as the spring when plug and unplug.
-if solder at distal >>> the spring will soft.
-if solder involve to the mid part of pin >>> the spring will hard.
The softer spring dose not damage the TRRS plug of the earphone in long term usage.