A DIY low profile Hiss-eliminator/Bass-deepener/Impedance-matcher for IEM's

The reason for this little project: http://www.head-fi.org/forum/thread/553094/continued-sidetrack-discussion-from-tiniest-portable-amp-i-can-build-nikongod-microtransformer-based-impedance-step-down-box 

So I got curious. I looked around and found some 0.27mm thickness M6 silicon steel laminates, then got some magnet wires from RadioShack.

Step 1: split the "E" piece to half. These pieces were from a large push/pull output transformer (roughly 100w). There is no need to use the whole E for this micro-power application. The C pieces are also a better size for the intended case ( an empty iPod body). 5 "E"s were splitted, so each transformer will have 5 pieces stack together to form the core.

Step 2: make bobbings. One brown paper tag is enough to make four bobbings. Stack 6 "I" pieces together and roll the paper strip around it, then tape it down using scotch tape.

Step 3: winding preperation. A 1/2" spad bit is used as the mandrel to hold the bobbing. Turn-countering is done using a pedometer connected to a magnetic switch. triggering is done using a little super magnet.

My make-shift "winding machine": The pen tube contains the magnetic sensor, and the little super magnet goes onto the chuck. Every time the magnet passes the black mark (on the pen), the pedometer counts one. Actually quite accurate/reliable.

Step 4: wind..... 200 turns of primary, 40 turns of secondary, per bobbing. After all four bobbings are winded, install 5 "C" pieces per transformer.

Then trim and install little "I' pieces.

Step 5: connect wires, do a test listen. The primaries on both bobbings (per transformer) are connected in series, so are the secondaries. The total turns on each transformer is 400T primary : 80 T secondary, gives a 5:1 voltage step down, 1:25 impedance step up (that will turn the 16 ohm iE8 into a 400 ohm load for the source). If necessary the secondary can be wired to parallel for ultra-low impedance IEM's (>8 ohms), though 10:1 step down is a bit too much IMO.

initial impressions (one hour burn-in) :

amps are Sony D11 headphone-out and my little desktop amp ( opa627->BUF634x2). phones are ER4P, then SM3.

With the transformers,

-- sound level antenuation: volume-10 (with transformer) has the same loud-ness as the direct-drive at "6".

-- no distortion even at volume-10. So I assume the core is large enough.

-- Mids are emphasized a bit, but not really a bad thing. The Vocal is a lot smoother than direct-driven. Pretty much no sibilance/glare.

-- recognizable treble lost, but just slightly, only noticiable upon quick A/B comparison.

-- recognizable micro-detail lost, noticiable when playing live concert recordings (gives a little less "live" feel). Not as transparent as the direct-drive. However it also masked a lot of "wild-ness", the final sound is not less pleasant.

-- bass texture slightly less visible. Total bass quantity seems to remaind the same, but the "flat"/"hard"/"dry" bass is gone, replaced with more round/full notes, much better to the ears.

So the verdict for now is:

-- bass: improved a bit.

-- mids and highs: different, not less enjoyable than direct-drive.

-- the over-all sound is more pleasant, especially for long-term listening. No fatigue.

One thing worth pointing out, though: the main purpose of using these transformers is to deepen the bass response of the amp/phone combo (say, a low impedance IE8 driven by an iPod will not give deep bass, the IE8's impedance is just too low for the iPod's internal output caps), and to reduce the hiss. But these benefits are not cashed-in with my test setup. None of my amps have hiss problem, even with the SM3. And my amp/phone combo's do not need bass response deepening ( the desktop amp is direct output, the D11 has 560uF OS-Con output cap which sets the corner frequency at 10hz with the 27 ohm ER4P). The advantage of using a pair of impedance matcher will be much more noticiable for DAP/IEM combo's with hiss or shallow-bass problems. It's said that the IE8 has too much mid-bass but not going deep enough, I wonder how much of that is due to the output-cap in the DAP being too small, setting too high a bass cut-off point.

hehehe, "deceptivly simple", eh.....Simpleness is in the eye of the beholder.

the completed transformers are a little over one oz each.

And, what do you know, transformer boxes had been in use for ages....This Koss T1 is not very portable, though.

inside.... lots of empty space. The transformers ratio is 12.5:1, they are not that much bigger than the ones I just put together.

The whole deal did take a few hours to get together, not quite as simple as I presented (so "deceptivly" was correct)....Spliting the E's, for example, was done using dremel so that was pretty slow. Once everything was ready, winding was the easiest part.

If you have changed your mind and want to start "rolling" now, let me know, I still have some more M6 pieces around.

It is already that way. Each bobbing has 40 turns of secondary on top of 200 turns of primary, there is no seperate "primary bobbing" or "secondary bobbing".  

I am using these turn #'s due to the total thickness requirement (< 8mm). Otherwise I would have doubled the turn #, that might improve the sound a little. 

Quote:

Originally Posted by jogor 

hi audiocats! awsome project there, thank you for this inpiring build and cool tips. have you tried winding the other side(primary/secondary side) on top of the other for better coupling? not sure if it would translate to better coupling (perhaps) and improvement. I sure do want to try this one.