DIY 75ohm impedance adpter review

[Chengjie]

I said last week that I bought a 3.5mm female to male cable and some 75ohm resistor, and today I just made the cable myself within about 20 min (only DIY one lod cable in my life before this one, so should not not hard for everyone).

I put 75ohm 1w waterproof resistor on each channel.
The IEM I use is etymotic er6i which is a 16 ohm low impedance IEM.
In order to test the cable, I first plug into my 2g ipod touch, turned the volume all the way up to 100%, and noticed the volume coming out of er6i is OK(without 75ohm adapter is ear bleeding), suitable for indoor listening only, definitely too low for outdoor noisy area.

Then, I hooked up to raging moose the connection is like:
er6i -> 75ohm adapter -> ranging moose -> cheap lod -> ipod touch
The hiss I usually get when use er6i without 75ohm adapter is gone after I connection the adapter(good). Even when I pause the music and turn the volume on raging moose to all the way up, still no hiss(without adapter, hiss is noticeable when no music playing). When raging moose turned on, the volume is 50% which is perfect for indoor listening(don't need to adjust any more like before).

Now about the sq, I guess this is the part most people interested.
The bass is tighter and slightly deeper(good part), a little bit more clarity and airy in the bass and details in vocal.
The part I don't like the adapter is that it makes the sound very bright. In particular, the vocal sometimes become overwhelmingly fatigue(the lip sound drives me crazy). I am not sure whether any further burn in will change the sq or not. Any one know if resistors require any burn in?

Overall, the improved bass makes some of my R&B songs sound more enjoyable, but the brightness of vocal makes my ears very uncomfortable at the same time.

Are the differences between listening with the adapter and listening without the adapter huge? Well, the differences are not huge like day and night, but if I did a blind A/B test, I could definitely tell the differences.

Listening with the adapter is more like ipod with acoustic eq on and brighter vocal and more accurate bass.

Total cost of the material for making 1 single adapter is around $2 (3.5mm female to male about $1.7, 10 pcs 75ohm resistors $0.69, shipping fee is not included), which is a lot cheaper than the one you can buy from retail store for 10 or 20 times the cost.

[Chengjie]

I wasn't sure what type of 75ohm resistor to use with audio cable.
There are like 1/2 watt, 1/4 watt, 1 watt and 2 watts.

[hotaudio40]

Originally Posted by Chengjie

I wasn't sure what type of 75ohm resistor to use with audio cable.
There are like 1/2 watt, 1/4 watt, 1 watt and 2 watts.

You could have asked

As far as I can tell, resistors Don't need any burn in time...
But all the resistors I use now are SMT and those are all metal film...

I'm sure thinking way back resistors did NOT need any burn in that I could tell...

You could have gotten away with 1/4 watt even, probably 1/8 watt....

1 and 2 watts are way too large.

You could have also got a pack of resistors on evilbay.

They use to sell packs by the 100s.

All values like from 1 to 100 Ohms, 10 of each or something like that....


Anyways, I'm thinking it is your headphones that sound "very bright" as the "RAGING MOOSE" is anything but high pitched.

It is more bassy to neutral then anything else....

But I use full sized headphones...


Thanks for doing the experiment though...

I haven't had time to even get around to it...

[Chengjie]

er6i is considered bright and cold sounding IEM that's for sure.
er6i with raging moose without adapter is very good combination. Honestly speaking, I like the bass of er6i when using adapter so much, but the sound gets fatigue very quickly, I have to turn the volume down a bit. I bet that's why etymotic doesn't make any impedance adapter for er6i.

Dave do you think different watt resistors can change sq?
I never seen 1/4 watt resistor before, but 1w resistor seems quite small to me, and I had no problem soldering them.

[hotaudio40]

Originally Posted by Chengjie

er6i is considered bright and cold sounding IEM that's for sure.
er6i with raging moose without adapter is very good combination. Honestly speaking, I like the bass of er6i when using adapter so much, but the sound gets fatigue very quickly, I have to turn the volume down a bit. I bet that's why etymotic doesn't make any impedance adapter for er6i.

Dave do you think different watt resistors can change sq?
I never seen 1/4 watt resistor before, but 1w resistor seems quite small to me, and I had no problem soldering them.

No I don't think the wattage will make much of a difference.
Not worth trying in my opinion.

But you have given me an idea.

Make a little filter.

An RC filter.

Like some amps have inside of them.

Like a 16 ohm and .1uf resistor in series, and then across each output to ground.

That will for sure cut the top end out a bit.

Don't do that yet though!!!

I'd have to do the math and try it out first to see if it does anything to my 16 ohm headphone ear buds...

[Chengjie]

Originally Posted by hotaudio40

No I don't think the wattage will make much of a difference.
Not worth trying in my opinion.

But you have given me an idea.

Make a little filter.

An RC filter.

Like some amps have inside of them.

Like a 16 ohm and .1uf resistor in series, and then across each output to ground.

That will for sure cut the top end out a bit.

Don't do that yet though!!!

I'd have to do the math and try it out first to see if it does anything to my 16 ohm headphone ear buds...

So by adding an RC filter, it will help get rid of the hiss when your amps drive low impedance and high sensitive IEM or earbuds?

[hotaudio40]

Yes, a simple RC filter would get rid of some hiss and attenuate the high frequencies.

But as to what RC filter would work the best, that might be a matter of trial and error.

You may have to try a few RC filters to see which one works the best.

You want to build a "low pass"

http://www.muzique.com/schem/filter.htm

[Chengjie]

Originally Posted by hotaudio40

Yes, a simple RC filter would get rid of some hiss and attenuate the high frequencies.

But as to what RC filter would work the best, that might be a matter of trial and error.

You may have to try a few RC filters to see which one works the best.

You want to build a "low pass"

http://www.muzique.com/schem/filter.htm

I am not going to try RC filter as I hardly know anything about electric circuit.
Although the hiss is noticeable when turn volume high, it is not high enough to bother the listening.
After several hours of using the 75ohm adapter, the sound is still too bright. In fact, the treble is unbearably bright. I had to lower the volume or unplug the adapter.

The er6i IEM just can't plug into a 75ohm adapter like its brother er4p does. The bright sound gives me headaches. However, I DO like the improved bass, vocal details and airy sound stage when using the adapter. Can't have all the goodies on one single earphone i guess.

I just noticed your website has changed. Now all of your products stay in appropriate price ranges and still remain competitive.

[hotaudio40]

Yes, leave the designing to me

I'll figure something out as soon as I get organized...

I've been so busy lately that I haven't had time to do anything else but build DACs.

Which is a good thing, but leaves me NO time for R&D, which I LOVE to do!

Yes, I've changed all the product listings and set the prices accordingly, been working on that.

I'm also going to change the look of the adds to make them look more "professional"

[adityavj]

Great! I have an ER6i myself and would love to pair it with a hotaudio DAC

Hope your R&D results in an adapter for IEMs