[flibottf]

I had a lot of hiss with my iRiver H120 / super.fi EB. Since I switch to my creative Zen Vision:M the hiss is gone... Complete silence out of it.... I guess the problem lies within the source and not the headphones.....

 

[lipidicman]

Quote:

Originally Posted by flibottf I guess the problem lies within the source and not the headphones.....

Exactly, but the problem will be more apparent with high sens, low imp phones as I said above. The point of the hissbuster is you can use more of the volume range on your player. With my CX300 I listen at about 25% of the shuffle's max. The hiss doesn't vary with the volume setting so by attenuating signal and noise the hissbuster will improve my experience

 

[j-curve]

Quote:

TimmyMac: If I'm looking at this right... most of the current goes through the little cross resistor then? And the phones only see a small amount of current?

True, and the larger current through R1 ensures that the voltage across the phones is a faithful, scaled-down replica of the voltage from the source.
Quote:

lipidicman: Right so I have 16ohm CX300 on a shuffle. Resistance figures so the impedance is unchanged?

Okay, Sennheiser's site says 112dB/V for the CX300, so assuming you want a -12dB hissbuster with 16 Ohms input impedance, the values would be R1=5.6, R2=12.
Quote:

audiomagnate: The MA-01 is rated at 100 watts per channel into 8 ohms.

It'll be capable of about 29V(RMS) output. I would expect to find a resistor of about 820 Ohms, 1 Watt rating, between the speaker outputs and the headphone socket. [Actually, a pair of those, one per channel.] That's the "internal R2" which you could safely measure with a multimeter with the amp powered down and unplugged.
The good part is that if R2 is present and sufficiently rated, you can then simply bridge the headphone outputs with 10 Ohm, 1/4 Watt resistors (i.e. R1), just like the IMPEDER but internal and permanent.

If you go in search of R2, please post back your findings (value & size used) - I'd be interested to know. It's quite possible some designs don't bother with that series resistor at all, in which case R1 alone won't work and neither will an external IMPEDER because the output impedance is so low. Then you have the same situation as a hissy soundcard or portable player, which is why the hissbuster came into existence.

 

[Bob_McBob]

Can you tell me where you got the female connector in your photos, j-curve?

 

[mcshaggy2]

Im curious, where did you find that inline 3.5mm jack?

Bob_McBob you crafty fellow.

 

[j-curve]

Um, guys, that's a bit spooky.

I'm writing this reply from the Head-Fi Twilight Zone...

Glad you like the metal shell connector. I think I got it in Akihabara, in the rabbit warren of component stores under the railway station. Believe it or not, at the time I was disappointed that I couldn't find gold to match the existing factory plug. My advice though, would be to stick with plastic. The knurled finish may look flashy but it's also liable to scratch your portable player, headphones or anything else it gets thrown in with. On the other hand, it does have the feel of quality, is made in Japan, and connects with a nice "click". Bet you really want one now.

 

[ericj]

In principle, yes.

As is the radioshack in-line volume control.

These are resistive voltage dividers. The other way to do this is just to add a series resistor, as the etymotic P to S cable does.

In fact, the easiest way to build your own ety impedance adapter is to buy the RS volume control, pop open the volume dial, take out the potentiometer, solder in two resistors, and hot glue it shut.

 

[z3000w]

Quote:

As is the radioshack in-line volume control. These are resistive voltage dividers. The other way to do this is just to add a series resistor, as the etymotic P to S cable does. In fact, the easiest way to build your own ety impedance adapter is to buy the RS volume control, pop open the volume dial, take out the potentiometer, solder in two resistors, and hot glue it shut.

Hmm...I didn't think about that. I may try this out later today!
I'm using a d2 with um2's. Could anybody recommend what attenuation would be sufficient to get rid of the hiss?

 

[wualta]

Isn't this the same kind of inline attenuator that all sorts of folks complain drastically changes the sound quality when it comes already attached to the headphones?

 

[PetCed]

Quote:

Originally Posted by j-curve /img/forum/go_quote.gif Modern headphones are too sensitive. How sensitive should they be? Some people find that previous favourites like the HD580 (at 102 dB/V) are hard to drive with portable players but I've had more frustration due to the opposite problem, i.e. background hiss from headphones which are too sensitive. Even the HD215 (which is only rated at 112 dB/V) throws out continuous noise from most soundcards and some headphone amplifiers too. For the sources I use, 95-105 dB/V seems to be a reasonable range of sensitivity and 100 dB/V would be optimum. [Note: Sensitivity (dB/V) shouldn't be confused with efficiency (dB/mW). This thread might help.] Now look at some of the crazy specifications for headphones in the marketplace today. Full-size cans run up to 123 dB/V, earbuds and canal phones even higher. An inline volume control is one way to eliminate background hiss. Here's another, simpler method. Recommended values depending on the reduction (insertion loss) desired, all resistors in Ohms:- For -10 dB, R1=15, R2=22 For -15 dB, R1=6.8, R2=27 For -20 dB, R1=3.3, R2=27 For -25 dB, R1=1.8, R2=27 For -30 dB, R1=1.0, R2=33 NB: Consider using a 1/2 Watt resistor for R2 as it may dissipate some heat when the volume is cranked. Input impedance is about 30 Ohms with headphones connected. I built mine into an extension cable. Sorry, no macro setting on the digital camera. [Aside from busting hiss, sound quality will be improved in some cases. e.g. If you're using a portable player with a digital volume control which truncates bits, you'll hear how bad it sounds at low volume settings. That's not the fault of the headphones(!), however it is indirectly caused by the headphones because they are too sensitive.]

Maybe this is something for us to make

It would not be any problems making this construction to be added within a 3.5mm connector. Problem is adding resistance will make the sound charastics different. But a lot of people seem to prefer this to hiss.

 

[Logistics]

Here's a little something from the guys site who does the cMoy pocket amp. And yes, this route of using a resistor in the signal path is a last resort as it does crud up the sound.

Quiet hiss in the headphones

The first step is to determine whether the hiss is being generated in the amp, or is coming from the source. If you unplug the source and the noise goes away, you've found your culprit: the source is just noisy. If the amplfier has a volume control at its input and changing the volume level results in a corresponding change in the noise level, that's another strong indicator that the noise is coming from the source. The only thing you can do about this (short of getting a better source) is to reduce the amplifier's gain, if you can. That way, you don't magnify the source's noise any more than you have to.

Reducing the gain can also help if the noise is being generated within the amplifier, because many of the noise sources within a heapdhone amplifier are directly affected by the amp's gain. The optimal gain is where the volume control is at about the 3 o'clock position when the music is as loud as you normally listen. This gives you a little bit of extra control to turn the music up for quiet passages or the occasional rock-out session. If you're using less than half of your volume control's range, the gain is too high: not only does that raise the noise floor unnecessarily, it makes the volume control "touchy".

If you've selected your amplifier's resistor values, another thing to check is whether they are too high. All resistors add noise to a circuit, with higher values being more noisy. This effect is called Johnson noise, after its discoverer. All you can do about it is lower the resistor values, if possible. You can play around with different values and see their effect on noise with my op-amp noise calculator.

If lowering the gain and resistor values is impossible or ineffective, try adding some resistance in series with the amplifier's output. If the amp design allows it, try putting the resistor inside the feedback loop first. (This is R5 in the CMoy pocket amp, and R8 in the PIMETA, for instance.) Putting the resistor inside the feedback loop is often effective, and has the fewest bad side effects. The incentive is to use as low a value as possible, to avoid side effects. Start with 10 Ω, and work your way up to 100 Ω at most. If that doesn't work, try adding the resistance outside the feedback loop: just put the resistor inline between the amp's output and the headphone jack. This gives a stronger effect, but with more bad side effects.

If you've lowered the gain and added up to 100 Ω outside the feedback loop and the noise is still there, give up on this tack. The problem is probably something more serious, like a broken component, interference, or oscillation. Read on for discussion of these topics.

 

[ericj]

Well, yeah. It's just that low impedance loads are more prone to high-frequency noise.

It's probably why sennheiser uses steel cables on some cheaper cans, fwiw.

 

[j-curve]

Quote:

Originally Posted by wualta /img/forum/go_quote.gif Isn't this the same kind of inline attenuator that all sorts of folks complain drastically changes the sound quality when it comes already attached to the headphones?

If you mean R2 plus headphones without R1 then no, that's a different beast altogether, with a high output impedance. The output impedance of a hissbuster is much lower, like a good quality source, so it shouldn't alter the response of the headphones. It may change the sound character of the source though, because the volume will be turned up a bit higher.
Quote:

Originally Posted by PetCed /img/forum/go_quote.gif Maybe this is something for us to make

Quote:

Originally Posted by j-curve /img/forum/go_quote.gif I wish someone would.

That would be great, really! Fitting 4 resistors into a 3.5mm shell looks like a bit of a squeeze to me. I'm sure I'm not the only one who would happily pay someone else to sort that out in a neat, robust way.

 

[wualta]

Quote:

Originally Posted by j-curve If you mean R2 plus headphones without R1 then no, that's a different beast altogether, with a high output impedance.

You mean the inline volume controls on some models of KSC-75 are simple series resistances, not pads?

 

[LaTo]

Good job!

I will try them on my UM2

But I have some questions:
- where can I purchase gold 3.5mm->3.5mm adaptor and quality resistor?
- how do you find values in your first post?

Look at this image:

If I have correctly understand:
one R2 on T
one R2 on R
one R1 between T & S
one R1 between R & S

Is this correct?

Thanks for all!