[The_Terminator]

I'm hesitant to try to improve the existing headphone jack as I don't really want to take apart the reciever.
What I like about my current experiment is it's easy to use. the volume knob works as it should, and everything seems to be hunky dory besides the hiss. My tone controls are set to zero, so they aren't causing the issue.
So is there a simple fix to remove the hiss?
I appreciate the suggestions on the breakout box, but that doesn't seem to be the way to go as I don't really see the value in it. I'm not worried about ripping my cable out of the receiver by accident.

 

[elmer_dudd]

Quote:

Originally Posted by The_Terminator /img/forum/go_quote.gif Hello everybody, I've been browsing these forums for almost two years now, trying to learn everything that I could about headphones and stuff. I've wanted to try a headphone amp for a long time now, but simply don't have the funds for it. Finally, I said to myself, "Self, you already have a decent reciever with a second set of outputs, why not connect a headphone input to those?" So, I went to Radio Shack and picked up the following item: Here is a better picture of what I was dealing with: Next, I went ahead and removed the phono plugs, and separated the wires like so: ...and connected them to the 'Speaker B' terminals of my Denon AVR-900 Receiver. ...Like so: So now I connect my Senn. 555's into this thing (being careful with the volume of course) and of course, it sounds way better than the headphone jack. The headphone jack has a weaker output with a much higher bass emphasis compared to my new headphone amplifier. I can use the headphones alone, or I can shut off the main speakers and leave the subwoofer on, which is a very thrilling experience with games and movies, and sounds great with music as well. And there you have it: the $5.50 (tax included) headphone amp. and now for the question: This headphone amp has a constant hiss in the background (noise floor?) that is always present. It doesn't change with the volume at all, so although it's annoying at first, my brain can eventually tune it out like white noise. Is there some kind of resistor or something that I can attach inline to one or all of the wires that will remove this hiss? Thanks in advance for all of our tips and replies. I appreciate them!

dude are you crazy?!! why would you want to get used to the hissing noise?? what if a snake crawls into your bed one night and you say to yourself "oh it must be that hissing noise i got used to, by overdriving my headphones with my massive hi-fi amplifier." or worse yet, what if you don't even hear that snake that slithers into your sheets and it takes the nugget or two out of your nutsack.
i'd try playing around with some rc filters if i were you, unless you don't like your testicles very much.

added: http://www.phys.unsw.edu.au/~jw/RCfilters.html
check out the low-pass-- if it doesn't eliminate it, it should at least make it lower and less noticable, i would think. i'm no expert of course, and i could be outright lying too in fact. but at worst, i'm simply just talking out of my bunghole.

2nd add: and what the heck is that red box in that last picture there?? you some kinda graphic artist or sumpthin??

 

[ICU]

WHOA. Try jogging with that amp!

 

[elmer_dudd]

hay it could be worse, i know this guy who tried to make a pair of headphones out of a couple of these things

(edit: and i still have the ringing in my ears.

)

 

[JahJahBinks]

IMO, the reason you are hearing the hiss is because you are driving the opamps in your receiver into saturation, a circuit that's designed to output to low impedance load doesn't have much voltage swing, a higher impedance load will require a higher voltage swing which is something your receiver cannot provide. If this is the case (I have to see the circuit to know exactly what is going on but from my experience this could be a cause), driving opamp into saturation is not something you want to have for a long duration.

 

[elmer_dudd]

man, this whole topic is giving me indigestion. (oh nevermind it was that funky hoagie i had for lunch)
i've done some stupid stuff with my hi-fi amp in my youth, so i know it's electronically protected pretty well (i even bought it at radio shack, believe it or not).. i wrapped my own speaker coil and glued it to a piece of paper and drove it from the center channel, and it tripped a built in protection circuit after it started popping like crazy when i maxed it out-- can't imagine what terminat'r's doing being even half as bad as that was

 

[The_Terminator]

Hey elmer dudd, that is some funny stuffs you posted there! I like the part about the snakes the best!

and about the jogging comment, I jog with my receiver all of the time. It's not that cumbersome, although I get strange looks when people see the 10,000 foot orange extension cord leading to my house.
(the orange is b/c it's rated for outdoor use.)

About the opamp saturation, that might be it. I'm not really worried that something here is gonna get fried, b/c I don't listen at loud volumes at all, or for long periods.
Actually, most of my headphone use is at work and on airplanes to stave off the boredom of some aspects of my job.

And would you believe it, the airlines are always giving me a hard time about dangling my orange extension cord out of the plane window.
...Some stupid nonsense about cabin pressure or some such.
(the orange is b/c that extension cord is rated for outdoor use.)

 

[elmer_dudd]

oh right, of course. cuz, you wouldn't want to use an underrated extension cord or anything like that

at worst, i think denon might have assumed that it's customers would be using their products in ways the typical manual would describe, and designed the speaker amps with a set of speakers in mind rather than headphones. all numbers aside, and imho, i'd think that a pair of headphones is going to transfer inherrently present interference or hiss a lot more readily than a pair of bookshelf speakers. how do you know it's not from dangling connectors/exposed wires on your connectors?
(hmm, i guess the hiss would increase with volume if it were from dangling connecters, wouldn't it)

 

[JahJahBinks]

Quote:

Originally Posted by The_Terminator /img/forum/go_quote.gif About the opamp saturation, that might be it.

One way to verify this is to listen at volume just audible then slowly turn up the volume, if there is no hiss initially then it appears after the volume goes up, it's a sign of saturation.

 

[audiomagnate]

All you've done, if you succeed in eliminating the hiss with padding resitors, is duplicate your receiver's original headphone jack circuit which is no doubt connected to the output stage, just like your $5.50 solution. A much more elegant, and even cheaper solution, is discussed here:http://www6.head-fi.org/forums/showthread.php?t=201098

 

[crimony]

Quote:

Originally Posted by JahJahBinks /img/forum/go_quote.gif IMO, the reason you are hearing the hiss is because you are driving the opamps in your receiver into saturation, a circuit that's designed to output to low impedance load doesn't have much voltage swing, a higher impedance load will require a higher voltage swing which is something your receiver cannot provide. If this is the case (I have to see the circuit to know exactly what is going on but from my experience this could be a cause), driving opamp into saturation is not something you want to have for a long duration.

I'm not convinced that's the case. This amp has an RMS output power of 60W into 8 Ohms, using the identity P = V^2/R with P = 60, R = 8, we get a required RMS voltage output of 22V at maximum output power, therefore a peak of sqrt(2)*22 = 31V. Hence the voltage gain and power gain stages of this amp must have rails at least +/- 31V. This is way higher than any headphone amp I have seen, and for a 120 Ohm load driven with those voltage levels we would be dissipating 4W RMS in the headphones (!).

Saturation in the first stage of the amp would be governed by the input signal and is generally unaffected by the attached load.

As the OP (and others) have suggested, it is more likely the noise floor of the amp causing this hiss, which is exacerbated by the high-impedance load. A resistive voltage divider network is the correct implementation, as has been noted.

 

[The_Terminator]

Not bad for your first post!!!

So what you're saying is, that with the correct resistor, I could reduce the hiss and have a higher quality headphone out than the stock headphone jack on the front of the receiver, correct?

 

[crimony]

Quote:

Originally Posted by The_Terminator /img/forum/go_quote.gif Not bad for your first post!!! So what you're saying is, that with the correct resistor, I could reduce the hiss and have a higher quality headphone out than the stock headphone jack on the front of the receiver, correct?

I'm not familiar with "tuning" the impedance Sovkiller is suggesting (not sure whether you try to match the amp O/P impedance with 'phones I/P impedance or some other value).

Construct the portion of the circuit on Rod Elliot's (esp) site with the 3 resistors (forget the switch and output jack), use the values from the 65W row of the table. If it's too loud, use the 100W row, too quiet, use the 40W row. Like you suggest, just soldering the resistors to your cables should be fine.

 

[SoundGoon]

Quote:

Originally Posted by elmer_dudd /img/forum/go_quote.gif dude are you crazy?!! why would you want to get used to the hissing noise?? what if a snake crawls into your bed one night and you say to yourself "oh it must be that hissing noise i got used to, by overdriving my headphones with my massive hi-fi amplifier." or worse yet, what if you don't even hear that snake that slithers into your sheets and it takes the nugget or two out of your nutsack.

That is one of the funniest things I've ever read here LMAO!!!!!!!

 

[The_Terminator]

Quote:

Originally Posted by SoundGoon /img/forum/go_quote.gif That is one of the funniest things I've ever read here LMAO!!!!!!!

Yeah, I thought it was hilarious as well.
I LOL'ed