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Many AV Receivers/Stereo Integrated amps do NOT use opamp powered headphone jacks - Page 4

post #46 of 215
Quote:
Originally Posted by JadeEast View Post
Not much to add to the discussion but here is a link with some info on resistor networks.

Meier Audio
Interesting article from Meier. Of course every headphone jack that is functional has an ouput impedance, even those that are attached to dedicated amps. A few dedicated amps have selectable gain switches (which use resistors) to optimize output for different phones. A few are optimized for certain types of phones. The rest, I have to assume, attempt to strike a happy medium that works with most phones, evidenced by the ubiquitous 32 - 600 ohm spec. I would assume that the designers of quality integrated amps are striving for the same happy medium as well. Why would they not?

In the search for the thing(s) that makes the design of speaker amps inappropriate for phones, this probably isn't it. I'd still like to find it, though, so I can know what a properly implemented headphone section is, and I can look for one in an amp, integrated or dedicated.

In the meantime, I guess I'll trust my ears. I don't hear a veil when plugged into my old Harman Kardon. My HD580s do have a strong mid bass (this is characteristic of them and well-reported by people with dedicated amps as well), and on some recordings (<25%) it can bleed over into the midrange causing a bit of muddiness (depending on how you define "muddiness" and what you're comparing them to). A 2 db cut at 500 and 1000 hz clears it right up. I think this is probably a much better way to deal with it than a different "happy medium," because I can turn it off when listening to the majority of recordings that don't have the problem.

It ain't rocket science.

Tim
post #47 of 215
Quote:
Originally Posted by billbillw View Post
I have the service manuals for more than a dozen modern AVR receivers, integrated amps, preamps, etc. Obviously I can't post them all, but maybe I can cut out a section of a few and turn them into jpeg images. Depends whether the manufacturers put copy locks on the files. I'll check over the weekend.
Interesting. Well, up until a couple of days ago, like everyone else who had paid attention here, I believed most modern integrated amps and receivers used op-amp based headphone sections. I have no preference. I'd just like to know what's true and what it means.

Tim
post #48 of 215
Quote:
Originally Posted by JadeEast View Post
Not much to add to the discussion but here is a link with some info on resistor networks.

Meier Audio
Very interesting article. I took another look at the schematic of my NAD and it has 470 ohm resisters in series. Is 150 ohm the optimal output impedance of a headphone jack, or should it match a particular headphone? It looks pretty easy to build an adapter that has a resistor in parallel to make the output impedance anything I need. Or is it more complicated than that?
post #49 of 215
Quote:
Originally Posted by scompton View Post
Very interesting article. I took another look at the schematic of my NAD and it has 470 ohm resisters in series. Is 150 ohm the optimal output impedance of a headphone jack, or should it match a particular headphone? It looks pretty easy to build an adapter that has a resistor in parallel to make the output impedance anything I need. Or is it more complicated than that?
I've dropped inquiries into another audiophile forum populated by a few designers and engineers and quite a few very serious audiophiles, for another perspective. I haven't gotten much feedback yet, but so far, I have gotten:

Quote:
I think much of the difference people hear between headphone amps/stages is down to output impedance. The effects of varying output impedance can easily be shown and heard and it varies hugely between stages.
A phone that sounds forthright and direct on one stage can sound recessed and soft on another because the output impedance is altering the transfer function in a non-linear way - certain frequencies are boosted while others are reduced.
I don't think there is anything about that statement that wouldn't apply to dedicated amps and integrateds as well. And then, when I pasted in the impedance curve for HD600s...

Quote:
That's a high impedance headphone and it will be less affected by the output impedance of typical amps. Pretty much anything half decent should drive it with very little change to the phone's basic tonality.
!0:1 is a good rule of thumb so given that the headphone doesn't drop below 300 ohms I'd ensure that the driving amp is <30 ohms output impedance.
The italics are mine and there to note yet another piece of information that is pretty much 180 degrees off of the conventional wisdom on Head-fi. At this point I don't know what to believe, except for my ears. Right now, they're listening to Robert Cray's "Shame and a Sin" -- Apple Lossless>Trends UD-10>'70s Harmon Kardon integrated>HD580s. I have the mid bass rolled back 2db at 500 and 1000 hz as described above because the bass on this recording is huge. The sound is wide, warm, clear and detailed. No digital harshness. Cymbals sound clear and natural with no hash or hiss. There is no mud. Bass seems very well-controlled, with a very quick, precise attack and no boom or hangover that doesn't sound like the normal sustain of the instrument. No grain to speak of.

Could it be better? Oh, I'm sure. How to find better, though, is going to come down to listening. And I'm sorry, but there seem to be so many contradictions and so much misinformation here that I'm beginning to wonder if it is even a decent source of information for narrowing the field for listening.

Peace out,

Tim
post #50 of 215
Thread Starter 
Quote:
Originally Posted by billbillw View Post
I gotta call BS to the emails that were sent by the manufacturers.
Well, I'd have to be quite a fool to claim I sent all those emails when I didn't send them because anybody on this forum can email the manufacturers and verify if I'm lying. If all these manufacturers sent me the wrong information then, well, I can't to anything about that.

I did some research and posted my findings here. Feel free to email the same manufacturers and post your findings. As I didn't make this information up, I'll expect you to get the same answers I did.
post #51 of 215
Isn't lower output impedance always better regardless of what headphones you connect to an amp?
post #52 of 215
Quote:
Originally Posted by odigg View Post
Well, I'd have to be quite a fool to claim I sent all those emails when I didn't send them because anybody on this forum can email the manufacturers and verify if I'm lying. If all these manufacturers sent me the wrong information then, well, I can't to anything about that.

I did some research and posted my findings here. Feel free to email the same manufacturers and post your findings. As I didn't make this information up, I'll expect you to get the same answers I did.
I wasn't calling BS to you, but to the manufacturers. I'm sure they sent you the emails that you claimed. I just don't belive that they gave you good info, at least not from what I've seen in many recent receivers.
post #53 of 215
My Harman Kardon AVR645's headphone out sounds like crap. It makes my RS-2's sound like 20$ cheap phones.
post #54 of 215
Quote:
Originally Posted by philodox View Post
Isn't lower output impedance always better regardless of what headphones you connect to an amp?
I don't think that's always true. Isn't the Ety P to S adapter just a resistor in series, which is no different than having the resistor inside the amp between the speaker outs and the headphone jack.

The DT831 and DT931 are other examples of headphones that are supposed to sound better with a 150 ohm adapter.

From the graph in the Meier article, headphones that are light on bass, like these 3, level out more with higher impedance. To a point that is. The graphs of 470 ohm output impedance doesn't look good, and from what I can tell, that's what my NAD has.

A post on the Ortho thread stated that output impedance doesn't effect orthos like it does dynamic headphones. That's probably why I like my NAD so much. I rarely listen to dynamic headphones from it. I listen mostly to orthos and stats.

I might try a little experiment and build a box that can switch between various resistor values wired in parallel. Maybe one resistor to drop the impedance to 32 ohms, another to drop it to 150 ohms, and to pass though the original 470 ohms. Please let me know if I'm off base here.

Edit: When you're talking about a resistor net here, having 2 resistors in series and 1 in parallel?
post #55 of 215
I'm interested to know as well if high source impedance is an issue.

It seems that that headphone jack impedance standard is 120 ohms. Some said Beyer headphones are designed with this in mind.

My speaker to headphone adapter is at about 120 ohms. I'm toying with the idea of increasing the impedance which would result in increased current flow through the headphone. However I don't know what would happen if I exceed the 120 ohms mark. And if source impedance have to be lower than headphone's impedance, my headphone happens to be 120 ohms as well.
post #56 of 215
I may be eating some of my words, but not all...

I just checked the service manuals for the Denon AVR-3803 and AVR-1905. Both use feeds from main R/L with inline resistors.
However, I'm quite sure that my older 4802 and 3300 both use opamp circuits. I'll check them when I get home.

I also checked the Sony STR-DA50ES and it was fed from the main R/L output with resistors.

However, the NAD 317 and the C320BEE both use opamp circuits. (Their service manuals are down loadable through Hifiengine)

I also checked the Yamaha RX-V3000 (not too old) and it used an opamp circuit. Perhaps newer Yamaha's do use opamps.

I don't have any access to Onkyo files.

Honestly, I don't know which method is better. It probably varies greatly in the execution and also with the headphones. I do know that my Senns were un-listenable when I had a Denon AVR-4802 in my main HT setup. They sounded distorted and terrible. The same headphones sounded very good with the NAD 317.

My initial response was due to very recent experience working on a few NAD integrated amps. I haven't been into any of their AVRs, so I don't know about them.
post #57 of 215
Thread Starter 
Quote:
Originally Posted by Seba View Post
My Harman Kardon AVR645's headphone out sounds like crap. It makes my RS-2's sound like 20$ cheap phones.
If you'll notice in my original post, HK said that their lower end AVR-146 uses an opamp. I also stated that a quick browse for that opamp model lead me to believe it isn't very good. Considering that moving up the line in one brand sometimes means a similar circuit design with different parts, perhaps their whole AVR line uses the same circuit for the headphone jack.

billbillw-Thanks for the comment on hifiengine. That gives all of us an objective place to answer the question of if an amp uses resistors or opamps. I was finally able to find out the Onkyo 9555 uses an opamp circuit. Sorry I misinterpreted your comment.

It seems like the class D (Panny XR57 and Onkyo 9555) and class T amps don't lend themselves to using resistored headphone jacks. Perhaps there is a design issue that precludes this.

The NAD 317 and 320BEE have been replaced. Perhaps they changed their design strategy for their new amps. Their newer models are not on hifiengine so I cannot check.

I do agree with you that perhaps people replying to emails were incomplete in that they didn't check every single amp when they gave me the answers.

If nothing else, perhaps I think this shows that resistored off headphone jacks are far more common than we would have otherwise believed from wandering around this forum.
post #58 of 215
Quote:
Originally Posted by odigg View Post
It seems like the class D (Panny XR57 and Onkyo 9555) and class T amps don't lend themselves to using resistored headphone jacks. Perhaps there is a design issue that precludes this.
I know from experience that Class T amps, for the most part, don't like a common ground. I have an electret that a previous owner modified both the headphone and adapter to TRS. I hooked it up to a T amp and there was a bad channel imbalance and strange, barely audible buzzing (for lack of a better word). The channel imbalance made them unlistenable, but the buzz, while low volume, would drive you crazy after a while. I've since read that this is a problem with all digital switching amps. Some type of filtering gets eliminated with a common ground.

However, I believe that the Qube from Qables is a class D amp. They obviously designed the circuit to get around the problem
post #59 of 215
Thread Starter 
Quote:
Originally Posted by billbillw View Post
I may be eating some of my words, but not all...

Honestly, I don't know which method is better. It probably varies greatly in the execution and also with the headphones. I do know that my Senns were un-listenable when I had a Denon AVR-4802 in my main HT setup. They sounded distorted and terrible. The same headphones sounded very good with the NAD 317.
I would argue that the opamp method is better - if it was done properly. And to me that's an important point. It's a lot harder to design a decent opamp circuit than it is to throw together a resistor network. With the opamp circuit you have to *gasp* test it to see if the sound actually sounds good. If you can get the equations right for a resistor network (and playing with these equations is much simpler than creating an opamp circuit), you'll end up with something that sounds much like, if not just like, the original speaker out.

So if NAD is actually thinking about their headphone jacks and Denon is not, that wouldn't surprise anybody. However, with the Denons I tried I can't say there was anything wrong with them. Denon did say they were using resistors off the main amp for the current models.

I'm not actually sure why somebody would use a poorly performing opamp circuit in the first place. Wouldn't a resistor network be easier and cheaper? Perhaps the relay used to switch the speaker out/headphone jack is too expensive
post #60 of 215
Quote:
Originally Posted by billbillw View Post
I may be eating some of my words, but not all...

I just checked the service manuals for the Denon AVR-3803 and AVR-1905. Both use feeds from main R/L with inline resistors.
However, I'm quite sure that my older 4802 and 3300 both use opamp circuits. I'll check them when I get home.

I also checked the Sony STR-DA50ES and it was fed from the main R/L output with resistors.

However, the NAD 317 and the C320BEE both use opamp circuits. (Their service manuals are down loadable through Hifiengine)

I also checked the Yamaha RX-V3000 (not too old) and it used an opamp circuit. Perhaps newer Yamaha's do use opamps.

I don't have any access to Onkyo files.

Honestly, I don't know which method is better. It probably varies greatly in the execution and also with the headphones. I do know that my Senns were un-listenable when I had a Denon AVR-4802 in my main HT setup. They sounded distorted and terrible. The same headphones sounded very good with the NAD 317.

My initial response was due to very recent experience working on a few NAD integrated amps. I haven't been into any of their AVRs, so I don't know about them.
There are some interesting points here. As you doubt the manufacturer's emails, I doubt that the NAD C320BEE uses op-amps. I don't contradict, I just doubt, and would like confirmation from elsewhere. I used the NAD as a HP amp for about a year, and though ultimately I grew dissatisfied, it was hardly a poor HP amp (in fact it seems to have general rep as a good one). But you're right to ask: what is wrong with op amps? Why should op amp mean cheap/nasty when some of the best dedicateds use op amps (my Cute Beyond is brilliant). In that sense, the resistor/op amp debate is irrelevant; it's what you hear when you plug in. And let's clarify MY argument here: I'm not saying, and have never said, that you can plug HPs into any old (or new) integrated/receiver and get great results (most current HT receivers sound lousy even on speakers). What I was referring to, and what my experience mostly is with, is the thousands of stereo integrateds/receivers from top brands, dating from around the years 1982 to 2005, available on Ebay for very reasonable prices. Of course some of these sound lousy, and a few HT receivers sound good (the Marantz SR4200 has a good rep), but it's wise to establish a general classification.

Incidentally, I'm not sure what you mean when you say your Senns sounded distorted plugged into a Denon receiver. Distorted? Surely you'll only get distortion when there's a fault.
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