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

post #1 of 212
6/25/08 at 8:56pm
Thread Starter 
Not too long ago I came across this thread. http://www.head-fi.org/forums/f5/usi...ed-amp-329395/

More than anything else, it prompted me to finally get some evidence to either support or disprove a statement that has been made repeatedly for years. "With receivers/integrated amps the headphone jack is an afterthought. They use a cheap opamp circuit."

I decided to just email different manufacturers to ask them if opamps powered the headphone jacks or if they used resistors connected to the main amp/speaker out. I contacted Denon, Yamaha, NAD, Cambridge, Onkyo, Marantz, Harmon Kardon, and Pioneer. For the sake of full disclosure, most of the emails started out by asking a general question about if their receivers/stereo integrated amps used resistors or opamps for the headphone jack. Then I said that while I was looking for an answer about all their equipment, I would provide them some specific models if they needed them. I wandered around the websites and picked models at random, making sure to include at least one of their less expensive models. The exception to this email format was HK and NAD. For them I only asked about specific models although NAD gave me an answer about all their amps.

Here were the replies to my questions.

Email Responses

Denon - All headphone jacks are powered via resistors off the main amp.

Marantz - All headphone jacks are powered via resistors off the main amp.

Yamaha - All models powered via resistors connected to the main amp.

Nad - All models powered via resistors connected to the main amp.

Cambridge - More expensive models use opamp circuit. All others (340A, 340R, 540A, 540R) use resistors off the main amp.

Onkyo - No reply yet.

Pioneer - VSX-818 ($250), VSX-1018AH-K (both AV receivers) - resistors. A-35R ($200, stereo integrated) - resistors. SX-A6-J ($650 stereo receiver) - dedicated opamp circuit.

HK. AVR-146 uses opamp. HK-3390 uses resistors. This makes sense as people have reported the AVR headphone out is not very good but the stereo amplifiers have good headphone jacks. They provided the opamp used and a quick search suggests it isn't very good.

Field Research
As I started to get these emails in I started to wonder if there was something deficient about resistored off headphone jacks resulting in poor headphone performance, and thus supporting the myth that most companies use cheap opamp circuits for the headphone out. I visited my local av store (a good one, not Best Buy) and tested a lot of different amps/AV receivers using a pair of HD580s. The most expensive was A $1200 Yamaha AV receiver. After that came a $1000 Arcam stereo integrated. The cheapest was a ~300 (on amazon.com) Denon. I also tested other Denons, Yamahas, some NADs, and a Cambridge Audio.

I was in the store for a nearly two hours. Not one headphone jack let me down. All provided clean sound and drove the HD580s well. I cannot say I found any problems that would lead me to conclude "this is a cheap opamp circuit." I did not hear any distortion indicative of an amp unable to power the headphones.

The Technical Argument

There is a fairly sound technical argument against using a separate opamp circuit to power the headphone jack in AV receivers/stereo integrateds. Let us first assume that a resistored off headphone jack uses two or three resistors. Any opamp circuit, even a horrible one, will require at least two or three resistors AND an opamp. It may also require other parts. It will also require more time to design.

This shows a contradiction in the statement ""With receivers/integrated amps the headphone jack is an afterthought. They use a cheap opamp circuit." If headphone jacks were really just an afterthought they would use resistors off the main amp. Using an opamp circuit means that the engineers and management decided to use something that took more time to design, cost more to produce, and performed less well. In short, using an opamp circuit means you spend more to get less.

The truth is that many (NOT few, and NOT just the expensive models) of the receivers you can buy use resistors off the main amp. This also means that many of the headphone jacks in AV receivers/stereo integrated amps are nearly as good, if not better, than many of the dedicated headphone amps people use. These headphone jacks should give you clean power, and plenty of it, for even your power hungry headphones.

Myth Busted? I think so. What myth is busted? The myth that most av receivers/integrated amps use opamp powered headphone jacks.
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post #2 of 212
6/25/08 at 9:13pm
*GULP!*

My old Realistic STA-2100D made for RadioShack by Pioneer in the early 80's sounds awesome!
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post #3 of 212
6/25/08 at 9:23pm
Quote:
Originally Posted by odigg View Post
The truth is that many (NOT few, and NOT just the expensive models) of the receivers you can buy use resistors off the main amp. This also means that many of the headphone jacks in AV receivers/stereo integrated amps are nearly as good, if not better, than many of the dedicated headphone amps people use. These headphone jacks should give you clean power, and plenty of it, for even your power hungry headphones.

Myth Busted? I think so.
Uhm... just because you can use a power amp with a voltage divider (using resistors) to drive headphones, does not mean it is "naerly as good, if not better, than many of the dedicated headphone amps people use". They headphone jack will not necessarily give you "clean power", but you can have lots of it (depending on how much it gets cut by using the resistor).

That conclusion is just not correct. Power amps are designed to drive speakers and their characteristics (low impedance, inefficient compared to headphones, requiring LOTS of voltage gain) while headphone amps are designed to drive headphones with different requirements.

Your conclusion is similar to concluding that having a Mack-truck in low gear is better than a sports car because it has SO much horse power that you need to cut it's power just to drive properly. Just doesn't work that way. Oh, and before somebody comments, lets not bring up the birth of the Shelby Mustang
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post #4 of 212
6/25/08 at 9:28pm
Ouch... In french we say its "jetter de l'huile sur le feu"...
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post #5 of 212
6/25/08 at 9:32pm
Quote:
Originally Posted by Headdie View Post
Ouch... In french we say its "jetter de l'huile sur le feu"...
It's that "jeter", and yes, this is true.
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post #6 of 212
6/25/08 at 9:40pm
The Mack truck example is brilliant.

No myth has been busted.
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post #7 of 212
6/25/08 at 9:49pm
Thread Starter 
Quote:
Originally Posted by greggf View Post
The Mack truck example is brilliant.

No myth has been busted.
Well part of my conclusion might be incorrect. But I stand by my statement that all the equipment I listened to gave no indications of having any problems with the HD580, or caused me to conclude the HD580 was lacking in sound quality.

To clear things up regarding the myth, I was talking about the statement that most integrated/av receivers use opamp powered headphone jacks.

I'll edit my post to indicate this.
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post #8 of 212
6/25/08 at 9:57pm
Quote:
Originally Posted by odigg View Post
Well my conclusion may be incorrect. To clear things up regarding the myth, I was talking about the statement that most integrated/av receivers use opamp powered headphone jacks.

I'll edit my post to indicate this.
The better receivers actually have a small headphone amp circuit in them with line level signal taken from input jacks.
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post #9 of 212
6/25/08 at 11:45pm
Thread Starter 
Quote:
Originally Posted by odigg View Post
Well part of my conclusion might be incorrect.
Yes, I've quoted myself. When I say "might" I mean "might" as in maybe.

There are a number of posts on many web forums(including this one) where people say that they found little or no improvement with a dedicated headphone amp compared to their resistor powered headphone jack. So I say my conclusion *might* be wrong. Not everybody would disagree with my conclusion.
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post #10 of 212
6/25/08 at 11:46pm
I had totally bought into that myth myself, though when I think about it I'm not at all surprised by this. The conventional wisdom that mainstream receivers and integrated amps power headphone sections with cheap opamps doesn't really make any sense. Stepping down the output with a resistor, just like stepped attenuators do, just like variable gain headphone amps do, seems like the more direct path. Does this mean that every decent receiver is as good as any headphone amp? Of course not. But it means that a couple of the core reasons given for the superiority of dedicated headamps (cheap op amps, not enough voltage) were simply wrong all along, that those who didn't hear an improvement over their headphone jack when they bought a headamp were not necessarily wrong (and it was not necessarily the fault of another component in their signal chain), and that it just could be that the headphone performance of your stereo's amp is exactly as good as your stereo's amp and not some kind of compromise or afterthought.

Quote:
That conclusion is just not correct. Power amps are designed to drive speakers and their characteristics (low impedance, inefficient compared to headphones, requiring LOTS of voltage gain) while headphone amps are designed to drive headphones with different requirements.
You may be right. Let's test it. What are the differing requirements you're talking about? What specifications would define those core differences between amps designed to drive headphones and amps designed to drive speakers? If you can just point me to what you're talking about, I'd be happy to do the research. I'd really like to know, so I upgrade the right thing. In the meantime, I'm a bit embarrassed. I've repeated that op amp myth several times myself, believing it was true.

Quote:
The better receivers actually have a small headphone amp circuit in them with line level signal taken from input jacks.
OK, odigg has written to and gotten responses from NAD, Cambridge, Denon, Marantz and Yamaha. Which better receivers did you have in mind?

Tim
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post #11 of 212
6/26/08 at 12:01am
I do not know the technical arguments.

i do know that the myth about most hp jacks on quality integrateds being sub-par is, in my experience, very wrong. For my first year on headfi I was reluctant to make this argument. I always got hooted down, typically be people who had spent alot on dedicated headphone amps. After ALOT of experience with dedicated amps (tube and SS) as well as many models of component stereo equipment I can say this....

Dedicated amps TEND TO BE overpriced and hp jacks (the "after thoughts") TEND TO BE sonically great and underpriced.

Sorry. It is my opinion.... what else can I say? I feel it is sort of a disservice to people's wallets to keep it a dark secret.....
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post #12 of 212
6/26/08 at 12:14am
Quote:
Originally Posted by senns&nonsense View Post
I do not know the technical arguments.

i do know that the myth about most hp jacks on quality integrateds being sub-par is, in my experience, very wrong. For my first year on headfi I was reluctant to make this argument. I always got hooted down, typically be people who had spent alot on dedicated headphone amps. After ALOT of experience with dedicated amps (tube and SS) as well as many models of component stereo equipment I can say this....

Dedicated amps TEND TO BE overpriced and hp jacks (the "after thoughts") TEND TO BE sonically great and underpriced.

Sorry. It is my opinion.... what else can I say? I feel it is sort of a disservice to people's wallets to keep it a dark secret.....
You may be right. I'd love to know so I don't have to go through a bunch of headphone amps to find out. If I'm going to spend $500 or $1,000, I'd really rather upgrade the quality of the amplfication of my entire system with that money if that is possible. So what are these core design differences between headphone amps and speaker amps? That, is the question.

Tim
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post #13 of 212
6/26/08 at 4:24am
Quote:
Originally Posted by senns&nonsense View Post
I do not know the technical arguments.

i do know that the myth about most hp jacks on quality integrateds being sub-par is, in my experience, very wrong. For my first year on headfi I was reluctant to make this argument. I always got hooted down, typically be people who had spent alot on dedicated headphone amps. After ALOT of experience with dedicated amps (tube and SS) as well as many models of component stereo equipment I can say this....

Dedicated amps TEND TO BE overpriced and hp jacks (the "after thoughts") TEND TO BE sonically great and underpriced.

Sorry. It is my opinion.... what else can I say? I feel it is sort of a disservice to people's wallets to keep it a dark secret.....
Ha! I could have written this post myself. If anyone likes to do a search, they'll find I was fighting this battle 3 or 4 years ago and getting shouted down each time. I knew the op amp myth was exactly that because I'd looked inside so many amps. I knew the "dedicated HP amps are always superior" theory was rubbish because I'd listened to so many great sounding integrateds/receivers. Nor could I follow the "you need a dedicated HP amp to get sufficient voltage/current/whatever" argument. Take a 50 watt integrated, step down the output, where is there insufficient power to drive a pair of headphones? Power simply doesn't come into it. Sound quality? If an amp gets great reviews, by users as well as reviewers, it can generally be considered a good HP amp unless it has a particular characteristic that clashes with the characteristics of the HP. This is called synergy, and has nothing to do with the superiority of HP amps. I'm currently using a Marantz PM6010 OSE amp and getting the best results I've ever got from my HD650s. I much preferred it to the LD MkV, though I admit I only let the LD burn in for around 50 hours. Even so, looking inside the Marantz gives me no cause to suspect it should be inferior. It even uses a double mono layout like the LD, though with a common power supply. Fact is, I have never understood the "if you're not going to buy a dedicated amp don't buy top grade headphones" line from theory, logic or experience. And frankly, I've long resented the dominating, almost bullying attitude of certain posters here whenever it's suggested that a good HP can perform well out of decent integrated/receiver.
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post #14 of 212
6/26/08 at 5:29am
Quote:
Originally Posted by tfarney View Post
I had totally bought into that myth myself, though when I think about it I'm not at all surprised by this. The conventional wisdom that mainstream receivers and integrated amps power headphone sections with cheap opamps doesn't really make any sense. Stepping down the output with a resistor, just like stepped attenuators do, just like variable gain headphone amps do, seems like the more direct path. Does this mean that every decent receiver is as good as any headphone amp? Of course not. But it means that a couple of the core reasons given for the superiority of dedicated headamps (cheap op amps, not enough voltage) were simply wrong all along, that those who didn't hear an improvement over their headphone jack when they bought a headamp were not necessarily wrong (and it was not necessarily the fault of another component in their signal chain), and that it just could be that the headphone performance of your stereo's amp is exactly as good as your stereo's amp and not some kind of compromise or afterthought.
Ok, lets first get one thing out of the way "cheap op amps" do not necessarily mean "not enough voltage", in fact power amps usually run fairly high voltages, more than enough to power opamps with more than enough voltage. There is nothing wrong with opamps, the reason that power amps use resistor dividers is because they are much cheaper than headphone amp circuits (same theory as stepped attenuator, it's a voltage divider; but different since it's used on output and also sets output impedance).

What do you think is in 90% of the "dedicated headphone amps"? Opamps 99% of portable amps are directly driven by them as well, and off battery voltages (8.4V usually).

It's also not less things in the signal path, the signal passes through an entire power amp before getting to the headphones vs going through a dedicated headphone amp.

Quote:
Originally Posted by tfarney View Post
You may be right. Let's test it. What are the differing requirements you're talking about? What specifications would define those core differences between amps designed to drive headphones and amps designed to drive speakers? If you can just point me to what you're talking about, I'd be happy to do the research. I'd really like to know, so I upgrade the right thing. In the meantime, I'm a bit embarrassed. I've repeated that op amp myth several times myself, believing it was true.
Impedance: Speakers are generally 2 - 8 Ohms, Headphones are generally 32 - 300 Ohms. The lower the impedance, the higher the amount of current that goes through them. With output resistor dividers on power amps, the output impedance is fairly large (120R usually?) as compared to usually 0R on headphone amps, that creates impedance mismatches between amp and headphone.

Sensitivity: Speakers are generally MUCH less sensitive requiring MUCH more voltage gain (20x or more) vs headphones which are easily driven by at 4x. Lower gain means less amplified noise (higher noise floor). The gain brings another issue, with the noise floor raised; it has to be dealt with, likely inline resistor with output creating an impedance adapter for the headphones and since headphones don't have flat frequency response, it will change how they sound.

That's about as much theory I can remember tonight. I'm sure there are tons of other reasons and I'm hoping for someone else to chime in as well.
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post #15 of 212
6/26/08 at 5:40am
I suspect the answer may somehow be in this obscure post by a Head-Fier named Joe Bloggs way back in 2003:


"Well, the headphone output on many amplifiers is just connected to the speaker amp via a high resistance resistor. It would cost them just a little more to build a proper resistor network (like the Grado headphone adapter) with low output impedance. . . "


Lordy knows I'm not a technical person, but it seems reasonable to me that some - most? - receivers and integrated amps use the cheapest possible single resistors rather than sophisticated networks of quality ones. So, even though stopping down the main amp power is the right way to go, compared to using cheap opamps (the way, say, a cd player headphone jack might), there's a good way to do it, and a cheap way to do it.

So all those integrated and receiver manufacturers using resistors instead of opamps is meaningless unless those resistors are done right rather than hastily and on the cheap as afterthoughts.

I'm having an engineer friend build a tube headphone amp for me now, and while I don't understand most of what he's doing, I do understand that parts costs - including resistors - varies wildly. Wildly.

There's no way a Yamaha or NAD is spending time - or money - on headphone jacks. Although, I must admit, they MIGHT be. Some of them.

The proof is in the pudding and in the listening. How do they sound?

I've had a standard hole in a cheap 1970's Pioneer receiver. In retrospect, it was atrocious. I've had holes in Sherwood and Kenwood and all kinds of -wood receivers, and can't even remember them.

I currently have a hole in a NAD intgrated - I don't even remember its model number - and the sound is okay. Not stellar. I had a great Creek integrated recently, but its headphone jack sound, now that I've had experience with dedicated headphone amps, was bad - about like the old Creek headphone amp, the OBH-11, I think it was, which I also had.

But, then again, just this last winter I had a GREAT headphone jack out of the current Denon integrated that's offered at Crutchfield. I expected nothing of it, based upon all the dedicated amps I've now heard and all the standard holes I've had. But gawd, it was very musical and powerful.

So, all it gets down to is, the Denon probably used better parts and a more sophisticated implementation of resistors than do the other receivers and integrateds I've had.

To be bitter about the "bullying" attitude Head-Fiers have shown re: standard headphone jacks vs. stand-alone headphone amps is understandable but wrong.

How many dedicated headphone amps have you heard? How many have you owned? How many standard jacks have you heard or owned? Could you hear a difference between them?

I know, I hate this, I hate this fact of headphone life, but, you can't reach any sweeping conclusions and you can't condemn Head-Fiers as bullying if you haven't bought and heard and bought and heard over and over again.

We all want things to be simple. We all want things to be cheap. It's just not possible for most people, most of the time, to keep buying and selling boatloads of gear.

But some people have, and many of them are veteran Head-Fiers who have now left Head-Fi and gone elsewhere, all because they've been accused of being bullies or elitists or whatnot by noobs who haven't done the necessary research and listening, but have, instead, made sweeping conclusions that support their preferred and hoped-for (and paranoid? and tightwadded?) conclusions, rather than the reality that comes from experience.
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