Are headphone amps snake oil?

[Joe Schmoe]

Suppose a person has a quality home audio device (not portable, and not computer speakers) with a headphone output, such as a CD player, receiver or integrated amp. Also suppose that the headphones being driven are very high quality (perhaps requiring a relatively large amount of power.)

In this situation, is there really an advantage to using a dedicated headphone amp, or is this just a snake oil claim by those who wish to sell such amps?

While we are on the subject, how about dedicated headphone-specific DACs?

 

[Votrax]

Suppose a person has a quality home audio device (not portable, and not computer speakers) with a headphone output, such as a CD player, receiver or integrated amp. Also suppose that the headphones being driven are very high quality (perhaps requiring a relatively large amount of power.)

In this situation, is there really an advantage to using a dedicated headphone amp, or is this just a snake oil claim by those who wish to sell such amps?

While we are on the subject, how about dedicated headphone-specific DACs?

Headphones don't require much power. As an example Denon's AH-D7000 (MSRP $999) headphones have an impedance of 25 ohms and are rated for a maximum input of 1.8W. The only advantage I see are the headphone amps with multiple outputs with volume control for each.

 

[Nemo128]

I will say headphone amps for iPods work from personal experience.

From a receiver, pfft. At least snake oil can be used as a lubricant. =)

 

[TLS Guy]

Headphones don't require much power. As an example Denon's AH-D7000 (MSRP $999) headphones have an impedance of 25 ohms and are rated for a maximum input of 1.8W. The only advantage I see are the headphone amps with multiple outputs with volume control for each.

I agree. A headphone amp is very simple. Here is a circuit.

Obviously two would be required for stereo. Very good op amp chips indeed, and yes, better than tubes can be had for less than a buck. The other components are very cheap. I'm sure you Cambridge has a circuit very similar on the headphone amp. It is fine.

By the way, I pulled that circuit from a DIY project as an upgrade! I can't believe your unit does not have something at least as good.

Op amp chips that are very linear are a dime a dozen.

A headphone specific DAC makes no sense to me.

 

[Joe Schmoe]

I'm sure you Cambridge has a circuit very similar on the headphone amp. It is fine.

It was your comment to that effect that prompted this (more general) thread. I wanted to give the dissenters a chance to voice their opinions. Also, if there are those who believe that headphone amps (and/or headphone DACs) do offer higher performance, I would like them to explain why.

In the short term, I expect I will love my new headphones. When the upgrade bug bites again (notice I said "when", not "if"), I want to know where I should spend the money for maximum impact.

 

[TLS Guy]

It was your comment to that effect that prompted this (more general) thread. I wanted to give the dissenters a chance to voice their opinions. Also, if there are those who believe that headphone amps (and/or headphone DACs) do offer higher performance, I would like them to explain why.

In the short term, I expect I will love my new headphones. When the upgrade bug bites again (notice I said "when", not "if"), I want to know where I should spend the money for maximum impact.

Remember in an earlier post, I said external headphone amps were close to funny wire. What I mean by close is this.

If you have enough power to drive you phones and you can't here hiss you are fine.

Generally headphone amps are pretty close to the circuit I sent you first. So what are the issues.

Well for one thing there is not enough power for some.

The bigger issue is signal to noise.

If you note in the first circuit I sent you the volume control is a pot ahead of the input to the chip. The issue is that signal to noise degrades as you turn down the volume. The chip is always wide open, and only the input to the chip is controlled. If you can't hear hiss from your headphones at low volume this is a non issue.

I did however manage to find a copy of the "gold standard" headphone amp circuit by veteran amp designer Lindsey Hood.

Now this circuit has a discrete push pull output stage for higher power.

However the circuit incorporates the variable gain feed back loop circuit of veteran British designer Peter Baxandall. This circuit, as the volume is turned down decreases the gain of the circuit and increases headroom. Along with it, signal to noise ratio stays constant. and does not decrease or degrade with decreasing volume.

Peter Baxandal's circuit is very elegant. I always use it controlling the volume of op amp based circuits.

Here is Lindsey Hood's headphone amp.

The problem is if you buy a fancy headphone amp, you won't know what type of circuit it has.

I know you don't like technical stuff, but the bottom line is this: - If you have enough volume and don't hear hiss you are fine.

 

[Exit]

Below is a site that specializes in headphones and headphone amps. It depends on the headphone you choose whether the site recommends use of a headphone amp or not, and they identify those headphones where a headphone amp is needed or benefits from use of a headphone amp. I used the site to pick a headphone that wouldn't require a headphone amp to save money, so I can't say much about headphone amps personnaly. It is worth browseing through the site to see what they have to say on the subject.

http://www.headphone.com/products/headphone-amps/

 

[mazersteven]

Some Headphones don't require much power.

Fixed.....

 

[gus6464]

It really depends on the headphone. My Beyers are 300ohm so they can benefit from an amp. Some Sennheisers that are 600ohm will benefit even more. If you have some cans that are <100Ohms then you shouldn't worry about it. The countless posts from you about this subject seems as if you are trying to start a flame war more than anything else. How about you just buy an entry level affordable amp and find out for yourself?

 

[TLS Guy]

It really depends on the headphone. My Beyers are 300ohm so they can benefit from an amp. Some Sennheisers that are 600ohm will benefit even more. If you have some cans that are <100Ohms then you shouldn't worry about it. The countless posts from you about this subject seems as if you are trying to start a flame war more than anything else. How about you just buy an entry level affordable amp and find out for yourself?

Actually the higher the impedance the less the need for an amp. The reason being is that no significant current has to flow, and op amps are much better voltage amps than current amps. If you headphone is 8 or 16 Ohm, then significant current has to flow, and the greater the need for a lower amp output style headphone amp.

I have always used Sennheiser high impedance phones, then I get good results plugging them into any headphone jack, be it on an outboard deck, mix panel or tape recorder. Any pro engineer I have ever been with does the same thing for quality checks. I'm yet to see one use a separate headphone amp. I just use the socket on the device I'm working with in production work, and everything works fine.

 

[WmAx]

Actually the higher the impedance the less the need for an amp. The reason being is that no significant current has to flow, and op amps are much better voltage amps than current amps. If you headphone is 8 or 16 Ohm, then significant current has to flow, and the greater the need for a lower amp output style headphone amp.

I have always used Sennheiser high impedance phones, then I get good results plugging them into any headphone jack, be it on an outboard deck, mix panel or tape recorder. Any pro engineer I have ever been with does the same thing for quality checks. I'm yet to see one use a separate headphone amp. I just use the socket on the device I'm working with in production work, and everything works fine.

Many portable devices may only produce around 1 VAC maximum output. With many headphones, this is simply not sufficient to power them when dynamic music is played. The same goes for headphone amps that work off a single 9VDC battery. Typically, <3VAC is available and there are headphones that need more than this for dynamic music. I have an AKG K340 that is very low voltage sensitivity. It needs >8 VAC for some of my most dynamic music recordings, or the amplifier will voltage clip.

-Chris

 

[jliedeka]

I have a couple of friends that use headphone amps exclusively. They don't have receivers or integrated amps. If you have a receiver and the headphone jack sounds good to you, you don't need a headphone amp.

Jim

 

[TLS Guy]

Many portable devices may only produce around 1 VAC maximum output. With many headphones, this is simply not sufficient to power them when dynamic music is played. The same goes for headphone amps that work off a single 9VDC battery. Typically, <3VAC is available and there are headphones that need more than this for dynamic music. I have an AKG K340 that is very low voltage sensitivity. It needs >8 VAC for some of my most dynamic music recordings, or the amplifier will voltage clip.

-Chris

Actually, I was not considering battery powered devices in the equation. However for mains powered units considered here, a headphone amp with the headphone chip powered by a 12V/-12 supply, would have no difficulty producing 20 volts clean output, and that would produce over 1.3 watts of power into 300 ohm phones. The current would be 0.07amps, and therefore could be driven straight from the opamp, without a power amp.

I gather from their website Sennheiser consider about 300 ohms optimal for driving straight from the headphone sockets of CD players etc. I would tend to agree.

Obviously for a battery powered unit using a 6volt battery pack the impedance would need to be about 30 ohms, for the same power. The current draw 0.22 amps. Just about possible for some chips.

The 30 ohm phones could try to draw 0.66 amps from the +12/-12 volt supplied chip, which would be too much for an op amp. However that would be absurd for phones, as the power would be about 13 watts, if the amp could provide it. The amp would clip. However if the volume were turned down on the CD player so it delivered six volts, the spl would be just as high and clean. The power of just over a watt is fine for the majority of phones.

So Phones with an impedance in the 100 to 300 ohm range will do best with most mains powered units, as long as the supply voltage to the headphone amp is adequate. Unfortunately the consumer does not know the voltage capability of the headphone amp. However units in the 20 to 50 ohm range should work with either, as long as you understand you will have to set the volume at a lower setting if the headphone amp has a supply voltage over six volts. They will still play just as loud though.

I tried my Sennheiser 525 phones on a variety of units in my racks this afternoon. I think their impedance is around 160 ohms. They played clean and loud enough on everything, although the RME Fireface 800 and Revox A 700 drove them the loudest, to deafening levels in fact.

We seem to have opened up a confusing set of issues in this thread.

However the simple bottom line is this.

If the headphones you picked play loud enough, clean enough, and you hear no distracting hiss from your headphones, then you will not benefit by putting dollars into a standalone headphone amp. If any of these criteria are violated then you likely will.

It is just that there has to be some technical understanding to see why this is so.

 

[jliedeka]

You are forgetting sensitivity. My Grado SR-60s pull 32 ohms but have a 98 dB sensitivity and work fine with low powered signals.

Jim

 

[emorphien]

I don't have experience with headphone amps but I've been interested in a unit that is portable with both amp and DAC built in. My desktop computer has lousy headphone output (sound quality, volume is fine) and an external unit (there are a lot of headphone amps that will act as USB DACs) would likely be a simple way to solve that. Getting one that combines an amp and battery solution could make it useful with portable players too. It would in many ways be a somewhat expensive toy that does solve my desktop headphone output problem and I could use with my laptop while traveling. I haven't done that much with my new laptop but my experience with a lot of past laptops I've had is that there is often some noise in the headphone line.

There are a lot out there in the roughly $200-300 range with all of that and the differentiation in price comes mostly from the features and how much the brand wants to overcharge you for the (mostly pretty darn cheap) components. As mentioned above DIY is popular in the headphone amp world, particularly for inexpensive small portable units. Some people like crossfeed, so that's certainly a feature to keep an eye out for if you're shopping. Some units have variable and some have fixed crossfeed, a lot have none at all.

For me, whether I want to DIY or pay someone else for a complete package depends on how much time and interest I have in making it myself. These days I don't have time, even though I might be interested.

 

[gus6464]

Actually the higher the impedance the less the need for an amp. The reason being is that no significant current has to flow, and op amps are much better voltage amps than current amps. If you headphone is 8 or 16 Ohm, then significant current has to flow, and the greater the need for a lower amp output style headphone amp.

I have always used Sennheiser high impedance phones, then I get good results plugging them into any headphone jack, be it on an outboard deck, mix panel or tape recorder. Any pro engineer I have ever been with does the same thing for quality checks. I'm yet to see one use a separate headphone amp. I just use the socket on the device I'm working with in production work, and everything works fine.

My DT770 has a slight hiss when hooked up to my receiver. Does this mean I should try out an amp?

 

[WmAx]

It would in many ways be a somewhat expensive toy that does solve my desktop headphone output problem and I could use with my laptop while traveling.

If your laptop has the required slot, I would suggest just trying an Echo Indigo I/O. These work well with most computers, but some computers have incompatible PCMCIA chip sets; but you would just want to do a Google search for compatibility / problems of your particular chip set model number and the Echo Indigo. Of course, if you have a headphone with very low voltage sensitivity, you will still need an external headphone amp. But the one on the Indigo is excellent and will work well for many headphones.

-Chris

 

[TLS Guy]

My DT770 has a slight hiss when hooked up to my receiver. Does this mean I should try out an amp?

The real question, is whether the hiss can be heard in quiet music passages. If not then you have no problem. If you can then get a good amp.

However, you might buy an amp and have the same problem, as it might just have a simple volume control ahead of the opamp. That is what the feedback volume control circuit of Peter Baxandall in the Lindsey Hood design is all about.

The headphone amp manufacturers never give you a clue about these sort of details. If you have the amp you will be able to tell. If you plug the phones in with nothing playing the hiss will stay the same as you turn the volume up and down. In the Baxandall circuit, the hiss will go to inaudible as you turn down the volume.

 

[walter duque]

I use older AKG headphones and plug it into my nakamichi DVD 10s DVD-player and they sound awesome, but it has a volume control for the headphones. So there might be a headphone amp build in. I am not sure.

 

[emorphien]

If your laptop has the required slot, I would suggest just trying an Echo Indigo I/O. These work well with most computers, but some computers have incompatible PCMCIA chip sets; but you would just want to do a Google search for compatibility / problems of your particular chip set model number and the Echo Indigo. Of course, if you have a headphone with very low voltage sensitivity, you will still need an external headphone amp. But the one on the Indigo is excellent and will work well for many headphones.

-Chris

Interesting. Thanks for the heads up. My laptop has no regular PCMCIA slot, only ExpressCard 54 so it won't work for me anyway since I haven't seen an ExpressCard version after a quick search.

Won't work with my desktop either though. I'm leaning towards the USB DAC+amp combined units at the moment but I know someone else who might be interested in that PCMCIA unit.