rant: Headphone amps are overrated

[JaZZ 0]

That's a fascinating thread. Thanks, Adrian, for inviting me to this forum! Sorry for my lengthy debut posting - but what can I do but lay all my cards on the table...

 

I would agree that amps are overrated, but not so much in this forum, as it seems, in clear contrast to Head-Fi, where I use to post. It's hard to find the understanding for the direct-path idea there, where it obviously is perceived as a red rag. The reason could be that the headphone amp often is the most expensive part of the individual setup, so no one likes to read that it's actually superfluous or a pure effect device. I have to confess that occasionally I was tempted to exaggerate it that way, but actually I just wanted to demystify it to a certain degree, make its real role clearer.

 

Which is primarily to amplify a signal. Is this really necessary in the case of a high-level source device such as an FM tuner or CD player, precisely: is a preamp indispensable, to drive a power amp? Definitely no! At least in most cases with not too extreme output and input impedances (...sensitivities, capacitances, cable lengths...). A reasonably designed passive attenuator based on resistors, potentiometers (both acting as voltage dividers) or transformers do the job equally well, with even clearly less alteration of the source signal. In fact in ideal cases the signal is virtually unaltered. No amp can reach such a high fidelity. Meaning: signal accuracy in the concerned path (!), not in terms of the subjectively perceived realism.

 

My direct-path career actually has begun with momentarily renouncing the preamp and using the only source with variable volume I had at my disposal then - an old Revox Tuner - to feed the power amp, with the goal to evaluate the fidelity of different preamps. Not a really great source, but the only thing that mattered was the deviation caused by the additional electronics in the signal path. I finally found the most neutral preamp in the form of the Conrad Johnson PV2. And also that the differences among the various preamps were quite big, as still was the one between the PV2 and the source sound. It was obvious that the amps smoothed and colored it in a euphonic way. The original sound was kind of dry in comparison. I can very well reproduce Mackie's experiences with the «direct path» in this context: improved transparency and clarity at the expense of smoothness and «musicality».

 

Later, with digital sources, I managed to compensate for the thus exposed «digital» artifacts by fine-tuning my self-constructed speakers' crossover networks, adapting them precisely to this specific sound. Interestingly the phono playback barely suffered from that measure, as it would have been in the reversed case. So the conclusion that the digital technics are to blame is not too unlikely in my opinion. On the other hand I remember the dry sound from the Revox tuner which then still was completely analog (as to the broadcasted music). So it's the weaknesses of the sources, generally speaking, which have to be masked by the smoothing amp electronics to make the sound «musical». Strange, but obviously true. However, in the case of my speaker rig I have sticked to the direct-path philosophy, taking benefit from the maximum transparency.

 

This excursion into preamps hasn't happened accidentally: Both direct-path versions have very similar effects. Renouncing the headphone amp and just plugging headphones into the line-out RCA jacks or using a passive attenuator, resp., offers the same advantages, such as increased clarity, transparency and transient speed, at the expense of a certain coherence and musicality. This may lead to the suspicion that those line-out amps aren't really capable of adequately driving headphones, which isn't their design purpose anyway. But I have seriously tested this. With my gear the low and relatively complex load represented by a dynamic headphone has turned out to have no influence on the signal - which is fed into a headphone amp and monitored through this one - when it's connected in parallel to its input (so that the line-out amp drives both headamp and load headphone at once).

 

But one thing I've learnt since my militant Head-Fi episode is that the majority of CD player's and even DAC's line-out stages are not really appropriate for driving headphones directly - mainly because of their high output impedance. My own equipment with its 5 ohm (Theta Pro basic II) and 20 ohm (Bel Canto DAC2) seems to be the exception in this context, whereas my DVD 963SA with its 200 ohm rather represents the normal case. The main issue with the high output impedance is the missing volume, the accompanying influence on the bass response is less striking. The common maximum output voltage of 2 volt (or more) is enough to drive even inefficient headphones, provided the output impedance isn't too high. High-impedance headphones are preferable in view of the output impedance factor as well as the actual purpose of line-out amps: to drive high-impedance loads. The HD 600 is one of the most suitable headphones around with its 300 ohm and its quite high efficiency. There hasn't been reported any damaged line-out stage because of such «misuse» and «overload»... but you never know.

 

The ideal value of a potentiometer for direct-path experiments appears to be 500 ohm. Probably not easy to find (so you may use 1000-ohm types instead for experiment purposes). Combined with a 250-300 ohm headphone, the resulting effective impedance (as to the electrical frequency response depending on the headphone's impedance curve) is around 100 ohm on the average, thus in the range of OTL tube amps. You can also use switched attenuators instead and dimension the resistors accordingly. And there's a cute little passive «amp» available: the ASL Reference Tools, which attenuates the signal in six steps using a transformer. Unfortunately its efficiency is very low, so even with maximum volume setting you need a HD 600 and loud recordings to get passably sufficient listening levels. (According to John Chapman from Bent Audio it should be no problem to build a much more efficient unit.)

 

But one thing it can serve for is to prove the nature of the source signal and to unmask the real role of amplifiers without leaving the door open for any refutation such as to suppose that line outs generally aren't able to drive headphones because they're not designed to drive low-impedance loads. The load impedance created by the transformer is high enough to be uncritical and passably comparable to amplifier inputs, whereas the output impedance in turn is low enough to be uncritical in terms of possible colorations in cooperation with the connected headphone. As to its sound: it's somewhat smoother, slightly rounded, with slightly reduced transparency and dynamics compared to resistor-based attenuators (leaning towards tube amps), but subjectively doesn't suffer from any loss of focus and detail, just presenting the music in a slightly smoothed manner, with somewhat greater coherence. Indeed it's a tiny step towards amplifier sound, but a really tiny one. The basic signature is the same dry and uncolored, highly resolving and detailed sound as from a typical resistor-based passive attenuator. Every amp I've compared to it seems like adding a lot of colors and warmth and smoothing the music signal in an absolutely convenient way, but sacrificing a lot of transient sharpness.

 

Imagine the details in a recording to be colored points, randomly distributed on a white surface. That's how the direct-path sound looks like. With an amp switched into the signal path, the points become larger and fuzzier, reducing the gaps and diminishing the white between them. That's how smoothness, coherence and colorfulness are increased and the reason why sometimes even details can be perceived as more striking (since they are «bigger» now). In comparison the source sound can be perceived as downright «empty». But no doubt: it's more transparent, more focussed and more dynamic. No lack of bass impact or extension at all. As to dynamics: It's well known that compressed music can sound more dynamic than uncompressed. The beat of a bass drum, e.g., is a more important event in a compressed recording because of its prolonged duration. The real dynamic events are very short and not really flashy to the ears. That's why even in terms of perceived «dynamics» amps seem to have no shortcomings, even rather the opposite.

 

To be honest: for most of my music listening time I use one of my two headphone amps: Earmax Pro and Corda HA-2. I fully agree with tee and its excellent posting: headphones provide an artificial sound anyway, so it doesn't make much sense to categorically maintain a purist standpoint. What counts is credibility, musicality, to be emotionally touched by the music reproduction. So I push all theoretical considerations aside and just enjoy the music. And even have to agree that through the amps it somehow sounds more realistic than through the passive attenuator. That doesn't mean the direct path sounds bad at all - but when I have the choice... Nevertheless, I'd really like to have John Chapman build me a perfect transformer-based attenuator once he has the time. And I think I would like it a lot. But it would cost even more than a really good (sounding) headphone amp.

 

So, finally, what's the merit of the direct path? It's the cheapest way to achieve excellent headphone reproduction with even the purest signal possible. The only precondition is a minimal technical skill to build the attenuator, either a potentiometer or a resistor-based switching type (which is more expensive). The main purpose in my perspective is a «scientific» one: to realize the role of amplifiers, their distinct sonic colorations. If one thing still is questioned: the general capability of line outs to drive headphones, one other thing can't be ignored: the considerable differences in terms of sonic signatures among amps. So the conclusion is justified that all ot them color the source sound more or less. Just as well to be understood as «more or less euphonically». (Tube amps are more on the euphonic side, but according to my experience they don't alter the original sound more than their solid-state counterparts.) One concrete benefit from this awareness is being able to question the sense of really expensive amps, with way oversized power supplies. (A guy on Head-Fi drives his R10 with a $15,000 amp.) You can be quite sure to have your money invested in a gigantic effect device.

 

I'm not sure if the extraordinary low load can damage some line outs. There are mixed opinions around, but (fortunately) no concrete damage event has been reported so far. There are millions of computer users which have their headphones plugged into their soundcards' line outs, myself included, and so far I haven't heard any bad news on this subject.

Edited August 26, 2003 by JaZZ

[JaZZ 0]

And BTW: this is a really beautifully designed forum!

[Northern Oak 0]

Sorry would someone clarify with me what others meant by direct-path idea ? Is it that you dun use an amp but what do you use then? Headphone out jacks? I'm really lost here. Thanks.

[ablaze 0]

Oak, whats commonly called the "direct path" on head-fi is simply going ampless ie. listening straight out of the RCA outputs of a CD player or DAC, withOUT a headamp. but as JaZZ has kindly outlined above, you have to go to some lengths to make an adapter.

 

JaZZ, thanks for sharing your thoughts on the "direct path". I started this discussion since I'm using a soundcard, and for me, connecting my headphones straight to the 1/4" line-out on my card is not a problem. I guess extrapolating to going ampless on a CDP is not as simple as I initially thought.

 

so JaZZ,

The ideal value of a potentiometer for direct-path experiments appears to be 500 ohm. Probably not easy to find (so you may use 1000-ohm types instead for experiment purposes). Combined with a 250-300 ohm headphone, the resulting effective impedance (as to the electrical frequency response depending on the headphone's impedance curve) is around 100 ohm on the average, thus in the range of OTL tube amps.

You're saying the ideal pot value would be a 500ohm pot? I've only seen 50k and 100k pots. 0.5k pot? I'm really not sure if such pots are available locally. maybe the other diy-ers can chip in?

 

anyway, thanks for taking the time to write that extraordinarily long post! I think people are still reading and re-reading to digest it all.

 

oh, and welcome to our humble abode

[Northern Oak 0]

Ah, I see ... now I know what you guys are referring to ... so effectively the direct path do not need a dedicated amp.

 

To a certain extent, it's true that you may not need amp. Why?

 

As I've been working on my DIY DAC, I have been the chance of looking through alot of DIY DACs schematics and I've realised that most, if not all, DACs have an output amplification stage before it goes out to the RCA output. So efffectively, there's already an amp in the DAC/Sound Card ...

 

This amp's could be as similar to the CMOY using integrated opamp or as discrete as a Gilmore amp. The only issue is whether this output amplification stage sounds good enough or is efficient to drive the cans.

 

 

[Mackie 0]

JaZZ, very impressive and insightful post. Hope to see more of these from U in the future.

[ablaze 0]

Oak, thats why. everything's sorta "amped" already, even without a dedicated headamp. somebody's gotta at least try out the direct path. doesn't anyone want to save the $$hundreds spent on amps?

[Northern Oak 0]

Nay, I guess it looks cool to have a $$hundreds amp sitting at the table top.

Edited August 27, 2003 by Northern Oak

[ablaze 0]

bugga. buy me a car if you want to flaunt your wealth

[Northern Oak 0]

Me?

Wealth ? No

Fats ? Aplenty!

Edited August 27, 2003 by Northern Oak

[ablaze 0]

OT: I wonder if I'll grow fat when I get a job and a wife

seem like all the married guys end up like -->

[Northern Oak 0]

The first signs to watch out for is your belly! It's very obvious!

[Northern Oak 0]

Mod, OT OT. Back to topics please!

[ablaze 0]

 

okok, back to topic:

JaZZ?

[Rameish 0]

Ahem! I still growing - just horizontally inclined.