March Audio HPA1

[RayDunzl]

Consider this; noise levels in a quiet room are around 30dB(A) , headphones may reduce this a bit. Considering you say you listen at max around 90dB(A) , how much dynamic range do you need? Looks like about 60 maybe 70dB

Listening to the TV News right now.

-40dB digital attenuation (from the analog attenuated 66dB SPL Leq at which I"m listening) reduces the sound (effectively) to silence.

 

[Headphonaholic]

Having auditioned prototypes of the HPA1 and DAC1 first hand, I can say quite confidently that there was no degradation of the audio quality that I could perceive. I listened with a wide range of headphones and no matter what, it sounded great. I didn't get a chance to compare head to head with the THX AAA 789, as it arrived too late, but the HPA1 definitely performed just as good. We're talking performance beyond what human ears can perceive. There was literally no evidence of noise at anytime. I imagine in most cases your headphone, or music will likely be the cause of any noise or distortion.

 

[March Audio]

I didnt wrote noise floor,I wrote THD+N but now I realize that was mistake and I really meant SINAD,but anyway... yes,DAC noise floor does not degrade if you attenuate,but it doesnt improve either and thats the problem,signal goes down,but noise doesnt,the ratio of signal to noise does degrade and apparent noise floor from listener perspective does increase.

Sure,I only need 70db signal to noise ratio,but then I would get O2 and Odac for combined cost of 200$ and not your amplifier for 400 - 500$ you expect to ask for it.If I am paying premium price,I want premium performance becose I enjoy the idea of proper engineering and want a positive placebo effect.The idea of 80db effective signal to noise ratio caused by degradation inducing excessively high gain amplifier does not seem like attractive way to spend money to me.

Its true resisitve potentiometers,mainly the small cheap ones degrade SINAD,its nowhere near as bad as digital attenuation,there is reason pots are made.They have channel balance problem and reliablity issues of moving mechanical device but they do prevent the problem of high digital attenuation killing the SINAD.

I would suggest either making it unity gain,giving it gain switch or using high quality stepped attenuator made from matched precision metal foil resistors.

What is THD + Noise? Sinad is exactly the same thing as THD + Noise. You need to be careful looking at SINAD as a headline figure. For example Amirs table of SINAD performance has some clear leaders, most of which because they output a far higher output voltage.

The noise floor remains the same, the apparent or listener perceived noise floor remains exactly the same. If you couldnt hear it before attenuation, you wont hear it after attenuation. Equally if you cant hear the noise floor, you wont hear music that is at or near that low level. You have lost nothing.

It is the dynamic range / SNR that changes.

Please feel free to buy the O2 or Odac, my amp may not be right for you.

Pots are horrid, balance issues, noise and degrade over time. Analogue volume control is *not* perfect. Analogue controls also degrade dynamic range/SNR once you hit the noise floor of the partnering amplifier, which may not be that far lower than the DAC. In fact speaker power amplifiers it most probably will be higher than the DAC.

Digital volume is very convenient in the app you are running on your phone or tablet.

The problem here is that you have lost real world context.

 

[derp1n]

Amir's SINAD graph does more harm than good with respect to audio science and laypeople's interpretations.

 

[March Audio]

How hard is to have two versions one with 0db gain and one with the 6db gain?

Actually its a real PITA Two circuit boards, higher costs due to lower manufactured numbers of each, plus managing inventory. Before you ask switchable gain will degrade the performance. Then of course there is the issue of confusion among less technical consumers.

 

[March Audio]

Listening to the TV News right now.

-40dB digital attenuation (from the analog attenuated 66dB SPL Leq at which I"m listening) reduces the sound (effectively) to silence.

Yes, this is an easy experiment anyone can try. Get your headphone amp playing at a normal comfortable volume and turn the volume down until you perceive silence. What reduction in dB do you get?

 

[March Audio]

To look at this a different way is to say that it is the highest possible volume level that has reduced and the lowest possible volume level has remained the same.

Nothing to be gained from reducing the lowest volume level further if it's already far lower than anything you can actually hear.

 

[restorer-john]

You ought to update your web site with some 'coming soon' product teaser shots or maybe a 'be one of the first to own our new HPA-1/DAC-1' limited edition numbered products signed by the designer himself type deals. Email for more information etc

 

[March Audio]

You ought to update your web site with some 'coming soon' product teaser shots or maybe a 'be one of the first to own our new HPA-1/DAC-1' limited edition numbered products signed by the designer himself type deals. Email for more information etc

You are absolutely right, I have neglected it.

It's actually a job for tomorrow as the second batch of (correctly printed) dac enclosures arrived yesterday. Units are already built and on test, so will be available for sale Monday.

First unit is going to Amir for test and review on Monday before going on to the customer.

Im Still plugging away at the headphone amp PCB layout.

Power amp cases should be with me next week and on sale shortly afterwards.

 

[RayDunzl]

Yes, this is an easy experiment anyone can try. Get your headphone amp playing at a normal comfortable volume and turn the volume down until you perceive silence. What reduction in dB do you get?

TV News as source again.

Normal = -10dB using the Benchmark DAC2 and HD650.

Tiny hint of sound at -60dB (less than occasional ambient sounds)

Nothing at -66dB. Barely something at -64dB. Legibility occurs around -48dB.

It's a little quieter now (11:45pm) than this afternoon.

YMMV.

 

[March Audio]

I tried with my HD6xx headphones and I lose it at about -72dB from a reasonably loud setting.

 

[March Audio]

1V would drive even the most inneficient headphone in the world to 90db.Most people dont listen that loud with average volume around 80db and peak to 90db.I think better thing to concentrate is low output impedance and high current capability,thats alot more usefull to vast majority of users than overkill voltages.If the amplifier wont have switchable gain setting,then I think +3db is already too much and +6db is total overkill.

Well I just tested what levels I listen at. I set a typical volume. The track was Higher Ground by The Blind Boys Of Alabama. A compressed low DR recording up to 0dB. Quieter more dynamic recordings I would turn up louder.

We have Lafmax of 94.6dB and a Laeq (the important bit for hearing damage/exposure) of 88.8dB. So already 4.6dB different to your view/opinion.

So this is with compressed rock music. What about say classical? I picked a Mozart piano concerto recording at random from my collection. I left the volume setting the same. Basically it was quieter than I would normally listen, and turned it up about 6dB.

You need latitude to account for different dac output levels (although admittedly few are below 2v), recordings, headphone sensitivities and of course personal preference. I have no doubt there are some that want to listen louder than myself.

Perhaps +3dB gain is enough, 0dB is probably not.

 

[Graph Feppar]

What is THD + Noise? Sinad is exactly the same thing as THD + Noise. You need to be careful looking at SINAD as a headline figure. For example Amirs table of SINAD performance has some clear leaders, most of which because they output a far higher output voltage.

The noise floor remains the same, the apparent or listener perceived noise floor remains exactly the same. If you couldnt hear it before attenuation, you wont hear it after attenuation. Equally if you cant hear the noise floor, you wont hear music that is at or near that low level. You have lost nothing.

It is the dynamic range / SNR that changes.

Please feel free to buy the O2 or Odac, my amp may not be right for you.

Pots are horrid, balance issues, noise and degrade over time. Analogue volume control is *not* perfect. Analogue controls also degrade dynamic range/SNR once you hit the noise floor of the partnering amplifier, which may not be that far lower than the DAC. In fact speaker power amplifiers it most probably will be higher than the DAC.

Digital volume is very convenient in the app you are running on your phone or tablet.

The problem here is that you have lost real world context.

I meant the noise floor degrades compared to using resistive attenuator,the apparent noisefloor from listener perspective does get higher if the DAC is attenuated digitaly versus using pot to turn it down.There is reason why pots are used when money,space and weight isnt issue.

I do agree digital attenuation is better,thats why I like the idea of this amplifier,the superior reliability and channel matching are winner in my book.My issue is that I think the amp should not have any gain if it wont have gain switch.

With regard to your SPL test,it just confirms what I say,you listen 2db louder with compressed music and 8db more with uncompressed.With HD650 thats like 650 mV rms for 100db peak.HD 800 would be 800mV,the extreme outlier that is Hifiman HE6 would need about 3.2 V for 100db so on unity gain amplifier it would get to only 96db.

Even this ridiculous headphone would play loud enough for you with 2db to spare on compressed music and would fall short of only 4db with more dynamic music.I think designing amplifier around this extreme outlier is bad idea,how many people in the world have HE6? How many people with HE6 plan to use your amplifier?
Becose increasing gain is no free lunch,if you want to satisfy these rare cases,it will be at the expense of majority,I bet there will be many times more users complaining of hiss,particulary the IEM users compared to HE6 owners who would get "only" 96db out of unity gain amplifier.

Its true for full sized open headphones the noise floor would not get audible even if you made your amp with +6db gain but sensitive closed headphones,particulary IEM could make the hiss audible.If you have 30db noise floor in your room and you have closed headphone with 30db isolation at 2 KHz+ frequencies then its like if the noise floor was 0db,and if you play dynamic music with 100db peaks then you need 100db SNR for hiss to be inaudible and with 20- 30 db of digital attenuation with full sized headphones and god knows how much with IEMs,you are absolutely in hiss territory.

Also the higher the gain,the higher the chance of unpleasant experience when one is blasted with loud sound.There was mentioned that crashing Windows or some other software issues could cause the digital volume to be turned full on,even if that wasnt the case,user error is in my opinion much more possible route to this noise blast issue.With +6db gain and Hifiman HE 400S it would blast you with 120db,IEMs would probably explode.

 

[rajapruk]

Some extra gain might be wanted for custom EQ for some people.
Variable gain is always a really nice feature.

 

[Graph Feppar]

Some extra gain might be wanted for custom EQ for some people.
Variable gain is always a really nice feature.

Thats good point but I still think 2V unity gain is enough,if you have HD800,relatively high voltage requiring headphone then 2 volts rms would afford you 105db + 3db sub bass boost to make it flat/extended.

 

[Graph Feppar]

Let me just say,becose I might appear as to be hating on March Audio HPA 1 that I love the idea behind this amplifier,I think high performance,affordable,without analog volume control,made in Australia by talented engineer is super cool and I want it.I think we need atleast two gain settings,a gain switch,that way everybody is happy,otherwise those that need low or high gain would be unhappy,you cant make HE6 owners and IEM owners happy at the same time with no analog volume control and no gain settings.

 

[derp1n]

Why should the entire world be held hostage to the HE6?

 

[Graph Feppar]

Why should the entire world be held hostage to the HE6?

Becose its headphone that requires most voltage.Its funny becose despite it being only relatively low 53ohm impedance,it needs 1 volt to reach 90db,compare that to 300 ohm HD650 that needs 0.2 volt for 90db or very similiar looking HE400S that needs 0.08 volt for 90db,this headphone is so extremly inneficient that its legendary.I am not entirelely sure but I think its most inneficient headphone ever made,atleast in modern times.

Due to it being such extreme outlier,I use it in argument becose it shows that you dont really need that many volts.There is this public opinion how HE6 needs speaker amps,how hard it is to drive when in reality even zero gain amp would play them to 96db which might me little too low for some but its definately not quiet or unusably low.

I like the website Innerfidelity,or atleast I liked it back when Tyll was still doing the measurements.It have this large database of headphone measurements and you can see that most headphones dont need much volts to play loud.

Why would it hold entire world hostage? Becose if you design amp to play HE6 to 100db or more,then that high gain would be excessive for most other headphones.All this can be solved by either having gain switch or analog volume control,most amps have on or another or dont have enough voltage to handle HE6 so its not problem.

Violectric V281 have crazy 35V rms output capability,but it have 5 gain setting.Most smartphones have about 0.4 V rms output and no gain setting.Please note smartphone often dont play loud enough with low impedance headphones like planars becose their output impedance is high so their 0.4V gets decreased to much smaller value,not becose 0.4V is not enough.

 

[DuxServit]

@March Audio: will you be sending this box to Amir for measurements?

Apologies for my “head-fi cynicism”— but it’s 4 pages of discussion and no measurements. This is the kind of thing vendors do in Head-Fi — whip-up excitement, promise the world, etc. etc.

 

[March Audio]

I meant the noise floor degrades compared to using resistive attenuator,the apparent noisefloor from listener perspective does get higher if the DAC is attenuated digitaly versus using pot to turn it down.There is reason why pots are used when money,space and weight isnt issue.

I do agree digital attenuation is better,thats why I like the idea of this amplifier,the superior reliability and channel matching are winner in my book.My issue is that I think the amp should not have any gain if it wont have gain switch.

With regard to your SPL test,it just confirms what I say,you listen 2db louder with compressed music and 8db more with uncompressed.With HD650 thats like 650 mV rms for 100db peak.HD 800 would be 800mV,the extreme outlier that is Hifiman HE6 would need about 3.2 V for 100db so on unity gain amplifier it would get to only 96db.

Even this ridiculous headphone would play loud enough for you with 2db to spare on compressed music and would fall short of only 4db with more dynamic music.I think designing amplifier around this extreme outlier is bad idea,how many people in the world have HE6? How many people with HE6 plan to use your amplifier?
Becose increasing gain is no free lunch,if you want to satisfy these rare cases,it will be at the expense of majority,I bet there will be many times more users complaining of hiss,particulary the IEM users compared to HE6 owners who would get "only" 96db out of unity gain amplifier.

Its true for full sized open headphones the noise floor would not get audible even if you made your amp with +6db gain but sensitive closed headphones,particulary IEM could make the hiss audible.If you have 30db noise floor in your room and you have closed headphone with 30db isolation at 2 KHz+ frequencies then its like if the noise floor was 0db,and if you play dynamic music with 100db peaks then you need 100db SNR for hiss to be inaudible and with 20- 30 db of digital attenuation with full sized headphones and god knows how much with IEMs,you are absolutely in hiss territory.

Also the higher the gain,the higher the chance of unpleasant experience when one is blasted with loud sound.There was mentioned that crashing Windows or some other software issues could cause the digital volume to be turned full on,even if that wasnt the case,user error is in my opinion much more possible route to this noise blast issue.With +6db gain and Hifiman HE 400S it would blast you with 120db,IEMs would probably explode.

No I am sorry but you have a misunderstanding here. The noise floor does not change with digital volume. It simply does not get higher.

What happens with an analogue volume control is that the whole signal, including that of the noise coming out of the dac, gets reduced. That will maintain the dynamic range until such point that the noise from the dac falls below that of the amplifier after it.

That's all well and good until you realise that the noise from good DACs is below your threshold of hearing by a significant amount.

So even with 3dB of gain nobody as of yet has been able to hear the noise coming out of my dac. So if you did have an analogue pot as volume instead you would gain precisely nothing because you would only be reducing the noise floor down from an already inaudible level.

What you would lose is accurate channel balance and have a mechanical system that will degrade over time and become noisy in itself.