March Audio HPA1

[Headphonaholic]

With no volume control ouside the computer I think the bigger issue is trusting the host OS not screw something up and start blasting at 0dBFS.

I can't say I have ever had this happen. I use the volume on my computer to control the speakers I use with it, been doing that for years. At worst if windows crashes in the right way sounds might get stuck playing. I've had that happen before but it was at the same volume it was at before.

 

[maverickronin]

Again I have not found this an issue. Been using computer audio this way for literally years. I use Roon and J River. They just dont do this.

I wouldn't expect Roon or Jriver (just playing audio) themselves to do that. I use foobar for straight music playback and have never had that problem with it. It's everything else in the background, especially if DAC1>HPA1 chain were set as the primary sound device. It's not uncommon for games or video players to output garbage at 0dBFS when they crash or for random applications to mess with the system volume.

If you have something else as the primary and only output to the DAC1 chain via WASAPI or something from a good audio player I wouldn't expect any issues but that limits it's use to specific known-good programs.

 

[Thomas savage]

When you have no fucking idea what you're talking about, you should start by posing questions in a much more polite manner.

Keep it friendly mate we don’t want to screw up Alan’s thread with unpleasant back and forth .

 

[March Audio]

I wouldn't expect Roon or Jriver (just playing audio) themselves to do that. I use foobar for straight music playback and have never had that problem with it. It's everything else in the background, especially if DAC1>HPA1 chain were set as the primary sound device. It's not uncommon for games or video players to output garbage at 0dBFS when they crash or for random applications to mess with the system volume.

If you have something else as the primary and only output to the DAC1 chain via WASAPI or something from a good audio player I wouldn't expect any issues but that limits it's use to specific known-good programs.

well, you have your solution dont you Dont mix your games machine with your hifi.

This is all a set up issue and all avoidable.

 

[Grave]

With 32 or 64 bit volume control it's really a non issue.

Remember analogue controls are not perfect either. Pots have serious issues with balance and will degrade over time becoming noisy. Switched resistor is better but still not perfect. PGA will degrade performance also.

An additional thought, how do you think music is mixed (predominantly) these days?

Sounds good to me.

 

[Thomas savage]

A properly implemented digital volume control seems like the least worse way of going about things to me. Iv never heard noise variations from a digital volume like I have from some pots.

 

[maverickronin]

well, you have your solution dont you Dont mix your games machine with your hifi.

Well, not if you want your games to be hifi too...I've got one setup at my desk that I use for everything. Your stack should work great for straight hifi, but I think people should be aware of the potential problems in mixed use situations.

I agree with you on digital volume control in general though. I keep the pots on my Stax amps all the way up and use my ADI-2 DAC's digital attenuation but it sidesteps the above issue by being outboard.

 

[rajapruk]

What is the SNR of the dac?

 

[trl]

Too bad it's Australian, will cost an arm and a leg just to get it to Europe

If we really insist, they will move the production to China/HK, as there is free postage around the globe.
Actually, might not be a bad thing to do that, but not sure the Q&A would be the same.

 

[derp1n]

Thanks for answering btw

 

[Pillars]

 

[Veri]

What is the SNR of the dac?

109.3dB is what the prototype screenshot claims

 

[Jimmy]

Just as a suggestion, since there are workarounds for not having volume control (using a preamplifier f.e.), you could include one in the design that could be bypassed by switches/jumpers.

I'm talking from my personal experience, but I would never buy a headphone amp without volume control or one with button controls (and memory). Sometime ago I listened accidentally to full volume with headphones and took a week to recover normal hearing condition, so never again I would trust such system on a non volume limited device (like a phone or mp3 player).

 

[Veri]

I don't think the volume control is a big problem. Personally.

 

[Graph Feppar]

I have been having an interesting discussion regarding gain with the beta testers of the prototype.

My advice is to make the gain as low as possible,I belive this design philosophy of needing to make the amp voltage high enough to play even the most inneficient headphones to ear damage levels 110db+ is not good.

I would dare to assume that 99% of all people would not need more than 2V rms,even HD650 a high voltage requiring headphone does 102db at 800mV rms,the HD800 does 102db at 1 V rms... making the amp have more voltage gain than necessary is bad becose then you must digitaly attenuate the DAC by huge amount.

I listen with peaks at max 92db,even if I had some uber lightly compressed highly dynamic music,I would not need more than 100db.The vast amount of time,I listen with HD650 at 92db peak,that is I really only need 250 miliVolt rms,that means I am turning my DAC down by 18db or more with amplifier that have zero gain.You trow +3 or +6db gain,that is even more digital attenuation.If I have kick ass 110db THD+N DAC,in practice its 80 to 90db becose I need the massive attenuation becose in reality I need small voltage and 2V rms is already big overkill.

I understand this desire to please everybody,what about those people who are slightly deaf,listen to some obscure ultra dynamic music and at the same time use most inneficient headphones and some crap DAC with low 1V rms output.You can make amp like that so even in most extreme combination of circumstances,nobody will ever complain of low output voltage,but this comes at the expense of vast majority of the users who will need to digitaly attenuate their DAC so strongly that they will perform like cheap motherboard integrated 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.

 

[March Audio]

Whilst I do agree with you to a large degree, I was a noise officer in a previous role so hearing protection is a important issue to me, people do have to take some responsibility for their usage. Having said that, the desire of some to have literally watts of output from their headphone amps bemuses me.

Going from 3dB to 6dB gain is a modest increase and does provide the widest compatibility, which is important for any product. Also, don't forget that not all music is mastered to, or spends much time hitting 0dB. Some feedback was that a little more gain would be useful. You can look at the innerfidelity website to get a wider view of headphone sensitivities.

With 32 or 64 bit dithered volume controls, a 32 bit data path, and noise floors as low as they are on any good dac, reducing volume digitally is just a non issue. If you can't hear the noise floor of a dac you have lost nothing. Everybody tells me the noise floor is utterly silent.

Output impedance is indeed important. Amir has measured the prototype at 0.8 ohms. Output current is +-150mA.

 

[Graph Feppar]

With 32 or 64 bit volume controls and a 32 bit data path reducing volume digitally is a non issue.

That is only half true.Yes,32bit ADC can attenuate alot before it starts trowing away music containing bits.The problem is that the THD+N of DAC degrades as its being attenuated digitaly.Whats the point of great performing amplifier if its performance is wasted becose the weak link in system is the DAC whose THD+N is turned to shit becose its turned down by 20 - 30db due to high gain of amplifier its connected to?

I like the idea of amplifier without volume control,but if this is combined with high gain and no gain switch,this will result in poor overall THD+N for 99.99% of all users except one or two 90 year old gentleman with ears stuffed full of wax like the "candle" scene from Shrek,with Hifiman HE6 and total amount of functional hair cells inside their cochlea smaller than sum of all good jokes ever told by Amy Schumer.

 

[March Audio]

No.

The noise floor of of a dac remains the same. It does not degrade. Distortion on many dacs is actually higher at 0dB.

What reduces is dynamic range/ signal to noise ratio. This is also actually true of analogue volume controls when you turn it down enough to hit the inherent noise floor of the amp.

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

 

[elira]

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

 

[Graph Feppar]

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.