LDM+ vs PA2V2 vs CMOY
Nov 10, 2006 at 2:24 AM Post #17 of 21
Quote:

Originally Posted by jcx
you really should learn to do basic amp/headphone #s

read http://headwize.com/articles/hearing_art.htm twice, once to avoid hearing damage from listening too long at too high an Average Loudness and the again to find the very high peak SPL of live music which your amp/headphone combination should be able to reproduce without clipping - most people are surprised by how much Headroom is needed



http://forum.lowyat.net/lofiversion/...p/t315593.html

the LDM+ apparently uses this op amp:

http://datasheets.maxim-ic.com/en/ds...A-MAX9724B.pdf

if you can read the data sheet you can get a very good idea of the LDM+ probable performance limit

while potentially not as dire as I initially thought because the maxim op amp uses a sw cap DC-DC supply inverter that doubles the available supply voltage, you need to work the details to get a reasonable performance estimate

despite the doubled supply voltage the story for driving Grados remains rather poor

looking at the 3V “OUTPUT POWER vs. LOAD RESISTANCE” graph it is clear to an engineer that the max9724 is in fact current limiting when trying to drive a 32 Ohm load like the Grado

taking ~27 mW at 32 Ohm load from the graph a fair assessment would multiply by 1.2**2 to estimate the 3.6 V supply behavior => 39 mW into 32 Ohms at 10% distortion, equivalent to 1.25 Vrms or 3.5 Vpp

so despite the doubled supply the max9724 is current limiting at a level that gives the same power limit as a iPod Shuffle using a split 3.6 V supply into 32 Ohms

Conclusion, my statement that the LDM+ is likely no better driving Grados than a Shuffle seems to still stand on fundamental technical grounds


Grados are generally 98 dB spl @ 1 Vrms, 1.25 Vrms ~= +2 dB re 1 Vrms

98 + 2 = 100 dB spl at clipping driving a Grado from a supply split 3.6 V battery amp like the iPod, and as a coincidence due to the max9724 current limit, the same number applies to the LDM+

The LDM+ would give higher power and desired dynamic headroom with higher impedance cans, the high impedance HD600/650 will actually be driven to higher spl levels than the Grados

But the best impedance match for the LDM+ is for 70-120 Ohm headphones


with 32 Ohms, the LDM+ 100 dB at clipping with the Grados doesn’t make it in my book

Ohsa 8 hr exposure limit is 90 dB, many people may listen at this average level (even if they probably shouldn’t)

Dynamic music can easily have +20 dB peaks, 90 + 20 = 110 dB

check out where 110dB is on the Headwize article chart of musical sources

The simple technical spec based conclusion is that a LDM+ will not drive a Grado to realistic spl, it will clip, possibly frequently

I can’t see advocating buying an Amplifier that can’t potentially drive the headphones to at least 110 dB without clipping

No you don’t need the capability often or even at all with some genres of “music” – much pop is already compressed to death, some with only 6 dB peak to average level will deafen you at average loudness that never clips even a LDM+ with Grados

http://en.wikipedia.org/wiki/Loudness_war

but it aint audiophile source,

LDM+ with Grados don't rate as a audiophile system - since it don't have HeadRoom
 
Nov 14, 2006 at 9:10 AM Post #18 of 21
does anyone know how the PA2V2 compares with a headroom total airhead? i've been using my airhead with ER4Ps but still unsatisfied with the bass. i plan on eventually getting a supermacro but need something bassy in the meantime. would the pa2v2 be a good choice?

thanks
 
Nov 14, 2006 at 9:19 AM Post #19 of 21
Quote:

Originally Posted by jcx
http://forum.lowyat.net/lofiversion/...p/t315593.html

the LDM+ apparently uses this op amp:

http://datasheets.maxim-ic.com/en/ds...A-MAX9724B.pdf

if you can read the data sheet you can get a very good idea of the LDM+ probable performance limit

while potentially not as dire as I initially thought because the maxim op amp uses a sw cap DC-DC supply inverter that doubles the available supply voltage, you need to work the details to get a reasonable performance estimate

despite the doubled supply voltage the story for driving Grados remains rather poor

looking at the 3V “OUTPUT POWER vs. LOAD RESISTANCE” graph it is clear to an engineer that the max9724 is in fact current limiting when trying to drive a 32 Ohm load like the Grado

taking ~27 mW at 32 Ohm load from the graph a fair assessment would multiply by 1.2**2 to estimate the 3.6 V supply behavior => 39 mW into 32 Ohms at 10% distortion, equivalent to 1.25 Vrms or 3.5 Vpp

so despite the doubled supply the max9724 is current limiting at a level that gives the same power limit as a iPod Shuffle using a split 3.6 V supply into 32 Ohms

Conclusion, my statement that the LDM+ is likely no better driving Grados than a Shuffle seems to still stand on fundamental technical grounds


Grados are generally 98 dB spl @ 1 Vrms, 1.25 Vrms ~= +2 dB re 1 Vrms

98 + 2 = 100 dB spl at clipping driving a Grado from a supply split 3.6 V battery amp like the iPod, and as a coincidence due to the max9724 current limit, the same number applies to the LDM+

The LDM+ would give higher power and desired dynamic headroom with higher impedance cans, the high impedance HD600/650 will actually be driven to higher spl levels than the Grados

But the best impedance match for the LDM+ is for 70-120 Ohm headphones


with 32 Ohms, the LDM+ 100 dB at clipping with the Grados doesn’t make it in my book

Ohsa 8 hr exposure limit is 90 dB, many people may listen at this average level (even if they probably shouldn’t)

Dynamic music can easily have +20 dB peaks, 90 + 20 = 110 dB

check out where 110dB is on the Headwize article chart of musical sources

The simple technical spec based conclusion is that a LDM+ will not drive a Grado to realistic spl, it will clip, possibly frequently

I can’t see advocating buying an Amplifier that can’t potentially drive the headphones to at least 110 dB without clipping

No you don’t need the capability often or even at all with some genres of “music” – much pop is already compressed to death, some with only 6 dB peak to average level will deafen you at average loudness that never clips even a LDM+ with Grados

http://en.wikipedia.org/wiki/Loudness_war

but it aint audiophile source,

LDM+ with Grados don't rate as a audiophile system - since it don't have HeadRoom



Well now we know that the LM4881 of the PA2V2 will rate as a audiophile system 'cause it has the heardoom
tongue.gif


(edit- ^funny typo^ )
 
Nov 14, 2006 at 5:53 PM Post #20 of 21
quick catch, I had fixed it before I saw your post, I guess I need to use spell check for everything

of course headroom isn't the only consideration, but I would consider it a minimal requirement to meet, an amp that is clipping (either voltage swing limited or output current choked) is a poorly chosen amp for the job
 
Nov 16, 2006 at 4:21 AM Post #21 of 21
I hadn’t realized iPods wasted so much battery V, my previous comments assumed they could swing within a few 10 mV of the battery V

Some actual measurements (Tek TDS3054, not caled this year, but earlier), 48 KHz 16 bit .wav, 1 KHz sine and triangle @ 0 dB



iPod Shuffle, 1st Gen, V1.13

1.67 Vpp unloaded, 1.58 Vpp with 33 Ohm load

=> 10 mWrms into 33 Ohms



iPod Nano 1st Gen, Rockbox

3.04 Vpp unloaded, 2.34 Vpp with 33 Ohm load

=>20 mWrms into 33 Ohms, no clipping

@ 10% distortion you can get ~ 30 mW (-24 dB 3rd harmonic from the Tek scope fft @ +2 dB volume step in Rockbox)



The Shuffle is a particular surprise, how come nobody touting its superior sound vs other iPods mentioned that it has 3 dB less output into 33 Ohm headphones like those distributed with it – is it possible that there is a software volume limit I missed?

The Shuffle’s output does go down to DC which with low Z headphones gives a few octaves more bass compared with roll off of the too small coupling cap on the other iPods


Comparing with these lower measured numbers for the iPods gives a better range of improvement possible with the LDM+ - assuming the LDM+ connects the MAX9724 to the LiIon battery directly

Under that assumption the LDM+ could give a small volume step of +1.6 dB vs the Nano’s output for no clipping, at 10% distortion the advantage is even less ~ +1.2 dB

So lacking measurements of the LDM+, I would say there is a little headroom advantage using a LDM+ vs a iPOD Nano – so small a difference that I can’t say which way real world measured comparisons would go, the difference is tiny

The LDM+ could be chosen for the low bass drive vs a cap coupled output iPod like the Nano, the LDM+ has a definite volume/headroom advantage over what I measured from my Shuffle

After taking measurements I watched the scope’s ppk measurement while listening to Grado SR60 headphones, back calc gives ~ 80-85 dB as the average spl that was comfortably loud, the highest V peak was <500 mVpp for acoustic/vocal music

Percussion was definitely “background” in this track, so it could readily be listened to with even the Shuffle driving the Grados, I didn’t quickly find anything in my collection at work with up front percussion, snare hits can require +20 dB power which is beyond the iPods or the LDM+ with the low Z and low efficiency Grado headphones when listening at 85 dB average level
 

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