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Hi,
(I've also posted this over in the Propeller Head Forum - apologies for the duplication)
Not sure if here is the correct venue, but here goes:
I own a Luxman SQ-N100 tube integrated that I purchased to anchor my office system. Rumor has it that it is also an exceptional headphone amp. In order to make some informed headphone choices, I'm trying to understand what the power output would be for headphones of different ohm ratings.
Given the info I've included below, is it possible to calculate headphone power output? ...say for 20, 36, 46, 62, 80, 100, 300 and 600 ohms? I realize that sensitivity comes into play, too, but those ratings are usually available in published specs.
If there is general formula I can apply, I'm happy to do the math. Thanks!
JJ
==
This is a quote from the review whose link I have included if you are interested - it describes the headphone circuit:
"Headfi fanciers will be excited to learn that their ¼" socket taps directly into the SQ-N100's main valve output stage. For ear speaker purposes, the output voltage simply couples through a pair of 470-ohm load resistors to attenuate its strength."
These are the Luxman specs:
Rated output: 12W + 12W (6Ω), 10W + 10W (8Ω, 4Ω)
Input sensitivity: LINE: 150mV, PHONO (MM): 2.2mV
Input impedance 47KΩ
Frequency response 20Hz - 50KHz (within -3 dB)
Total harmonic distortion 0.3% or less (1 kHz rated output)
S/N ratio 90dB or more
Input LINE: 3, PHONO (MM): 1
Output SPEAKERS: 1
Functions Remote control applied (sound volume), head phone output
Tone control (bypass enabled), AC inlet
AC outlet X 2 (non-interactive, total 200W max.)
Circuiting system Mullard type UL connections
Vacuum tubes used ECC83 X 1, ECC82 X 2, EL84 X 4
Power consumption 95 W (Electrical Appliance and Material Safety Law),
71 W (no signal)
Power supply AC 100V (50/60Hz)
Accessories Remote controller, power cable
Dimensions 297W X 162H X 210 (258) D mm
(I/O terminals in brackets, including operating knobs)
Weight 11.5kg
Follow Ups:
The 470 Ohm resistor is a really crappy choice, and you should probably pass on using the headphone jack knowing this. It would have been soooo much better for them to use two resistors per channel as a low impedance voltage divider. With a 470 Ohm series resistor on both channel, you're going to get wonky bass out of most headphones since the 470 Ohm resistors add to the output impedance of the amp.
Having said that, you can build yourself a little box that takes the speaker level inputs and has a proper selection of resistors to pad down the signal. I have seen some companies make similar devices advertised as converting the output of powerful headphone jacks for use with IEM's.
Just to give you an idea of how bad this setup is, let's assume you have some 50 Ohm headphones that are somewhat power hungry. Your amp makes 10W into 8 Ohms, or roughly 8.9V of output. Now we plug in the headphones and we'll assume that the 8.9V of output is still present into the new load of 530 Ohms (it may rise a bit). You now get 0.83V average (this will depend a bit on the frequency of signal going to the headphones) into your 50 Ohm headphones which is 13mW of power :(
If we put a voltage divider on the output that is a 12 Ohm resistor in series with a 4 Ohm resistor, then take the output from the junction of that pair, we'll magically get 100mW and damping won't be an issue.
Back in the day it there was a standard for adding a headphone jack from speaker jacks, and I believe it was a pair of 110 Ohm resistors, but headphone impedances have dropped a lot since then, and just adding series resistance is no longer adequate.
It looks like you will be getting the following for headphone output...
Based on the rated output of 12 watts into 6 ohms, that calculates to 8.5 volts over the 6 ohms load:
Power = (V*V)/R or (8.5*8.5)/6 = 72/6 = 12 watts
For the same voltage output into 502 ohms (or the 470ohm resistor plus a 32 ohm headphone load) you get 143.5 milliwatts.
For a 300 ohm headphone (that would be 470 + 300 = 770 ohm load) you get 0.0935 millwatts.
Assuming my calculations are correct, you are not going to get much output for headphones. IMO, the 470 ohm resistor should be changed to a lower value to be able to drive a good set of headphones.
To be practical, the 470 ohm resistor should be no higher than 47 ohms. With that value you would get 0.911 milliwatts for 32 ohm headphones and 207 milliwatts to drive a 300 ohm headphone. Those are much more realistic power output values for decent headphone listening.
If you are going to go with a nice set of planar magnetic headphones you will likely need even more power. Doubling the output power from the headphone jack can be done by halving the proposed internal resistor from 47 ohms to 28.5 ohms (or something close to that value).
Ed
We don't shush around here!
Life is analog...digital is just samples thereof
Thank you for the calculations - appreciated. The math is over my head...but the calculated outputs seem a little low based on the Six Moon review. The SQ-N100 reportedly drove several top-tier headphones (Audio-Technica WHT-5000, Sennheiser HD800, AKG K702, Grado PS-1000) with ease and bested several well-regarded headphone amps.
Are there other variables that I'm missing? It's entirely possible that I'm asking a question whose answer I don't have the background to fully understand.
Can be viewed from different perspectives. If you tend to listen at low volume levels, low output headphone amps will serve the purpose well but if you tend to listen at higher volume levels, the lower output is an issue.
A 470 ohm resistor in line is a bit high but, from a design point, you don't know what headphones were used to test the output or what type of volume restriction was used in its design. A headphone output jack could very well be designed with safety in mind and the power output limited so high output levels can be avoided (and human hearing protected).
People could also plug in in-ear monitors, which are very sensitive, and the 470 ohm resistor makes perfect sense with these type of headphones. A user could also choose Audeze LCD-3 headphones and the output would not be sufficient with those headphones.
If you drop that resistor to 47 ohms, like I suggested, the output of approximately 1 watt can be very high power for many headphones. If you own the aforementioned Audeze headphones, 1 watt may still be a little low powered.
It is a matter of what is enough. I own a Schiit Lyr 2 headphone amp and it is capable of 6 watts/ch at 32 ohms and that is a lot. The output circuit has a sensing circuit to prevent over powering headphones but the amp is capable of lots of power with every headphone that I've tried. The owners manual makes a statement about taking care with volume settings due to the high power.
I have several vintage pieces of audio gear that uses a load reducing resistor like your amp uses and I don't recall any of them using a value as high as 470 ohms. All of these vintage amps have much higher power output than 12 watts/ch.
As a result, I was a little surprised by the 470 ohm rating for the power reducing resistor. Considering the fact that its capable of 12 watts into 6 ohms, dropping the output with a 470 ohm resistor is a bit of overkill but like I already said you do not know what they were designing for.
Have you tried any headphones with this amp? What type of volume level are you used to listening to?
Ed
We don't shush around here!
Life is analog...digital is just samples thereof
I wouldn't consider myself a head-banger...maybe occasionally ; ) The majority of my listening is orchestral, small group jazz, and 70s funk and rock. On the whole - very moderate volumes.
I have Shure SRH-1540 headphones and Shure SE535 earphones...both very easy to drive. I chose them because they perform well directly out of my iPhone, iPad and MacBook or paired with a DragonFly Red. I travel quite a bit - my "road kit". On the road, TIDAL is my music source.
I've tried both 'phones with the Luxman. Definitely an improvement over the DragonFly (although it's hard to separate the DAC and headphone amp variables since I'm using a different source with the Luxman). My perception of "better" is based on improved fullness with both. The SRH-1540 volume is very comfortable at ~9 o'clock, fuller and louder at 10 o'clock, and uncomfortably loud at 11 o'clock; the SE535, a little less.
I attended a CanJam headphone conference earlier this year and decided I'd like to own an open-backed headphone for home use...either 1) Focal Elear, 2) Sennheiser HD800/800S, or 3) Audeze LCD-X or LCD-3. Since I intend to pair them with the Luxman, this thread is background to [hopefully] an informed purchase. Ultimately, since the Luxman is small, it will be possible to take it somewhere and actually audition all three cans before I purchase...not sure where, though.
Someone else suggested connecting headphones directly to the speaker taps. Thoughts (relative to my 3 possible purchases)?
I appreciate the feedback...thanks.
You definitely want resistors in line to drop the output a bit. You may not need the resistors for the HD-800 headphones but I wouldn't try it on the other headphones.You also have the problem where you do not want to hook the two negative speaker outputs together. You want a resistor between the negative speaker output and the common negative hookup on the headphone. I believe most amplifiers would balk at shorting the negative speakers outputs together.
Single ended headphones have individual hot connections for the left and right sides but share a common negative hookup. You don't want to try hooking that to your speaker outputs. You may get away with that on some amps but I don't think you want to fry anything. Before you hook the grounds together make sure it won't damage anything.
Ed
We don't shush around here!
Life is analog...digital is just samples thereof
Edits: 07/12/17
" I believe most amplifiers would balk at shorting the negative speakers outputs together."
So far I have seen very few that the individual outputs are balanced to ground. I happen to have one, and DIY amps with 0-4-16R output taps have grounded the 4R and used the secondary for some cathode fb. With SS amps, if you want to bridge them, you count on the negative already being tied together and connect only to the positives.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
In order to keep things simple, let's assume there are only four electrical parameters. They are voltage, current, resistance and power. They are related to each other by equations known as Ohm's Law. The following three equations are used for calculating power:
Power = Voltage x Current
Power = Current 2 x Resistance
Power = Voltage 2 / Resistance
Therefore, in addition to knowing the resistance of the headphones in ohms, you also need to know either the current flowing through the headphones or the voltage applied to the headphones in order to calculate power.
For example, if you have 600-ohm headphones and your headphone amplifier applies 2-volts to the headphones, power would be calculated as follows:
Power = 2 2 / 600 = 4 / 600 = 0.00667-watts = 6.67-miliwatts
Another example: Suppose you had 32-ohm headphones with 1-volt applied.
Power = 1 2 / 32 = 1 / 32 = 0.0313-watts = 31.3-miliwatts
I hope this helps.
Good luck,
John Elison
John, thanks for this - appreciated! The calculator is helpful, too.
If I'm reading your info correctly, it doesn't seem that I have enough information on the Luxman to calculate what the power output would be at any given resistance (headphone ohm rating) - am I correct??? Apologies if I'm missing something - this stuff is Greek to me.
BTW...I'm sure you don't remember, but we met years ago at one of MuzikMike's Ribfests - I had a blast; miss him.
No, there's not enough information given on the Luxman to calculate power at the headphone output, but most components with headphone jacks have enough power to drive just about any headphone. Therefore, I wouldn't worry about it.
What headphone are you planning to use? I own three headphones. I bought the original Grado HP1 headphones back in 1991 and they still work just fine. I bought Grado RS-2 headphones in 2003. Then, just a couple of months ago I bought some Koss electrostatic headphones and they sound awesome.
Yeah, Muzikmike's Ribfests were a lot of fun. I miss him, too.
Best regards,
John Elison
Ok...so, at least on the surface, I understand what it takes to use the calculator you supplied. Thanks.
I own a pair of Shure SRH-1540 headphones that don't really need a lot of power to make decent sound...with the Luxman however, they are much more full-bodied and articulate.
I attended a CanJam Conference this past March (NYC) and came away interested in the Audeze LCD-X, LCD-XC, LCD-3, and the Focal Elear. I've since become curious about the Sony MDR-Z1R. My budget will be up to ~$1500 new or used.
JJ
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