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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!
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)
from the specs we can deduce that it can produce an output voltage of at least 9Vrms (10W into 8Ohms) using V= SQRT(P * R). When driving low impedance headphones (20 Ohms) that voltage will generate 4W. When driving high impedance headphones (300 Ohms) that voltage swing will generate 0.270W. There will be no current limitation because the Luxman can drive 10W into 4 Ohms.
Whether these powers are enough to drive headphones loud depends on their sensitivity. A look online suggests that HD600 (300 Ohms) have 97dB/mW sensitivity and need 63mW to reach 115dB SPL so the Luxman has capacity to deafen you with those headphones. Another quicklook at the Audeze website suggests 1 -4W to drive LCD3s (110 Ohms). The Luxman would give you 0.7W.
I am assuming that the headphone jack is connected directly to the speaker outputs and there is no series resistor.
Hi...thanks for the info.
The Six Moons review mentions a 470 ohm resistor per channel (left/right) in the headphone circuit as the only difference between the headphone and speaker signal paths (the only real reason for my question - just curiosity). How will that affect things?
The 470 ohm resistor will limit the power into the headphones and will make the power delivered less dependent on the headphone impedance. If the headphone impedance was 470 ohms also then half of the power available would be dissipated in the resistor and half in the headphones. For the 300 Ohm HD600 the 9Vrms available will now become 3.5Vrms due to the potential division of 300 and 470ohms (9 * 300/(300+470)) and so the power reduces from the 270mW originally calculated to 41mW (by V^2/R)
For the 20 ohm headphone case the voltage is reduced to 9V * 20/(470+20) = 0.36Vrms and the power becomes 6.6mW (down from 4W!). Again, how loud the headphones go depends on their sensitivity.
Another factor is the source resistance seen by the headphones. If the headphone impedance is not flat with frequency then there will be a non-flat response curve. Damping factor may also play a part - not sure how important it is for headphones. Benchmark media have written several white papers about, in their view, the importance of driving headphones from a low source resistance.
Or hook the speaker outputs directly to the cans...
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
...and down the rabbit hole I go! ; )
I'm trying to feed my curiosity in these things - this is a nice bite to digest.
Yes, the review does imply that...but other than a mention of "overkill power rating", there is no hint of what the headphone output actually is at different resistances. Also, there are no planar-magnetic or electrostatic headphones among the test cans which can present different challenges to a driving amp than dynamic driver headphones.
I received my answer elsewhere...given the information supplied in the published specs and the review, it is not possible to calculate headphone power output (need more info). Thanks.
Electrostatic cans will need a High Voltage or polarizing voltage supply - which requires a different connection.
Given that the unit can drive speakers and headphones, I would think that the 'challenge' of planar cans would not be a great challenge-
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