LPA-2

STEREO – HEADPHONE AMPLIFIER

LINE SIGNAL AMPLIFIER

                        Pic 1. LPA-2                                                  Pic 2. LPA-2 with SIA-5.V2 module

The LPA-2 is a High-End headphone module for demanding application in the medium and high power range, available in various versions. It is universally applicable, so that practically all headphones with an impedance of 16 Ω... 2 kΩ can be driven extremely distortion-free. The largest amount of power, over 2 x 1200 mW, is delivered by the LPA-2 module, with a headphone impedance between 22..100 Ω. The high current delivery ability of the fully DC voltage-coupled unit using the most modern components also allows the parallel connection of several sets of headphones, depending on their impedance.

The low resistance outputs provide an exact damping for the connected headphones. With its compact construction, this module can be retroactively built into many devices. The extremely

low, flat module unit height (only 16mm) means that it can easily be installed into just 1 section of an existing 19" rack. The integrated stereo volume control is in each case a selected ALPS-version with a 60 dB control range. Available either in the flat version with a continuously variable volume control, or in a rest work variant with 21 incremental volume steps, as well as intermediate positions too. The excellent synchronization between both channels is, during normal working conditions, from -40.. 0 dB less than typ. 1 dB, and -30.. 0 dB < 0.5 dB in the control range. An additional basic amplification can be enabled by using jumpers in 3 stages in order to adapt the headphone sensitivity : +1 dB, +6 dB, +12 dB ranges (- 6... +18 dB with the SIA-5 board) A special slot permits installation of an optional new miniature symmetric SIA-5 ore the newest SIA-5.V2 ultra low noise board to achieve excellent sound performance and a high impedance 2 MΩ stereo input. 10 MΩ impedance for the SIA-5.V2.

For the integration of the SIA-5 board in the LPA-2, jumpers are provided for module adaptation. The unmatched low noise and the excellent frequency and phase response allow the LPA-2 to  operate additionally as an asymmetrical stereo amplifier with level control for particularly low ohm loads or long cables. Distribution amplifiers (1 stereo signal via several channels) can be built up easily with cascades of several boards and flat ribbon cable connection technology. Because of these features headphone distribution amplifiers with one stereo input and several outputs for different musicians with in each case individually adjustable volume controls are possible. The LPA-2 resists short circuits to ground on both outputs without damaging the unit. The LPA-2 is fastened using a 7mm drilled hole. The LPA-2a with incremental potentiometer needs a 9mm hole for mounting on the front panel. The shaft diameter of the respective potentiometers is 6 mm.

The input signals, output signals and the power supply are connected via a 14 pole plug on the

board. The symmetrical power supply is usually provided by the device to be reequipped, as supply voltages already often exist within it. If an internal power supply is not at hand, suitable mains adapters (PWS-04a, SMPS-14T and SMPS-24T) are available. 0.5 m of flat ribbon cable and 14 pole plug connector are included in delivery.

AUDIO QUALITY

The extremely low distortion at 1 kHz load with both channels in simultaneous operation display similar measurement curves. The steps of the measuring curve result from the amplifier switch-over of the Audio-Analyzers only. The distortion performance (THD k2..k9) was registered at 1 mW to 1500 mW at 62 Ω load. The distortion levels for higher headphone impedances are even lower and hardly detectable!

The left scale shows the distortion degree in %, the lower scale displays the corresponding output power in mW. The green marker shows the total distortion at 2 x 500 mW of 0.00006% (-123 dB).

TECHNICAL DATA (measured with +/-19 volts of supply voltage, +6 dBu level and 0 dB gain, if not otherwise declared, without SIA-5 input board (without symmetrical inputs)

Power supply :                                    +/- 12...+/- 19 V (max. 1 mV Noise)

Power consumption no-load :         32 mA, with additional SIA-5 : 52mA

Max power consumption:                  230 mA max. at 22 Ω, with additional SIA-5 : 250 mA max. at 22 Ω

Gain :                                                    - 60...0 dB (Incremental poti with 21 steps or stepless, typ. < 1dB matching from - 40..0 dB)

Input impedance :                              10 kΩ unbalanced, 2 MΩ with balanced input (SIA-5 integrated)

Input voltage max. :                           +23,5 dBu

Output impedance :                           < 2 Ω

Output voltage max. :                        + 24,0 dBu (with gain > 1 dB)

Dynamic, full volume:          139 dB at 300 Ω, 138 dB at 68 Ω, with A-weighting filter typ. > 140 dB !!!

Distortion + Noise (THD + N) :         20 Hz...22 kHz < 0,0005 % at 2x 500 mW, 33 Ω

THD-Distortion 1 kHz (k2..k9):           < -115 dB at half power, typ < -120 dB

Intermodulation 250/8kHz :              typ. 0,0001 % at 2x 500 mW, 100 Ω load

Frequency response :                       0 Hz...22 kHz less than ± 0,01 dB, 0 Hz..100 kHz <± 0,2 dB at 100 Ω

Large signal bandwidth:                  0 Hz...> 180 kHz at 100 Ω

Slew Rate :                                          typ. 20 V/μsec

Crosstalk L < > R:                               110 dB at 1 kHz 100 dB at 10 kHz

Max. power at THD (k2-k9) < 0,1% :

Output noise

with following gain :                                                  + 0 dB                    + 1 dB                    + 6 dB                    + 12 dB

Noise unweighted (20 Hz...22 kHz eff.) :          < - 116,0 dBu       < -116,0 dBu        < - 113,5 dBu       < - 109,0 dBu

Noise weighted (A-weighting eff.) :                  < - 119,0 dBu       < -118,5 dBu        < - 116,0 dBu       < - 111,5 dBu

Noise weighted qp (CCIR 468-4) :                   < - 110,0 dBu       < -109,5 dBu        < - 107,0 dBu       < - 102,5 dBu

LINEAR AMPLIFIER SIA-5.V2 module with extremely low noise symmetric input

Pic. 3 SIA-5.V2

SIA-5.V2 is an universal, professional 2-chanell desymmetrization and adjusting amplifier in mini form based on instrumentation amplifier (see also picture 2). With this module asymmetrical inputs can be adjust at symmetrical studio equipment. Especially important in development was extremely low noise (dynamic at gain 1: 135 dB !) and extreme low distortion. Phase characteristic throughout  the 20 Hz...20 kHz is under ± 0,2º. Symmetric inputs of SIA-5.V2 achieve typical CMRR equal 3000 / 1 or - 70 dB ! Amplifiers are suitable to adjust for example devices with -10 dBv inputs (like PC-Sound Cards) to outputs from studio devices with +4 dBu or +6 dBu standard level. Output level and maximal possible output voltage (Headroom) remain constant in symmetrical and asymmetrical configuration.

Input impedance : ................................................ 10 MΩ symmetric, 5 MΩ asymmetric

Max. input voltage : .............................................. + 24,7 dBu

CMRR : ..................................................................... > 60 dB at 1 kHz (typ. > 70 dB), > 60 dB at 10 kHz

Max. output voltage : ........................................... + 24,7 dBu an 10 kΩ

Output impedance : ............................................. < 50 Ω

Lever difference left < > reght ............................. typ. < 0,01 dB

Nonlinear distortions 1 kHz (THD k2..k9) :.......... ≤ 0,00004 %, ≤ 0,00005 % bei + 18 dBu

THD+N (THD + Noise 20Hz..20kHz) : .............................. ≤ 0,00024 % von 20 Hz..10 kHz ≤ 0,00022 % bei + 18 dBu ≤ 0,00018 % bei + 23 dBu

THD+N 1 kHz +23 dBu an 600 Ω : ...........≤ 0,00012 % (-118,0 dBu) !!!

Intermodulation 60 Hz/8 kHz : .............................. ≤ 0,00040 %

Intermodulation DIM100 : ..................................... ≤ 0,00030 %

Lake People Electronic G100 versus MTX Monitor V3b-1

Following you can see very interesting comparison between very well know and very good headphone amplifier Lake People Electronic G100 and another little bit worse as LPA-2 headphone which is implemented in MTX Monitor Controller preamplifier from Funk Tonstudiotechnik (http://funk-mtx-v3-monitor.blogspot.de). Because of LPA-2 has some parameters even better as audio analyser it is very difficult to perform such measurements and such result would be not visible in this diagram.

MTX Monitor V3b-1

Measurement at 50 mW

THD+N  measurements  ware performed in range of 50 Hz to 10 kHz with 40 kHz measurement range. This means that in a limited frequency band (50Hz...20kHz) parameters would be about 1-2 dB better but it gives us information about the quality of the device and not only about performance in the audible band. Therefore also higher harmonic frequencies of G100 distortions up to 10th harmonic are clearly visible. Measured each time on average load of 150 Ohm. Green curve G100, blue MTX-Monitor.V3B-1. In fact typical power at normal listening is between 0,1....50 mW. All other special circumstances occur in specific cases.

It should be noted very smooth and low noise carpet at MTX without any picks. At 20 mW, which is typical output power, G100 generate many harmonic distortion of main frequency where seventh is a very unpleasant audible. MTX has no such harmonic frequencies at all. Also higher harmonic of 1 KHz frequency at G100 are high where MTX has no any harmonic  above 7th at all.