Aphex 124A的電壓轉換器(Audio Level Interface http://www.aphex.com/124A.htm)，專門用來對付家用跟專業用器材匹配的問題。到手了之後，哇，聲音豁然開朗，很多細節都跑出來了，鋼琴聲也對了；果然即便用相同的DAC，後端搭配的電路不同，聲音品質也有天壤之別。
124A Audio Level Interface



MANUAL:http://www.aphex.com/wp-content/upl...MANUAL-124A.pdf
The Aphex Model 124A Audio Level Interface is designed to allow use of -10dBV consumer hi-fi equipment with +4 or +8dBm professional / industrial / broadcast audio systems. It provides an extremely clean, reliable two-way buffer so both systems can operate at maximum performance levels, matching impedances and operating levels.


FEATURES
Matches Consumer IHF equipment to Professional Equipment
Dual Buffered Interface
Transformerless Outputs
Servo-Balanced Inputs and Outputs
Recessed Controls
Pushbutton 600 Ohm Input Termination
Clip Indicator
Self Powered
Superb Signal Quality

APPLICATIONS
Two-way interface amplifier for connecting any unbalanced device such as a cassette deck, equalizer, CD player or DAT deck to the IHF inputs and outputs. The balanced inputs and outputs go to a studio console, patchbay or other line level equipment. The different gains and impedances are matched for optimal performance.
Line driver. The servo-balanced input and output stages of the 124 can be used as a very effective line driver for long lines. The output stage provides a short-circuit proof, low impedance source that will be relatively unaffected by the impedance of the cable. Gain may even be taken to boost signal level. In this application, either the unbalanced IHF or balanced high level inputs may be used. For the latter, the IHF inputs and outputs are simply jumpered.
Signal splitter. The 124 may be used to provide two high quality balanced outputs from a single unbalanced mono signal A"Y" connector is used to split the incoming signal to each of the IHF unbalanced inputs.
IHF distribution amp. The very low output impedance of the 124 allows it to drive a considerable number of unbalanced devices such as cassette decks, VTR's, power amps, etc. Balanced or unbalanced inputs can be selected by patching the various inputs and outputs.
PERFORMANCE
Aphex products are well known for their audio performance. The 124 is no exception. Inputs and outputs are transformerless, for wide, flat frequency response and perfect square waves to preserve transients. Hum and noise rejection are very high while the noise and distortion are almost non-existent. The 124 is so clean it is a perfectly transparent interface for digital equipment.

Two-Way Buffering
The 124 is actively balanced and buffered in both directions, with very low output impedances. A more expensive type of balanced input circuit is used for even higher hum and noise rejection. In addition, all inputs and outputs are carefully filtered for freedom from RF interference.
Some other devices are passive in one direction, simply using resistors to lower level from +4 to -10. The passive circuitry unbalances the input, eliminates all common-mode rejection allowing for hum and noise pickup, and presents a rather high impedance at the -10 output, permitting even more noise to enter the system.

Servo-Balanced High Level Circuits
Although more complex and costly, servo-balancing has many advantages over conventional balanced circuits. On the inputs, it means that high common mode voltages, such as induced hum from a nearby AC line, are compensated for, preserving headroom that is sacrificed in other devices (balanced input overload is greater than +30dBm with common mode input voltage tolerance of over 200 volts rms). The input impedance of 100K Ohms allows bridging over 600 Ohm balanced or unbalanced line with negligible loading effects. Front panel switchable 600 Ohm load allows for input line termination when required.
On the outputs, servo-balancing means that the outputs may be used balanced or unbalanced (single-ended) at any time by simply grounding either unused pin. The servo compensates for the voltage loss on one side so there is no 6dB loss of level as with other systems. The outputs are also short-circuit proof, so nothing is damaged if the wrong pins are grounded. Output impedance is very low so long lines are driven effortlessly. A front panel indicator will flash red when the balanced output level is 5dB below clipping.

Compact Package
The 124 is housed in an all metal package which is compact and self-powered. It may be attached to its dedicated piece of equipment; rack mounted singly or in pairs using the optional rack mounting kit.


SPECIFICATIONS - Aphex Model 124A Bidirectional Audio Level Interface

AUDIO
Bandwidth 5Hz - 100 kHz (+0, -0.5dB)
Dynamic Range 99 dB
THD 0.005
Channel Isolation > 70dB
CMRR (typical) > 45 dB
INPUTS
IHF Input Connectors RCA Jacks
IHF Input Impedance 18 k Ohms
IHF Input Level -10 dBV; peak +15dBV (ref. 1V)
Balanced Input Connectors XLR 3-pin Female
Balanced Input Impedance 100k Ohms with front panel 600 ohm termination switch
Balanced Input Level +4 dBm (+8dBm via internal jumpers); peak +30 dBm
OUTPUTS
IHF Output Connectors RCA Jacks
IHF Output Impedance 150 Ohms
IHF Output Level -10 dBV, peak +18dBV (ref. 1V)
Balanced Output Connectors XLR 3-pin Male
Balanced Output Impedance 65 ohms
Balanced Output Level +4dBm Front panel adjustable ± 6dB, peak +25dBm
OTHER SPECIFICATIONS
Power Requirements 100, 120, 220, OR 240 VAC, 50-60Hz
Dimensions 1.75"H x 8.25"W x 7.25" D (44.5mm x 209.5mm x 184.2mm)
Net Weight 3.5 lbs (1.6 kg)