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audio-gd DAC Head Amp Pre Amp Power Amp DIY Kits Cables

Neutral Flavor DACs+Head Amp
Dedicated Head Amp

FUN  NFB - 12 NFB-5 NFB - 10WM C-2.1 Phoenix


Headphone Amplifier With Preamp output
Applies ACSS

Price: USD350 (Exclude shipping cost)
Weight: Approximately 5kg
Dimension:  W240 X L300 X H80(MM)
Accessories: Stock power cable X1

Summarize: Fully discrete amp without any OPA (While ACSS input) , couple caps ,non- feedback analog output stage and non-feedback Class A power supplys .
       Applies all audiophile grade components, including DALE resistors, EVOX caps (German brand), custom order NOVER (UK brand) caps, all audiophile grade input & output sockets.

Sound Characteristics:  Because ACSS is fully non-feedback with very low distortion, the sound is neutral (neutral and faithful) because it has no feedback effect. It can show how good or how bad a recording or source is.
       Neutral in my mind, is neutral and faithful-like, C-2 doesn't have any particular character, like our other ACSS products, its sound depends on the source, C-2 reveals to you the merits or shortcomings of your source. It only drives the headphone without coloration. I think, use of the word "neutral and faithful" will be better than the use of "neutral".
The C-2 owners can replace the single-channel OPAs with Audio-gd single-channel discrete OPAs for choosing different flavors. (The OPAs are only used with RCA input.)


 The C-2 owners can replace the two single channel OPA604 opamps with Audio-gd single discrete OPAs for choosing different flavors. But while owners replace the OPA they must not install it in the wrong direction. See the photo below to confirm correct installation direction. (The OPAs are only used with RCA input, not ACSS input.)

About ACSS:
         ACSS (Audio-gd Current Signal System) is Audio-gd's system for transmitting audio signals in the current domain. This concept, first seen in 1966, we have used for many years, and since 2006, have evolved the technology to include all audio signals in our systems from the digital source to the power amplifier. Since 2005, ACSS comp5nts have become Audio-gd's most popular products.

The C-2 functions:
Front plate:
 Volume knob: Control the volume level of the headphone/pre amp.
      Gain button: Push in for high gain (+13DB), out for low gain (+4DB). Only available while using RCA input. ACSS input is always set at High gain regardless of the Gain button for the best sound level.
button: Push in for preamp output, out for
headphone output.
      Selector knob: Select
input signal between 1(RCA) and 2(RCA) and 3(ACSS)
Design Features: 
The C-2 applies ACSS (Current Audio Signal Transmission) technology. The heart of our ACSS technology is in the ultra low distortion BPM-7110 V2 module. The sound of C-2 is neutral and faithful-like, very neutral and sounds exceptionally clear and transparent. Soundstage is precise, three dimensional and huge, detailed and lifelike midrange, and transparent treble with tight and extended bass.

     C-2 has three pairs of inputs: one set of ACSS current mode input, and two single-ended RCAs inputs. If the input signals are coming from RCAs, they are internally converted into current signals and then amplified. To use the C-2 as a preamplifier, there is one set of RCA output for your power amp connection.

    In order to minimize interference and distortion of sound quality, the left and right channel circuitries are completely separated. To achieve a perfect performance, C-2 also applies the complex Class A parallel-stabilized voltage supply to get a purer power supply so that a better sound quality is guaranteed.

     C-2 uses an all aluminum alloy chassis to prevent the eddy current of the transformer from interfering with the circuit board.

About volume in ACSS circuits:

 C-2 use ACSS technology, which is very different from conventional technology.

 In conventional technology the gain is fixed, like 3DB or 6DB.

 ACSS circuits in fact have 0DB gain and are fully non-feedback, so it is a completely different circuit.

     In ACSS technology the "gain" changes with volume, and while you turn off the volume, the "gain" is -80DB (in conventional technology it can't work lower than 0DB).

     While you are listening in normal volume, the "gain" may be around -50DB, or between -80 to +13DB.

     The volume control is also different from conventional technology. Conventional technology volume control is placed at the input, and attenuates the signal.

     But in ACSS, it is placed at the ACSS modules output, where the output is the current signal, not the voltage signal. The volume control is I/V conversion, and the volume depends on the current (I) conversion to voltage (V). (Like D/A chips output I/V conversion)

     The sound quality benefits from I/V conversion volume control. Mark Levinson also knows that current volume control has great benefits, so in their Top End preamp NO.32 volume control, they use many components to change the signal to become current signal (I), then through the R-2R network to control the volume, and then changed back to voltage signal (V) again. But C-2 is simply a more complete work in terms of the current signal, and technically, it is superior to conventional technology.


(The C-2 applies the OPA604 in default configuration.)
]The C-2 owners can replace the single-channel OPA604 opamps with Audio-gd Discrete single-channel OPAs for choosing different flavors. But while replacing the OPA owners can't install it in the wrong direction. See the photo below to confirm correct installation direction. (The OPAs affect sound flavor only with RCA input.)


Single EARTH


Sounds fairly neutral.

Single MOON


Sounds a bit tube-like, that is, a little soft, warm and musical.

Single SUN


Sound a bit dynamic.

C-2   Specification

Improvement may result in changes in specifications and
design without notice.


Head amp / Preamp
S/N Ratio
115db (Input short)
 Output Level
Output Power 62 ohm: 1000MW
100 ohm: 1000MW
4DB (Gain setting L)
13DB (Gain setting H)
Volume Characteristic Applied I/V change volume control
Output Impedance
1.5 Ohms (HP amp)
Input Impedance
47K Ohms (RCA input)

2 Ohms (ACSS input)
Frequency Breadth
2Hz to 130KHz (ACSS input ,1V output level)
Power Requirement
1 Version  100-130V  AC 50/60 Hz
2 Version  200-260V  AC 50/60 Hz
Power Consumption
18W Class A
Operating Temperatures
-10 XC to +80 XC
Operating Humidity
5 % to 90 % (without dew)



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