Audio-gd NFB-1AMP

NFB-1AMP (Release in 15th June.)#

The full balanced design based on Master 9

Main features

• Fully balanced class A design built by discrete analog stages without any OPA or coupling caps in the signal channels.
• Non- feedback ACSS analog output stage.
• 8000mW at 40 ohm output, 16DB gain can drive the low sensitivity headphone very well.
• Class A PSU's for DC supply.
• Uses most Hi-end grade parts and exactly matched transistors, OCC wires.
• Four-channel 100 steps digitally controlled relay-based volume control avoids channel imbalance and improves sound quality .
• Supper Exponential Volume Characteristic, easy match the volume with very high headphone / speaker without change the gain mode.
• 5 groups input: RCA X2, XLR X2, ACSS X1
• Preamp output : XLR / RCA / ACSS
• Headphone amp output: 4pins XLR X1 / 6.3MM X1
• Static storage mode control software for avoid disturb sound quality , the MCU output once control data and save in the perform parts ,then stop output data until users next operation.

Impedance matching#

There are a lot different DACs in worth, they had different design and output impedance . For avoid the sound quality effect by different DAC's output impedance, in the NFB-1AMP, it had design two pair single-ended class A FET buffers in the input . All the input signals through these FET buffers, the output impedance had become very low, even the source had high or low output impedance. The FET buffers working on pure class A state, and it is so short signal journey , it can keep the sound quality without coloration ,dry and harsh.

Core#

NFB-1AMP had the same ACSS design with our top grade model Master 9 . It is a pure class A design built by discrete analog stages without any OPA or coupling caps in the signal channels. They seem complex , but in fact they are the most simple design the world has ever had , their a lot components to process the power supply. The simplest and shortest signal journey brings out the most neutral and least colored sound. The ACSS is a non-feedback technology made with discrete amplifiers. Most people know the global feedback design can offer better specs in test measurements, and non-feedback can't do well in test measurements but can offer better sound for the human's ears. Here is a conflict of the classic circuits. But the ACSS opens a new field, it can offer a least coloration sound which is more neutral with very low distortion and high linearity. So it can retain the dynamics, detail and neutral sound but not sound bright or harsh. All signal gain is in current area, all transistors work in class A mode. The NFB-1AMP has all components exactly matched before installation.

Strong class A output stages#

The NFB-1AMP had design a pare diamond difference output stages, every parts had exact matching before assemble so don't need any human adjustment . The output stages had four pair 15W transistors ,they also working under class A state . Drive most headphones can working under pure class A state

Power supply#

The class A parallel connection PSU has very high input impedance to avoid pulse through the PSU from affecting the preamp and low output impedance with very fast speed and high linear, so it is a very clean power supply. The NFB-1AMP applies seperate linear PSUs for the display and control parts, avoid the disturbances through power line from affecting the amplifier.

Volume control#

The volume control is also different from conventional technology. Conventional volume control technology is the volume control implement in the analog amp input stage through a volume pot to reduce the signal . The volume pots quality effect the sound quality direct , the low quality volume pot cause lost the detail and channels imbalance cause the soundstage distortion . Even the high performance volume pot still cause the detail lose. Whatever quality volume pots, must cause the S/N worst . But in the NFB-1AMP , we applied the I/V conversion volume control , the volume control just a variable passive I/V conversion place at the ACSS amp 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 the voltage (V). (Like R-2R D/A chips output passive I/V conversion) It can keep the signal frequency band flat and not lost any detail. It can't degrade on sound quality in every volume level . After the volume , there are four groups diamond non-feedback buffer output stages offer the very low output impedance . 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 current signal (I), then implement the volume control , and then change back to voltage signal (V) again. But NFB-1AMP is simply a more complete work in terms of the current signal, and technically, it is superior to conventional technology. The less conversion bring much neutral sound . In NFB-1AMP is applied a digital control relays based volume control. .NFB-1AMP has total four channels through changing the DALE resistors to control the volume for avoid channels imbalanced ,achieve the best performance and sound quality of the gear. NFB-1AMP have 100 steps volume control, very smooth control for both high / low sensitivity headphone and speakers. While users change the volume, the combine relays break or close, it may had slightly switch sound on output and disappear while stop change the volume.Static storage mode control software: In most control softwares design, the MCU will continuously output data to the perform parts , the MCU had the very high speed, so the output data become high frequency impulses disturb the audio signal circuits make the sound worst . This product had applied static storage mode control software , the MCU output once control data and save in the perform parts while just power on and users operate ,then stop output data until users next operation. This design make the sound quality improve on the clear and transparency .

Technical specification#

S/N Ratio	>125DB (Volume minimum)
THD	<0.002 %
Gain	Gain : +16DB
Volume characteristic	Two sets Exponential Volume Characteristic
Headphone amp Output Power	9900MW / 25 ohm 8000MW / 40 ohm 3500MW / 100 ohm 1200MW / 300 ohm 600MW / 600 ohm
Preamp Output Level (Max)	10V @ RCA 20V @XLR 2.4MA @ ACSS
Output impedance	1 ohm
Input impedance	47K ohm @ RCA 94K ohm @ XLR <10 ohm @ ACSS
Frequency Breadth (XLR input)	20Hz - 20KHz ( +/- 0DB ) 1Hz - 220K (+0DB, -3DB)
Channels cross	> 120DB
Channels imbalance	< 0.05DB
Power Requirement	Version 1: 100-120V AC 50/60 Hz Version 2: 220-240V AC 50/60 Hz
Power Consumption	30W @240V or 120V
Package Weight	Approximately 5KG
Dimensions	W240 X L360 X H80 (MM, Fully aluminium )
Accessories	AC power cord X1