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NAD M51 vs C510

I'm having a hard time understanding something - I'm shopping around for a new DAC, and the NAD M51 comes highly rated. About a year ago, NAD released the C510 with identical specs. However, it's $500 cheaper than the M51 with the difference being the M51 boasts a better power supply. I asked the sales rep what that means in the real world, and he literally said "I couldn't tell you." So if the 2 units have literally identical data sheets, what does one get with an improved PSU? Specs below, from the service manual for each unit:

M51:

Rated distortion (THD+N with AES 17 flter) <0.0005% (ref. 1 kHz 0 dBFS)
<0.002% (ref. 1 kHz -60 dBFS)
IM distortion <0.0001%
Signal-to-noise ratio < -123 dB (ref. 0 dBFS 2V out)
Channel separation > -115 dB (ref. 0 dBFS Volume -1dB)
Sample rate 32 kHz to 192 kHz (USB and digital S/PDIF)
Frequency response ±0.5 dB (ref. 20 Hz – 96 kHz @ 192 KHz sample rate)
Output level 2V (ref. input 0dBFS)

C510:

Rated distortion (THD+N with AES 17 flter) <0.0005% (0dBFS)
<0.002% (-60dBFS)
IMD Distortion 0.0001%
Signal/Noise Ratio <-123dB (ref. 0dBFS 2V out)
Channel Separation >-115dB (ref. 0dBFS Volume -1dB)
Sample Rate 32kHz to 192kHz (USB and digital S/PDIF)
Frequency Response ±0.5dB (ref. 20Hz - 96kHz @ 192kHz sample rate)
Output Level 2V (ref. input 0dBFS)
caustic386

Showing 2 responses by auxinput

auxinput
2,921 posts
 

I took a look. These appear to be very similar. The audio output stage and power supply sections appear to be exactly the same, hence the same specs. However, the center section of the board on the M51 is more densely populated and appears to have a smaller DSP or IC in the digital receiver area.

M51:

http://d250ptlkmugbjz.cloudfront.net/info/IMG/jpg/Interieur-15.jpg


C510:

http://www.hifisentralen.no/forumet/attachments/hi-fi-generelt/287297d1415136705-nad-c510-p1020896.jpg

It seems, like stevecham said, it’s a slightly different feature set. IF the C510 operates like a digital preamp, there’s some additional processing on the bitstream data to make this happen.

auxinput
2,921 posts
 

Reading on these, it appears both M51 and C510 can be used as "digital preamp".  Both have a output buffer stage, which should be able to drive an amplifier directly (i.e. no need for a preamp in between, unless you want a specific preamp to help shape the sound).  There is no analog or resistor based volume control.  The "volume" attenuation is done all in DSP by upsampling the PCM signal and changing the original 16/24-bit word to 35 bits and then reducing the actual waveform mathmatically.  This is similar to how Oppo does the digitial volume (bit in 32 bit realm).  Everything is done in DSP software and output in PWM DSD type voltage injections.  There is no conventional ladder-based DAC chip in use here. 

I've never heard one of these, so I cannot comment on sound quality.

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