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JIMV
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The Dragonfly

If I read the review correctly, this DAC only has one output, an analogue line out. I think the manufacturer missed a mark there. The device is designed to be used with a computer. I would venture to say the vast majority of folk who listen to music from a PC do so using desktop speakers, many/most powered. Would it not make sense to provide a phones out so as to let folk using powered speakers plug the inputs directly into the DAC??

As it is, I would need to buy some sort of a headphone amp to use with the DAC and Powered speakers...

Or do I msunderstand this device??

 

JIMV
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I might not have been

I might not have been clear...What is the purpose of the device? There is a host of class B DAC's out there. This device is different mostly in its size and convenience of use with a computer. I believe the device should have been optimized for use as a DAC in the typical computer setup, one with a system consisting of the PC and a set of powered speakers. As it is, it seems optimized for use with a PC as a source in a typical audiophiles normal stereo setup...If so what is the advantage in such a small size.

 

Edit...several hours later....I just read the manufactrers comments and I have to say I must be missing something. I thought the device outputted a line level signal, not a speaker signal but the manufacturer seems to use the output for both so I have no idea what this thing does...

JRT
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The product litereature says
JIMV wrote:

   ...I just read the manufactrers comments and I have to say I must be missing something. I thought the device outputted a line level signal, not a speaker signal but the manufacturer seems to use the output for both so I have no idea what this thing does...  

 

The product literature says that this thing outputs 2 volts, presumably meaning 2 Vrms at 0 dBFS signal level at 1 kHz. 

The literature also says that it delivers 125 mW (0.125 W) into a 32 Ohm load, in describing headphone output. 

square root of (0.125/32) = 0.0625 Amps = 62.5 mA into that 32 Ohm (nominal) headphone load. 

125 mW / 62.5 mA = 2 Volts  ...which corresponds to the 2 Volt output rating. 

Amplifiers used for audio are most usually (there are esoteric exceptions) designed toward providing near-constant voltage gain while exhibiting high input impedance and low output impedance (within the domain of the design operating conditions). That holds true for the low level amplifiers at the outputs of your CD player, the preamplifier, and the amplifiers driving your loudspeakers, though the latter can produce higher output voltages and much higher currents to drive the relatively low impedance loads presented by loudspeakers. 

Constant voltage gain means that the voltage across the output is a fixed multiple of the voltage across the input. The amplitude of that input voltage varies, but the amplifier's voltage gain is near-constant.  The high input impedance means that the amplifier does not draw much current from the source providing voltage across the amplifier input.  The low output impedance means that as the amplifier delivers voltage across the load impedance and as that load impedance draws current from the amplifier, that output voltage of the amplifier should not be significantly affected by variation in the load (within design limits), rather it should maintain that constant voltage gain. 

So whether the amplifier on the output of this device is driving the load presented by 32 Ohm headphones, or the 100k Ohm inputs of your Parasound Halo JC1 mono-blocks, the output of the device should swing the same 2.0 Vrms at 0 dBFS at 1 kHz.  The specifications of your Parasound Halo JC1 tell me that it provides 28.28 V at the output per 1.0 V at the input, which is 56.56 Vrms with 2.0 Vrms input.  56.56 Vrms across an 8 Ohm resistive load will draw 7.7 amperes, 400 Watts, which also happens to be the rated output of that Parasound Halo JC1. 

Your Oppo BDP-95 also happens to be rated at 2 Vrms output at 0 dBFS signal level, on the single ended outputs (the RCA ports), and double that on the balanced outputs.  But other devices may have different outputs.  The Adcom GCD-750 CD player that you bought 12 years ago had 3.0 Vrms output at 0 dBFS on the single ended outputs, and double that on the balanced outputs.

 I should mention that headphones usually present a much lower impedance load than a high impedance amplifier input.  So do not assume that preamplifiers designed to drive the high impedance inputs can deliver enough current to drive headphones, as many of them cannot, at least not at adequately high levels. 

A signal level of 0 dBFS corresponds to a very high level crest in the recorded material.  Less well mastered material has suffered more compression, is louder, is therefore played back with more attenuation in nominal level, and presents maximum crests at lower peak SPL as compared to well mastered material suffering less compression.  Well mastered material has a nominal level that corresponds to 85-86 dB summed (with uncorrelated phase) at the listening position (what each ear would receive) at -20 dBFS at 1 kHz.  From a stereo pair of loudspeakers that is 82-83 dB from each loudspeaker separately at -20dBFS at 1 kHz, measured at the listening position.  But with headphones that is 85-86 dB at each ear at -20 dBFS at 1 kHz, which is 105-106 dB at 0 dBFS at 1 kHz. 

To complicate matters a little further, 0 dBFS samples of frequencies near half the sampling rate with peaks centered between samples, would have signal peaks near +4dB above 0 dBFS.  But recorded material has a low pass corner below that and the practical limit is a little less than +3 dB above 0 dBFS.  So you want the analog side downstream of a DAC to have at least 3 dB headroom above 0 dBFS digital signal level (I'd like to see headroom of at least +6 dB in downstream analog section above 0 dBFS in digital domain, at onset of amplifier clipping, signified by crossing 5%THD threshold). 

Looking at Sennheisers' specifications for their HD600, it is rated as having a nominal impedance of 300 Ohms, and a power sensitivity of 97 dB at 1 mW, which corresponds to a voltage sensitivity of 97 dB at 547.7 mV.  With 2 Vrms across that 300 Ohm load, it draws 6.67 mA, dissipates 13.33 mW, and should produce 108.3 dB (again, based on the manufacturer's published specifications).  So this little amplifier, if it indeed swings 2 Vrms across 32 Ohms load, should also be able to do so across 300 Ohms, and should be able to drive the Sennheiser HD 600 to near reference level.  But there are a lot of ifs in that. 

I have not yet read the article, so I don't know how well this thing stood up to objective testing and subjective opinions of the reviewer(s).   I am a subscriber.  And I received the magazine in Saturday's mail, but have not yet taken the time to read it yet (thumbed through, read the lead editorial on the way back from the mail box, got distracted with real life events, and haven't gotten back to reading it yet).

Sumflow
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Dragonfly use
JIMV wrote:

I thought the device outputted a line level signal, not a speaker signal but the manufacturer seems to use the output for both so I have no idea what this thing does...

It is really very simple.  Once you set it up,"plug in earphones, headphones, or a cable to your powered speakers or amplifier, and you are ready to listen.

JIMV
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Thank you...I was completely

Thank you...I was completely misunderstanding the device.

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