Review and Measurements of Benchmark DAC3

[Purité Audio]

The Dac 3, variable analogue input, used with the AHB2 ( three levels of gain) is extremely versatile.
Keith

 

[Kal Rubinson]

The Dac 3, variable analogue input, used with the AHB2 ( three levels of gain) is extremely versatile.

Yes but the gain flexibility of the AHB2 is the most critical element.

 

[Olli]

https://benchmarkmedia.com/collecti...mark-dac3-b-digital-to-analog-audio-converter

I wonder how this will measure when fed via digital outputs from an RME AES card:
https://www.head-fi.org/threads/ben...fier-impressions.876705/page-17#post-14510156

PS: anyone waiting for a Benchmark DAC without a volume control should click the link above for a teaser pic from Benhcmark

It‘s out: https://benchmarkmedia.com/collecti...mark-dac3-b-digital-to-analog-audio-converter

 

[igufi]

OK, finally, finally we get to test the statement Benchmark has made about superiority of their headphone amplifiers. For those of you who have not tracked that discussion, it starts with this paper from Benchmark: https://benchmarkmedia.com/blogs/application_notes/12838141-headphone-amplifiers-part-1

In a nutshell, they say that real headphone loads cause far more distortion than dummy (resistive) loads always used for headphone reviews and measurements. To wit, they show these two measurements, the first being with a dummy load:

View attachment 13329

The Benchmark is in navy color at the bottom showing much better performance than the other two competing amps in pink and green. But that is no their point. Their point is that once you replace the dummy load with a real Sony MDR-V6 headphone, their distortion figures do not change but the competitors do:

View attachment 13330

I confirmed that both my Topping headphone amplifier and RME ADI-2 DAC (or was it the Pro?) are sensitive to headphone loads. And indeed their THD+N in above graph shows similar frequency dependence to competitors of Benchmark above.

What was left was verifying that the Benchmark indeed performed as well as they say it does using my instrumentation.

For that, I tried to set my APx555 analyzer very closely to what they have above. I did not have a 60 ohm dummy load but used a 50 ohm which is close enough. Levels were matched nearly the same at 0.5 watt per above graphs. Bandwidth of the analyzer is set to 90 kHz as opposed to 80 kHz but again, close enough.

Here are the results comparing the RME ADI-2 Pro output versus DAC3 using a 50 ohm dummy load:
View attachment 13331

We get pretty nice graphs with the RME ADI-2 Pro now beating the Benchmark DAC3 by good margin (4 to 7 dB).

Now let's replace our dummy load with the real Sony MDR-V6 headphone:

View attachment 13332

Ah, that ain't good! While the RME ADI-2 Pro output changes as I had measured with my other analyzer, so does the Benchmark DAC3!!!

Reading through the paper from Benchmark, it is from DAC1, not DAC3. Benchmark has newer papers on DAC3 with similar claims.

Not shown but I tested with an IEM at much lower level and it too caused a variation in response that was identical between the two amps.

Summary
It is good of Benchmark to raise awareness of measuring with real headphone loads. But the notion that their headphone amplifiers have distortion profiles that are headphone independent, do not seem true. My measurements show similar susceptibility to other high-performance amplifiers.

Sure, if you have a much higher output impedance than what Benchmark has, the effect will be exaggerated. But the core problem remains in all implementations including that of Benchmark DAC3. Bummer!

P.S. I measured the output impedance of Benchmark DAC3 at 0.7 ohms.
View attachment 13333

Was the discrepancy between the Benchmark advertised THD+N results and @amirm 's measurements ever clarified by @John_Siau?

 

[Graph Feppar]

This is using 256 k point FFT so there is 50 dB of process gain/lowering of noise going on there. Actual level then is around -120 dB. I am also using 16 times filtering to smooth the noise floor further.

Doesnt the process gain only increase SNR and not distortion? I am not pro but I was thinking that by using longer FFT window,the noise will appear lower becose incoherent signals sum to lower value than coherent ones like harmonics of distortion.

 

[amirm]

Doesnt the process gain only increase SNR and not distortion?

Correct.

 

[amirm]

Was the discrepancy between the Benchmark advertised THD+N results and @amirm 's measurements ever clarified by @John_Siau?

No, there was no resolution. They could not find anything wrong with the one I tested.

 

[bona998]

@amirm - I was just wondering about this poor unbalanced linearity. Does it affect headhone amplifier ? The question is from what point the analog signal is taken before it goes to the headphone amplifier stage. Are you still in possession of DAC 3 ? Is it possible to run linearity test using headphone output ? This could be quite important info for headphones users.

 

[amirm]

@amirm - I was just wondering about this poor unbalanced linearity. Does it affect headhone amplifier ?

Unfortunately that was a loaned unit so I cannot measure the headphone out. For linearity I always test the DAC portion alone.

 

[sonci]

The Dac 3, variable analogue input, used with the AHB2 ( three levels of gain) is extremely versatile.
Keith

That feature is also in my '88 Jvc ax1100, GM volume..

 

[hrbngr]

So the Benchmark Dac3 B (no amp) is now out w/a list of $1695, so what would be the DAC only version for the RME ADI-2 Pro be? I did find this link, but not sure if equivalent. http://www.rme-audio.de/en/products/adi_2-dac.php

 

[Music1969]

Hi all

Can someone please help with an explanation of how the DAC resolution is calculated.

From the Stereophile's DAC3 measurements:

"When the DAC3 decoded dithered 16- and 24-bit data representing a 1kHz tone at –90dBFS, the increase in bit depth dropped the noise floor by more than 30dB (fig.5), indicating that the Benchmark's resolution is at least 21 bits. "

https://www.stereophile.com/content...ne-amplifier-measurements#2AYOgQ4CP5C3xjXs.99

So using the above numbers, what's the formula to get to 21 bit resolution?

Thanks in advance

 

[Music1969]

Oh, so is it using the 1 bit = 6dB rule of thumb?

So 30 dB drop in noisefloor = 5 bit increase from 16 bits, so 16+5 = 21 bits?

 

[Graph Feppar]

Can someone explain to me why would anybody want the crazy high output voltage that Benchmark DAC has? On one hand I would fear it will destroy the amplifier its connected to becose vast majority of DACs have output of 2V rms, 20V rms thats just batshit crazy high in my opinion. On other hand, I wonder what kind of advantage does it bring, I am sure Benchmark know what they are doing, what am I missing?

Does the Benchmark have some switch to lower the output voltage or is this done by digital attenuation? How does this not destroy the input stage of most amplifiers? I have no formal electronic engineering education but I know transistors have certain voltage after which they get damaged. I know the insulating layer in MOSFET gets "pierced" by the electric breakdown. I am not so sure what happens to BJTs and JFETs, I guess they are harder to kill but 20V is 20V, I cant imagine how the input op-amp can survive that.

 

[DonH56]

Benchmark targets the pro audio market that uses much higher signal levels. Standard studio level is +4 dBu, about 1.23 Vrms (~3.5 Vpp) whilst consumer level is around -10 dBV (about 0.3 Vrms). Most studio equipment will handle >20 dBu (7.8 Vrms, ~21 Vpp). The mixer I use at church overloads around +30 dBu ~25 Vrms), other stuff around 27 dBu (17 Vrms) -- the U.S. standard is +24 dBu (~12 Vrms) without clipping to provide the headroom needed for live recording and processing when multiple tracks are combined (mixed) etc. and getting well above the noise floor (can be high in a live sound environment).

Don't know how they handle volume, usually a hybrid analog/digital approach. They could be using a higher gain stage for pro levels and lower (or not adding a gain stage) for their HT mode.

HTH - Don

 

[Kal Rubinson]

Does the Benchmark have some switch to lower the output voltage or is this done by digital attenuation?

Low impedance passive pads on the XLR outputs implemented by internal jumpers.

How does this not destroy the input stage of most amplifiers?

Responsible use of the volume control!
I've used the DAC3 directly into power amps (Benchmark and others) or into my analog preamp and, although I could have lowered the gain, I have not done so. My reason is that my setup changes frequently and getting at the internal jumpers (on 3 DAC3s) is more than tedious.

 

[RayDunzl]

Can someone explain to me why would anybody want the crazy high output voltage that Benchmark DAC has?

Because it's there?

Works fine here with my DAC2, essentially the same output. If I remember correctly, it maxes at +23, instead of +24.

The DAC volume control is not used here (but could be and has been), so, full output, and feeds the preamp for distribution among the Krells and the JBL monitors.

Volume levels at the preamp become 30/151 - quiet listening, 50/151 - moderate, 100/151 - loud. Peamp volume control is stepped, a little more than 1/2dB per step, never stared at it too hard, just twist the knob (maybe spin is a better word, since it has no stops).

As for the headphone output on the DAC2, with HD650, it is about 10 digital dB too loud for my taste (maybe more on some material), so, I turn down the signal (digitally) before it gets to the DAC when using the phone out.

 

[Graph Feppar]

One thing that I thought when reading about Benchmark is that it would make great DAC for driving electrostatic amplifiers becose those need huge voltage gain. It would be alot easier to turn 20V signal into 1000V than 2V signal. If there was electrostatic amplifier made to be paired with Benchmark, it could have one less gain stage, it would simplify things, make its parts cost, noise and distortion lower than similiar amp made to work with normal 2V DACs.

 

[RayDunzl]

One thing that I thought when reading about Benchmark is that it would make great DAC for driving electrostatic amplifiers becose those need huge voltage gain.

The high voltage is for the static membrane bias supply... DC volts, at, maybe, 2500V on mine, the speaker plugs into the wall. There's only leakage current, no power there.

The power amplifier need not be special. The speaker leads connect to a step-up transformer inside the speaker, with maybe a 1:100 ratio. High voltage, but very low current demand at the panel itself. The amplifier (through the transformer) differentially drives the front and rear of the panel, the steel stators, to simultaneously attract/repel the statically charged membrane.

That's my "real world" report.

"crossover" - just independent low and high pass sections, and the bias supply (upper right corner), and signal transformer for the panel, upper center.

The panel is at the top right of this schematic.

 

[Graph Feppar]

I am not expert on electrostatic speakers but Stax headphones do have high voltage not only on diaphragm but also on stators, both the DC bias and AC music signal are high voltage. The transformer is cheap and simple solution, it isnt as good as proper amplifier becose amp will have flatter frequency response and be more linear. I never listened to Stax energizer or Kevin Gilmore amps but all people say the amps sound better than the energizer.

Oh and also... electrostatic amps absolutely do need power! Its like MOSFET, you can turn it on with almost no current but to switch it on and off rapidly, like happens with AC music signal requires alot power, thats why gate driver ICs exist, the charging and discharging of the stator capacitance requires significant currents to flow and when multiplied by the high voltage, thats large amount of power.

You are right that the DC bias voltage thing does not have almost any power and only negligible current leakage.