Denafrips Terminator Plus (With Gaia) Measurements

Content and analysis made possible thanks to support from https://headphones.com, and https://patreon.com/goldensound supporters.
The Terminator Plus was purchased for review using funds from Patreon and will be resold after.
The Gaia was loaned for review by Vinshine Audio.

ChitChat:

The Terminator Plus is the flagship DAC in Denafrips’ product range, accompanied by the flagship Gaia DDC.
I had previously posted measurements of the T+ which had been done in collaboration with SoundStage! Network. You can see those here: https://goldensound.audio/2021/07/21/denafrips-terminator-plus-measurements/

But now that I have a unit in-house I wanted to redo those measurements and also to test for measured differences when in use with the Gaia.

At the end of the article is also an examination of whether this DAC is true ‘NOS’ or not.

Let’s have a look at these two products a bit first.

Starting with the DAC itself, there are a fair few interesting design elements.
The power supply is contained in the main chassis, and is formed of two large O-type transformers, and a number of supercapacitors, 4 of which feed the digital section and 12 feeding the analog section. Definitely looks like the price tag is getting some justification!

The main board itself is comprised of the Digital Signal Processing board on the left, and the Analog board on the right, linked together by the OXCO clock board on top.

TP Layout.jpg

The Terminator Plus adopts a slightly different isolation approach than many. Instead of galvanically isolating inbetween the USB board and the rest of the unit, the isolation is between the whole DSP board and the analog section.
This has the benefit of meaning that all other inputs including I2S are also isolated from the analog section, but with the slight concern that it could have an effect on the DSP components themselves as they are not isolated from the PC/host device, or grounding given as the DSP section likely has to have a ground connection which would be shared with the rest of the device. This is speculatory however.

The other obvious aspect is the sheer number of capacitors! There are…well ‘a few’ to put it lightly.
The reason this is done is because for power filtering, many smaller capacitors in parallel provide lower ‘Equivalent Series Resistance’ (ESR) than a few big ones. So whilst this takes up more space, and will make things quite tricky if this dac needs a capacitor replaced, it is on paper a good approach.

And then of course we have the ladders themselves. And you’ll notice that the ladders connect directly to the output. There is no output buffer stage like in most dacs. This has the advantage of having less components in the signal path and ideally better signal purity/integrity and the opportunity for better objective performance. BUT, it does also mean that the Terminator Plus output impedance is a whopping 1250Ω!
Whereas most DACs will be somewhere in the realm of 100Ω.

This high output impedance means that you should try to avoid using longer interconnects and definitely avoid using a passive preamp.
It also means that the input impedance of the amplifier you pair it with needs to be considered, and an active preamp buffer may be of benefit.

So, let’s have a look at how it performs!

Before we look further though, I do need to note that in a fair few of the measurements taken there is some behaviour that can best be described as ‘odd’.
This is because Denafrips’ DSP present in this DAC seems to get quite confused and behave irregularly when some steady state and other test signals are thrown at it. This made measuring this DAC quite difficult as many tests needed several attempts to get a ‘correct’ result.

This is not a ‘problem’ for normal music and in listening to it I’ve not had anything occur which seemed incorrect, but it is important to note that there does seem to be some heavy DSP going on here.


Measurements:

Test Setup:

– Audio Precision APx555 B-Series Analyzer with 200kOhm input impedance
– Audioquest Mackenzie RCA/XLR cables
– USB Source: AMD PC via ifi iGalvanic 3.0 and iUSB 3.0
– All measurements shown in this post are taken with USB input to Gaia, clock-synced with terminator, Balanced output, 44.1khz sample rate, Sharp filter, unless otherwise specified
– Full reports containing additional data and test configurations are attached
– Exact analyzer/filter configurations for each measurement are detailed in the full reports

Full Measurement Reports:

Reports available here:

Dynamic Range (AES17): 124.3dB

SNR: 109.8dB

Noise Level RMS (20-20khz): 2.175uVrms

Noise Level RMS (20-90khz): 3.79uVrms

DC Offset: 400uV active, 372uV idle

1khz 0dBFS:

1khz -3dBfs:

1khz 0dBfs DSD512:

DSD performance is incredibly similar to PCM. And the harmonic structure is also very similar but with a rise in the upper frequencies, and higher noise floor.
Denafrips does not give too much info about the ’32 step FIR filter’ but it seems that DSD is being converted to PCM and played on the main ladder. (There is an easy way to check this, I’ll post that once I’ve moved it back out of the listening setup)

THD+N / Frequency:

40khz AES filter
20khz AES filter

THD+N is flat across the frequency spectrum, good to see! Some DACs have a rise in distortion in upper freqs.

Linearity:

Linearity with bandpass filter

Example of the DSP messing with the signal a bit here. Where these spikes occurred and to what extent depended on how many steps I had the test set to do/what level intervals were measured and is a result of the DSP, not a hardware issue. John Atkinson of Stereophile encountered a very similar issue when measuring the Terminator:

Linearity without bandpass filter

SINAD/THD+N vs output level:

The ‘R2R Sawtooth’ area seems to be at about -40dB, but is very well contained and there is not a particularly drastic jump.
This effect is explained in more detail in the Rockna Wavedream Measurements.

IMD (SMPTE) vs Output Level:

Crosstalk:

Crosstalk rises quite significantly into the upper frequencies.

-90.31dBfs 1khz Sine (Recorded with 192khz ADC Sample Rate):

Filter Ultrasonic Attenuation:

Idle Noise Spectrum upto 1.2Mhz:

44.1khz Jitter (USB):

48khz Jitter (USB):

Jitter performance is good, but honestly not as good as I’d have hoped given the expense put toward and the marketing surrounding the OXCO clocks.

Further testing including looking at performance with and without the Gaia can be found in the Gaia measurements post.

Multitone:

This was another test that I really struggled to get a ‘normal’ result for. I typically use 1.2 million point FFT with 3 averages, but could barely get one run to go without issue, let alone three. Many of them ended up looking like this:

So I had to just do one average, and after a few runs managed to get a proper result which also lined up with the results from the previous unit measured by SoundStage! network.

It DOES concern me that the DSP seems to be altering not just steady state sines but complex multitones like this. I have a full review coming and to be clear it DOES sound very good, but still, a bit concerning that we don’t really know how music could be being altered.

Is it NOS?

TLDR: No

The Terminator plus is advertised as being NOS (Non-Oversampling) capable, and that in the OS modes it upsamples to 1.536mhz.
Unfortunately, it seems both of these claims are untrue.

Now before you read further I want to be clear: I think the T+ is a great DAC, this is NOT me saying the DAC is bad or looking for reasons to trash it. My review will be quite positive.
But just because something sounds good, it is NOT an excuse for false marketing. If your product cannot do something, do not advertise it as being able to do that thing.
A car can be the fastest car, the best car, but if it doesn’t actually have a turbo in it, don’t call it ‘turbocharged’ just cause it’s quick.

I don’t even think that NOS is necessarily strictly speaking always a good thing. And many people will prefer oversampling. But regardless, be truthful about your product.


Looking at NOS first; NOS means non-oversampling. The DAC does not do any interpolation or filtering in the digital domain, and as a result, the DAC will simply hold the output level, and when a new sample arrives, it moves the output level up/down to meet that new sample, then holds there until the next sample, repeat.
This means that for an impulse response, where there is silence, then one sample, then silence, it will look like a square.

Sample 1: still 0/silence. Dac continues holding at 0 output
Sample 2: Higher level, DAC moves output level up to meet it, then holds
Sample 3: 0 Again, DAC immediately moves down to meet it, then holds
Sample 4: Still silence, DAC will continue holding.

Here is a real world example of that from the Phasure NOS1 DAC:

1625233476653.png

But here is the Terminator Plus Impulse:

1625233785647.png

Not very square! So what’s going on? Well, it is because the DAC is linearly interpolating, adding samples in a straight line from one sample to the next. It IS oversampling.

Terminator Plus impulse (Green)
NOS impulse (Blue)

After sample 1, the T+ moves in a straight line toward sample 2, knowing where it is in advance. It does not hold, and instead immediately begins linearly interpolating once again back toward sample three.

Why is this a concern? Well firstly, Linear interpolation has more treble rolloff than actual NOS, and so as we saw on the Ares 2, the ‘NOS’ mode has about 3dB higher rolloff than a true NOS DAC does.

1625234079036.png
Linear Interpolation gives a squared sinc frequency response
PI/2 ( so 22.05k @ 44.1k sample rate ) SIN(PI/2) / (PI/2) gives us -3.9dB droop for a NOS
PI/2 ( so 22.05k @ 44.1k sample rate ) (SIN(PI/2) / (PI/2))^2 gives us -7.84dB droop for a for a linear interpolate

Additionally, where NOS will have the directly vertical activity at exactly 44.1khz (or whatever the sample rate is), linear interpolation creates random added distortion as the angle of signal from sample to sample changes constantly. This is more akin to IMD and likely more audible.

1625233960520.png
15khz sine wave, denafrips ‘NOS’

So no, unfortunately the Terminator plus ‘NOS’ is just linear interpolation oversampling, not actual NOS.

What about that ‘oversampling to 1.536mhz’?
Well, this we can check as well.

Firstly, when looking at the wideband spectrum, we can see a big spike at 352.8khz, which moves to 384khz when we give the dac 48khz source rate files.

We can therefore rule out 1.536mhz OS right away because the spur at 352.8khz would not be visible because 1.536mhz sample rate gives a bandwidth of 768khz.

We can see similar behaviour on the Schiit Yggdrasil, which upsamples to 192khz, and so we see a spur at 192khz and multiples upwards.

Schiit Yggdrasil ‘MIL’ wideband view of 1khz tone.

Secondly, we can utilise the 2.5mhz sample rate of the APx555 to look a bit deeper at what’s happening.
Looking at both the ‘NOS’ and OS impulse responses, we can see a stepping behaviour, indicating the true speed the ladders are operating at.

OS Sharp
‘NOS’

Between each sample there are eight ‘steps’, indicating again an OS rate of 8x or 384khz/352.8khz.

So it would seem that no, the T+ does NOT upsample to 1.536mhz, and also cannot run NOS.
I do not know why these seemingly false claims about the product are made, especially when it objectively performs very well for an R2R dac, and subjectively sounds very good. There does not seem to be much reason to lie, but whatever the reason, false marketing should always be called out even if the product is otherwise very very good (which the T+ is, it sounds great).




2 thoughts on “Denafrips Terminator Plus (With Gaia) Measurements”

  1. Thank you for this highly informative review and measurements of the the Denafrips Terminator + DAC. I have a newbie question.

    Your comments about the high output impedance (1250Ω/xlr) and importance of considering input impedance of the paired amplifier leave me wondering if the Terminator + would be a match for my Pathos Logos MKll integrated amp which has an input impedance of 32 KOhm unbalanced and
    20KOhm balanced.

    Can you provide any guidance on this pairing?

    Reply

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