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Beresford TC-7520 Review (DAC)

amirm

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This is a quick review and measurements of the Beresford TC-7520 USB Stereo DAC. It is on kind loan from a member. Seems like it was released back in 2009 at a cost of US $249.

I like the look and feel of the TC-7520 with instant random access to inputs:

Beresford TC-7520 USB Stereo DAC review.jpg


Being an older design it is limited to 24 bits/96 kHz.

Beresford TC-7520 Measurements
Let's start with our usual dashboard:

Beresford TC-7520 USB Stereo DAC Measurements.png


Distortion is not bad at -105 dB but there is plenty of noise to push SINAD down to 93:

best USB DAC stereo review.png


The bigger issue and why this is a truncated review is that the two channels are not in sync as you see in the waveform and phase differential. It is a constant delay so if you change the frequency, phase shift changes with it. So clearly a broken implementation.

Conclusions
With a SINAD that misses the 16 bit mark despite product being released decades after introduction of CD, we could easily dismiss the TC-7520 as being a competent product. But add the channel delay difference and this just doesn't make any sense. Needless to say, I can't recommend it.

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As always, questions, comments, recommendations, etc. are welcome.

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Helicopter

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Sort of interestingly, the English company crowdsourced the later Caimim version of this with opamps picked by an online community. I think we have pretty well dismissed opamp rolling and its unfortunate the design is flawed.

Stereo delay might be useful if one speaker is hidden behind the TV. :facepalm:

Amir, you are on quite the roll. 7 reviews since Thursday!
 

m8o

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The bigger issue and why this is a truncated review is that the two channels are not in sync as you see in the waveform and phase differential. It is a constant delay so if you change the frequency, phase shift changes with it. So clearly a broken implementation.
Reminds me of 1st gen (and probably several generations after) dac designs which multiplexed two channel decoding with a one channel DAC pipeline, resulting in a time delay between left and right channels. It never really bothered me [I don't think at least] but it was said the time delay caused some people to get nauseous or uncomfortable or something like that.

This really piques my curiosity about what's behind this delay. I have to imagine [hope?] it's not still what I described above.
 

Francis Vaughan

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The delay looks to be about 0.02ms. So two samples at 96khz. If it really is a constant delay there is no problem with the implementation. As noted above, most early CD players multiplexed a single DAC with much the same result. There was much criticism from the vinyl fanatics back then that this was yet another dreadful flaw in digital. But it is no different to a change in listening position of less than an inch.
One suspects that the issue here is in the digital processing, but still there is no actual flaw.
 

JohnYang1997

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The delay looks to be about 0.02ms. So two samples at 96khz. If it really is a constant delay there is no problem with the implementation. As noted above, most early CD players multiplexed a single DAC with much the same result. There was much criticism from the vinyl fanatics back then that this was yet another dreadful flaw in digital. But it is no different to a change in listening position of less than an inch.
One suspects that the issue here is in the digital processing, but still there is no actual flaw.
The sample rate tested here is 44.1khz instead of the maximum 96khz, which means it should be exactly one sample of delay between channels.
 

JohnYang1997

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The delay between channels leads to rising phase difference vs frequency. The difference will be audible. It makes the sound more rounded, mid forward and warmer. I have measured a usb dongle having the same issue and was puzzled why it sounds different.
 

nagster

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Mr. amirm
Thank you as always.

You need to reduce your work as you are chased by audio equipment every day.
But I also want to see a series of measurements for improperly designed equipment.

32tone
Linearity
J-test
Gain
Noise level
THD+N vs level
THD+N vs frequency
IMD vs level
etc...

Bad examples are also one of the knowledge.
Once an automated technology for measurement and review making has been developed, please do bad 32tone too.
 

Francis Vaughan

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It makes the sound more rounded, mid forward and warmer.

How? The time difference is identical in effect to moving one loudspeaker back by about 2cm, or your head by a similar distance.
If you fed the DAC with a mono signal and summed the outputs into mono you would have a problem. Output at 20kHz would be close to zero. But in normal use the channels are separate. Which channel has the proposed problem? Is one channel delayed or the other channel forward in time?

The sample rate tested here is 44.1khz instead of the maximum 96khz, which means it should be exactly one sample of delay between channels.
Yes, one sample. I misread Amir's comment and interpreted it as being constant with sample rate, not frequency.
 

JohnYang1997

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How? The time difference is identical in effect to moving one loudspeaker back by about 2cm, or your head by a similar distance.
If you fed the DAC with a mono signal and summed the outputs into mono you would have a problem. Output at 20kHz would be close to zero. But in normal use the channels are separate. Which channel has the proposed problem? Is one channel delayed or the other channel forward in time?


Yes, one sample. I misread Amir's comment and interpreted it as being constant with sample rate, not frequency.
You may want to try for yourself. This is what's happening with dB magix ac3 I used to have. I can't explain exactly why but as it's touching how our brain processing sound, it's too out of scope for me.
Yes it's one channel "waited" a clock cycle. Most likely LRCK in i2s. (can have different causes tho)
 

AnalogSteph

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Amir, please remeasure with SPDIF input.

Anyone wanna bet this one uses a PCM27xx/29xx as a USB receiver? An older, buggy one with the documented 1-sample offset between channels, and of course 16-bit only since that's all they'll do? Those of us who've been around for a bit will no doubt remember how USB output used to be limited to 16 bits for years until XMOS and the like came along.

If not upgraded, this DAC should have shipped with a PCM1716 DAC chip - DR 106 dB(A), THD+N -96 dB. It could be upgraded to a WM8716 (112 dB(A), -92 dB / -97 dB at -1 dBFS).

Since distortion looks fine as-is, I imagine noise will come in closer to spec once you can actually get 24-bit samples into the thing.
 

Francis Vaughan

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You may want to try for yourself. This is what's happening with dB magix ac3 I used to have. I can't explain exactly why but as it's touching how our brain processing sound, it's too out of scope for me.
Yes it's one channel "waited" a clock cycle. Most likely LRCK in i2s. (can have different causes tho)

Hmmm, you found a product that didn't sound quite right, and discovered a one sample offset, and concluded that the offset was the cause of the poor sound. That doesn't prove it had anything to do with the offset. Perhaps it was just a bad product.

Again, if you move a loudspeaker by 2cm you get exactly the same offset in time. One would have to assume that doing so would cause the same problem with the sound.

One would want to create a DBX trial with some appropriately processed audio to test this.
 

JohnYang1997

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Hmmm, you found a product that didn't sound quite right, and discovered a one sample offset, and concluded that the offset was the cause of the poor sound. That doesn't prove it had anything to do with the offset. Perhaps it was just a bad product.

Again, if you move a loudspeaker by 2cm you get exactly the same offset in time. One would have to assume that doing so would cause the same problem with the sound.

One would want to create a DBX trial with some appropriately processed audio to test this.
Loudspeaker in the room is masked with all the reflections. If you are in an anechoic chamber you will definitely hear such effect. And so with headphones/earphones this effect is prominent. I obviously did blind test that was in 2019. The difference is big. If you recreate it yourself you would hear it very clearly. And when you are used to the sound, you will hear normal DAC as too poppy too spitty.
 

holbob

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Noughties hifi wigwam clique members are going to be LIVID with you Amir!
 
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