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Denon DA-500 Vintage R2R DAC Review

amirm

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This is a review and detailed measurements of the vintage (?) Denon DA-500 DAC. It was kindly purchased by a member on the used market and drop shipped to me. Interest was to find historic products with something cool about them. In this case, it is the "alpha" processing in the DA-500 which interpolates samples and supposedly some version of it lives even today in Denon AVRs. Looking around, clean DA-500 DACs cost about $220.

Nice to see a wide, room chassis compared to cramped little DACs we see today:

Denon DA-500 DAC Coax SPDIF Stereo Review.jpg

Of course there was no concept of USB input at the time so the only inputs are Toslink and Coax:

Denon DA-500 DAC Coax SPDIF Stereo back panel vintage 20 bit Review.jpg

Ah, the fun days of hi-fi when high-end gear could get away with an attached cheap mains cable!

The heart of the DA-500 is BurBrown (now TI) PCM1702 sign-magnitude dual-segment R2R DAC. For this reason, it seems to still be cherished today.

Denon DA-500 DAC Measurements
Let's start with our classic dashboard before we get fancy:

Denon DA-500 DAC Coax SPDIF Audio Measurements.png


Interesting that it output higher than 2 volts. Likely a good number of sales were made compared to other DACs due to higher than normal volume!

SINAD which is the relative sum of noise and distortion is in "poor" bucket using today's standard, falling short of even CD's 16 bit dynamic range despite the unit sporting a 20-bit DAC. I am going to jump to linearity test now to tell us how this DAC works:

Schiit Modius  DAC Coax SPDIF LInearity Audio Measurements.png


Whenever you see a zigzag like this that settles below 90 dB, it indicates that the DAC is simply throwing away extra bits in our 24 bit samples and is just using 16 bits. This type of conversion is bad as it generates steps in response that result in fair bit of distortion. Proper conversion with dither (noise addition) needs to be performed. This is important today due to existence of 24-bit content but at the time this DAC came out, the only source was 16 bits so it is partially forgiven. I say partially because the DAC was 20 bit capable so truncation should have been to 20 bits, not 16. That would have sharply lowered the impact above.

The truncation creates the busy "grass" that you see in the FFT above. If I feed the DAC 16-bit data (without dither), it cleans up that spectrum (SINAD remains the same):

Denon DA-500 DAC Coax SPDIF Alpha Processing FFT Audio Measurements.png


The output would be the one to the right. Notice how the dominant distortion and power supply spikes remain and hence the reason SINAD does not change.

There is a dealer demo mode in this unit using secret key combinations which allows one to turn off Alpha processing which is on by default. Turning it off and using the suggested -80 dBFS sine wave gives us the display on the left. Our main tone has a skirt around it now and there are some higher order spikes close to 20 kHz. We can better see what is going on in time domain, scope display. Indeed Denon suggested dealers use a scope to show this feature!

Denon DA-500 DAC Coax SPDIF Alpha Processing Audio Measurements.png


The sine wave is compute generated and does not have dither. As a result, we see distinct steps in output level because they are rather coarse in 16 bit context. Turning on Alpha processing which interpolates between samples adaptively (switching between algorithms based on content), we get rid of steppiness. The waveform is distorted though and hence the reason the spectrum still had all the noise and harmonic distortion. Likely if an analog scope of the era was used, this would look smoother.

Let's repeat the test but now using a modern DAC (Schiit Modius). We don't have alpha processing here but what we do have is the ability to turn on dither on the source samples:

Schiit Modius  DAC Coax SPDIF Time Domain Audio Measurements.png


It may look messy due to noise smearing the samples as we step from one value to another. Have we done any good? Yes. Let's look at this in frequency domain:

Schiit Modius  DAC Coax SPDIF Audio Measurements.png


Notice how we have achieved perfection on the right with dither. All harmonic content has disappeared like magic! We just have our main 1 kHz tone now and nothing else. There was a cost however: noise floor came up. We have taken the energy of those harmonics and randomized them throughout the spectrum. That noise may be audible but is much less annoying than not dithering. Low level signals sound gritty and harsh without dither.

In real life content is not a computer generated sine wave. Almost all production is performed using 24-bit samples. If 24-bit is then converted to 16 using dither, then we don't have to worry about steppiness and resulting harmonic distortion that is seen on the left. In this regard, the Alpha processing in Denon doesn't do anything useful. Even without dither, 24-bit content has good bit of noise (rightmost 4 bits is guaranteed to be noise) so it self-dithers by itself to some extent. So one way or the other, we have a situation far from -80 dB undithered test signals.

Personally I like to get the high-res master in 24-bit format so I don't have to worry if the producer knew to properly dither the content. This would obviate everything we have discussed so far.

For completeness, here are a few more measurements:

Schiit Modius  DAC Coax SPDIF Jitter Audio Measurements.png


Schiit Modius  DAC Coax SPDIF Dynamic Range Audio Measurements.png


Denon DA-500 DAC Coax SPDIF IMD Audio Measurements.png


Conclusions
I suspect most of you don't have interest in this DAC. But hopefully found it educational with respect to mention of Alpha processing in Denon AVRs and general signal processing concept of dither.

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

Appreciate kind donation using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 
Thank you or this indeed. I actually have a sony professional cdp d500 as my main cd player and I love it. In the Sony this is the same chip, pcm 1702, but in dual mono configuration, I couldn’t know If it gives it a benefit to use 2. Probably because it makes it easier to have balance outputs would be the reason for this. Funny thing is, it is, subjectively a great sounding cd player, but obviously only used for 16 bits redbook cds. I had it hooked to a modern dac, but lately for kicks I went back to use the r2r one. there is definitely an audible difference, and knew full well that it’s not as accurate than modern delta sigma dacs, but somehow I like it. I don’t want to get into the reviewer senseless lingo here to describe the sound, but it’s pleasing to me... (being political here... I know what I like about it... ) I know, subjectivity... Way back I worked in radio broadcasting, so I´m very familiar with he sound of em and it might be this familiarity that makes me biased. On another note, it’s not relevent to this review, but it’s sound is not the main reason I like this cdp. It’s such a robust hyper reliable thing, with great tactile feedback, ultra fast loading, and any cuing functions you can think of, and obviously all kind of digital outs, including aes ebu. I wouldn’t want anything else for cd transport at any price. They sometime show up around 200$ in the used market and it’s a great score for anybody that uses cds.
 
Any chance we can see a square wave? Denons Alpha processing was said to not show ringing when on square waves.
 
Any chance we can see a square wave? Denons Alpha processing was said to not show ringing when on square waves.
I ran but did not save it. It was ringing.
 
Very interesting!

Over time, Denon has claimed to improve the precision of alpha. For non dithered sources like vintage PCM recordings, it might actually make a difference. But as I suspected, the reason Alpha is not a must have today is the availability of high res audio and “Super Bitmapping” and dithering with modern recordings.

The underlying DAC performance is poor but could you hear a difference between ALPHA on and off even if the measurement is the same due to smoothing?

It makes me wonder how Ultra AL32 might perform or if you added it to the front end of modern DACs where the base performance is better.
 
But how would it perform using an audiophile mains cable? ;)
 
I just looked it up and apparently this was sold from 1994 to 2000 and cost 700DM (couldn‘t find US pricing).
It‘s a real shame then that many AVRs don‘t do better than this today.
 
Excellent review. Many thanks for the educational aspects. I have to admit that I wouldn't mind having that thing paired with a nice vintage class A amplifier and some eighties' large KEF's for an epic retro listening room.
 
The digital receiver on this unit wouldn’t have supported anything other than 16-bit input 32/44/48 kHz. Could sending it 24-bit data add noise?
 
The main cable looks like it would be the first thing to break; cable break after few time moving the device around.

I interpreted the panther the same: the faule (lazy) panther who does not care about measurements at all and want's to chill.
Every time measurement is for educational reasons or others, use this panther.

By that logic you also need an educational-panther.
How about an angry-panther, if the product is bad?
 
I arrived too late to the party. Wanted to give some of these R2R DACs a try for fun, but I am not going to pay 100 USD für most likely fake ICs from chinese Ebay vendors ;)
 
I arrived too late to the party. Wanted to give some of these R2R DACs a try for fun, but I am not going to pay 100 USD für most likely fake ICs from chinese Ebay vendors ;)
Cloning an IC is certainly possible, but for it to be a profitable venture, those forgers would need to sell millions. That’s not being done. Steal the IP and use it in cheap products yes, make lookalike products using cheaper parts and IC, yes as well, but I wouldn’t worry about a buying vintage gear that have a « fake IC ». This doesn’t make sense. You didn’t arrive too late for the party, quite the opposite, dacs and digital gear lose so much value (unlike reputable brand amps) that it’s a great time to do that, trying them just for fun. The example I give in my post higher up, that Sony player, used to sell over 2000$. they can be had for one tenth of the price.
 
I think he means pin compatible chips with fake brandings, something that seems to be fairly common indeed.
 
I think he means pin compatible chips with fake brandings, something that seems to be fairly common indeed.
Is it common? You say « seems » » I personally never rans into evidence of that in ICs, but I may be wrong. just think of the production facility of Texas Instruments, and the volume at which they can spit out chips. I have a difficult time believing that someone could produce swap ins at a price that would be cheaper than just buy from them. Now Maybe there is a semi market for discontinued tech, but really? How many r2r pcm1702 dac chips copy would a compagny be able to move in a year today that would justify such an investment, reverse engineering, tooling, and production? Again, difficult to believe but I’ve been surprised by China before. Now, you may mean something else than r2r, but still, to be pin compatible, it also need to at least work, and you can’t just put a totally different tech in another design. The output stage wouldn’t be compatible.
 
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