Multi-bit DACs from yesterday and today

Multi-bit DACs from yesterday and today

Since I listen primarily to 16-bit/44.1 kHz sources and have found the decoding capabilities of the USB DACs and DACs using sigma-delta chips musically challenged for that purpose, I searched for alternative ways. I backtracked and then moved forward.

Listening Set-Up

Magnavox CDB650 + Sony CDP505ESD
used as CD transports

Raspberry Pi 3B+/Volumio/Allo Digi One
+
Anker Power Bank

1:1 line level audio transformers
as digital filter
between DAC and preamp 😊

Near-field 

Altec 755Cs in 618 Cabs

Main System 

Man Cave HiFi

Audio Alchemy Dac In The Box

 To alleviate my disappointment with the performance of my Philips CD921 bitstream CD player, I bought this Dac In The Box in the 90s with the optional high current power supply. After the Philips CDP died, this unit soldiered on, hooked to the digital out of my Sony DVP NS755V.

While taking the circuit board out of its case, I realized that this may have been the ancestor of the Topping D30 due to its packaging. The main difference is, the D30 is powered by a cheap (potentially noisier) wall wart containing a Switch Mode Power Supply. OTOH, the basic DITB was still equipped with a linear power supply with a real transformer - silicon steel laminations + copper windings - a luxury item nowadays!

The CS8412 input receiver dwarfs all the other ICs including the 2 x Analog Devices AD1860 18-Bit DAC chips. Unlike the Burr-Brown PCM-63P below (or the Philips TDA1541), the AD1860 has a built-in op-amp that serves as an I/V converter. There's provision for coaxial and optical inputs but no USB. "Designed and manufactured in USA" is something we rarely see nowadays...

This was a highly-rated budget DAC in the 90s. Almost 30 years later, I still find it to be a pleasant sounding unit - detailed yet smooth overall, with a nice midrange and good frequency extension at both extremes. Maybe I'm yearning for more dynamics, because compared to the three other DACs, this is not as musically exciting. However, I'd much rather listen to this than either of my CS4398 chip'd DACs.

Adcom GDA600 - specs

Another American-made device from the 90s, this DAC was designed to a high standard. Because of the 2 x Burr-Brown PCM-63 DAC chips in its circuit, it has developed quite a following amongst classic multi-bit DAC aficionados. This DAC chip, along with the Philips TDA1541A S1/S2 single/double crown and the Ultra Analog U20400A, are considered the epitome of multi-bit DAC design.

To the left is a well-regulated and filtered power supply, while to the right is the digital and audio board, liberally populated by period correct plastic film capacitors for audio coupling. Just like the Audio Alchemy DITB, this predates USB. Instead, there are two coaxial inputs, an AES/EBU input and optical input plus a digital coaxial output.

The digital bits are fed to a CS8412 input receiver, oversampled eight times by a Burr-Brown DF1700 digital filter and processed by 2 x Burr-Brown PCM63P 20-Bit DAC chips (one for each channel). Finally, two Adcom 7AA op-amps serve as an I/V converter for each channel's output.

The sound of the GDA600 is very authoritative and detailed. It easily has the best extension at the frequency extremes. Starting from the deep and well-controlled bass all the way to crisp and extended highs. I found the midrange just a touch lean and dry. The sound field is the widest in this survey but not quite as deep compared to LPs or even the Audio GD below. It sounds very exciting due to the excellent rendition of dynamics. The tonal balance is very neutral and should appeal to listeners who value accuracy and detail.

This is a popular model amongst DIYers for tweaking and parts upgrades. Maybe replacing the op-amps with FET equivalents and the plastic film caps in the audio signal path with paper in oil type will warm this unit up a bit.

Muse TDA1543 x 4 mini DAC

This was a very popular entry-level Non-Over-Sampling  (NOS) available at Amazon and eBay until a couple of years ago when supplies dried up. I got this unit from the used market for an Alex above the original going rate of $55, shipped.

To keep costs down, 4 x TDA1543 DAC chips are employed to produce line level output without resorting to an active I/V converter stage for each of the two channels.

Polyester Wima caps replaced the original electrolytic output caps

I replaced the stock electrolytic output caps with film types and the stock SMPS wall wart with a linear power supply. 

SMPS vs Linear PS

With these two simple upgrades in place, this DAC portrayed a natural and vivid midrange which is musically captivating. After extended listening, I realized that the frequency extremes were truncated. It also lacks the ability to resolve complex musical passages which get compressed and congested. Based on my experience with TDA1543 chip'd CD players, an active I/V converter may address these issues. That said, I'm not sure if it is possible to get this level of musicality in reproducing a jazz trio or chamber music for under a Ben! 

Audio GD R2R-11 - specs

Mid 2018 model

Audio-GD is an audio company that prides itself with using discrete components in their designs. Since this is an NOS type DAC, the digital bits are processed directly (no oversampling filter) by an R-2R ladder (2 x DA 8 modules as pictured below) to convert digital data into analog signals. Unlike the older two DACs above, the Amanero USB input supports PCM, DSD and DXD.

From the Audio GD website

I will skip the technical description and let this picture speak for itself. Suffice it to say, I love the handcrafted/cottage industry vibe. Hence, the $384 landed cost is justified!

 This DAC has a tube-like three-dimensional quality and clarity in the midrange. The layering of vocals and instruments in the sound field easily bested the other two even if it wasn't quite as wide as the Adcom. Very good extension at the frequency extremes, second only to the GDA600. Excellent in presenting micro dynamics (even better than the Adcom), there's no need to turn the volume up to high SPLs for excitement. However, at the louder side of the spectrum, the GDA600 has the upper hand in control and authority.

I listened to the R2R-11 in the neutral setting since the warm setting was too mushy in the context of my two set ups. Although I'm just an occasional headphone listener, I heard the same tubey quality through my Grado SR80 headphones. With my CS4398 DACs,  I always found the coaxial input to sound superior to the USB. However, with this unit I could not detect a difference, so the Amanero USB input must be doing a good job!

This DAC reminded me very much of my JLH 1969/Nobsound NS-02g Class A amp - a solid-state device that tries very hard to emulate a tube unit. Almost there, but not quite...

The DAC Wrap

After listening casually and intensively to these four DACs this past year, I realized that I want the virtues of all four devices without their vices - the dynamic presentation at louder levels of the GDA600 and the micro dynamics of the R2R-11, the transparency and tube-like quality of the R2R-11 (is it because of NOS?🤔), the frequency extension and detail resolution of the GDA600, the wide sound field of the Adcom and depth of the Audio GD, the long-term listenability of the Audio Alchemy AND the affordability of the Muse Mini TDA1543x4. Can I have my cake and eat it, too?😊