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?😊

KS12027 Horn

The KS12027 horn perched on top of my repurposed Altec 861 cabinet loaded with an Altec 414A woofer should actually be residing inside a ~ 4 cubic foot slanted cabinet with a Western Electric WE713C compression driver  bolted to its throat + a WE728B 12" woofer = Western Electric WE757A monitor speaker system.

I was honored to host this KS12027 horn and provide more modest accommodations for a couple of weeks courtesy of my audio preservationist buddy John Piro.

He rescued this KS12027 horn with a damaged 0.7" aperture and repaired/modified it so that mere mortals like myself can sample its delights using a more pedestrian 1" exit Altec 802 compression driver. 

Mono Hi-Fi set up: Neat P58H + Calrad SV16 + GE RPX or DL102, JEL SE2A3 mono integrated amp with Hashimoto H-203S OPT.

All of my listening was done with the above set up.

Altec 414A + mod'ed KS12027 + 802 + GPA34852

From the moment I mounted the KS12027 + Altec 802 combo above the Altec 414A woofer, the first adjective that came to my mind and stuck for the rest of its stay was, natural! Just like its WE/Altec 32 and KS12024 relatives, this is also a horn that doesn't sound like a stereotypical horn. In fact, the articulation (attack and decay of notes) and overall presentation of harmonic overtones via the KS12027 is even more natural and realistic. It made the Altec 32A/32C and Azzolina KS12024 sound merely like very high quality Hi-Fi which mainstream audiophiles may find more appealing. These findings were echoed by my friend Ding during his recent visit to the man cave.

Altec 32C, KS12027, Azzolina KS12024

Even if I loved the KS12027 so much, I didn't want to get attached to something I may never be able to own. So this past weekend I met up with John at a ham fest and handed back this valuable piece of audio history. After giving him my rave report, which is hardly representative of what most audiophiles like nowadays, he was not dissuaded. He is still seriously considering reproducing them. 😎

Darling Amp, JE Labs Style

It's been 20 years since jc morrison started hosting the new york noise audio design exhibition at his Hoboken, NJ loft. One of the highlights of that year's exhibit was Darlingfest '99 as reported by Jeremy Epstein in the final issue of Sound Practices. The Darling amp was the brainchild of Bob Danielak and was published in Sound Practices Issue 15.

Jeremy's octal driven Darling amp made a lasting impression on me but I never got a chance to build my own version due to a busy performing schedule.

While I was organizing my workshop in the basement this past winter, I found power and output transformers from a Sony TC500A tape recorder + other parts to build a Darling amp.  

The chassis cleaned up nicely with a wire brush. Then I drilled, cut and punched the necessary holes before spraying a fresh coat of silver Hammerite.

I chose the 6F5 hi-mu triode with a cool grid cap as the input/driver tube.

To qualify as a Darling amp, the indirectly heated 1626 transmitting triode  output tube is de rigueur.

The TC500A donated a healthy 6CA4 rectifier.

!!!WARNING!!! 

The voltages found in this circuit can be lethal, build at your own risk!!!

My interpretation of a Darling amp is ready for testing and listening!

Bench Testing

Both channels driven

P = V²/L

2.415 x 2.415 = 5.832/8 = .729 or 729mW per channel

Hum and Noise = 1.8mV

100Hz

1kHz

10kHz

I did not expect this level of performance from the cheap looking Sony OPTs, which I also verified while listening to the amp!

Bass extension is surprising from this 3/4 watter! It is deeper and tighter compared to my Tango'ed SE171A amp. However, in the midrange, the true Directly Heated Triode shines. The 1626 was just a touch veiled in comparison. Although it sounds more powerful than the similarly rated SE171A, it also doesn't overload as gracefully. I remember hearing a similar phenomenon when Steve @ Angela Instruments asked me to build the Simple 5691 > EL34 SE amplifier. The Simple 45/2A3 clips with more finesse. Is the cathode causing the relative lack of transparency and harder clipping?

The days of $5 Type 45s and 2A3s are long gone. But NOS 1626 tubes can still be acquired for under $10 a piece. Since it has a cathode, with careful wiring less than 2mV noise is achievable on AC heating which is quiet enough for me even on headphones. There's no need to hunt for hard to find 25-75 ohm, 2W hum nulling pots. That's just a couple of reasons as to why a Darling amp derivative is one of the cheapest and easiest routes to a DIY SET amp nowadays.

Did I mention that it also does a great job driving headphones?

headphone adapter/attenuator schematic for 
efficient headphones ex: Grado SR80, Koss KPH30i/Porta Pro
Lower efficiency/high impedance classic headphones like the 600 ohm AKG K240 Monitor, 
Sennheiser HD420, HD6xx and Orthodynamic/Planar magnetic: Echo TDS-16, 
Fostex T10 and Yamaha YH-1, can be driven directly from the speaker terminals

Happy listening!

Thrift Store CD Players for Red Book Aficionados

Multi-bit CD players

When I started using and hacking Dynakit tube equipment, they were about 25 years old on average. During that same time frame, I bought my first CD player which was fitted with the Philips cutting-edge TDA1541 16-bit DAC chip. 

Fast forward some 30 years later, SACD and DVD-A have been commercial failures, CD sales have been on steady decline and took a recent nose dive in sales. Except for cool LP lovers and bandwagoners, most people nowadays are either downloading or streaming their music.

So I'm buying cheap CDs unloaded by downloaders and streamers. Stuff I couldn't afford or justify in the 80s and 90s, while hunting for unloved CD players whose lasers may die any time soon...

Yep, I don't go with the flow, I never did... 😉

Sony DVP NS900V

After rediscovering the 16-bit Magnavox CDB 473, I wasn't too keen on acquiring another sigma-delta chip'd multi-player. However, for 1% of its original selling price, this Sony DVP NS900V was an irresistible deal! The fit and finish on this unit exudes quality.

Red Book Mastered CDs decoded by this machine sound polite but lack the excitement delivered by the better multi-bit players below.😒 That's why I didn't bother to take under the hood pics.😜 Maybe the SACD performance is slightly better than the Denon DVD-2910? Even if this is a slower handling machine for CDs, I can use it as a transport when my Philips lasers die. 😉

Shure SV40

Very robust build! The all-metal construction makes this Shure SV40 seem as hefty as the NS900V above. Not sure who OEM'd this unit. I read references to NEC and see traces of Sony in the transport. 

SV40

This Burr-Brown PCM54HP chip'd unit is very audiophile-oriented. The midrange has depth and detail, with a tight and deep bass + extended highs. Even if I'm yearning for more warmth in the midrange, I understand why Burr-Brown multi-bit DAC chips have an avid following. It is well deserved! 

Scott DA952

I didn't want to pay the $7 tag for something that looked chintzy, but then it was a $1 red tag sale day and it had a red tag, so I relented.

YM3020 DAC

The YM3020 is a 16-bit Yamaha chip. A buck got me a dark, mechanical and 2-dimensional sounding player. 😞 Mediocre at best. I should have spent the dollar on a CD instead. 😔

Fisher AD-870

Fisher was acquired by Sanyo in 1975, so I took a chance on this '86 Studio-Standard CD player hoping that it might have a Sanyo LC788X chip which are supposed to sound decent. No dice, it was fitted with a Yamaha Y3015 chip.

Y3015 DAC

Another mediocre CD player. 😞 It sounded bright, mechanical and flat. I don't know what's going on with these Yamaha chips.😖 At least my six bucks went to charity.😊

Magnavox CD2000

This Magnavox CD2000 and its CDB492 twin are entry level models from the late 80s to early 90s. They were manufactured in Mexico, equipped with the CDM-4 transport and the economy Philips TDA1543 16-bit chip, which has found its way in a few high end DACs like the Border Patrol, amongst others. 

Instead of the  "16, 18 or 20 bit, dual or quadruple DAC, 4, 8 or 16 X oversampling" emblazoned on the front panel, this was an understated "16-bit dual D/A converter + Digital Sound Processing" print. I didn't find a Philips SAA7220 oversampling/digital filter chip inside so it's safe to assume that this is a non-oversampling circuit. Based on my internet research, the output stage has a brick wall type analog filter(?). Here's a video of the CDB260 which looks very similar under the hood.

CD2000/CDB492

These machines don't have the ability to resolve detail like the Burr-Brown'd Shure SV40 above or the two TDA1541 players below. However, the midrange is seductive and a fine aperitif to Non-OverSampling (NOS). If you are squeamish about not being in the in crowd, skip this broken/defective design. This is strictly for music lovers!

Magnavox CDB610

I've made it my mission to rescue any 16-bit Magnavox/Philips CD player I find in the wild.😄 This CDB610 was made in Belgium in the early 90s. It has a more upmarket feel compared to the Mexican-made CDB492/CD2000.

CDB610

Even with the SAA7220P/A oversampling/digital filter chip added to the TDA1543 DAC, this machine couldn't sonically equal its TDA1540 or TDA1541 siblings below. Based on sheer musicality alone, the NOS Mexicans above and Sony CDP190 below have the upper hand over this Belgian. However, I'd rather listen to my Red Book CDs via this Belgian than through a time slicing DVD/multi-player. 

Sony CDP190

I found this '89 model Sony CD player along with a pair of Rat Shack Minimus 8s at a thrift store I've frequented for years but never found anything interesting. It doesn't look too promising under the hood. Well, there's nothing there....except behind the front panel.

CDP190

I was surprised to learn that somewhere behind the SMD and SOIC laden circuit board of this early '90s entry level Sony is a Philips TDA1543A DAC chip. The "A" version was exclusively designed for the Japanese input format which is not I2S compatible, unlike a regular TDA1543. Sony did a good job using its in-house chips for oversampling and digital filtering because this machine sounds cleaner than the similar spec'd CDB610.

The midrange of the NOS CD2000/CDB492 + slightly more bottom and top end extension = CDP190!

Sony CDP505ESD aka CDP222ESD

This model belongs to the Sony ES (Elevated Standard) series. In spite of the deluxe parts - Nichicon and Elna caps, discrete bypass capacitors surrounding the TDA1541 chip (instead of SMDs in most Magnavox/Philips) - I don't think this was truly a top of the line model since it was also sold as a mid-range CDP910. Besides, the real Sony ES models I've seen were all metal. Even if this has slightly more heft than the CDB650 above, the chassis is also a plastic + metal composite. It is safe to say that both models were designed to compete head on. Sony used its own CXD1088 digital filter instead of the Philips SAA7220P/A, B or C found in Magnavox/Philips CDPs.

CDP505ESD

Compared to the Belgian made CDB650 below and the CDB473, the TDA1541 + CXD1088 combination renders a clean and clear midrange, tighter and deeper low end response + more extended and airier highs. The net result is a slightly recessed midrange tonal balance. Perhaps this sounds closer to the truth, but I prefer a bit of sugar coating. 😉

Magnavox CDB650

The CDB650 player received a highly favorable review in the March 1987 issue of Audio. A couple of months later, in the June 1987 issue, Walt Jung wrote an article on how to make it sound even better. This spawned a cottage industry of modifications to Philips based CD players. The build quality was a notch better than the later CDB47X series, which did away with heat-sink fins for the power supply.

CDB650

IMHO, the "filtered output" was a useless expense. It causes a very audible high frequency roll off. (Did the Philips executives in Eindhoven really think Red Book CDs sounded that harsh then?) The money saved from that filtered circuit could have gone into better quality parts like Sony did above. Used via normal output jacks, this model sounds as good as the later CDB473. The midrange has a three-dimensional spatial rendition the TD1541 DAC chip has become known for + very good extension throughout the audio bandwidth. 

I am preserving the Magnavox CDB650 and Sony CDP505ESD in their original form for posterity since TDA1541-equipped machines have become a rare sight in thrift stores lately!

Magnavox FD1041

First generation 14-bit, 4 x oversampling Philips/Magnavox CD players with all-metal transport and chassis have achieved collectible status. I had to settle for this entry-level, mid-sized player with a plastic CDM-2 transport and a plastic + metal chassis to sample the sound of the first generation Philips DAC chip. 

FD1041

Philips employed 2 x TDA1540 14-bit DAC chips + the SAA7030 digital filter to yield (close to) 16-bit resolution in their first generation machines. The frequency extremes is probably at par with the economy TDA1543 equipped players above, if not better. But definitely not as extended in the frequency extremes nor does it have the ability to resolve detail like the CDB650, CDP505ESD and some of the better TDA1543 chip'd CDPs. Instead, one is rewarded with a glorious 3-D midrange. A certified classic!

TDA1541 + TDA1543

Aside from having produced musical sounding DAC chips, the Philips swing arm laser/transport design was very stable (least prone to mis-tracking) and reliable. As the saying goes in technology, always buy from the original inventors. Philips and Sony invented the CD format and based on this informal survey, the best sound came from these two manufacturers.

Philips Swing-Arm CD Transport

 Unlike classic tube equipment which can be repaired, restored and/or modified, the lasers in these 30-year-old CD players have a finite life. AFAIK, replacements are either very expensive or unobtainium. Be wise and don't gamble too much $$s. 

As enthusiastic as I may seem about Red Book CDs, I believe that this technology never quite equalled the LP in terms of musical satisfaction. I only enjoy it now since the software is practically being given away.