nos TDA1541 tube DAC

I've become cynical of the latest is best mentality because in my 30 years of searching for sound that pleases my ears, I've always gone back to move forward. From this experience, I've learned to use planned obsolescence to my advantage by investing in old school components that have achieved classic status.

 There is a common denominator between the Philips TDA1541 DAC chip and the Western Electric 300B directly heated output triode vacuum tube. The former brought digital sound to everyone’s homes in the '80s, while the latter amplified talking pictures in movie theaters in the '30s. Both have also been rediscovered for their distinguished musical abilities.

This tubed TDA1541 sans oversampling multi-bit DAC evolved from my frustration with its bitstream and delta-sigma successors, revisiting and studying multi-bit CD players and DACs, performing Magnavox CDP + DAC mods, and other digital audio experiments.

!!!WARNING!!! 

The voltages in this circuit are potentially lethal! Build at your own risk!

If you are a metrics-obsessed audiophile who spends more time arguing in audio forums instead of listening to music because you can't trust your own ears and would rather buy a component approved by a hifi guru and/or his/her test equipment, STOP 🚫! You'll be offended by the contents of this blog, especially this project!

However, if you agree with Radiotron Designer's Handbook, 3rd edition published in 1940, that the THD metric should be abolished and better test procedures and standards established, you may proceed.😊

This project starts with the deconstruction of an already obsolete DAC board still available from eBay sellers. Since the TDA1541 chip has been out of production for over 20 years, I scavenge them from the CD player graveyard.

I incapacitated the analog section of the DAC board by removing the high speed/fast slew rate op-amps and low ESR signal capacitors, which will be replaced by a slower and harmonically more satisfying circuit from a bygone era. 

Non Over Sampling (NOS) measures like a broken component but my ears prefer musicality over accuracy, so the SA7220P chip was tossed and the circuitry bypassed. Speaking of accuracy, to what? I wasn't at the recording session, so I don't obsess about it.😉

This picture shows the spots where I tapped the right (AOR 6) and left (AOL 25) analog outputs of the TDA1541 chip. The DAC's delicate and jagged left and right analog output stream will be connected via shielded cable to a cutting edge I/V converter + vacuum tube smoothing circuit advertised and marketed by savvy Mad Men as retro-tech art.😎

I was very impressed by the sonic flavor introduced by the Western Electric 396A/2C51 in the buffer section of my 21st century Xiang Sheng DAC 01A. But in this particular application - gain stage + buffer -  the WE396A couldn't deliver the Carnegie Hall and Village Vanguard atmosphere I was trying to recreate. Caveat: the yellow WE logo doesn't offer a 100% satisfaction guarantee. 

So I rewired the B9A 9-pin sockets for a pair of 6CG7s, which I've already used successfully as a buffer for my TDA1543 DAC. These are the Noval-based equivalents of my favorite medium gain (mu)/medium transconductance (gm) 6SN7 octals, esteemed for their linearity as an audio amplifier. 

The circuit topology is very similar to my line stage preamp with the first triode section configured as a gain stage direct coupled to the second triode section wired as a low impedance cathode follower/buffer. No negative feedback is applied in the circuit to maintain signal purity. This tube circuit also functions as a sound processor, which is beyond the abilities of fast slew rate op-amps.😄

I recycled a power transformer from a Heathkit mono FM tuner. Using a 6X4 tube rectifier, the rectified 480VCT  @ 60mA secondary feeds a capacitor input filter, then the B+ rail is split via 2 x 15H @ 30mA chokes to provide 295 volts of ripple free DC to each channel. The 6 volt DC supply, which lights up the 6CG7 filaments, is provided by a separate filament transformer. This archaic method of building a power supply enhances the DAC's tonal character!

Finally, I assembled the Back to the Future DAC on an organic 3/4" thick Baltic-Birch bread board. Even if it has a USB input, DSD, MQA and other so-called Hi-Res files are downsampled to 16-bit/44.1kHz PCM. That makes it 100% compatible with at least 90% of music streamed on the web. Since it makes my two-for-a-buck 4.75” silver discs from thrift stores and flea markets come to life, I don't ask for more.

Let's have some chips...

The reputation of this ubiquitous DAC chip was built upon regular production run TDA1541s, which can still be acquired for under $50. BTW, this is a DEM (Dynamic Element Matching - see TDA1541 FAQs) chip, not an R2R ladder DAC chip, as it's commonly misidentified. 

So there's no reason for angst if hand-selected and tested single and double crown S1 and S2 TDA1541A chips command SothēBy's prices or reside in private audio museums in Asia. Buyers should actually beware of high dollar re-stenciled regular TDA1541s studded with crowns. They will work but won't sound any better than the chip I meticulously unsoldered from an '80s junked Magnavox CDP.

1kHz square wave from Stereophile Test CD3
Stock Magnavox CDB560 CD player

Fortunately, I got a chance to sample a genuine single crown S1 graciously donated by Gary B. This select chip made my DAC sound a bit more transparent and cleaner, with a touch more detail and resolution. But I have to reaffirm that not having an S1 isn't a deal breaker. In fact, the darker and warmer sounding regular TDA1541s and TDA1541As can be a blessing in systems that are a bit hot in the top end. 

1 kHz square wave from Stereophile Test CD3
nosTDA1541tube DAC

 Not very relevant to this NOS DAC project, but AFAIK, the only difference between TDA1541A and the non-A is that the A can do 8x oversampling while the non-A is limited to 4x. But let's not go there anymore. Been there, done that...

NOS and Digital Filters

Before I even became aware of NOS DACs, I had been using line transformers as digital sound processors. If you're worried about non-oversampled digital artifacts destroying the irreplaceable diaphragms of your Altec 3000 super tweeters, look for bandwidth limited military surplus transformers. 

But the true analog-sounding line transformers JE Labs uses are those that have a flat response from 30 to 15,000 cycles, like the bokeh'ed pair of Western Electric 111C repeat coils and the UTC A-20s in front. There are so many sleepers out there branded with more letters and numbers, so don't limit yourself to UTC or WE.

My Analog Distortion Generating DAC

I’m happy to report that this repurposed '80s state-of-the-art digital music maker using Mid-Century Modern era devices and sensibilities has been fulfilling my analog-biased musical expectations at the end of this second decade of the 21st century. The DAC bread board doesn't exactly match the LeCorb and Mies aesthetics of my man cave, but I've been enjoying digital encoded music like never before, such that I can't get myself to rebuild it on a nicer chassis.

Many thanks to Gary Bronner and Pete Boser for their contributions to the JE Labs digital audio museum, as well as to the patrons of this blog!

🎄Happy listening and have a great holiday season!🎄

References

Dutch Audio Classics

I/V Converters

Ryohei Kusonoki

Lampizator

Thorsten Loesch

Non-Over Sampling

Magnavox CDB465 Mods > TDA1541 DAC Kit > Arcam Delta Black Box

Magnavox CDB465

The Magnavox CDB465 was the no-frills entry level model marketed ca. 1987. Its more upmarket contemporaries were the CDB460, CDB560 and CDB650. Since it shares the same DAC and audio section as its more expensive siblings, they are sonically on equal footing.

I wanted all my modifications to be reversible so I installed IC sockets for the audio op-amps and SAA7220 digital OverSampling filter. The original electrolytic output caps were replaced with 4.7uf WIMA polyester caps.

Since there were no "bulging" electrolytic power supply capacitors and the AC line current draw monitored on my Variac was very normal, I didn't deem it necessary to recap the entire unit.

Typical dual op-amps found in
80s vintage Philips/Magnavox CD players:
NE5532N and LM833N
+
the FET-input OPA2604AP

This modification follows the footsteps of Walt Jung's article on page 74 of the June 1987 issue of Audio. Walt discussed the importance of op-amps with fast slew rate and higher quality output capacitors for better audio performance. Although the Burr-Brown OPA2604APs I chose date from the late 90s, they are still sonically respected due to their FET-inputs, which supposedly give them a "tubey" quality.

There's a plethora of cheap Burr-Brown op-amps from Chinese sellers, but I didn't want to risk getting fakes. So I searched hard and found some for less than $5 each from a seller in Texas.

The polyester caps + OPA2604AP op-amps cleaned up the sound. I heard less digital screech at the top end and an overall improvement in definition across the audio band.

I don't consider cutting traces in the PC board and using jumper wires à la Lampizator as reversible. So I ordered this plug 'n play NVKaudio NOS/re-clock module for $30/shipped from Bulgaria. I was quite taken aback by the improvement in sound when I installed this NonOverSampling module in place of the SAA7220 digital OS filter. The high frequencies opened up, the midrange became more luminous, detail and definition improved without additional harshness and it had better dynamic contrasts. It was an experience reminiscent of the first time I fired up my DIY no-negative feedback PP2A3 amp in the early 90s.

To objectify these two modifications, the op-amp/output cap upgrade gave at least a 10% improvement, while the shift to NOS = 40%! If this NOS modification was known in the 80s, I probably would've been more amenable to CD technology then. Oh well, as they say, better late than never. 😊

My problem now is, I want a stand-alone TDA1541-based DAC to connect to my Pi 3B+/Allo DigiOne or any digital transport. Can it be done on a modest budget? 

TDA1541 Chinese DAC Kit

This fully assembled DAC board sans TDA1541 chip cost $50 shipped from China. For another $30 I got an R-core power transformer with dual 15V + dual 9V secondary + 120/240V primary windings. Within less than an hour, I had a TDA1541 DAC on a breadboard ready for listening.

 It has 3 digital inputs including a PCM2704-based USB interface + optical or coaxial feeding a CS8412 receiver. The audio section came with single NE5534N op-amps (2 per channel) and polyester WIMA caps in the output section. Adjacent to the empty TDA1541 socket is a socketed SAA7220P/C digital oversampling filter. With seven heat-sinked regulators and a battery of filter capacitors, I surmise that every section of this DAC is independently filtered and regulated.

The topology reminded me of the innards of D/A sections of upmarket CD players and DACs from the TDA1541 era. For example, the TDA1541 socket is surrounded by film-type capacitors, which is a recommended upgrade to the SMDs found in mainstream mid-80s Philips/Magnavox CD players.

Using a TDA1541 chip I scavenged from a dead CDB2041, I fed this DAC with the output stream of the modified CDB465 above with its SAA7220 digital filter re-installed*. Honestly, I could not conclusively discern a difference between the output of this DAC and the modified audio section of the CDB465. This can only mean that this DAC must be doing something better...

*NOTE: removing the SAA7220 digital filter disables the digital coaxial output of any Philips/Magnavox CD player from the TDA1541/1543 era

The stock Adcom GDA600 offers better detail resolution and definition + a smidgen better extension in the frequency extremes compared to this TDA1541 DAC. But there is something organic about how the TDA1541 DAC presents music especially in the midrange, which makes it musically more satisfying.

Left = NVKaudio NOS module 
Center = SAA7220P/C
Right = JE's DIY NOS module

After a couple of days, I upped the stakes and upgraded the NE5534Ns op-amps to FET-input OPA604s. Then I pulled out the SAA7220P/C digital filter and inserted a simpler NOS module I made from a 24-pin socket and three jumper wires (above, right) based on a tip from this DIYer's website. Thanks, man!

Please note that my 24-pin socket/3-jumper wire NOS concoction doesn't work with CD players, only with outboard DACs. The NVKaudio NOS module works with both CD player and outboard DAC. The good news is, in a DAC application, I don't hear a sonic advantage using the NVKaudio NOS module over my cheap NOS concoction.

With the OPA604s installed and the SAA7220P/C chip replaced by my DIY NOS module, the TDA1541 Kit (fed by the digital stream of either a Magnavox CDB650 or a Sony CDP 505esD) overtook the modified CDB465 with the NVKaudio NOS module in terms of midrange warmth and definition across the audio band. The edge in detail retrieval that the Adcom GDA600 had was narrowed, while the NOS TDA1541 DAC with op-amp upgrade pulled ahead in terms of midrange warmth and dynamics.

I didn't consider a further upgrade to Burson or Sparkos discrete op-amps because they are expensive and by nature, these devices rely on negative feedback (NFB) to achieve linearity. IME as a vacuum tube DIYer, NFB satisfies the scope and meters but not my ears. 😜

Arcam Delta Black Box

Arcam and Musical Fidelity both claim to have produced the first outboard D/A processor. Here are links to Stereophile's review from the late 80s of the Arcam Delta Black Box and Musical Fidelity Digilog. 

I lucked out on a Delta Black Box which needed some work. Fortunately, a service manual is available online. After replacing a couple of fried resistors, music!

Musical Fidelity Digilog
Courtesy of Google

I also wanted to try a Digilog, but in hindsight, it was a good thing I couldn't afford those that came up for sale. Based on the picture above, it was a textbook, albeit deluxe, implementation of the TDA1541 DAC chip. Except for the digital input receiver section, the D/A circuit topology is very similar to the CDB465 and Chinese kit above -  TDA1541 DAC output > op-amp ICs in the audio stage > coupling caps at the output to block DC offset.

I'm not sure if the TDA1541A S2 (dual crown) chip in the picture above was originally supplied with this unit, probably not. Stereophile's favorable review of the Digilog over the Arcam Delta Black Box is probably the reason why they command higher resale prices. 

Arcam Delta Black Box

In stark contrast, the Arcam Delta Black Box is actually the more sophisticated design. It used discrete components with Class A operating points, instead of audio op-amp ICs. The audio stage is a direct coupled design = no capacitors in the signal path. The op-amps visible are part of a DC servo circuit that controls DC offset at the output.

It did have a tendency to sound a bit hot on the top end. But I could hear its untapped potential, excellent bass definition and extension + a midrange that is still very TDA1541-like. Since there are no capacitors that I could "tune to taste" with paper in oils, I carefully unsoldered the SAA7220P/B digital OS filter and installed a 24-pin socket. 

Running the Delta Black Box in NOS mode got rid of all the nastiness in the top end. The high frequencies opened up with shimmer and airiness, the midrange became more focused and bass response and extension is the best I've heard from CDs so far. It was clearly better than my mod'ed CDB465 above with NVKaudio NOS module, op-amp upgraded and NOS TDA1541 Chinese DAC kit and stock Adcom GDA600. Although not quite as lucid in the midrange as the Audio GD R2R-11, the frequency extremes were much better.

Now that I've heard a few TDA1541 DAC topologies and have compared them to a PCM-63 based DAC + a discrete R2R design, I'm quite confident that my ideal DAC would use an NOS TDA1541 DAC chip coupled to a tube output stage.

PS: I can't hear the difference between the TDA1541 and TDA1541A. I have no experience with the specially selected S1 or S2 samples. Does anyone care to send me a sample (or two) to try? 😉

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.

Listening Room - Minimalist no more?

Among the audio systems of my friends, this is the only set up that has no LP playback ability. Neither does the owner have interest in DVD-A, SACD or a music server/streaming device - only16 bit linear PCM sampled at 44kHz red book mastered CDs, period!

Since our last visit, a Northstar CD transport replaced a CEC TL51X, while another belt-driven CEC TL5 CD transport is being contemplated. The NOS (Non-Over-Sampling) Zanden Signature DAC equipped with a double crown Philips TDA1541A-S2 chip remains. Now you know why I hunt for unloved TDA1541 CD players from the 80s.😎

The most significant change in this system, however, is that
the Phy-HP Co-Ax speakers have been replaced by a pair of field coil powered Western Electric descendants - G.I.P. Monitor 1s.

According to the owner, the JE Labs line level preamp +
SE10 mono-blocks give life to GIP Labs! He is such a good friend. 😉