Line Transformers for Digital Audio

Altec 15356 + UTC A20

While browsing at Books Kinokuniya in NYC in the 90's, this Noguchi ad from the November 1994 MJ Audio Technology issue inspired me to experiment with line transformers as digital sound enhancers. Since I was living on a post-grad assistantship budget back then, importing this pair from Japan was out of the question.

Sony PS1 + Magnavox/Philips NOS TDA1543 CDP Mod

 A revival of interest in CDs is imminent, sparked by Pope Francis' recent visit to a mom and pop record store in Rome.😉

from djmag.com

So before software and hardware prices go through the roof, here are two affordable ways to get maximum pleasure out of CD playback for thrift store/flea market and/or DIY-inclined souls.

Over ten years ago, this early first generation Sony Playstation 1 developed quite a following amongst audiophiles as a CD player because of Art Dudley's favorable write up in Stereophile. The market has probably softened up a bit since then, because I managed to snag two PS1s at '08 prices before the pandemic. 

Not all PS1 consoles were created equal - only the machines fitted with the AKM AK4309AVM Sigma-Delta DAC chip have audiophile credibility. Since I've seen some unscrupulous sellers asking $100+ for this obsolete game console, it pays to know two tell-tale features of the desirable PS1:

1. "SCPH-1001" designation

2. A pair of audio output RCA jacks on the back of the console

Don't forget the controller, which I pictured above and below, otherwise there's no way to command the player to play, stop or skip tracks. 

Sigma-Delta DAC chips never struck me as unbearably bright, strident or fatiguing. The main reason I reverted back to a multi-bit DAC in the Box in the 90s was because my bitstream'd Philips CD921, and later the sigma-delta Sony DVP NS755V, sounded boring and lifeless. That said, the Sony PS1 is the most exciting sigma-delta chip'd CD player I've heard! 

This is a must read: Michael Lavorgna's Sony PS1 Epitaph in Twittering Machines!

However, to my ears, here's a better machine for Digital Sound Processing Redbook CDs. 😉

In my thrift store CD player upload, these TDA1543-equipped twins stood out as very musical sounding machines, meaning, not for audiophiles, but more for people who love music. I actually prefer these Mexican-built non oversampling models over their slightly more upmarket Belgian sibling, the 4 x oversampling CDB610. 

 These were the entry level Philips CDPs from the late 80s up to the early 90s until they were superseded by inferior-sounding (at least to my ears) bitstream machines like my dreaded Philips CD921.😏 Stock, I'd choose these over the AKM chip'd Sony PS1 for sheer musical pleasure! 👍

I also highly recommend the Sony CDP190 with a TDA1543A + an in-house 4 x oversampling chip and filter. But in the 5 years I've been thrifting CD players, I've only found one, while I've managed to collect duplicates of the CD2000 and CDB492.

Grundig CD8150 analog output section

There is no known service manual or schematic for the Magnavox/Philips CD2000/CDB492, so I searched for other contemporaneous badge engineered Philips CD players. I found the Grundig CD 8150 service manual at HifiEngine.com, which employs a very similar, if not identical, circuit topology. I verified that the machine is indeed non oversampling. In lieu of the SAA7220P oversampling and filter chip, Philips engineered a brick wall filter in the analog output section, which they cleverly marketed as Digital Sound Processing.😊

I wonder if this circuit could have been the inspiration for Ryohei Kusunoki’s non-oversampling articles for MJ in the mid 90s.🤔

My audio buddy Ding R wanted me to improve his CDB492 with a tube output stage, since numerous DIYers have managed to shoehorn a tube analog output stage inside a plastic chassis CD player. But I wasn't keen on making a perilous fire hazard compromise. Besides, I'm also a purist and believe that only a tube-rectified and/or choke-filtered power supply should power tube circuits, nearly impossible to fit inside a CD player chassis.

8-pin DIP sockets, BB OPA2604 op-amps + Mylar capacitors

The inspiration for this simple-to-implement modification dates back to Walter G. Jung's article in the June 1987 issue of Audio. I removed the LM833 op-amps in the signal path of the analog output section, installed 8-pin DIP sockets and listened to check if the FET-input Burr-Brown OPA2604s and Mylar WIMA caps in place of the original electrolytics could improve the CDB492's musical performance. 

Magnavox/Philips CDP Teardown by msylvain59

The most laborious part of this modification is gaining access to the underside of the motherboard. Watch msylvain59’s wonderful video above for a detailed teardown of a very similar Philips CD player. Handle the ribbon cables and connectors carefully! Given the age of these components, a crack or tear is enough to render the machine useless.

The motherboard is now ready for upgrades.
 Take note of the op-amp orientation; otherwise, the machine may emit
smoke and nasty burnt electronic component odors!

 

 After handling over a dozen 80s era CD players, I have yet to encounter bulging or leaky power supply capacitors. These machines used high quality Japanese-made Nichicon capacitors. In contrast to current audio trends, I don’t endorse across the board capacitor replacement. I'm all for replacing parts judiciously!

Operational amplifiers (more info) or op-amps were developed during the vacuum tube era. Due to the inherent high gain nature of op-amp topology (video), negative feedback is necessary to control gain and/or linearize the circuit. Ever since I started DIY’ing tube circuits, I learned that negative feedback has to be implemented judiciously (or even dispensed with) in pursuit of ultimate sound quality, which also applies to solid-state. Because of this, I don't see the logic behind boutique-priced discrete op-amps. But if that's how you get your audio fix, have fun rolling! ✌️☮

To my ears, the Burr-Brown OPA2604 + WIMAs gave a smoother, cleaner, clearer and less grainy sound. The superior TDA1541 DAC chip in the Magnavox CDB465 with op-amp + output cap upgrade offers better resolution of detail + a marginal improvement in musicality. However, the most musical CD sound I've enjoyed to date is still from the digital stream of a JVC, Magnavox/Philips swing-arm or Sony transport piped into my nosTDA1541tube DAC. But then again, I'm biased! 😆

 

Ding called after his first listening session with his JE Labs-modified CDB492, "...are you sure that's all you did to this machine?"

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

JVC CD Players from the Thrift Store

Since my last CD player upload, I've acquired these three JVC CD players. It is stacked from the bottom to the top sonically according to yours truly. 😎

JVC XL-Z411 

I bought this primarily for the coaxial digital output since the price was right.

Dutch Audio Classics listed the DAC chip as a Panasonic MASH MN6623BM, but this unit sports a MN6471M bitstream DAC chip. Early bitstream sound with no nasties but also more hash than music. Not my cup of tea. 😏 

It’s a very nice CD transport though!

JVC XL-V75

If it's meant to be, it'll happen...I've been looking for this chip inside Fisher badged Sanyo CDPs only to land one in a JVC. Best of all, it only cost me a dollar!    

The Sanyo LC7881 DAC chip gives the Philips TDA1543 a run for the money. 

 If forced to split hairs, this CD player offers slightly better resolution and extension in the frequency extremes than the TDA1543 DAC'ed Magnavox CDB 492/CD2000 I reviewed here.

JVC XL-Z444

This unit shares the same Optima 4s transport as its bitstream chip'd brethren above. In case you're not a fan of the Burr-Brown family of multi-bit DAC chips, you can use it as a CD transport since it has digital coax output.

Not as warm and analog sounding to my ears than a TDA1541 equipped Magnavox/Philips or Sony but this Burr-Brown PCM56P chip'd player still gets the music right just like the older Shure SV40 I reviewed here. I will not argue with those who believe it's more extended at the frequency extremes. However, I'd argue back that the midrange of TDA1541 CDPs sound more life-like.

Happy listening and hunting!

The Good, the Bad and the Ugly TDA1543 NOS DACs

In spite of its humble origins, I praised the musical abilities of the Philips TDA1543 DAC chip found in late 80s to early 90s budget CD players. Below are two affordable (under $30) Non-OverSampling DAC boards I sampled that use this ubiquitous chip.

Non-Oversampling 16bit/44.1kHz TDA1543 DAC Boards

Don't even consider the DAC board to the left, which can be found all over eBay

 for $16-$20/shipped. Powered by this beefy linear wall wart PS, this is by far the worst-sounding DAC I ever heard! It has no redeeming qualities whatsoever. Enough said. 😣

For another $10 + the same linear PS, the DAC board to the right is a decent music maker. Unfortunately, it went out of stock as soon as it was delivered to my doorstep. Even if the Muse Mini TDA1543x4 (more info) sounded dynamically more appealing, this single chip'd DAC board seemed harmonically purer and more authentic. In hindsight, I should have hoarded all the units offered by that lone seller. 😆

!!!WARNING!!! 

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

Tube Buffer Circuit (one channel)

Since this TDA1543 DAC was configured with a passive I/V converter that already has a decent voltage output, I thought a med-mu 6CG7 tube buffer/cathode follower might mitigate the slight opaqueness in the midrange, improve both dynamics and the (lack of) definition in the frequency extremes - qualities which betray the budget origin of this rather musical DAC chip.

The Ugly 😄

Even if the TDA1543 was [and always will be] a budget DAC chip, the experiment paid off, taking this NOS DAC board to another level. 😊

Listen to lots of music, build a project or better yet, do both!
Stay safe! 🍻

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? 😉