Charles Altman from Altman Micro Machines explains what is more important for digital audio is the sampling rate of our media rather than number of bits. Have a read on his page. Don’t worry, I’ll wait.

Thanks for coming back.

So the higher the sampling rate, the better it is for our “signal reconstruction”. Hey, that’s what a DAC does basically.

So how about some real life example? How does Monica’s TDA1545A cope with higher sampled material.

And thus, I began my experiment.

But I hit a snag. Apparently, high resolution test tones are not easily available. 44.1/16 versions abound but not higher rez. Fortunately, you could create your own high rez wave files by using Linear Tech’s excellent LTSpice.

I also have a bigger problem in that I don’t have a media capable of high resolution. For the sake of you dear readers, I have to spend money… [another excuse to buy!] and I bought a John Kenny modified I2S Hiface module.

The signal path is now… Mac Mini -> jkenny I2S Hiface -> I2S Monica. Software is Channel D’s Pure Music Player and music library is via iTunes.

Oh yeah, did I mention I built a new I2S Monica as well?

Did I mention I had to haul the whole Mac Mini setup to the listening hall?

All this done [phew!], began feeding test tones. Please note that these test tones are created using the described sampling frequency. Note that no software/hardware upsamping nor over sampling is performed at all.

44.1kHz sampled

1kHz sine wave

10kHz sine wave.

16kHz sine wave

As you could see above, 10kHz above, the DAC is struggling to reconstruct the sine waves.

96kHz sampled

1kHz sine wave

10kHz sine wave.

16kHz sine wave

10kHz is still decent but 16kHz is a stretch…

192kHz sampled

1kHz sine wave

10kHz sine wave.

16kHz sine wave

Wow! 16kHz is no problem here!

So what does all this tell me?

The problem of digital audio is not in the equipment. It is in the material. We just need higher sampled data to begin with.

If fed high resolution material, our “vintage” DAC chip is far from an old clunker. It is still capable of reconstructing the signals properly.

In other words, Old is Gold.  ha ha!

The post Old but Gold appeared first on diyparadise.

If you are using digital media, you’ll use a DAC. Depending on how you store your music, this will have a bearing on how you interface this digital data out. Every format has its pros and cons, so let’s have a look here.

For digital media, to my knowledge, you have 3 choices today. SPDIF, USB and Firewire.

SPDIF is the de facto standard digital output. It’s available on CD/DVD players as “Digital Output”. Many media players like the Squeezebox has this too, as well as many PC soundcards. SPDIF even has an optical version, Toslink. A sonic upgrade can be experienced instantly if you ditch the lousy RCA socket and opt for BNC. Why oh why does everyone still use RCA then? For convenience rather than sonic reasons!

A major problem with SPDIF is that the SPDIF receiver in your DAC got to retrieve the clock signal from the incoming SPDIF. And this is a major problem. The older but still very popular obsolete CS8414 has a typical 200ps while the modern DIR9001 manages much better at 50ps. Irrespective of what comes after this, the fact that the recovered clock isn’t optimum will have a huge bearing on sonics later.

USB DAC is really popular these days. The most popular implementation is Texas Instrument’s PCM27xx chips. These are pretty good “as is” but still a lot can be improved on. Again, there is the question of how is the clock recovered?

There are better implementations of USB which do not use TI’s generic PCM27xx chips but I haven’t tried these yet.

Firewire is said to be the best but far from readily available. And too expensive at this point.

Which interface to use also depends on what is your source. If you are using CDs, SPDIF is most logical solution. If you store your music on hard disk, then USB or I2S via a SD card player is viable. The above briefly describes the pros and cons while the convenience of which format is really up to you. If you don’t mind a little trouble, go for the best sound!

My current favourite, however, isn’t any of the above. It’s via I2S! Provided you have a very good I2S source!

I started dabbling with I2S when I tapped out this signal from my old Marantz CD63 way back in 2003. The CDM12 transport isn’t that great and though the sound was already a huge improvement over SPDIF, there is still something lacking there. But hey, if you could ditch SPDIF, try this!

Later I played around with USB-I2S as well as USB-I2S-EIAJ in USB Monica. As good as all these sound, it’s still not a pure I2S solution. The interface is still via USB. You could say the weak link is how the PCM27xx chips derive the I2S out. I hope to have the resources to tackle a better way of doing USB one day…

Anyway, my current favourite digital player (The Digital Turntable) has, in my mind, the most direct route to I2S. A DSP chip reads WAV file data from a non-moving media (the SD card), then outputs I2S signal which is fed to a CS8405 chip to generate SPDIF. Both the DSP chip and CS8405 is clocked by a low jitter clock.

Since a good quality I2S is available, feeding directly to an I2S DAC chip (or through Black Crow for an EIAJ DAC chip) is all we need! Replacing the clock with a lower jitter implementation (like Kwak clock below or the plug-n-play Tent XO module) and I assure you your jaw will drop listening to music through this combo!

Okay, okay, enough about all this. So these are what we have here.

Above pics show the 3 implementation, coupled to mojo. They’ll couple nicely to mojo2 as well. mojo/mojo2 PCB has 6 PCB holes which couple nicely to the I2S-EIAJ, USB-EIAJ and SPDIF-EIAJ modules.

4 are EIAJ signals while the right 2 are your power connections to power the modules.

So instead of forcing you to buy a USB Monica or a SPDIF Monica, you now have choices and since this is in module form, you could play around slowly.

Hey, if there’s sufficient interest, how about an EIAJ selector to select from multiple inputs?

The post Let’s pay some attention to our Digital Interface appeared first on diyparadise.

The culmination of all the hard work, experiments and listening tests of all the DIYers here! Most significant tweak has to be the “3 transistor mod” suggested by Paul Needs and Paul Hynes. Who would have thought we have such a bottleneck there? A major major upgrade in sonics in every way!

Shown here built up with the Paul Hynes regs and CCS2 plus 3 Audioslaves for the I/V stage.

Now offering mojo2 PCB.

Note that only one supply is needed as the PCB traces provide power to the individual regulators.

The PCB has been designed to fit Paul Hynes CCS2 and Regulators particularly the 5.4V and 0.83V regs. So no more string of diodes etc. If you prefer the simplicity of the original mojo, it is still being offered for sale. If you are budget conscious, you could build whichever reg you prefer and fit into mojo/mojo2.

mojo2 kit.

The kit has all the SMD components (resistors, capacitors and ferrite beads) soldered on so you only have to mess with the through hole components. [yes, thanks for the applause!]

It has everything you need except — regulators, Black Gates capacitors and output coupling capacitors. Oh yeah! Solder, elbow grease and the most precious commodity of all – time.

mojo2 map.

The map above shows CCS2/5v4/0p83 regulator pinouts.
If you fit in the Paul Hynes 5v4 regulator at “5V” location above, you only use Output and Ground.
If you are budget conscious, you could use Audioslave here or even a LM/LT1086-5V regulator as the pinout is the same – I, O and Gnd.
The rest of the regulators are straight forward.
The 12V and 18V regulators share the same pinout as the 5V reg, namely I, O and Gnd.
If you don’t want to use regulators here, just short I and O together but be careful with the CCS2 as it can’t take >17VDC.

However, due to the tight fit, the electrolytic capacitor of the CCS2 may come into contact with the solder joints on the 0.83V regulator, a simple suggestion of insulation tape on the top of the capacitor should do.

As mojo2 accepts EIAJ input, you could just feed EIAJ signal to it directly. Shown here is my current favourite digital player! Sounds best on a chopping board!

Though not shown, the ribbon cable feeds directly to the EIAJ input of mojo2.

The QA550 SD card WAV player reads bits and bytes directly from your SD card where a DSP chip does all the hard work here. This chip then outputs I2S signal to a CS8406 I2S to SPDIF convertor then outputs SPDIF downstream. This is where you hook up your DAC and let your digital receiver process this SPDIF and extracts I2S/EIAJ signal back to feed to your DAC chip.

Now, we could circumvent all this data processing and simplify it. All the attendant processing can’t be good for the signal no? Since there is already I2S signal onboard (straight from the DSP chip), we could feed to our I2S-DAC chip!

Monica’s TDA1545A requires EIAJ so here comes Black Crow! An I2S to EIAJ convertor board.

The above shows Black Crow’s pins directly mounted on the I2S pads of the QA550 which its designer very nicely provides us. The oscillator was also removed and now fed by a single supply version of a Kwak Clock 7. I’m too lazy to build one so I bought some DIYer’s version. [Thanks Patrick!]

So how’s the sound?

Going I2S is worth it! Installing the Kwak Clock (or some other low jitter design) pays off well!

Dare I say it?! Digital has never sounded so analog!

The post What’s better than mojo? mojo2! appeared first on diyparadise.

There are 2 Paul Hynes’ regulators we want to introduce here. Well, if you include the CCS, then there’s 3.

First, there’s the 5.45V regulator for TDA1545A VDD. Then there’s the 0.83V regulator for the TDA1545A VREF. Lastly there’s the CCS2 for feeding the 5.45V regulator.

So first step is to identify how to incorporate all these regs. Ideally we would like to place them as close as possible to the chip which we want to regulate its voltage. So in this case, we want to place them as close as possible to the TDA1545A chip, yet without leaving a mess of spaghetti wiring. (pray hard…)

Here’s what I did. Found that the best place to wire in the 5.45V reg is on the PCB where the 220uF cap is supposed to go. If you have both caps installled, then you could solder them at the bottom of the PCB.

Ditto to the 0.83V reg, best place is on the PCB where the 47uF caps reside. Note polarity.

Now there are many ways you could integrate these regs in. One way is to cut the PCB trace, disconnecting the string of diodes to VDD but if you don’t want to, you could desolder the 1N4148 diodes (all or at least both at each end).

The Paul Hynes regs’ pins are labeled I(nput), O(utput) and G(round). Descriptive enough? When mounting the 0.83V reg, I found it’s easier to desolder the I lead and wire it this way. This goes to the CCS2 input.

More pics here.

Aha… Integrated with Monica SPDIF-EIAJ module. Note that power for the module is taken from this mojo board. For better isolation, i put in a ferrite bead too.

Hey! Since we are on a roll, might as well add 2 more regs! Now there’s a reg for each channel of the SS I/V stage as well. [These new regs will be called ACDC in line with our preference to name our minor products over rock bands.] In order to do this, don’t install any jumper on LSUPPLY.

And so that’s what I did. So we now have regulators for every stage of Monica.

Err, this guide helps explain better how to power the individual stages of mojo.

And what does all this hard work give you?

Aye caramba! Muchhhhhhhh better sonics! SE-PA-RA-TION is superb!

Since I’m such a nice guy, for those who are more budget conscious, you could use AudioSlave here and retain the original CCS structure. You’ll need to break the PCB trace linking the string of diodes to TDA1545 VDD (pin 5) though. Err, with AudioSlave, you could go up to 25VDC.

There you go! Have fun!

The post Mojo-fy your mojo! appeared first on diyparadise.

mojo will be as a kit for now.

As you could see, I fancy black solder mask and silver plated PCBs these days. Looks and sounds awesome. Hee hee.

Parts List
24 Ohm Resistor x2
100 Ohm Resistor x2
820 Ohm Resistor x2
1000 Ohm Resistor x4
Takman 1/2W 5600 Ohm I/V Resistor x2     WOW!
Ferrite bead x6
1mH inductor x3
1N4148 Diodes x6
1N4007 Protection Diode x1
LM317 x1
Panasonic 47uF FM x2
Panasonic 220uF FM x3
200 Ohm Trim pot x2
Low Noise Red LED x10
Toshiba 2SK170 FET x4     WOW!
BF245C x2
BF245A x2
ZTX651 x6     WOW!
ZTX751 x4     WOW!
4-pin header pin

Notice that the ultra-low profile sockets and those excellent 0.1uF Panasonic film caps have already been soldered in for you. All together now….WOW!!!!!!

Assembling mojo
With mojo, first thing to do is to solder in the low-lying components – resistors, inductors and ferrite beads. From left to right, the resistors are 24ohm, 2 pcs of 100 ohm, 2 pcs of 820 ohm and lastly 4 pcs of 1kohm resistors at the far right end. The inductors are all 1mH.

And now you solder in the transistors. From Right to Left, 4 pcs of 2SK170, 4 pcs of ZTX751 and 6 pcs of ZTX651. The cascaded FET CCS we should come to it in a moment. Leave it blank for now. All transistors and FETS are to be installed such that they can be read nicely as viewed from the Left side, meaning viewing from the string of 1N4148 diodes end.

Update on 15th March 2009. New PCB corrects this already, so no “transistor cross legging” required.
Here is the painful part. This PCB’s cascaded FET section was designed for 2SK170 but this has now been ditched for BF245x which have a different Gate and Source pintouts. As such, I’ll have to trouble you to cross the legs of the FETs and protect them from shorting through heatshrink tubings. The FETS are 2 pcs of BF245C and 2 pcs of BF245A.

Now you could solder in the FETs. Note location of BF245C and BF245A. If you place them in the other way, the circuit will still work, but you’ll always have a niggling doubt as to whether this circuit could be further optimized. And it could! If you place these FETs in the prefered location.
Stuff the electrolytic caps, the LEDs (all have the same orientation) and trim pot.

Here’s another guide.

Power supply wiring is shown here. 15-24VDC, entirely up to you.

Customization
Here, I leave this entirely up to you to customize your mojo as everyone has different needs, so too with mojo! The resistor marked “RES” you could use this to drop voltage between the I/V stage and the TDA1545 circuitry. Shown here is a metal oxide 2W 33ohm resistor. Alternatively you could leave out this resistor and utilize the power supply connections beside to separately power your TDA1545 circuitry. Hey, whatever tickles your fancy ok?

If you feel like powering the SS I/V Left/Right channels with different power supplies, I’m certainly not going to stop you! Simply supply a separate VCC to “LSUPPLY” as shown. However, both channels will share the same ground. Should you desire to have the same supply for both channels, then just put a jumper on “LSUPPLY”.

Giving Monica some mojo!
Shown here is mojo being “mated” with USB Monica. Remove the TDA1545 chip from USB Monica, transfer to mojo PCB and plug in this double sided header pins. Note that one end of the header pins have larger plugs than the other. The larger one goes to mojo while the smaller one plugs into existing EIAJ conections (pins 1-4 of TDA1545). If you reverse this header pin, it won’t fit.

USB Monica, given some mojo, will sing for you even better than before!

Update on 15th March 2009. Mojo kits purchased on 15th March and onwards require no rework on your part.

Corrections on the PCB
I’m known as a klutz. I’m also hopeless at proof reading. So despite many attempts, I still made mistakes on the PCB. Here I rely on your grace to correct them on my behalf. Actually I corrected some. Places where the trace has to be cut, I have cut them with this cool PCB drill I just bought… Now you need to apply these jumpers.

The post Give me Mojo! appeared first on diyparadise.

If you have been to our forum lately, you’ll notice that what started as a thread whereby martinbls laments the “slow sound” he got from Monica, slowly evolved into a thread where with fellow members contributing, we now have another winner tweak for Monica! And all of the ss i/v stage users!

Okay, martinbls asked the question. Member assendor (hats off the most diligent member on the forum now! Thanks a lot Jonas!) then gave him some suggestions, of which the most potent was his mentioning of Nelson Pass’s First Watt B1 Buffer Preamp. The basic idea is to convert Monica’s highish output impedance to a nice low impedance.

Then member PaulN, (sharp as he always is!) saw the potential right away and suggested incorporating the JFET stage Q100, Q101 (and likewise Q200, Q201)
directly at Rudolf Broertjes’ SS I/V Gain Stage, just before the output capacitors.

All other components are not needed as we already have 1/2 Vcc from the SS I/V stage.

It’s one thing to suggest, but another to build it right away and report to the forum! Within couple of hours, I was kinda shocked to receive an email from PaulN saying he has built in the tweaks and reported the positive results!

Boy oh boy! Now that is something!

So today, even though I’m supposed to be working… I thought I could sneak in half an hour for this tweak. Well, that eventually became couple hours of listening!

Okay Mr Nelson Pass recommends 2SK170 low noise audio transistors. I don’t have this and it’ll be quite a pain to acquire them since my local (as in within 10 miles) supplier does not have it either.

But then I have lots of 2N3819. Okay, the noise figure isn’t as beautiful as 2SK170 but I’m like a hungry man looking for food. If it’s edible, I’m going for it!

So I incorporated the 2 FETs per channel into Monica3. Some soldering acrobatics is required here. Hey, I know YOU are one solder gymnast! Send me pics of your best work!

Now I didn’t put in any resistors before or after the FETs. I’m always of the (stubborn) opinion that if it’s not needed, then we don’t put them in. Yes, I’m aware these are RF transistors. Yes, I’m aware non-oversampling DAC has the 44.1kHz component riding… Yes, I’m aware I’m stubborn. You enjoying yourself there?

Ha ha!

Now the sound? PaulN’s excitement is justified! I have been communicating with him quite regularly the past few months and I really trust his ears. He makes me feel like I have tin ears due to his excellent hearing ability. Hey, wait a minute, most folks make me feel the same way. Perhaps I need to check my hearing…

I’m digressing. But PaulN is right! The power of a good tweak is everything is better! Better definition, better detail retrieval, better bass, even transients improved! … Damn it, why didn’t I think of this earlier?

As such, I take my hats off (both literally and non-literally to PaulN, Mr Nelson Pass, assendor and martinbls. You guys have just completed Monica!

You see, all this while I have been pensive about this as I never like her highish output impedance. I thought a good solution would be to couple with our tube preamp which through its output transformers would solve this impedance “thingie”. Well, now even with the tube preamp, the improvement is still amazing!

Okay, I can see you nit-picking there! Nah, I don’t think I’ll bother with 2SK170. You see, the signal voltage we are dealing here is about 1Vrms. The 2N3819’s noise figure isn’t anywhere close. Well, perhaps one day I’ll try 2SK170 but for now, I’m just happy to listen!

Okay, here’s another tweak which only YOU can work it out.

You know, for the recent audio show, actually we have Monica3, Charlize2 etc built up for the show. However, just a week before the show, wanted to try something different (like we have so much time in the world just before the show…)

I like the idea of a DAC-preamp, so wanted to integrated Monica3, our new volume control and the tube preamp all into one chassis. Hence we have this girl…

Since the electronics and the external power supply is all the same, the only possibility for such an improvement is the fact that we have greatly reduced the number of interconnect links between component.

Let’s see, Monica3 to Passive Preamp (our new volume control), then Tube Preamp.

That’s 2 interconnect cables plus 4 RCA connections (plug/socket) per channel.

Why heck, our interconnect cable is no slouch. It’s the same wire we use in the internal wiring. And it’s shielded as well.

Why heck, we liked it so much, we later incorporated Charlize2 into the whole mix! So look ma, no interconnects!

So, the BEST interconnect is NO interconnect cable!

The post More ways to kick arse your system! appeared first on diyparadise.

Once upon a time, in a galaxy far far away, lived a Diyer by the name of CY Liew (whom by the end of this article we should give you a nickname!) who can’t decide between the TDA1545, TDA1543 and its many parallel permutations (or mutations). He could, of course, build many many DACs and choose one (what I would do) but he felt that such an approach is sooooooo “unmacho”, soooooo 20th century. So our friend here who, by the way, wears a soldering gun like a cowboy wears his gun, did the most logical thing any Diyer would like to do — build all of them in one chassis and switch to your hearts content.

And so begins the story… *cue music intro*

First of all, let me explain the features. The 4 switches at the right are for, from Left to Right, TDA1545, TDA1543 with active I/V conversion thru OPA627 opamp, then 4xTDA1543 and lastly 8xTDA1543. Cool moi?

Switch at center is power switch. At the far left, this is where it gets better… battery! Yeah our hero here can’t decide which he likes so Mr-Indecisive did the most manly thing there is. Instead of talking about the sound, he built all his doubts into this little box and listen it for himself. Now this is a MAN.

So there you have it! An out-of-this-world, whatchama-call-it, switch-as-you-please, whole-loads-of-fun DAC.

Also known as User-Selectable TDA1545, 4xTDA1543, 8xTDA1543 with passive I/V conversion and TDA1543 with active I/V conversion with both Mains AC and Battery Powered Option Non-Oversampling Digital Analog Converter(s). Phew!

Colloquailly also known as “Gua Tak Boleh Tahan” DAC! [insert foreign phrase of your language meaning “out-of-this-world cool until i’m almost stuck to the wall reading about this”.]

Anyway, one fine rainy Saturday morning, we had a listen to all the DACs in my humble system. It was so easy to select between DACs! All in all, there is a huge difference between them DACs. I prefer the 1545 in my system while CY “DAC Man” Liew prefers the single TDA1543 with OPA627 I/V conversion in his.

As you can see, we Diyers have lots of fun!

So folks, let’s give DAC-Man a round of applause for his wonderful engineering! DAC-Man welcomes praises at liew dot cy at gmail dot com.

PS: Err, DAC-Man, can we have an amp that switches between 45, 2A3 and 300B? Sorry, can’t resist!

The post A Deck of DACs appeared first on diyparadise.

Finally! The long-awaited, much-anticipated, long-overdued , oft-asked, finally see daylight… *drum roll please* Yup, in collaboration with Calv Acoustic Labs, DIY Paradise brings you… Non-Oversampling Digital Analog Converter Kits! (if you are cheap, use your business card box to house the dac) (i’m even cheaper. no box is best box!) *see below*

Half a kit, full kit, what the difference?
Yup folks. At offer here is DAC full kits. You get everything you need to build the part. Well not "full" in the strictest sense of the word, but "full" enough. You still need to get your RCA sockets, wires, casing, battery, solder, calories, sweat… The power supply side is not supplied, as it is diyparadise’s aim to promote going battery (though the PCB could be wired for separate power supplies). Remember, have battery, can travel. Besides after you built your DAC, bring your battery powered DAC and a mop to your hifi dealer, so that after listening to your DAC, they can mop up their drool! So here you go.

The TDA1543 DAC kit page.

The TDA1545 DAC kit page. DISCONTINUED

"Monica 2" – The TDA1545 DAC kit with asynch reclocking.

Update Dec 4, 2004: All you need to know about these DAC kits.

Testing, testing… Good!

Palm Top Dac, Pocket DAC, Mini DAC…

Perhaps you prefer a more conventional "box"? With power switch, LED at the front?
Shown here is 4.5Ah battery that lasts ~40 hours with this DAC. Sub for a more petite batt of your liking.

You can easily take out the guts and modify to your heart’s content!

www.diyparadise.com

The post DAC Kit appeared first on diyparadise.

Well, almost…

History of the DAC
Idea was conceived while watching some horrible B-grade movie when thoughts suddenly drifted to all those ideas/thoughts/experience “stolen” from everyone/everywhere on the Great World Wide Web. Then Head Honcho of Calv Acoustic Lab lended a GIGANTIC helping hand by laying out the PCB design. Needless to say, never bothered to finish that stupid movie.

Pre-requisite to build the DAC
As long as you can solder properly, know how to use a multimeter, know how to work logically and of course, relax with your favourite beverage (milk, coffee, tea, toddy, stout, beer, sake…), you are ready!

Work logically : Solder in all components except for CS8412 and TDA154x. Power up and measure that power supply voltages are correct. Then in goes last 2 chips. Power up again to make sure that power supply voltages are still correct. With TDA1545, check that one end of R18 is at 1/2Vdd while the other end is at some other voltage (~0.8V in mind). Then hook it up.

Don’t Worry, Be Happy
First of all, a very important point to know about these non-os DAC kits is that there is no gain stage involved. Thus the output voltage you get is just the pure voltage as generated across the current-to-voltage resistor. In other words, passive I/V conversion.

Because of this wonderful reason, these DAC kits will not put out 2V output like most conventional CDPs. If you are using single DAC chips, it’s more like 0.5-0.6V. If you parallel the chips ala 4xTDA1543 or 8xTDA1543, then the output level is higher. Remember, these are current output DACs so when you parallel the DACs, the current adds up and you get more current, hence more voltage output. 4xTDA1543 gets you to almost 2V while 8xTDA1543 gets you more than 2V.

If your system is low gain and needs all the swing from your DAC stage, do NOT be alarmed that you need to crank up your volume from 10 o’clock till 1 o’clock to get back the same listening level. There is nothing wrong going on here. It’s just that the DAC output voltage is lower, that’s all. It’s no different like connecting a lower sensitivity speakers at the output. You just need to crank up the volume, that’s all.

If you feel that it is important to listen at 10 o’clock as opposed to 1 o’clock, then feel free to add in a gain stage. This is where I’m stubborn, obstinate to the point of being a pain in the you-know-where. The decision to eschew convention is partly based on my experience of haven’t heard any gain stage at the DAC level work so brilliantly without destroying the purity of the DAC stage.

I have listened to opamp stage (even using OPA627), tube stage (using the ubiquitous 6922 variants etc) blah blah blah… but never liked its “flavourings”. Each time, my ears tell me that no gain stage is still better. Of all the gain stages I have heard (okay, I haven’t heard that many), the one most faithful to the DAC is the 12B4-based gain stage. With its mu of ~6, it’s just nice! However, due to its very microphonic nature, again, it’s hard to recommend.

Briefly pros and cons of a gain stage
Pros: more output, better dynamics, better bass.
Cons: loss of “sonic purity”, sometimes loss of micro detail as well.
So if you feel like you need a gain stage, you are on your own! *diabolical evil laughter ensues…*

Troubleshooting the DAC
This is the fun part. Okay, there is this Mr Murphy and his darn wonderful Law that makes this page necessary. After soldering everything and verifying all voltages are correct, here are some troubleshooting tips.

Problem : No sound. LED doesn’t light up when you pressed “Play” on your CDP.
The LED is just an indicator. More importantly, check pin 28 of CS8412 (the pin closest to LED). It should read ~5V when no music is playing and ~0V when you pressed “Play”. If it is ~0V when you pressed “Play”, then chances are you got the LED orientation wrong. If you still get ~5V, this means CS8412 was unable to “lock” to the incoming SPDIF signal from your CD transport. Check that you got the 75ohm, 100nF caps at the input wired correctly. Check also the PLL filter (470ohm, 220nF, 3300pF) are all placed correctly.

Also, measure Frequency at pins 1/2/3 of TDA154x pins. (Measure at the leads of the chip!) All of them should read something when music is playing. Pin 2 should read ~44.1kHz. If you could get some frequency measurement at these pins, this means all the digital signal is reaching TDA154x, then it’s highly probable that you have a dead TDA154x chip. If not, you could have a broken connection somewhere between CS8412 and TDA154x.

Problem : Distorted sound.
Check that you got the right I/V and Ref (R18) resistors in!

Problem : Got sound but I’m hearing things I’ve never heard before! Is there another backup singer on this track?
This is spooky. Call an exorcist!

Problem : My friends love the sound and wouldn’t return my DAC!
Those selfish bastards! Get new friends and new DAC.

Problem : My wife loves the sound! She said this diyparadise guy is her new hero. I’m jealous!
Lie to her that I look like a toad.

Problem : I can’t decide between mahogany wood, ABS plastic, or stainless steel chassis.
Ask your wife.

Problem : My dog/cat runs away when I play your DAC!
Are you using a super tweeter? If your system capable of up to 44kHz? Maybe your pets are irritated by this super-sonic noise. Hey, at least they can’t ruin your audio gear! They are also leaving you to listen in peace. So what’s the problem? Do you also experience less mosquito bites? I heard that mosquitoes hate this frequency too.

What else?
There’s certainly room for improvement! You could start a search for your “perfect” gain stage. You could build a super clock for asynchronous clocking between CS8412 and TDA154x. Details will be available soon.

Remember, this DAC kit is meant to give you a start in the wonderful sonic world of non-os. Now that I’ve got your attention, there are certainly many steps ahead in this wonderful journey.

Enjoy!

www.diyparadise.com

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Cloning Monica

Well, well, well, since her debut, Monica, and subsequently Monica2, has been so well received by so many audio enthusiasts worldwide that if you haven’t heard of her, you better get out from your cave! Inevitably, success brings its pitfalls. The obvious being :

1. being zapped out of life. Yeah, I have no life these days, quietly soldering and soldering, fulfiling the sonic hunger of audio enthusiasts all over.

2. I feel so good, so inspired, whenever I receive emails thanking me for such a wonderful piece of audio equipment! Well, as the cliche goes, Monica is MORE than an audio equipment. : )

3. Time and time again, I have found her jiving with gears costing more than 20x her selling price! Just proves what an amazing value she is. No wonder you guys are so in love.

4. I get so many veiled attempts at finding out how I build my baby. How I “inject” pixie dust and create music magic. Seems like quite a number of folks intend to CLONE Monica.

Oh well, since you try so hard to “dig” info out of me (short of sending the mafia to my door), let me come clean with you. If you want to clone Monica, at least do it right.

In this context, I define the “cloning” of Monica as utilizing the TDA1545A dac chip in similar configuration. Note that I don’t run TDA1545A per the datasheet. I use 2.2kOhm for the I/V resistors, 22kOhm for the Vref resistor and bias this pin at 1/2VDD. Nothing scientific but definitely different from the rest.

So if you want to clone Monica, at least do it right!

PCB
Needless to say, very critical component here. First started out with silver plated PCB but then switched vendor due to inconsistent quality problem. Current PCBs are all GOLD plated. We do this mainly for lead free reasons so that our European brothers and sisters could enjoy Monica’s magic too. You could say another reason is more “selfish” so that I breath in less lead in the solder fumes and won’t be so stoopid in the long run. You know what folks say about lead damaging our brain etc et etc? You know, me doing silly things like selling Monica too cheap. : )

Double sided with the top layer being one huge ground plane. Single side PCB just won’t cut it ok? Beside every electrolytic, there are provisions for you to solder in a small ceramic bypass cap for more effective power supply bypass.

Components
Digital circuitry is less fussy but eletrolytics are best with Low Impedance caps. I started with Sanyo Oscons but due to availability problems, then switched to Panasonic FCs and FMs. I find them just as good with insiginificant sonic difference.

The regulators are just basic 78xx series type. Nothing special I know but listening tests with shunt regulated types didn’t yield that much sonic difference so… why bother? More importantly 3 separate regulators are used for the digital receiver’s digital/analog circuitry and the reclocker circuitry.

On the analog side, caps have come and gone but only one cap, I will NEVER change (until I can’t source them anymore). And this is the non-polarized Black Gates N series 4.7uF 50V at the output. Have compared them with couple of polypropylenes etc but these little BG beat them all in terms of TRANSPARENCY. Well, size as well, ha! It is my aim for my audio gears to sound as transparent as possible, never interfering with the music. Meaning, the equipment does not get in the way of the music. You could try other caps, of course, but this will be your sonic preference, not mine. Entirely up to you here.

The power supply circuitry consists of a constant current source feeding a shunt regulator. The LM317 and resistor sets the CCS of 50mA while the series diodes form a shunt regulator. All this to regulate 5V. Absolute 5V is not critical but absolute stability is. As TDA1545A draws only 5mA max, the regulator combo only has to cope with 10% variation in its current. Such an easy job! It is for this reason that the power supply filtering is very clean here. Very nice. So much so that all the details in your music comes through unhindered. If it’s there, Monica will sing for you. She’s a great gal!

I once offered standard Black Gates for the power supply bypass beside TDA1545A. Not necessary at all as simple Panasonic FCs do a great job here. So don’t get too hung up on the Black Gates name. Not all of them are gold. The standard stuffs are really no big deal. Reserve your respect for the BG N series!

Other nifty details
Well, TDA1545A uses low profile sockets – which costs more but sounds better.
The PLL filter caps, it’s imperative to use polypropyelene for the 3300pF cap.
We love Monica when she sings with 80MHz oscillator.
The flip flop chip has to be ACT series or higher. With ACT, it’s good up to 125MHz. DO NOT USE the much cheaper HC and other slower series.
Only lead free solder is used throughout.

Assembly

	A local sub-contractor (read virgins born under the Virgo sign only) stuffs the PCB and solders in most components. Well, THAT was supposed to be the case but it was not meant to be as virgins are so hard to come by these days… So intead, I have normal folks like you and me stuff the PCBs but to preserve the magic, we only solder on full moon nights.
	I then solder in the surface mounted components and also wire in the jumpers. much tender loving care goes into this…
	Yes, they are hand soldered. Only lead free solder please.
	Taking a much needed bath!
	Testing stage. One full CD of songs will be spun. Current favourite is Tom Waits but could be any CDs. I build connectors wired to SPDIF output from a CD player, then there’s another connector at the analog output ends, hooked up to an amp, and then speakers. I guess a cool way to test her is to measure the soundstage produced from every Monica (ha ha!). Please don’t ask me to!

There you go. I hope you learned something about how I build Monica. You guys who want to clone Monica, I hope you find something useful here.

Thanks and enjoy your Monica!

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