Hello DIYers.

You may have came across my USB Convertor. That was meant as a temporary solution while I crack my head over a proper USB DAC. The USB Convertor outputs SPDIF (your vanilla digital output) which you could then feed your DAC. Now if you are looking for a dual usage DAC (meaning for both computer and CD/DVD player type), then this will be a good, albeit compromised, option.

However, if sonic quality is your utmost concern, then there is simply no business converting from USB to SPDIF then to DAC format again.

Therein lies a problem. Almost all the USB receiver chips in the market I know only outputs I2S and not the EIAJ format required by Monica’s TDA1545 chip. Boy, this isn’t fun.

I built a few circuits to convert I2S to EIAJ but wasn’t successful. More studies later… then I realized I need to climb up the highest mountain in this region, consult the guru there and sprinkle some pixie dust.

Nah, the guru wasn’t much help. In the end, after lots of diligent nights (and wee early morning hours) of pouring over datasheets and building prototypes, I finally got it done.

USB – I2S – EIAJ – Monica!!!

Let me be anal here and declare this as the first USB DAC using an EIAJ based DAC chip!

[You could make me fall flat on my face with big dollop of humble pie by pointing out to me which USB DAC in the market that uses an EIAJ based DAC chip.]

So what’s the big deal you may ask? Well, as always in audio, less is indeed more. Going through one less data conversion, the gain in sonic quality is…. va va voom! Like the real Monica!

If you are new to computer audio, I suggest you take a read of my computer audio pages.

So this PCB consists of a USB receiver chip, an I2S-to-EIAJ convertor and asynchronous reclocking scheme, TDA1545A circuitry and of course, Rudolf Broertjes’ SS I/V Gain Stage. All in one smoking PCB!

Simple enough eh? It looks simple from the top but underneath, there’s quite a lot of surface mounted components soldered on.

You could power her at 12VDC though 18VDC is said to sound better especially for the SS I/V stage. If you intend to go this high, I’d suggest heatsinks for the LM317 chip.

Better still, note that L3 is a diode instead of an inductor or ferrite bead. If you remove L3, you could power TDA1545 circuitry through J2 and power the SS I/V stage circuitry separately through J4. How about that? ; )

Wiring is very simple. Just hook up power supply (you provide of course), and output to RCA sockets of your choice. Input is simply USB from your PC. I’ll suggest a USB cable of type A jacks and off you’ll go!

No software to install, and no PC casing to dismantle.

Why heck, install both USB Monica and Charlize in one little case and you’ll have a smoking PC audio system!

Due to complexity of build, no kit is available yet. Assembled/tested USB Monica could be purchased from our e-Store. http://store.diyparadise.com

For once, let’s end it short and sweet.

And spend more time with Monica!

Update on 27 Nov 2007!!!

Plug and Play USB Monica in hard wood chassis like Monica 3 available now!

Enhanced PCB featuring some changes ala Monica 3. Note the Super E Black Gates… Yummy!

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Improving Your diyparadise Products

Yeah! Improve your already awesome gear!

What?! Improve these already kick arse products!

Yeah baby, we are talking about serious kick arse here!

Let’s face it. No design is perfect, every design can be improved upon. If someone says his design is “blameless” or “perfect”, you know that person has been boozing too much. Or maybe he’s some salesman.

So on this page, I’ll try to list down improvements you can make to your diyparadise products.

Up the value quotient!

Improve sonics!

Get your friends jealous!

blah blah blah… Okay, let’s start.

USB Convertor

The easiest and best improvement will be to modify the SPDIF output stage. Right now this circuit consists of a simple TTL-SPDIF convertor. Just solder the primary of your digital pulse trans across the vias labeled SPDIF OUT, and solder the secondaries to your output RCA wiring. You could use the Newava Technology S22083 1:1 pulse trans, available from Digikey. Or the Scientific Conversion SC982-04.

The more observant among you will notice that the Newave is a 1:1 trans while the SC is a 4:1. By right, the latter is more appropriate as SPDIF output is only 0.5V so stepping down the signal voltage is correct but I never noticed anything wrong using the former. So rest easy and just do it.

I don’t recommend you getting a toroid and winding some wires and passing it off as a digital pulse trans. Just because you use silver doesn’t mean anything at all. These trans are engineered/optimized for digital communication, not some hack job.

Charlize and Charlize2

Believe it or not, we have done so much work to Charlize2 that if you have the first version, just go grab the follow up version! I’m sorry but you can’t mod your 1 to our 2. [hey, you can’t mod your wife to look like Charlize okay?]

Guess the best upgrade you could do is to try various power supplies and see which works best. In our opinion here, nothing beats a high quality rechargeable sealed lead acid battery. Have tried various makes and all sound different. Read Graham and Denise’s report here.

Rudolf Broertjes’ Solid State I/V Gain Stage

If you have been following the diyers forum, you may notice that Ronald Verlaan and later Ole Schüsseler suggested LEDs instead of diodes for D2/D4 and D10/D14.

Another useful tweak is SUPER E the output Black Gates capacitors. I know these caps are facing extinction so please grab them now while they are still available [please don’t ask from me. Oh well, if you have to, they are 1000 EUROS a pop!] You know folks like to say Less is More but in this instance, More is the way to go!

This gain stage runs off at 12V but at higher voltages, she sounds better! Please be careful here as the power supply capacitor C22 is rated 25VDC only. So make sure you don’t go higher. [I use 24VDC myself and she’s been singing for months.]

The I/V resistor could be swapped to your personal preference. Use whichever audiophile approved boutique part as you (or your wallet) sees fit. My personal preference here is the excellent Riken Gold but as these parts are no longer in production, I’m sorry I can’t give/sell you any. [that’s not true. i’ll gladly trade for gold bars.]

Oh yeah, measure voltage across the I/V resistor and adjust the trim pot for half of your power supply. If this voltage is too high/low, some roughness or distortion may be present. Not good!

Monica2

If you have installed the RB SS I/V kit, the above applies but also, utilizing lessons from the USB Convertor’s digital pulse trans tweak, put the trans at the INPUT. Yeah,

RCA Socket —> 1:1 digital pulse trans —> Monica2 PCB’s digital input

Use the recommended Newava trans above.

Again on the forum, another forum member esidarapyid, recommended polystyrene capacitors across VDD/GND and VREF/GND on the TDA1545A chip. This is another awesome tweak! As these are bypass capacitors, the values aren’t critical. I had good results from 100pF to 1200pF. Silver micas are great too!

Then Paul Needs contributed another awesome tweak here. Instead of referencing Vref to 1/2VDD, Paul suggested referencing to one diode drop, thus the last diode. To perform this tweak, remove the 22kohm resistor (labeled “223”) and solder as shown.

Don’t be a klutz and short other pins. As always, solder/desolder ONLY on an electro-static safe sheet/mat, like the anti-static wrapper that houses your diyparadise product.

Paul also suggested giving a bit more current to the constant current source. Currently it’s set at 50mA but Paul suggested going for 70mA. To do this, you need to have about 18ohms at R10 in above pic. If you are lazy to desolder R10 and solder in a 18ohm resistor, you could just parallel a 100ohm on top of the 22ohm of R10.

Use Whitesnake!

I have been using various DIY 75ohm coaxial cables and have been pretty satisified with them until one day Gabriel suggested this white-colour-unassuming-but-thick-as-garden-hose cable. It’s so thick that I wondered how smart can it be?

Sorry for lame joke. Anyway, I tried it out and… Wow! Totally smoked whatever digital cables I had before. It was so good that one customer even ditched his purchase of a USD200 cable.

USB Monica

Right now we have the Enhanced USB Monica, but if you have the previous version, you could apply the tweaks to the RB SS I/V stage and also TDA1545 circuitry. Actually the Enhanced version already has these tweaks done. See how luck you folks are?

Note that the polystyrene Paul Needs tweak is not done on your PCB version. Only in finished products. [please don’t ask me for polystyrene caps either. if you wish, i’ll exchange for 2 gold bars!]

Aha! Since she’s software controlled, you bet your software has an effect on her sonics too! I like Macs here, as well as Linux. I stay away from Windoze as much as possible…

My sincere thanks to these gentlemen mentioned above for their ideas, suggestions and generosity.

Please note that the finished products (or “Plug and Play”) incorporate all the above mentioned tweaks.

Hey! Aren’t we on a roll here? Let’s continue…

Use wood!

Wood chassis really sounds beter. Looks better too!

Hifi products tend to look industrial, coming in cold soulless steel or aluminium, with little touches of wood for a “touch of class”.

Pure bollocks. Try housing in wood chassis and listen for yourself.

Not to be discounted, nor under-estimated.

Having a good brew in hand.

Silence in the listening area. Give your wife your credit card and ask her to shop for hours! [be smart. call the credit card company to cap a limit first!]

Great music. Please, not those audiophile crazy, sound effect mumbo jumbo junk passing off as music. I mean MUSIC! REAL MUSIC! You should be able to make an emotional connection with the music. Listen, appreciate, emphatize, celebrate… And stop all that analyzing shit. See, there’s “anal” in “analyze”.

Lastly, as with all diy projects, please exercise caution, especially with electro-static discharge, when performing these tweaks. I have said it before and I’ll say it again. The soldering iron is mightier than the pen/sword. But this doesn’t mean you could wield it like crazy. BE CAREFUL.

Good luck!

Improving Your diyparadise Products – Part 2

a. k. a.

How I Made My Friends Shit in Their Pants!

Oh yeah! If you did all the mods above PLUS these mods :

Bad Naughty Connector

Have never been a believer of cables and connectors but done right, with technical backing, I certainly ate the humble pie!

Powering Your Monica

Clean power, like clean water, is still the best.

I bet your friends will shit in their pants when they come over to listen to your system!!!

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My USB Convertor

Here’s a very simple USB convertor. Plug this to your USB port, and all your music signal will go through it. No programming needed, no soundcard necessary. Just plug and play.

The star here is PCM2706. It’s a pretty cool chip that could do three functions. It could be a USB headphone amp, it could output SPDIF data and also I2S data.

I played with it, and unfortunately the internal DAC’s output is already over-sampled and kind of… sucks. Okay, okay, that’s too strong a word but if you are bitten by the Non-Oversampling magic, conventional DAC (meaning those oversampled types) really turn you off. What’s the magic word again? As Monica said it herself, “makes me puke”! Ha ha!

So instead, i’ll offer her as USB Convertor instead. Takes in USB and outputs either SPDIF or I2S. Headphone amp circuitry components will not be offered.

Also, will be offering as a kit here. Don’t worry, I’ll make it simple for you. I’ll solder in the 2 chips instead, so you just have to solder in those little surface mounted resistors/capacitors.

Afraid of SMD? Don’t worry! I’ll show you in a video how to solder SMD. Sorry, the clips aren’t very clear as I’m really an amateur here. I’m really better in front of the camera. Also, I kept my mouth shut so as not to distract you from viewing how to solder SMD. You know I’m quite a chatterbox…

smd-tutorial

Components

R8, R9 22ohm. SMD resistor “220”

R7, R14 1.6kohm. SMD resistor “162”

R15 1Mohm. SMD resistor “105”

R10 360ohm. SMD resistor “361”

R11 100ohm. SMD resistor “1000”

C5, C6, C8, C9, C10 1uF. SMD capacitor

C13, C14 10pF. SMD capacitor

C7, C12 47uF “Low ESR” electroltic capacitor

C11 100nF metallized polypropylene

L1 Ferrite bead.

Y1 12MHz crystal

And of course, the USB jack. Note the placement in photos above.

This is all you need! Solder SMD components FIRST, then only the Thru-Hole components.

To configure for SPDIF output, short R12. To configure for I2Ss output, short R16.

I built one in 15 minutes, then brought to a friend’s place to test. We copied a track from a disc to lossless WAV format. Then played through his notebook and compared to his DVD player. The same system was used except the source where we are comparing DVD player to notebook+USBconvertor combo. Boy, the latter is definitely more organic!

For a limited time only (feel free to question my sanity), 10 such USB convertor kits will be offered at USD25 only.

Order from http://store.diyparadise.com.

Your assembled USB Convertor should look like this. Note orientation ofo USB jack. Note that I shorted R12 for SPDIF output. If you desire I2S output, short R16.

If you desire a slim profile, you could lay down the 47uF caps like this.

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Computer Audio is Soooooo Much Fun!

Boy, I have been having so much fun with computer audio, or do you prefer the term “PC Audio”? Playing music through a PC is addictive. We’ll look at the hardware side first before going to the software end.

I admit I have been late to this “PC audio party” but as they say “better late than never”! And I’m glad I joined the party! The sonics has so much potential compared to conventional CD playback and most folks believe this is mainly due to much reduced jitter when playing through PC. You see, with conventional CD playback, we almost can’t escape from using digital output (SPDIF) format. The Achilles’ heel of SPDIF has to be the way the critical Bit Clock is recovered from it.

This is the work of the digital receiver (like CS8412, CS8414 etc) and we are limited by how well it recovers this clock signal. CS8412 for example has jitter specifications of Bit Clock of 200ps. Not very impressive! Monica’s asynchronous reclocking (as shown the light by Kunosoki san more than 20 years ago) ameliorates this but it’s no way a solution either.

With computer audio, let’s say this together. “To hell with SPDIF!” Ha ha!

Back to hardware, the Squeezebox is a little computer gadget that appeals to geeks like you and me. It streams (wired or wirelessly) audio files stored on your PC to your hifi system. Of course, if you do it wirelessly, you could have your noisy PC in one room and your hifi set in another. Wonderful!

To be honest with you, I know nuts about playing music through a computer but ever since I got a Squeezebox, have to start a crash course on it!

Fancy having a dig at DIYing your own Squeezebox? Well Ole Schüsseler here shows you how to do it with his Linux based Audio Appliance.

So what if you don’t want a player like the Squeezebox and prefer to play from your PC? Sure, no problem! Back then you’ll need at least, a good quality soundcard, but nowadays, there are USB DACs to consider. Yup, takes USB data and converts to analog signals.

The Wonderful World of USB DACs
You see, operating systems (at least for Windows and Macs) are smart enough to know that when they detect a USB DAC, all audio signal will be routed through there. Of course, you could control not to do this as well, but unless your soundcard has better sonics, it’s good to consider USB DACs.

USB DACs like Texas Instrument’s PCM2706 (used in My USB Convertor) not only functions as a USB DAC but also as a headphone amp, USB-SPDIF convertor as well as USB-I2S convertor. The last function is the most interesting as once converted to I2S, we could hook up many DAC chips directly. DAC chips like TDA1543, TDA1541… etc. Like this:

If you want to try this yourself with my USB Convertor,

Pinout of I2S on my USB Convertor pin 1 is GND pin 2 is Word Select leave pin 3 blank pin 4 i Bit Clock pin 5 is Data

I guess you know which pins to connect to which pins right? Told you it’s very easy! Power your DAC chip separately though. Don’t be cheap and use the USB’s 5V supply. If you do so, don’t complain if it doesn’t sound good ok?

If you are ooo-laa-laa over sonics of Monica, then this isn’t so simple. Monica’s TDA1545 chip uses EIAJ format instead of I2S. The main difference between both signal formats is the where upon the DATA signal is sent. I2S sends the DATA signal at the beginning of the Word Select signal but EIAJ sends at the end.

No, please don’t ask me why can’t those folks sit down and agree on one format. I have no idea. But look at SPDIF. The very few instances where all folks concerned agreed on a format but it turned out to be a lousy format. Oh well…

Anyway, I tested and built a pure USB Monica, taking in USB signal to I2S then converted to EIAJ then fed to TDA1545. Give us a few more weeks and you can jive with her soon! [USB Monica is ready!]

Squeezing more juice out of the Squeezebox
Back to the Squeezebox. I’m sure many will be wondering how does the Squeezebox compare to audiophile CD players? Well, stock player is nothing to shout about however never ever under-estimate the power of DIY! I’ll share with you 2 mods I tried here.

The very first upgrade every Squeezebox owner should do is to replace the stock power supply adaptor with a beefier unit. One capable of at least 1A (2A is better). Some folks prefer linear supplies while some prefer switching. My preference is switching power supplies but don’t let me influence you. Go try yourself. Just make sure it outputs 5V REGULATED and you’ll be fine. Oh yeah, pay attention to polarity too since we are dealing with DC voltages here.

For the adventurous diyers, the first mod is considered too easy, no fun at all. The second mod, you need to pull out your Torx T10 screwdriver and dismantle the Squeezebox unit.

This is a relatively easy tweak. Easy to understand and easy to implement if you are good with soldering surface mount components. If your soldering skills isn’t up to par, then forget it. Find someone to do this for you. Remember as with all mods, you can kiss your warranty goodbye so if you are not up to it, don’t try to be cheap here. It ain’t worth it brudder.

What we want to do here is modify the SPDIF circuitry. If you trace the digital output RCA socket, you’ll find it ends at pin 6 of chip U15. This is just a 7404 invertor chip. What we have here is that the invertor output goes through a coupling cap then 2 resistors to ground. The resistors form a voltage divider to scale down the output of the invertor from TTL logic level to SPDIF level. If you find all this Greek, don’t worry.

By right, there isn’t a lot of problems with this circuit but due to the very noisy environment of the Squeezebox (what more with a wireless card nearby), we don’t want all the noise to be carried all the way through the digital output (via SPDIF format) to your DAC and the rest of your audio chain. And the easiest way to accomplish this is to use a digital pulse transformer.

The digital pulse transformer accomplishes 4 things.
First it breaks the ground. The SPDIF signal ground is no longer the Squeezebox unit’s ground. This is possible due to usage of transformers.
Secondly, I believe the trans has better driving capability then just a the invertor and voltage divider circuitry.
Third, with a trans, we could benefit from its common mode rejection capability. Meaning, it rejects noise common to both signal and ground. Like in a noisy environment inside the Squeezebox.
Lastly, we could better match the impedance output impedance with the usage of suitable trans.

So first remove L8 and L9. Then desolder the R67 107ohm resistor. One end of R67 goes to ground while the other end is tied to R66. There’s a mistake in above diagram though. Primary (red dot, pin 1-4) has ratio of 1 while secondary (pin 5-8) has ratio of 2. So you should wire pins 5-8 facing the 7404 invertor chip and the other end (pin 1-4) facing output RCA socket. To anchor the trans, I soldered one leg (pin 8) to junction between 107 and 245ohm resistor. Thus pin 5 goes to ground. Pin 1 (red wire) goes to SPDIF output. Pin 4 – SPDIF ground. (If you are fussy, replace 245ohm resistor with 300ohm for even more accurate 75ohm output impedance.)

Now you know why I’m enjoying computer audio?

Moving on to the Software side

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