Category: DIY


Headphone amplifier – RJM Sapphire v4.2

The story of this amplifier began with the need to trade my beloved Hifiman Arya Stealth for closed-backs because I only use headphones when I am in the office and open-back headphones are disturbing others.I found a trade deal for ZMF Atticus with Eikon pad and I traded without even listening to them. As expected, they sound much less exciting than the Arya Stealth but they still sound good for closed-back headphones.

However, as their impedance is 300 ohms, I needed something more powerful than my portable Cayin RU-6 and the integrated amplifier in my Topping DX3 Pro. I had the RJM Sapphire v4.2 boards laying around from a group buy and also a Modu Shop enclosure I bought a while ago that was just the right size for this build.

The documentation in the RJM website is very informative and contains a detailed BOM file that includes formulas and example values for different gain values. If you still have some questions you can also search by keyword in the DIYAudio topic, which also has a lot of info.

RJM Sapphire v4.2 schematic

I opted out for the open loop configuration with a 21 fixed gain as I will be using it with only one pair of headphones so far. That’s why JP1, R2B, R2C, R3X are not installed on the board. You can find info on those in the BOM file.

This photo was taken in the middle of soldering the components to the boards. Resistors are different types in the different positions, of course they are consistent between right and left channel board, just because that’s what I had in my parts bin.

RJM Sapphire v4.2 PCBs

The trickiest part of amplifier building, drilling the enclosure, front and back panels. I am getting better and quicker with each amplifier and of course with all the mistakes I made in the past.

Front and back pannels drilled

In the next photos the amplifier is 99% ready and already tested with a cheap pair of headphones for stability, oscillations and temperature issues in any of the transistors.

DIY RJM Sapphire Headphone Amplifier Build Inside

Without matching any of the transistors or even measuring their hfe at all I was able to adjust the output DC to values within +-10mV which is good enough for unmatched parts.

DIY RJM Sapphire Headphone Amplifier Build Inside 2

I forgot to take one more photos when I earthed the chassis, the output and the potentiometer, but just to remind you if you are building it – always take care of your grounding.

I will also make sure to upload more photos when I 3D print a volume knob and close the lid.

As I expected, a more powerful amplifier was definitely needed with the ZMF Atticus, they sound much meatier and with better control with more power from the RJM Sapphire.


Interfacing a HD44780 LCD with Raspberry Pi over I2C

I have decided to add a 16×2 LCD to my Raspberry Pi 3 based network audio player with PCM1794 DAC in order to see what is currently playing and the bitrate of the output without having to check my phone. I don’t like the number of wires that parallel LCD connection requires so I started looking for a 16×2 LCD with I2C interface which is not too expensive.

I found a very cheap 16×2 LCD on Aliexpress and even cheaper I2C backpack for it. I personally chose green foreground with black background as it looks nice in my enclosure, but there are other options too:

First test:

I decided to use LCDproc as it is a mature solution that works (almost) out of the box with HD44780 based displays over I2C, it just needs a driver and proper configuration. It is easy to control it via a telnet-like TCP protocol with Python, PHP, C++ or any other language of choice and it has many options such as managing a scrolling text, widgets, icons etc. which reduced my code to only a few lines.

My Github repository contains everything needed to pair HD44780 based LCD displays and LCDProc on Raspberry Pi via I2C. It includes installation instructions for installing on Moode or other Raspbian/Debian based OS.

  • play.php – My script to fetch currently playing song on Moode Audio and push it to the LCD via LCDProc, you can edit this one to fit your needs
  • client.php – LCDProc PHP client library by Peter Clarke (@theapi)
  • LCDd.conf – My /etc/LCDd.conf which works perfectly with the display linked above
  • – Driver for LCDProc HD44780 I2C displays by @wilberforce. You should copy it to /usr/lib/lcdproc/

I am running Moode Audio v6.2.1 which is based on Raspbian so it should work with any other Debian/Raspbian based OS, and most likely with Ubuntu too. I have written a small script which parses /var/local/www/currentsong.txt (a file automatically updated by Moode) and displays currently playing song/output bitrate info on the LCD. You can rewrite the script to work for any other OS, display size or purpose.


My take on the PeeCeeBee V4H amplifier

While I was browsing the forum I found a popular schematic called PeeCeeBee V4. It had a lot of positive reviews from the DIYaudio members who had already assembled it and it looked simple and easy to assemble for someone with not so much knowledge in the solid state amplifiers.

The author (Shaan) created and published a more powerful version of it called PeeCeeBee V4H which was able to push 150W into 8ohm load on +/-56V PSU, just about the right power to satisfy my somehow low sensitivity ATC SCM11 (v2/curved) speakers.

PeeCeeBee V4H schematics

Gathering the parts

I ordered PCBs from the author himself including genuine pairs of 2SK1058/2SJ162 needed for 2 channels which he shipped to me in Bulgaria. Shaan’s PCBs are of extremely good quality and visual appearance.

While I was waiting for the delivery I called Novatech Ltd to order a custom winded 40-0-40VAC @ ~550W toroid.

For the PSU I chose to use six Cornell Dubilier(CDE) SLPX 12,000uF 63V for a total of 72,000uF or 36,000uF per rail because they seem like the best bang for the buck. I bought all the capacitors used in the PSU and amplifier boards at from Stefan at All capacitors are genuine, the prices are the lowest I could find and they deliver all over the world. All other passives needed for the amplifier I have bought from and Farnell. All resistors are 1% or better, all small capacitors are Wima.

Assembling the boards

I decided not to waste time ordering a custom PCB but rather paint a universal PCB with black spray paint as the other PCBs are also black. Assembling the PSU board was pretty quick, it consists of a bridge rectifier, 6x 12,000uF capacitors and some snubbers.
PeeCeeBee V4H PSU painted

PeeCeeBee V4H PSU done

For the assembly of the amplifier boards the author of the schematic/PCBs provides a great instructions and there is nothing more than I can add to it to make it easier.

Here are some photos from the assembly of the amplifier boards.
PeeCeeBee V4H Assembly Step 1

PeeCeeBee V4H Assembly Step 2

The hardest thing of all the V4H assembly for me was drilling the aluminium heatsinks and tapping the holes. I have used a 2,5mm drill to make the holes and a M3 tap to make the thread. Make sure to take your time and use alcohol while drilling and tapping instead of oil. Alcohol is better for aluminium. It is nearly impossible not to break a drill or a tap when using a hand drill machine instead of a drill machine with a stand or a table drill machine. Breaking a drill or tap inside the aluminium heatsink is a very bad experience because there is no way to get it out of there without destoying the hole/thread.

Warning: REALLY, TAKE YOUR TIME WHEN DRILLING AND TAPPING! If you ruin even one hole/thread you need to redrill all other holes because the transistors are in exact positions from one another.

PeeCeeBee V4H Assembly Step 3

The last picture was with resistors needed for the setup process consisting of VAS (Voltage Amplifier Stage) biasing, offset trimming and mosfet biasing. The process is very well explained in Shaan’s instructions.

First listening tests

PeeCeeBee V4H Test Run

After a few days of settling my first impressions are that the sound is very natural and pleasant to the ears. Overall I am completely satisfied with it. I will write a more detailed review of the sound once I have something good enough to compare to in the same room/setup.

My current setup is:
Source: DIY Volumio > XMOS > PCM1794 Source
Interconnects: DIY OFC Silver Plated Interconnects
Amplifier: DIY PeeCeeBee V4H Amplifier
Speaker cable: Chord Odyssey 2
Speakers: ATC SCM 11 v2(Curved)

I will update the post with the final look of the amplifier once I finish the enclosure.

Links for PCB info/order:


Xiaomi M365 scooter dashboard with ESP32 and 1.3 inch TFT screen

I have recently added a nice digital dashboard to my beloved M365 electric scooter. Thanks to Dani M. and the other contributors to the project I was able to make the scooter a lot smarter.

The dashboard calculates and displays daily statistics including mileage, avg. speed, time and energy used, remaining battery mileage and battery level. When you start driving the screen changes to speedometer, wattmeter and some other realtime metrics. There are a lot more screens containing battery and ESC temperatures, BMS statistics containing voltage for each cell, total battery cycles, estimated battery health percentage, pinpointing defective cells and much more.


Required components:

– You must join the creators’ English or Spanish chats in Telegram in order for your ESP32 serial number to be activated(it’s free):
– Download all required files (firmware, manuals, 3d printing STLs etc.):
Ptodorov’s Mirror
ESP-WROOM-32 (should be the same form factor in order to fit)
1.3″ 240×240 ST7789 SPI TFT
– 1N4148 diode (I had BYV26 on hand)
– 100R and 680R resistors
– 3D printed housing, you can find .stl files in the download (I printed this with my Ender 3 printer, but if you don’t have one you can ask/pay someone to print it for you)

Flashing the firmware to the ESP32:

Before connecting anything to the ESP32 you should flash it’s firmware.

Install ESP32 1.0.0 board in your Arduino IDE from Tools > Board > Boards Manager (Warning: ESP32 1.0.1 version will not work, choose 1.0.0 from the dropdown). Install ESP32WebServer and ESPmDNS libraries by Ivan Grokhotkov via Sketch > Include Library > Manage Libraries. Connect your PC/Mac to the ESP32 using a MicroUSB cable. In Arduino IDE choose ESP32 Dev Module from the Tools > Board menu. Change the upload speed from Tools > Upload Speed to 460800.

Now open the .ino file from the M365_Loader_v12 folder and fill your home wifi ssid and password in the //WLAN Station parameters variables. Click the Upload button and wait for it to finish. Now open Tools > Serial Monitor and take a look at the log, it should connect to you home WiFi and display it’s assigned IP address. Take note of this IP address and using a browser open http://[the_assigned_ip]. You should see a blank page with an upload box in it. Choose the FW_0.23.3-TFT.bin file from the project folder and click Upload. When it’s ready the web page will be reloaded.

Wiring it up:

Now you can disconnect the USB cable and warm up your soldering iron. Make all connections to the TFT and the M365 power button board according to the following schematic:

Xiaomi M365 ESP32 dashboard

Warning: Do not connect microUSB to the ESP32 when it’s wired to the VCC of the M365 mainboard. If you need to debug with Serial Monitor or refresh the ESP32 you should only leave GND and BUS connected to the M365 and disconnect the VCC wire.

Xiaomi M365 ESP32 dashboard

Xiaomi M365 ESP32 dashboard enclosure

Xiaomi M365 ESP32 dashboard fitted

Xiaomi M365 ESP32 dashboard charging

In order to activate your license you should open the ESP32 settings from your PC browser and fill in your Telegram alias, note your ESP32 serial and send it in the Telegram chat in order to be activated.


Pure OFC Silver Plated Pseudobalanced Interconnects (DIY)

I consider interconnects one of the most important cables in the audio system because the signal level they are transitioning has a low amplitude which makes it sensitive to noises. On the other side, devices on both ends of interconnects are usually sensitive to characteristics of the cables like capacitance and resistance.

Today I will show you how to make a pair of very high quality DIY interconnects using a 99.9998% OFC silver plated wire in a pseudobalanced(semibalanced) configuration. Pseudobalanced(semibalanced) interconnects usually employ a shielded cable consisting of 2 insulated wires and a shield which is connected only on the input end.

Cable: Audiophonics 11467 – 2m (6.5ft) (supplier)
– Cores: 2×0.5mm silver plated OFC
– Shield: silver plated OFC
– Insulation: PTFE
– Total diameter: 3mm
– Costs only 4.92EUR per m

Sleeve: Audiophonics 7835 – 3m (9.75ft) (supplier)
– Cable diameter: 1.5-5.5mm
– Costs only 0.83EUR per m

RCA Plugs: Rean NYS373 – 4pcs (official website / my supplier)

– Maximum Cable Diameter: 6.1mm
– Solid build, long lasting
– Gold plated contacts
– Easy to solder
– Costs only 2EUR each

Total cost: 20.33EUR

Input end (a.k.a source):
At the input end you should join the black insulated conductor with the shielding for a pseudobalanced configuration (only at the input end !). Like this:
DIY Silver plated OFC Input End

And then solder it into the RCA plug:
DIY Silver plated OFC Input End RCA

Outpud end (a.k.a. destination):
At the output end you should leave the shield unconnected at all and make sure it can’t accidentally touch any of the metal parts of the RCA plug. Use only the black and white insulated conductors as shown:
DIY Silver plated OFC Output End

And then solder the insulated conductors in the RCA (don’t forget to slide the rca outer shield to the cable before soldering the connector on the other end):
DIY Silver plated OFC Output End RCA

Make sure to mark permanently which side is input on both channels so you won’t make mistakes when connecting the cable.

Mine looked like this after I was done:
DIY Silver plated OFC Pseudobalanced Interconnect


Inexpensive PCM1794 DAC based on a cheap Chinese board

I was in need of a DAC which will be used as my main audio source. The requirements were simple:
– Digital inputs switching. I wanted to use the same DAC whether I am listening from my DIY Volumio streaming device or watching a movie/playing Xbox.
– Of course I also want the best sound quality.

After reading this article, the PCM1794 datasheet and talking to a friend of mine who works in a professional audio equipment manufacturing company I decided to try the PCM1794 from Burr Brown for this project. I did a quick search on Aliexpress for readily available PCBs based on PCM1794 and I came across one that looked well made. The PSU part is well separated utilising:
Four separate transformer windings with 3 bridge rectifiers (MCU+LCD; digital section PSU; analog section PSU)
Five on board regulators (LM7805 for the uC/LCD, LT1968-3.3V for the AK4118 and PCM1794 digital supply, LM317(5V) for the PCM1794 analog VCC, LM317/337(+-15V) for the opamp supply.
Ground planes

The board costs only 47$ so I expected cheap capacitors and probably fake AD827 opamps. After 20 days I received the board. I was right, they used cheap caps(except the big filter Nichicons, which seem good) and the opamps are probably fake at this price so I started planning mods to the board.

The first thing I did was to test the board before doing anything so I know if it works as expected. I plugged in all required windings, plugged my set-top box as digital source with an optical cable and flipped the switch…

F*ck… The thing is not even working…

Chinese PCM1794 AK4118 board

The first thing I did was to measure all the supplies. I found out that the LT1968-3.3 had 2.0V at its output so the AK4118/PCM1794 didn’t get enough voltage to work. I desoldered the LT1968 and soldered a LD1117V33. It finally worked. Good thing is I don’t have to return it to the seller and I can start with the mods.

After inspecting the board and following some traces I have annotated the photo of the board of all planned mods for convenience.

PCM1794 DAC planned mods

I have done the following modifications:

1. Change all big diodes in the rectifier bridge to SB5A0 fast recovery diodes because the old ones were standard Chinese diodes with shady letters on them.

2. I checked all resistor values according to the following OPA1611(single version of OPA1612) schematic and found out that the 8200pF capacitors were actually 220pF(marked on board as 820pF) and the 2700pF were actually 270pF(marked on board as 270pF). Resistor values were right according to this schematic.
OPA1612 as I/V converter
Changed those to Wima FKS2 capacitors with the right values and also changed the 2200pF metallized film capacitors in the feedback of the I/V stage with same value Wima FKS2.

3. Changed all electrolytic capacitors to Nichicon UPS which are low impedance, high temp range capacitors suitable for PSU usage. Some of the capacitors were 47uF instead of the 10uF according to the PCM1794 datasheet.

4. The final thing to do was change two of the AD827(probably fake) to two OPA1612 opamps in the I/V stage and change the third AD827 in the differential to single convertor stage to OPA2132.

PCM1794 AK4118 OPA1612 OPA2132 DAC

I will now let the DAC burn in for a couple dozen hours and I will start listening!

15.01.2019 UPDATE:

Below is a picture of the full setup in a temporary enclosure consisting of the following:
– A DIY AC filter
– 2x15VAC+2x9VAC R-Core transformer feeding the DAC board
– 2×7,5VAC feeding the XMOS reclock and Raspberry Pi
– Raspberry Pi 3 running Volumio fed by a LT1083 + CRC filter PSU(on the black prototype PCB)
– JLSounds XMOS, with it’s reclock fed by an LM317 + CRC PSU(also on the black board)
– The modified chinese PCM1794 board
– An LCD display+MCU+rotary switch that came with the Chinese board used to switch digital inputs and display current signal frequency, considering to remove that and put a white on black OLED connected to the Raspberry to display current song, bitrate, res etc.

While still burning in, the sound of the PCM1794 is amazing. TBH I have never expected such a detailed sound that is still warm and pleasant to listen to from a delta-sigma DAC except for the most expensive Sabre pros. I don’t believe the TDA1541 myths anymore.

The good thing is that the whole streamer/DAC costed less than 250$ including the trafos, raspberry, xmos, memory card, DAC board and all the components for the upgrade. It allows me to listen to music from online streaming services such as Spotify and Tidal, USB SSD and I can still switch to the toslink coming from my TV with one click and use the DAC for Xbox(pass-through) and Netflix.

raspberry volumio xmos pcm1794

I will make a full blog post about the whole streamer/DAC once I am done with lower noise discrete PSUs and the enclosure.

UPDATE 10.02.2019:

As a final update to the DAC board I decided to replace all the analog audio power supply LM317/337 regulators (opamp supplies and PCM1794 AVCC supply) with DIY discrete regulators with very high Power Supply Rejection Ratio and very low outpud impedance in the audio spectrum. The schematic is designed by a friend from our local audiophile forum (Thanks, Sandy!). Some measurements of the discrete regulator:

The red line is the noise of the discrete regulator, the blue line is the self noise of the measurement setup. WARNING: The numbers are offset by 100dB because of the measurement setup, so -30db must be read as -130dB:
Discrete regulator measurements

So the PSRR of the discrete regulator is ~ -125dB.

For comparison, measurements of the previous regulators (LM317). WARNING: The numbers are offset by 60dB because of the measurement setup, so -20db must be read as -80dB:

LM317 PSRR measurements
LM317 measured PSRR: ~ -83dB

Also, the discrete regulator has a lot better reaction to load impulses compared to the LM317/337.

I hate soldering SMD to such tiny boards with my not so good soldering iron but the end result is worth it. A photo with the all three discrete regulators soldered and fit to the board:
PCM1794 Discrete Regulators Fitted


DIY Silver Plated OFC Shielded Interconnects

Today I will be sharing with you a quick guide for a very high quality DIY interconnects at a reasonable price consisting of a silver plated OFC shielded cable from Schutz Kabel and gold plated RCA plugs from Amphenol.

Cable: Schulz Kabel SL 1 – 2m (6.5ft) (official website / my supplier)
– Core: 64×0.1mm silver plated single copper cores
– Shield: 120×0.1mm silver plated single copper cores
– Outer insulation: PVC with natural rubber
– Middle insulation: Thermoplastic elastomer
– Core insulation: Polyethylene
– Costs only 3.68EUR per m

RCA Plugs: Amphenol ACPR-* – 4pcs (official website / my supplier)

– Maximum Cable Diameter: 7mm
– Solid build, long lasting
– Gold plated contacts
– Easy to solder
– Costs only 2.5EUR each

Total cost: 17.36EUR

Note: If you choose to use another RCA plugs or cable make sure that the outside diameter of the cable is not bigger than the RCAs’ maximum cable diameter otherwise you may find it impossible to fit and fix it in the RCA. For example, the Schulz Kabel SL 1 has an outside diameter of 6.5mm and cannot fit in the popular Rean NYS373 RCA plugs which I found the hard way 🙂

(click to enlarge)
DIY Silver plated OFC Interconnects


Playstation 3 NAND Downgrade guide ( CECHC04 / COK-002 , Teensy 2.0++)

After searching for some time on the Internet on how to downgrade a 60GB PS3 with the COK-002 board, I couldn’t find a guide which explains which testpoint on the COK-002 that is in my PS3 corresponds to the appropriate NAND chip leg. The only thing I could find is that I can use a NAND CLIP to read/write the NANDs but I didn’t feel like giving 60$ and waiting 15 days for a NAND clip that I will use only once.

There are 2 images I found showing which testpoint corresponds to every pin of the Progskeet v1.2 board and the same image for the Infectus board, but I could not find such an image for the Teensy++ 2.0, so I used the image for the Progskeet, along with an image of which Progskeet pin(GP1 etc.) corresponds to which NAND chip pin name (WP, ALE, CLE, I/O1 etc.) to create a diagram of which testpoint on the mainboard goes to which leg of the NAND chips made by Samsung.

PS3 NAND COK Connections


So now you can use this diagram not only for downgrading/dumping/writing the NANDs with a Teensy++ 2.0 board, but with any other board available on the Internet.


You must provide a stable 3.3V PSU to both the PS3 board and the Teensy, and don’t forget to unite the GNDs. You can use any PSU which outputs 3.3V @ 1.8A+, the easiest option will be to use a PC PSU.

Short list of the downgrading procedure:

  1. Prepare your Teensy++ 2.0 by using the teensy_loader applications to flash the NANDway .hex file into it
  2. Install Python for Windows and PYserial
  3. Find out which COM port does the new Teensy NANDway use by opening the Device Manager and looking into the Ports(COM&LPT) category
  4. Take apart your PS3 using one of the million videos online for reference
  5. Very carefully solder all the wires according to the diagram above
  6. Solder the other end of all the wires to the teensy board
  7. Find a 3.3V 1.8A+ PSU and solder it to the PS3 mainboard(see the diagram) and to the Teensy++ 2.0
  8. Solder the Teensy++ 2.0 GND to the PS3 mainboard GND
  9. Now on your PC, with the PSU on, the USB cable connected to the Teensy++ 2.0 board run the NANDway python script by issuing the following command in CMD: “ COM4”, where COM4 will be the port number you seen in the Device Manager.
  10. You’re done 🙂

Tools used to dump/downgrade/write the NAND chips:

Teensy++ 2.0

NANDway. Now united with NORway in the same repo.

Useful information on the Teensy++ 2.0 PS3 topic here.


A solid-state tale. Slone’s Figure 6.21 or micro-ZUS (uZUS)

After finishing my last solid-state amplifier I was away from the DIY audio scene for some months but a few weeks ago something bad happened to my last amp. My roommate was helping my move my audio components from my car trunk to my apartment and he accidentally dropped my solid state amplifier down the stairs. The amplifier didn’t have an enclosure and all the components were mounted on a wooden board so you can imagine what happened to the PCBs after that accident. It was time for a new build! After browsing the Bgaudioclub forum I came across a great thread about the Randy Slone’s favourite amplifier schematic from his book The Audiophile’s Project Sourcebook. I don’t know if it’s ok to post the schematics here, but if I infringed any copyrights please drop me a mail to remove it.

Randy Slone Figure 6.21 Schematic

As the schematic is relatively complex for a homemade PCB. I found out that a forum mate had some PCBs left and I bought two. Then I ordered the parts required for this build from Comet/Farnell. The problem was they didn’t have the 2SK1058 and 2SJ162, so I ordered them directly from the USA to be sure that I won’t come across fake transistors. A few days later I had everything to begin with the build.

Randy Slone Figure 6.21 PCB

Almost all the components on the PCB were SMD including many transistors and I don’t have a reflow station so it took a some hours to solder everything on both sides of the PCBs. After I soldered everything, mounted the transistors to a heatsink and connected the cables I plugged the amplifier into the mains. Hm, there wasn’t anything coming out from the speakers… I wondered what’s wrong, but then I pressed play. The amplifier was perfectly working, it was so quiet that I could not hear any noise coming from my speakers… NICE!

Randy Slone Figure 6.21 Done

There are silicone insulation pads between the transistors and the heatsink, I just cut them to match the size of the transistors and therefore you can’t see them.

The PSU:

It is a classic unregulated PSU consisting of a 500VA copper shield insulated transformer with a 39-0-39VAC secondary, 4x HER607 diodes shunted with 4x 33nF caps and 2x 15,000uF/63V filter capacitors(+100nF MKPs). An EMI filter is added before the trans.

Randy Slone Figure 6.21 PSU Schematic

First impression:

My first impression of this amplifier was “WOW”… As soon as I pressed play the room was filled with warm yet very dynamic sound with plenty of bass considering my bookshelf speakers /B&W 685/. I listened to the following tracks at first: Sade – Jezebel, Sade – No Ordinary Love, Candy Dulfer – Lilly Was Here, AYO – Without You, Zazz – Je Veux, Steve Strauss – Mr. Bones and some orchestra.  I knew that the 22uF bipolar Nichicon Muse at the input was not the best choice for this amplifier/for any amplifier/ but I still liked the sound. After an hour or so listening, the capacitor started to settle down and the sound became more transparent and colorful. I didn’t have enough time to let the amplifier settle down and listen to it because I went on a vacation for a few days. I will post a follow-up with more details about the build and the sound when I get back in a few days.

So far this is the best DIY solid-state amplifier I’ve ever heard!


TDA1541 and ECC88 DAC Part 1

It all started a few months ago when I put together a TDA1541+OPA49720 schematic on an experimental board along with a regulated PSU based on LM317/337. The plan was to push the digital signal from PCM2707 to the TDA1541 via I2S. The moment I started this thing I was immediately amazed by the sound of TDA1541, it sounded very warm to my ears and I decided I need to finally build a proper USB DAC, as I listen to all my music collection(FLACs,APEs,WAVs) with my PC as a source.

However, at that time I didn’t have enough time to continue with this project so I put everything in a cupboard and now I decided to finish it finally. The schematics were revised and SPDIF input is now planned along with the USB so DIR9001 is needed.

I found a nice PCB(thanks to Simonov) from my favourite forum Bgaudioclub to move over the parts from the experimental PCB as a PCB is always a better option, especially for audio/video circuits which can easily “catch” RF noises.

Click for the first part of the DAC schematic (before the tubes).

PCB picture:

A forum mate’s implementation as mine is not ready yet. Pictures of my DAC coming shortly.

As for the tube stage I decided to use a CCDA circuit inspired by a post in the diyAudio forum. The SK170 is used to null out the DC voltage offset in the output of the TDA1541. As you can figure out, the OPAMP section of the board above can be obstructed when using a tube output stage like the one I’m writing about. Here is my redraw of the circuit. The output is around 1.2Vpp which is enough for my purposes.

And the PSU:

As you can notice, this PSU has an EMI filter circuit before the transformer. The transformer has 2 secondary windings – 250VAC and 7-12VAC. The anode supply is then filtered and regulated by a capacitor and an IRF840 mosfet. The voltage rises slowly to keep the tubes safe by charging C3 through R14 to a reference voltage created using 4x75V zener diodes(D1-D4) which makes the regulator output 243V after the ~7V dropout of the mosfet. The heater supply is a classic LT1083 regulator circuit. Output voltage must be adjusted to 6.3VDC via R17. If you have a transformer with a 6.3V secondary you can heat the tubes directly from the secondary winding dropping the heater supply part, but that can increase hum.

I use PCM2707 in a standard circuit for a USB to I2S converter, in order to add an USB input to the DAC. A post will follow with pictures and sound quality review when my DAC is completely ready.

Thank you for reading.