Category: DIY

09
Jan

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.

20
Jul

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

30
May

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.

image

CLICK ON THE IMAGE FOR BETTER RESOLUTION

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.

Important!

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: “NANDway.py 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.

17
Aug

A solid-state tale. My favourite amp.

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.

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.

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!

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.

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!

15
Aug

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.

15
Aug

Grounding of power amplifiers

Ground loop currents flow through A -> B to the protected earth at point B, and then to mains ground via B -> C. They cannot flow through the audio path so this topology is resistant to ground loops even with unbalanced inputs. The limitation on system performance in the presence of a ground loop is now determined by the voltage drop in the input cable ground, which is outside the control of the amplifier designer. A balanced input in theory cancels out this voltage drop completely.

Seen in Audio Power Amplifier Design Handbook 5th Ed. by D.Self

15
Aug

My first tube amplifier (Part 1)

After discussing the schematics with members of Bgaudioclub I decided to build my first tube amplifier using the E180F and 6B4G vacuum tubes. I drew the schematic(thanks to 50AE) in Eagle and I will be starting to build this amplifier shortly. The costs will be more than in the solid state amplifiers I have built so far, therefore I need to spare some cash first.

The schematic:

As you can see the schematic includes an EMI filter before the transformer and makes use of 5ц4м(5z4) as a full-wave vacuum tube rectifier. The transformer has secondary windings outputting 290-0-290VAC, 5VAC, 6.3VAC. The combination of D1,D2,RP2 and C10 is a “hum control” circuit I saw here as it is recommended for directly heated tubes with AC. There is nothing fancy in the other part of the schematic. I expect this amplifier to have a solid and balanced sound which is not too coloured as the state of the tubes matches their documentation, yet nice to listen to. I will keep you posted when I have any progress on this project. Feel free to comment the schematic! Thank you for reading.

14
Aug

Plamen’s LM3886 Gainclone

Concept:

As this was my first DIY amplifier I decided I need to create something easy to assemble yet good sounding. I started to plan the build. After some reading I decided to use the schematic posted by Alex Wong for 2x LM3886 per channel in parallel

A DC speaker protection circuit is added and therefore I needed another small transformer to power it. I also added and EMI filter before the transformers which greatly reduced the hum I can hear from the speakers.

PSU:

As this is not a top-notch sonic quality amplifier I decided not to spend a fortune on the PSU. I also think that this particular amplifier won’t sound much different with a regulated PS. I don’t have schematics for the PS, but it’s just a 400VA 2x25VAC toroidal transformer > 2x 20A rectifiers with each diode shunted with a 10nF cap > 8x 4700uF 50V Low-ESR caps. If you decide to build a Gainclone I can tell you that the filter capacitors in the PSU have tha largest impact on the sound characteristics of the amplifier so be sure to experiment a bit with their capacity/type. All AC cables are twisted to reduce noises. The yellow DC cables are made of 1.5mm2 solid core OFC.

Enclosure:

I really wanted a good and solid enclosure which still doesn’t look like most of the DIY amplifiers I see on the internet. I really liked the enclosures Alex Wong uses in his projects, especially BPA300, but I really didn’t feel like paying 100$ for an enclosure of a 100$ amplifier… So I decided to DIY a bit. The floor and the right side of the box are cut from leftovers of a laminate flooring from my apartment using a regular cutting saw table and then put together using little aluminium profille that I had lying around. The heatsinks are then screwed to the lower panel.

The upper/lower/front panel is made of a bent material called Etalbond but black or white plexiglass will look even better. As you can see the potentiometer is put on a L-shaped piece of aluminium bolted to the wood panel and it’s shaft goes through a hole in the front side of the Etalbond/Plexiglass panel.

Conclusion:

I had a great fun building this amplifier and I recommend it to beginner/intermediate users of the DIY audio scene. It sounds good, especially with a tube preamplifier. I’m sure you don’t expect that sound from a chipamp, but LM3886 and LM1875 are really good. I gave this amplifier to my brother as a present because I am planning to build my next solid-state amplifier in the next few days. Thank you for reading, now grab the soldering iron and do something cool!