Category: Digital

The DIY LPRO-101 ruibidioum clock generator. This box together with some additional electronics on a separate PCB will transform this LPRO unit into stand alone equipment. I’ve always wanted a good and affordable frequency standard for my home lab. Searching the eBay one might find quite a lot of solutions. The good thing is that nowadays we have plenty of options.

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Here is an interesting schematic diagram for USB DAC based on the famous PCM2706 chip by Texas Instruments.

The design incorporates opto isolators to reduce the high-frequency garbage and prevent it from entering the analog part of the DAC. Like most of the DIY minimalistic designs, this one uses passive low-pass analog stage at the output of the DAC chips. The current to voltage conversion is done passively (duh) thanks to R19 and R17. Those are subject to experimentation to obtain the optimum value. Too high the resistor value and you get increased THD. Too low means you get lower output level.

PCM2706 + 4 x TDA1543 – LINK

Here is a way to make an I2S output from your CD player. This one includes a reclock option inside the CD player.

This idea uses a standard cat5 network cable. I personally don’t like the idea of reclocking the I2S bus and then sending it over the cable. A way better solution would be to include a low clock source inside your DAC. This source could have two outputs. One used to make the reclocking and feed the DAC chips with clean clock. The other output could be sent out over the same cat5 cable (using the 4th pair inside the cable) to the transport. This would make the transport a slave to the DAC and will practically eliminate it as a source of any troubles.

This project is based on the IL715 digital isolator chip, manufactured by NVE Corporation. This is a simple isolator schematic and a PCB.
Here is the technical datasheet for this chip:

[LINK]

The IC is pretty easy to use. They made the pinout as suitable as it can be. For this project I decided to make a sort of an adapter PCB which can be mounted on suitable female headers to the main PCB. I also decided to put a local voltage regulation just to be on the safe side. Local voltage regulation is proven to a good practice. I’m not quite sure if it serves a good purpose in this particular project but it does no harm either 😉

Of course from the datasheet you can see that there are several variants to this chip depending on the needs. The PCB itself does not change so it’s suitable for all the types. For example when doing a local reclocking near the DAC ship and driving a master clock directly to the DAC’s form external master clock source, you will need to send this clock back to the digital part of the system. This one will feed the digital filter and the servo processor(and of course all the other IC’s that need a clock supply). In this case you can use IL717 IC.

The schematic itself is pretty straightforward as the application is a no challenge to any designer. This is what it looks like:

IL715, IL716, IL717 DIGITAL ISOLATOR SCHEMATIC

And this is the PCB:

IL715, IL716, IL717 DIGITAL ISOLATOR PCB

The complete manufacturing files are available for download HERE

This project is provided to the DIY community for free. Commercial use is not allowed!

This project is about the ESS Sabre ES2093 DAC chip. This one is the least expensive DAC chip from the whole line up of DAC’s manufactured by ESS Technology. What i wanted to do here is to make something like an evaluation board which can be almost universal.

ESS Technology might not be quite a famous among audiophiles or electronics fans. They have this kinda odd marketing policy that puts them on the edge of OEM and retail markets. However thy are manufacturing some very high specs chips (DAC’s and ADC’s) and supply them to many manufacturers of high quality AV components like OPPO and many others.

The famous Buffalo DAC is built around an ESS 32-bit DAC. More info on this one can be found here:
http://www.twistedpearaudio.com/digital/buffalo.aspx

Of course with this project I’m not aiming on beating a complete high-end DAC’s like the Buffalo. What I want is to have this board as an upgrade to any low-end delta-sigma DAC. Besides the fact that it is a low-cost chip does not mean that it’s not worth a try. I believe that a proper designed board and a good power supply can make a low-cost DAC like the ES9023 sound very good. The history knows some good examples of CD players using low-cost DAC’s but sounding very good indeed.

More info about the ES9023 DAC chip can be found here:

http://www.esstech.com/PDF/ES9023%20PB%20Rev%200.2aPB%20110117.pdf

Unfortunately this is just a product brief but it gives some basic information. Due to the ESS Technology policy I can post the complete technical datasheet. If you want to have it you would need to contact some of the local ESS Technology distributors.

As you can see this little DAC offers a complete solution. It includes digital filtering, DAC, and output stage. However I’m including a buffer option on the PCB as I don’t really know the driving capabilities of the DAC alone. Some fancy cables actually have huge parasitic capacitance and can make the life hard for the little DAC.

So this is what the schematic looks like:

You might note that the DAC is powered by 3.6V (and not the standard 3.3V). This is due to the output swing hitting the supply rails. The chip has an internal charge pump that generates the negative rail so that the output signal is centered around the 0V (no coupling capacitor required). The manufacturer had increased the supply voltage to 3.6V to prevent the output stage from clipping.

Few words about the power supply circuit. The output buffer formed bu IC6 and IC7 is powered by a simple voltage regulators 7815 and 7915. Nothing interesting here. The DAC chip is powered by a low noise low dropout voltage regulator with a series pass element. Q2 and IC4 form a voltage reference. Its output is filtered by a low-pass filter formed by R2 and C6 and fed to the non-inverting pin of a low-noise opamp IC5. The output voltage is set by the two feedback resistors R3 and R4. C7 is placed across the opamp to improve stability.

The overall noise performance of this regulator is outstanding. The opamp’s noise is critical. For lower cost version you can use NE5534 but some additional compensation is required. Don’t forget to include a 33-68pF capacitor between pins 5 and 8.

I have included an input for an external clock source. This is implemented with one SMB connector. The solder joint SJ1 serves as a switch point. If you are using the external clock SJ1 must be desoldered.

The jumper JP1 is there to set the input format. It can be either left justified or Philips – I2S. The JP1 settings a re the following:

JP1 – CLOSED – I2S
JP1 – OPEN – LEFT JUSTIFIED

The output buffer stage is formed by two unity gain opamps. Those are subject to a personal taste of course. I have made the PCB with sockets to make it easier to switch the opamps.

This is how the pcb looks like:

The PCB has a small prototyping area just in case. Many modifications might be needed so its always a good thing to have some place for additional components.

I’m including a complete project manufacturing files available for download HERE

EAGLE BRD file – HERE

Update 09.12.2012 – I have made some changes to design. Revision B is now available for download.

Update 22.03.2013 – Added EAGLE *.brd files for downloading

THIS PROJECT IS AVAILABLE FOR PERSONAL USE ONLY. COMMERCIAL USE OR MANUFACTURING PCB’S FOR SALE IS NOT ALLOWED.