Mr White's "Opus", designing a simple balanced DAC

[Lucas Unger]

Originally posted by BrianDonegan


The board I used actually had an error on it (two of the I2S pins are reversed on the outputs). It also uses a relay that is not very common. We can probably redo it with something like G6H relays and fix the layout problem, then post it.

That would be great. It would give some switching capability until the I2S multiplexer arrives.

Regards,

L

[hbarki]

Hi Russ/Brian,

I have question on the LCDPS assembly:

1. The kit comes with insulator pads for the voltage regulator - am I really supposed to insulate the regulator from the heatsink? What happens if I do not insulate the regulators?
2. Do I need to solder the heatsink legs onto the PCB?

Thanks

[Russ White]

Originally posted by hbarki
Hi Russ/Brian,

I have question on the LCDPS assembly:

1. The kit comes with insulator pads for the voltage regulator - am I really supposed to insulate the regulator from the heatsink? What happens if I do not insulate the regulators?
2. Do I need to solder the heatsink legs onto the PCB?

Thanks

1) Yes, you should, but it is not absolutely required. The tabs are live, so your heatsink will be live if you do not. the kit comes with all you need, so there is no good reason not to.

2) No, in fact I do not so I can reuse heatsinks more easily.

Cheers!
Russ

[BrianDonegan]

If you do not use the insulators, you will need to use some thermal grease, otherwise you will not get good heat conduction to the heatsink.

[BrianDonegan]

Here are the copper and silk for the relay board with needed corrections. You can connect two I2S sources, with a single output.

The transistor is a BC546, resistor is 1K-10K, diode is a 1n400x. Relays are 5Volt Omron G6H or equivalent.

Connect 5VDC to the + and G terminals. Put your switch between G and B. Shorting G and B will throw the relays and select source 2.

In my DAC, I connected USB to source 2 and S/PDIF to source 1, then used VBUS from the USB receiver for power. This way, if there is no USB source connected, you cannot select USB, and S/PDIF input stays active (input 1). There are a million ways to do it though. You could also set the PS for your S/PDIF receiver to 5V and shar power with it.

[neb001]

I finally got around to putting the third dac board into my dac stack yesterday. After hooking it up all three sets of RCA's output static with a faint background of audio playing. If I disconnect the third dac board playback occurs without issue. I haven't troubleshot it much yet but would like ideas on what to check for if possible

The current configuration consists of one LCPS feeding a spidf board and three DAC boards, two of the original version and one of the new version.

Does the LCPS have enough juice to power 3 dac boards and a spidf board? Should I put together another LCPS and split the four boards into two sets for power?

Also, I noticed that the LCDPS is not sold seperately on the opus dac page, is this by design?

Sorry for asking so many questions, and thanks in advance for your help

[Russ White]

Neb001, I would have to see more wiring details.

It very much sounds like there is a short some place.

You might want to email Brian and I directly so we don't clutter up the thread. Pics would be good.

Cheers!
Russ

[hbarki]

Hi Russ/Brian,

I just looked at the Ballsie schematic and thinking about ordering it once I get to assemble my Opus/ASRC.

I have some questions on this module - apologize if these seems like dumb question - I am not EE, and trying to learn audio design stuff.

1. From the description and schematic, looks like it can take the TWO pairs of + and - balanced inputs from Opus (per channel, in dual mono setup), and output as ONE pair of "filtered" + and - balanced. I don't quite understand what does "filtered" exactly mean - could you please explain?

2. How does this filtering improve the sound of Opus (isn't simpler = better?).

3. I am looking at the datasheet of LM4562 (http://www.national.com/ds/LM/LM4562.pdf). On page 25, there is a diagram of balanced to single ended converter. Using this setup and 2 op-amps, is it possible to take the TWO pairs of balanced voltage output from OPUS (setup in dual mono); use the op-amp to subtract the + and - (and vice versa) to get one pair of balanced output at the end (one + and one - after subtraction)? Is this what the ballsie will do to Opus output in dual-mono setup? Not obvious to me from looking at the ballsie schematic

4. When you run Opus dual mono without using ballsie (direct to XLR), do you only connect one + and one - to the XLR jack, or do you pair the two + and two - together to the XLR jack? Tried to look at some picture in this thread, but not so clear.

5. just to confirm - so I need a Bipolar supply, and NOT the LCDPS to power the ballsie?

Thanks in advance for your patience in reading this mouthful of questions and trying to explain it to a newbie.

[Russ White]

Originally posted by hbarki
Hi Russ/Brian,

I have some questions on this module

1) The first part of the amp is a simple instrumentation amp with optional caps which makes it a low pass filter. The filter rejects signals far beyond the audio range. We tap the point just prior to the second stage in case you still want Balanced output that is simply filtered (or just buffered if you omitted the caps) The second stage is a classic Bal -> SE converter.

2) See #1 The first stage has two purposes, it acts as both a buffer to the next stage and a filter. It actually is very simple.

3) See our user manual for the opus. In mono(dual differential mode) you run 5 wires from the opus. Each signal (+ and -) is carried via two wires through load sharing resistors wich are located on the ballsie. The ensures that the filter stages of the Opus see the same load. There is only one signal involved it is just transported via 4 wires with 2 being the inverse of the other 2 .

4) You connect all 4 plus a GND. See the manual.

5) technically you could use either, but yes, use the LCBPS(bipolar).

No problem.

[DarrenWadsworth]

I have one spdif reciever, 2 dac boards and one LCPS. Eventually I want to add a USB reciever board.

1st. Can I use the LCPS for the first 3 things? If so, is there a wiring diagram that can show me what goes where. I have this, but it is only for single DAC:



If not, what will I need to get?

Will I need to change any of that if I get the USB module?

Thank you

Darren