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

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#1,222
Russ White said:
Hello,

Its 2VRMS.
Click to expand...


Hi Russ,

So if I am running balanced, does it mean I should get 2V from each leg, which adds up to 4V?

I finally get my Opus working without the noise (you're right, it came from the I2S wiring).

The sound level from my Opus is slightly lower than my single ended CD player (in A-B listening comparison using the input selector switch). I was expecting it will be significantly higher than single ended, since I am running the Opus balanced all the way to the power amp.

Perhaps I should try to bump up the analog voltage from the power supply? I have it setup at 7.5V (no load) to power both left and right DAC boards.

Thanks,

HB
 
#1,223
hbarki said:


Perhaps I should try to bump up the analog voltage from the power supply? I have it setup at 7.5V (no load) to power both left and right DAC boards.

Thanks,

HB
Click to expand...

I'm no expert, but the DAC boards have on-board regulators, so I think that upping the source voltage will not give you any additional voltage on the analog out.
 
#1,228
Here is the transformer that has my attention. Go Plitron! Yes, yes, it has the hassle of being a PC mount unit, but it has 3 secondary windings. (17V, 17V, and 9.6V) Imagine one transformer (the aforementioned Plitron) for the analog circuits in the DAC enclosure and another transformer (as yet to be specified) for the digital circuits.
 
#1,230
That transformer can supply the digital part too from that 9.8V. It doesn't need to be a separate transformer, separate rectifiers connected to the same winding should do just fine. Or even separate circuits fed from the same rectifier bridge...
It's just a little too much for 5V, that's kind of bad. I wold like the 6Vca one...

LE: Russ, you posted in the time I was writing mine 🙂
 
#1,232
Russ White said:
Actually just using the one transformer should give you excellent results.

You could use the 9.6V secondary to power the DAC,REC,ETC... and the dual 17.5V secondaries for the ballsie.

You can actually power both sides of a LCDPS from a single secondary. Just wire them as a parallel load.

Cheers!
Russ
Click to expand...
The Plitron has enough juice on the 9.6V side to do a lot. It is a 40VA transformer split down the middle 20VA on the 9.6V side and 20VA on the 17V side. I was letting my mind run a little with the extreme division between analog and digital circuits.

If you look at Plitron's schematics for these units, you will see that they intended for 5V and +15/-15 volt outputs. Kind of a nice design.
 
#1,233
USB jack

I spent some time researching the USB connector that I am going to use in my Opus DAC enclosure. I found this nice type A jack with flying leads. It has gold plated contacts, and is also available in a type B jack.

Data sheet

Link to USB type A jack at L-com.com

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.
 
#1,235
Re: USB jack

orthoefer said:
I spent some time researching the USB connector that I am going to use in my Opus DAC enclosure. I found this nice type A jack with flying leads. It has gold plated contacts, and is also available in a type B jack.
Click to expand...


You should probably go with the type B jack if you can get both. A-A cables shouldn't exist according to the standard since peripherals must always have a type B, so it might be hard to find or replace a cable. Besides, it's good to stick to the standards 😛
 
#1,236
USB jack take 2

error401 said:


You should probably go with the type B jack if you can get both. A-A cables shouldn't exist according to the standard since peripherals must always have a type B, so it might be hard to find or replace a cable. Besides, it's good to stick to the standards 😛
Click to expand...

Crud. Somehow in my rats nest box-o-cables I have many more USB A/A cables than A/B cables. Nevertheless, you are right, it woulld be best to stick with the standard. I didn't know that the standard was for peripherals to have the B connector, but now I do.

I am going to get one of these instead.

Datasheet
 
#1,237
I've been trying out a Cambridge 640C with bypassed output stage for some days now. I'm really excited about this dac, and looking forward to receiving my pre ordered kit. 🙂

Just one tip though. It's tempting to plug the dac directly into the power amp, but this is not a good idea. Even though the WM8740 is quite load tolerant, it is obviously not very happy with capacitive loads. With a 320pF load the frequency response and impulse response is severely compromised.

A good unfiltered buffer is therefore recommended. Low input impedance in apparently not a problem, but the capacitance should be as low as possible, at least under 100pF.
 
#1,239
I just received my Twisted Pear Opus DAC parts, and I have to say Brian and Russ are amazing. The level of engineering, preparation, and execution that has gone into this kit is phenomenal. Even the boxes that the parts are shipped in show superb planning. Good work guys. I think we will hear similar comments as people start to receive their parts from the most resent batch. I've already assembled my boards. Now I need to do some testing--still waiting on the Plitron transformer though.
 
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