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

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#1,261
Hi Painkiller,

Great work! Your picture does a good job showing how the modules can fit together with nice short connections. You could actually do the whole DAC section as one stack and still keep the connections short if you turn the USB module upside down and put it on top of the metronome. 🙂 But the you did it certainly very good too!

Cheers!
Russ
 
#1,263
Hi,

Yes, I would very much like to do firewire and USB2.0, and I plan to someday. For the now the most daunting obstacle is the thought of having to write drivers.

I wish I could find something a bit more plug and play like the PCM2707 was. 🙂

I have no idea when, but if I could find a relatively simple hardware solution I would do it sooner rather than later.

Cheers!
Russ
 
#1,264
Does the disable jumper on the Metronome do the same thing as the bypass dip switch? Or does the bypass disable the reclocking, while the bypass only disables the resampling? Or am I way off base yet again? 🙂

Also, is there an elegant way of connecting the bypass jumpers to a panel mounted switch beside directly soldering wires to them? I've been trying to look for some sort of header with crimp pins, but having no luck so far. Any help would be greatly appreciated.

Thanks,
Neb
 
#1,265
Russ White said:
Your picture does a good job showing how the modules can fit together with nice short connections. You could actually do the whole DAC section as one stack and still keep the connections short if you turn the USB module upside down and put it on top of the metronome. 🙂 But the you did it certainly very good too!
Click to expand...

I figured I didn't want to stack it too high, as I'm going to put it in a slim enclosure. And this was the shortest possible signal path.

The sound is now better than my super-modded pioneer DVD-player. I ended up using the XXHighEnd player from phasure.com, because it actually sounds better than the others I've tried.

I do have some problems with noise in the 192kHz mode, so I'm now using the 48kHz mode. It's only apparent with some songs, and only in the right channel. Strange.

By the way... would a 22.58MHz clock be directly compatible for upsampling to 176.4kHz? Or a 11.29MHz clock for 44.1kHz?

And another question... Which clock signal is used if the metronome is set in bypass mode?
 
#1,266
Painkiller said:
And another question... Which clock signal is used if the metronome is set in bypass mode?
Click to expand...

In bypass mode you should disable the on board clock. On the current boards there is a pin header and jumper (labeled "disable") for that. On older metronome boards you can still disable the clock you just need to solder a wire to pin one of the XO and pull it to GND to disable. Then wire the master clock from your receiver or other clock source, you should not use ore than one master clock source at the same time. What I have done when I want to switch clocks is to use a 2 pole switch to disable the clock and switch in the external clock (SCK on PCM-IN or PCM-OUT depending on your clock source). You will then also set bypass high. The will pass the PCM through without reclocking.

As far as clock frequency selection, I think your best bet is to refer to the datasheet, as you have a lot of options there.

Cheer!
Russ
 
#1,267
neb001 said:
Does the disable jumper on the Metronome do the same thing as the bypass dip switch? Or does the bypass disable the reclocking, while the bypass only disables the resampling? Or am I way off base yet again? 🙂

Also, is there an elegant way of connecting the bypass jumpers to a panel mounted switch beside directly soldering wires to them? I've been trying to look for some sort of header with crimp pins, but having no luck so far. Any help would be greatly appreciated.

Thanks,
Neb
Click to expand...


The disable jumper simply turns off the on board clock, so you can supply your own on either the input or output SCK pins (they are connected on the PCB).

The bypass mode simply passes the input PCM through the same as it came in.

There are a quite a few 1" pitch connectors that will work for running wires to switch etc.

Here is one:
http://www.futurlec.com/Connectors/HDCONNS2.shtml

They use header pins which can be soldered and then inserted into the connector.

One thing to keep in mind, is that the device should be reset if you change the configuration. Cycling the power is the simplest way.

I think rather than switching bypass/clock on and off, it would be much better just to use an OTTO to switch between going direct from your receiver, or the metronome. Just a single switch, and no reset.

Cheers!
Russ
 
#1,268
The reason I was hoping to use the bypass jumper was to try to reduce the length of the I2S wire run; as with the OTTO it would be a bit longer. But since having to cycle the power every time it's switched is a bit of a hassle I think I'll use the OTTO.
 
#1,270
glt said:
In the v1 version of metronome, bypass (no upsampling, just re-clocking) doesn't require a reset/power cycle
Click to expand...

Interesting, did you check that the output was the same as the input after switching on bypass (from on non-bypassed state) without a reset?

It very well may be, I have not tested that case. In any case that would be he same between both versions of the board.

Cheers!
Russ
 
#1,276
Grounding

Hi,

I am using SPDIF - Metronome - Opus (dual mono) - Ballsie.

When probing around with my DMM, it looks like none of the aluminum spacers on all PCB are grounded to the chassis.

Is it OK to connect all of the following to the chassis:
1. Analog DC supply ground
2. Digital DC supply ground
3. 120V AC ground (green wire)
4. XLR and RCA output ground from Ballsie (pin #1 XLR)

If it is OK to do this, is there any benefit?

Thanks!
 
#1,279
luvdunhill said:
has anyone come up with a simple logic circuit that could be used with the OTTO to allow use of a tactile switch and a couple LEDs to switch between the inputs and have a LED status to show which input is selected? this would be very nice 🙂
Click to expand...

You can use a circuit like this one I just drew up:
alt_latch.png


I haven't tested it in this specific application, or with the values in the schematic, but it should work fine.

74HC74 is a D flip-flop, the value of D is copied to Q and inverted at Q-bar on the application of a rising edge at CLK. CLK is generated by the switch and a pulldown resistor, so pressing the button generates a rising edge. Q-bar wraps around to the D input, so each time CLK is triggered, the value toggles. A J-K flop could be used as well with a small adjustment. You can string LEDs directly off the Q and Q-bar outputs with a single current limit resistor (Q and Q-bar are obviously mutually exclusive), just make sure the 7474 chip you choose can source the current. You'd connect Q or Q-bar to drive the relay board.

The value of the capacitor may need to be changed; it counteracts switch bounce (it charges 'instantly' through the switch, but discharges slowly through the resistor, so when pressed it holds the voltage high and allows the switch to bounce for a few ms without the logic value changing). Find the right value by experimentation, or pull out your time constant formulas.

The circuit will start in an indeterminate state. If you don't like that, you'll need to add a power-on reset circuit (resistor and cap) to the preset or clear inputs. If you don't use one, they should be tied to Vcc.

Edit: A cap closer to 1-10uF range is probably more appropriate. 4.7uF would seem to work well, with decay taking approx. 50ms.
 
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