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Dimdim  
#1 Posted : Sunday, December 1, 2013 1:51:54 PM(UTC)
Dimdim

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I have 2 x Amanero USB boards sending I2S into an OTTO II which in turn feeds a B3SE:

UserPostedImage

They are controlled by an Arduino running my version of HiFiDuino's code (TFT HiFiDuino).

I am having a strange issue. Upon powerup the OTTO II is not letting any signal through. No matter what I do with the control lines.

I have 0E shorted to ground and am sending 0V or 3.3V to S in order to do the switching.
The OTTO-II is powered by the same PS that powers the B3SE (see connector on B3SE's power terminals).

The problem goes away when I power cycle the OTTO-II, i.e. disconnect its power and then reconnect it (with the DAC in operation). After doing that, everything works as it should.

Anyone else come across something like this?
Brian Donegan  
#2 Posted : Sunday, December 1, 2013 2:28:37 PM(UTC)
Brian Donegan

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It's possible that the cap on the DAC power terminals is causing strange behavior by slowing the power up. When you cycle the power, the cap will already be charged and the startup will be fast.

As an experiment, can you try removing the cap and see if the problem goes away?
SCompRacer  
#3 Posted : Tuesday, December 3, 2013 1:36:26 AM(UTC)
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Are you using a pull up resistor on your OTTO? I've had OTTO act strange without one.
DQ828  
#4 Posted : Tuesday, December 3, 2013 10:14:42 AM(UTC)
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This has nothing to do with the question but the coax cable you are using (RG50 I think) looks exactly the same as the cable I have used for RCA interconnects, it was advertised as having a silver coated copper core but I eventually realised the core was magnetic, so much for the copper. The cables actually sounded pretty good but they sounded even better when I reversed the wires & used the shield (which is silver coated copper) for the signal, kind of defeats the whole shield thing but they do sound very nice.
Dimdim  
#5 Posted : Wednesday, December 4, 2013 12:06:13 AM(UTC)
Dimdim

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First of all I'd like to thank all of you for taking the time to look into my problem.

I did some more troubleshooting and concluded that the problem was not a delay in the startup sequence but had to do with the pullup resistor.

I have designed a Buffalo shield for my arduino that provides galvanic isolation as well as some other goodies. It has 3 isolated digital outputs, two of which work pretty much the way the Otto needs them to work:

UserPostedImage

Looking at the VO1 (optocoupler) section, R2 is the pullup resistor. The prototype shield that I was using had a very small resistor, less than 1K (left there from a previous experiment).

When I swapped it out for a 4,6K, the Otto powered up just fine, letting I2S pass through. However, I couldn't get it to switch to the other input because I couldn't get the voltage down to an appropriate level (it only went down from 3.3V to 2.7V). I am contemplating using a lower value for R2, something less than 4K, and seeing how it goes.
Dimdim  
#6 Posted : Wednesday, December 4, 2013 10:53:31 PM(UTC)
Dimdim

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It seems that now that I have gone down to 1.8K for the resistor everything works as expected. :)

Thank you all for your interest!


P.S. DQ828, the specific coax was not my choice, this DAC is not my build, I just put in the Arduino controller, but I have passed your comment on to the DAC's builder. :)
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