[mythtv-users] OT: Re: HDMI_SPDIF directly to reciever

James bjlockie at lockie.ca
Sun Jul 6 04:21:28 UTC 2008

Alen Edwards wrote:
> James wrote:
>> OTAlen Edwards wrote:
>>> James Lockie wrote:
>>>> Alen Edwards wrote:
>>>>> James Lockie wrote:
>>>>>> Brian Phillips wrote:
>>>>>>> I think I can say why yours is working correctly.
>>>>>>> Your signal is a purely electrical SPDIF signal.  Even though 
>>>>>>> it's not
>>>>>>> according to the -0.5 to +0.5 spec, it works because SPDIF is 
>>>>>>> pretty
>>>>>>> versatile.  I have driven SPDIF signals successfully with 0V to 
>>>>>>> +5V swings
>>>>>>> (not recommended, but it produces sound) and I have driven SPDIF 
>>>>>>> signals
>>>>>>> successfully with 0V to +250mV swings.  Again, not recommended 
>>>>>>> but it
>>>>>>> produces sound.
>>>>>>> Brian
>>>>>> Am I risking frying my motherboard or receiver?
>>>>>> _______________________________________________
>>>>>> mythtv-users mailing list
>>>>>> mythtv-users at mythtv.org
>>>>>> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>>>>> You certainly are risking frying the receiver.  If that goes, 
>>>>> there is a small chance it could take out the MB.
>>>>> Build the network or buy the adapter.
>>>>> Allen
>>>> Yamaha said my receiver expects 5 volts.
>>>> ASRock never answered (that was a month ago).
>>>> There is 0 volts on the RCA.
>>>> Why do I get sound if there is a zero volt signal?
>>>> I tested my voltmeter on a battery to verify it works.
>>> You should read 0 volts with a S/PDIF signal.  They are 0 volts DC 
>>> and the AC is too high a frequency for my and apparently your 
>>> voltmeter to read.  If  you had a TTL signal, you would register 
>>> about 2 volts with the VM set to DC.  If your RX expects 5 volts and 
>>> your MB reads 0, I would guess it would work and you won't hurt 
>>> anything (don't sue me, I can't pay anyway).
>>> Allen
>>> .
>> I bought a new meter and it says 1.4V DC :-(
>> I put a picture up at: http://lockie.ca/test/voltage.jpg but I doubt 
>> it is very helpful.
>> So if my RX expects 5V (DC?) and it is getting 1.4V DC and I have 
>> sound, do I need the circuit?
>> TTL is +5V, and SPDIF is -.5 to +.5V so what is my MB outputting?
> That is more like it.  This indicates that you have a TTL signal on 
> the MB, as I do.  A TTL signal is going to go between almost 0 and 
> something above 2 volts, let's say 3 volts.  The signal is going to be 
> low (0 volts) half the time and high (3 volts) half the time so the DC 
> value will measure half way between the two or about 1.5 volts.  This 
> is not an exact number but it is not 0 VDC, which is what you would 
> measure with a spdif signal.
> I would bet that your Rx expects spdif levels of larger than .2 volts 
> and less than something.  You say it can take up to 5 volts, which 
> again I would double check if I were you.  If that is correct, then 
> you should be OK.
> When I was faced with exactly this situation, I built the network.  I 
> would not be worried about sending too little signal in your situation 
> but rather double check that you are not sending too much.  It may be 
> just fine, it all depends on the details of the circuits involved.
> Allen
I was first thinking of hooking my DVD player SPDIF up to my receiver.
Here is what I asked Yamaha:
> The voltage output from the 2 pin S/PDIF on my cdrom may be 5V or it may
> be .5V.
> What voltage does the digital coaxial input of the receiver expect?

Their answer was:
> Hello, typical voltage is 5 volts.

I will ask this:
I am hooking up a computer motherboard SPDIF/HDMI which is a TTL signal 
to http://www.yamaha.co.jp/english/product/av/products/ht/rxv1000.html
so I need to know the minimum and maximum voltage the coaxial digital 
input of the receiver will accept.

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