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HDMI_SPDIF directly to reciever

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bjlockie at lockie

Jul 3, 2008, 7:44 AM

Post #1 of 19 (1175 views)
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HDMI_SPDIF directly to reciever

I found this article on the wiki and I have a question.

>Most MythTV systems these days are built using a motherboard with integrated
>audio and video. However, the SPDIF signal is unfit to be wired directly to
>a SPDIF compatible digital audio receiver. The reason is that the signal
> is a TTL signal, while it should be a signal swinging between -0.5V and
>+0.5V. This requires that a simple circuit be built, using some resistors
>and a capacitor, but the signal can not be used to drive a long cable and
>thus additional components like a 74HCT04 are needed to amplify this signal
>to acceptable levels.

>This article describes how you can build a SPDIF TOSlink transmitter
>circuit, using just two components.

I have an ASrock ALiveNF5-eSATA2+
(http://www.asrock.com/mb/overview.asp?Model=ALiveNF5-eSATA2%2b&s=AM2)
that says it it has an HDMI_SPDI header on the motherboard.
I wired it up directly to a female RCA jack and connected it to the
coaxial digital input on my receiver.

This article implies what I did shouldn't work but it does.

Do I have a weird motherboard and this probably won't work on other
motherboards?

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peter at vanderwal

Jul 3, 2008, 1:10 AM

Post #2 of 19 (1152 views)
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Re: HDMI_SPDIF directly to reciever [In reply to]

I suspect, that while technically the SPDIF is supposed to be -0.5 to
+0.5, most amplifiers probably work fine with 0V to 1-5V.

I actually shelled out the $10 for ASUS adapter (so I get both RCA and
Optical), but I don't recall it having any active components on it other
than the optical driver.

> I found this article on the wiki and I have a question.
>
>>Most MythTV systems these days are built using a motherboard with
>> integrated
>>audio and video. However, the SPDIF signal is unfit to be wired directly
>> to
>>a SPDIF compatible digital audio receiver. The reason is that the signal
>> is a TTL signal, while it should be a signal swinging between -0.5V and
>>+0.5V. This requires that a simple circuit be built, using some resistors
>>and a capacitor, but the signal can not be used to drive a long cable and
>>thus additional components like a 74HCT04 are needed to amplify this
>> signal
>>to acceptable levels.
>
>>This article describes how you can build a SPDIF TOSlink transmitter
>>circuit, using just two components.
>
> I have an ASrock ALiveNF5-eSATA2+
> (http://www.asrock.com/mb/overview.asp?Model=ALiveNF5-eSATA2%2b&s=AM2)
> that says it it has an HDMI_SPDI header on the motherboard.
> I wired it up directly to a female RCA jack and connected it to the
> coaxial digital input on my receiver.
>
> This article implies what I did shouldn't work but it does.
>
> Do I have a weird motherboard and this probably won't work on other
> motherboards?
>
>
> _______________________________________________
> mythtv-users mailing list
> mythtv-users[at]mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>

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brian.phillips at gmx

Jul 3, 2008, 8:17 AM

Post #3 of 19 (1146 views)
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Re: HDMI_SPDIF directly to reciever [In reply to]

James wrote:
> I found this article on the wiki and I have a question.
>
>> Most MythTV systems these days are built using a motherboard with
>> integrated audio and video. However, the SPDIF signal is unfit to be
>> wired directly to a SPDIF compatible digital audio receiver. The
>> reason is that the signal is a TTL signal, while it should be a
>> signal swinging between -0.5V and +0.5V. This requires that a simple
>> circuit be built, using some +resistors and a capacitor, but the
>> signal can not be used to drive a long cable and thus additional
>> components like a 74HCT04 are needed to amplify this signal to
>> acceptable levels.
>
>> This article describes how you can build a SPDIF TOSlink transmitter
>> circuit, using just two components.
>
> I have an ASrock ALiveNF5-eSATA2+
> (http://www.asrock.com/mb/overview.asp?Model=ALiveNF5-eSATA2%2b&s=AM2)
> that says it it has an HDMI_SPDI header on the motherboard.
> I wired it up directly to a female RCA jack and connected it to the
> coaxial digital input on my receiver.
>
> This article implies what I did shouldn't work but it does.
>
> Do I have a weird motherboard and this probably won't work on other
> motherboards?

The article talks about how to take an electrical SPDIF signal that is TTL
and convert it to an optical TOSLINK signal. While I can't vouch for its
accuracy, 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

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allen.edwards at oldpaloalto

Jul 3, 2008, 8:33 AM

Post #4 of 19 (1145 views)
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Re: HDMI_SPDIF directly to reciever [In reply to]

James wrote:
> I found this article on the wiki and I have a question.
>
>
>> Most MythTV systems these days are built using a motherboard with integrated
>> audio and video. However, the SPDIF signal is unfit to be wired directly to
>> a SPDIF compatible digital audio receiver. The reason is that the signal
>> is a TTL signal, while it should be a signal swinging between -0.5V and
>> +0.5V. This requires that a simple circuit be built, using some resistors
>> and a capacitor, but the signal can not be used to drive a long cable and
>> thus additional components like a 74HCT04 are needed to amplify this signal
>> to acceptable levels.
>>
>
>
>> This article describes how you can build a SPDIF TOSlink transmitter
>> circuit, using just two components.
>>
>
> I have an ASrock ALiveNF5-eSATA2+
> (http://www.asrock.com/mb/overview.asp?Model=ALiveNF5-eSATA2%2b&s=AM2)
> that says it it has an HDMI_SPDI header on the motherboard.
> I wired it up directly to a female RCA jack and connected it to the
> coaxial digital input on my receiver.
>
> This article implies what I did shouldn't work but it does.
>
> Do I have a weird motherboard and this probably won't work on other
> motherboards?

More than likely you have a receiver that doesn't get blown up with the
5 volt input that is coming from your MB. Imho, you took a risk when
you hooked it up and you won. It may degrade over time so if I were
you, I would add the circuit I am about to describe.

I use this circuit to take the S/PDIF signal off my MB and drive a
decoder. This should be able to drive a long line of 75ohm coax. Use
RF TV 75 ohm coax or video coax -- usually has yellow ends. Don't use
audio coax. For RF coax, you can either get cable to RCA connectors or
use Type-F to RCA adapters. I prefer the adapters but either way is fine.

For the output, I took a blank plate that would cover a PCI slot. I
drilled a 1/4 inch hole and put an RCA connector with a solder lug on it
in that hole. I got a connector for my MB (4 pin in my case) and
plugged the key hole. I wired up the ground to the ground lug on the
rear panel. I wired the s/pdif lead to the RCA connector through this
network. First, a 100nF capacitor (I used 82nF because that is what I
had) in series with a 330 ohm resistor. The resistor goes to the center
pin on the RCA connector along with the end of a 100 ohm resistor. The
other end of the 100 ohm resistor goes to the ground lug.

This network will attenuate the almost 5 volt TTL signal by 1/4.3 or
about 1 volt, which is the s/pdif spec. The output impedance will be
76.7 ohms, close enough to 75.

I hope someone finds this information useful :-)

Allen

joehenley at kc

Jul 3, 2008, 1:37 PM

Post #5 of 19 (1124 views)
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Re: HDMI_SPDIF directly to reciever [In reply to]

I think I'd check with Asrock first. It's possible the header outputs
are exactly what you need (no caps or resistors required). Better safe
than sorry.

Good luck,

Joe Henley
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allen.edwards at oldpaloalto

Jul 3, 2008, 2:07 PM

Post #6 of 19 (1126 views)
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Re: HDMI_SPDIF directly to reciever [In reply to]

Joe Henley wrote:
> I think I'd check with Asrock first. It's possible the header outputs
> are exactly what you need (no caps or resistors required). Better safe
> than sorry.
>
> Good luck,
>
> Joe Henley

If you have a DC voltmeter you can measure the voltage. If it is TTL,
you will see 2+ volts. If it is s/pdif, you will see virtually nothing.

Allen

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peter at vanderwal

Jul 4, 2008, 10:49 AM

Post #7 of 19 (1089 views)
Permalink

Re: HDMI_SPDIF directly to reciever [In reply to]

> Why do I get sound if there is a zero volt signal?
> I tested my voltmeter on a battery to verify it works.

Not every mobo produces TTL levels on the S/PDIF header. Some produce -.5
to +.5

My ASUS S/PDIF module has no components between the RCA connetor and the
mobo header, just wire and PCB traces.
Since it produces the correct levels, it must be doing in on the mobo.

To answer your question. Assuming the output is swinging between -.5 and
+.5 the average DC voltage is zero. If your voltmeter is set for DC then
it will read 0V. Set it on AC and it will probably indicate something
near 1V

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bjlockie at lockie

Jul 4, 2008, 3:23 PM

Post #8 of 19 (1087 views)
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Re: HDMI_SPDIF directly to reciever [In reply to]

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?

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allen.edwards at oldpaloalto

Jul 4, 2008, 3:51 PM

Post #9 of 19 (1092 views)
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Re: HDMI_SPDIF directly to reciever [In reply to]

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

bjlockie at lockie

Jul 4, 2008, 5:10 PM

Post #10 of 19 (1087 views)
Permalink

Re: HDMI_SPDIF directly to reciever [In reply to]

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.

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roo.watt at gmail

Jul 4, 2008, 6:08 PM

Post #11 of 19 (1088 views)
Permalink

Re: HDMI_SPDIF directly to reciever [In reply to]

2008/7/5 James Lockie <bjlockie[at]lockie.ca>:

> 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.

James,

If your voltmeter is on a DC range and the output is bipolar, +0.5V
and -0.5V then that will "average" out to 0V. This is irrespective of
the data travelling over the spdif as it is Manchester Coded.

Try an AC range on the voltmeter if you have one.

HTH,

Roo.
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allen.edwards at oldpaloalto

Jul 4, 2008, 9:49 PM

Post #12 of 19 (1063 views)
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Re: HDMI_SPDIF directly to reciever [In reply to]

Peter VanDerWal wrote:
>> Why do I get sound if there is a zero volt signal?
>> I tested my voltmeter on a battery to verify it works.
>>
>
> Not every mobo produces TTL levels on the S/PDIF header. Some produce -.5
> to +.5
>
> My ASUS S/PDIF module has no components between the RCA connetor and the
> mobo header, just wire and PCB traces.
> Since it produces the correct levels, it must be doing in on the mobo.
>
> To answer your question. Assuming the output is swinging between -.5 and
> +.5 the average DC voltage is zero. If your voltmeter is set for DC then
> it will read 0V. Set it on AC and it will probably indicate something
> near 1V
>
> _______________________________________________
> mythtv-users mailing list
> mythtv-users[at]mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>
>
My Voltmeter read something like 2 volts DC on my ASUS M3A MB. I would
look again for something on that module. Perhaps they are very small
surface mount components. Set to AC, it didn't register. Frequency
probably too high for the voltmeter.

Anyway, that is how I knew that my MB was putting out TTL levels and the
circuit described worked great.

Allen

allen.edwards at oldpaloalto

Jul 4, 2008, 10:09 PM

Post #13 of 19 (1063 views)
Permalink

Re: HDMI_SPDIF directly to reciever [In reply to]

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

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bjlockie at lockie

Jul 4, 2008, 10:09 PM

Post #14 of 19 (1062 views)
Permalink

Re: HDMI_SPDIF directly to reciever [In reply to]

Roo wrote:
> 2008/7/5 James Lockie <bjlockie[at]lockie.ca>:
>
>
>> 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.
>>
>
> James,
>
> If your voltmeter is on a DC range and the output is bipolar, +0.5V
> and -0.5V then that will "average" out to 0V. This is irrespective of
> the data travelling over the spdif as it is Manchester Coded.
>
> Try an AC range on the voltmeter if you have one.
>
AC is 3 something.
So if my receiver expects 5V and it is getting less, am I hurting it?

> HTH,
>
> Roo.
> _______________________________________________
> mythtv-users mailing list
> mythtv-users[at]mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>
> .
>
>

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allen.edwards at oldpaloalto

Jul 4, 2008, 10:16 PM

Post #15 of 19 (1064 views)
Permalink

Re: HDMI_SPDIF directly to reciever [In reply to]

James wrote:
> Roo wrote:
>
>> 2008/7/5 James Lockie <bjlockie[at]lockie.ca>:
>>
>>
>>
>>> 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.
>>>
>>>
>> James,
>>
>> If your voltmeter is on a DC range and the output is bipolar, +0.5V
>> and -0.5V then that will "average" out to 0V. This is irrespective of
>> the data travelling over the spdif as it is Manchester Coded.
>>
>> Try an AC range on the voltmeter if you have one.
>>
>>
> AC is 3 something.
> So if my receiver expects 5V and it is getting less, am I hurting it?
>
>
>> HTH,
>>
>> Roo.
>> ___________________
>
If you are getting 0 DC and 3AC, I am surprised. I would expect it to
be the other way around (0AC and 2-3DC). No matter, less it good and
your receiver is probably saying it can take anything up to 5 volts and
it can probably take much less, like maybe .1 volts. Some people on
this list have said their equipment works all the way to .025 volts. I
would double check your numbers and readings then try it.

Allen

johan.vanderkolk at dommel

Jul 4, 2008, 11:44 PM

Post #16 of 19 (1050 views)
Permalink

Re: HDMI_SPDIF directly to reciever [In reply to]

On Fri, 2008-07-04 at 22:16 -0700, Alen Edwards wrote:
>
>
> James wrote:
> > Roo wrote:
> >
> > > 2008/7/5 James Lockie <bjlockie[at]lockie.ca>:
> > >
> > >
> > >
> > > > 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.
> > > >
> > > >
> > > James,
> > >
> > > If your voltmeter is on a DC range and the output is bipolar, +0.5V
> > > and -0.5V then that will "average" out to 0V. This is irrespective of
> > > the data travelling over the spdif as it is Manchester Coded.
> > >
> > > Try an AC range on the voltmeter if you have one.
> > >
> > >
> > AC is 3 something.
> > So if my receiver expects 5V and it is getting less, am I hurting it?
> >
> >
> > > HTH,
> > >
> > > Roo.
> > > ___________________
> >
> If you are getting 0 DC and 3AC, I am surprised. I would expect it to
> be the other way around (0AC and 2-3DC). No matter, less it good and
> your receiver is probably saying it can take anything up to 5 volts
> and it can probably take much less, like maybe .1 volts. Some people
> on this list have said their equipment works all the way to .025
> volts. I would double check your numbers and readings then try it.
>
>
> Allen
>
> _
Summarizing:

the signal is digital manchester coded and probably bipolar, so will not
contain a DC component.
It's sampling rate is up to 96kHz, to high for most multimeters.
Multimeters do not measure peak values, but only average (they are even
"calibrated" in RMS (root MEAN Square). So you will never know what peak
voltages are actually present.
Only way to be sure is to use an oscilloscope.

know it does not help, but clarifies a shortfall in the measuring
technique..

Johan
> ______________________________________________
> mythtv-users mailing list
> mythtv-users[at]mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users

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johan.vanderkolk at dommel

Jul 5, 2008, 12:01 AM

Post #17 of 19 (1051 views)
Permalink

Re: HDMI_SPDIF directly to reciever [In reply to]

On Sat, 2008-07-05 at 08:44 +0200, Johan wrote:
> On Fri, 2008-07-04 at 22:16 -0700, Alen Edwards wrote:
> >
> >
> > James wrote:
> > > Roo wrote:
> > >
> > > > 2008/7/5 James Lockie <bjlockie[at]lockie.ca>:
> > > >
> > > >
> > > >
> > > > > 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.
> > > > >
> > > > >
> > > > James,
> > > >
> > > > If your voltmeter is on a DC range and the output is bipolar, +0.5V
> > > > and -0.5V then that will "average" out to 0V. This is irrespective of
> > > > the data travelling over the spdif as it is Manchester Coded.
> > > >
> > > > Try an AC range on the voltmeter if you have one.
> > > >
> > > >
> > > AC is 3 something.
> > > So if my receiver expects 5V and it is getting less, am I hurting it?
> > >
> > >
> > > > HTH,
> > > >
> > > > Roo.
> > > > ___________________
> > >
> > If you are getting 0 DC and 3AC, I am surprised. I would expect it to
> > be the other way around (0AC and 2-3DC). No matter, less it good and
> > your receiver is probably saying it can take anything up to 5 volts
> > and it can probably take much less, like maybe .1 volts. Some people
> > on this list have said their equipment works all the way to .025
> > volts. I would double check your numbers and readings then try it.
> >
> >
> > Allen
> >
> > _
> Summarizing:
>
> the signal is digital manchester coded and probably bipolar, so will not
> contain a DC component.
> It's sampling rate is up to 96kHz, to high for most multimeters.
> Multimeters do not measure peak values, but only average (they are even
> "calibrated" in RMS (root MEAN Square). So you will never know what peak
> voltages are actually present.
> Only way to be sure is to use an oscilloscope.
>
> know it does not help, but clarifies a shortfall in the measuring
> technique..
>

This article might be interesting. I also mentions that the data is not
bipols, but merely capacitive coupled (or using a transformer), removing
a DC component. This will then only work using the "manchester like"
coding, as standard digital signals may remain too long at a "1" level
to be passed through a cap or a transformer.

http://www.epanorama.net/documents/audio/spdif.html

> Johan
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allen.edwards at oldpaloalto

Jul 5, 2008, 2:38 AM

Post #18 of 19 (1036 views)
Permalink

Re: HDMI_SPDIF directly to reciever [In reply to]

Johan wrote:
> On Fri, 2008-07-04 at 22:16 -0700, Alen Edwards wrote:
>
>> James wrote:
>>
>>> Roo wrote:
>>>
>>>
>>>> 2008/7/5 James Lockie <bjlockie[at]lockie.ca>:
>>>>
>>>>
>>>>
>>>>
>>>>> 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.
>>>>>
>>>>>
>>>>>
>>>> James,
>>>>
>>>> If your voltmeter is on a DC range and the output is bipolar, +0.5V
>>>> and -0.5V then that will "average" out to 0V. This is irrespective of
>>>> the data travelling over the spdif as it is Manchester Coded.
>>>>
>>>> Try an AC range on the voltmeter if you have one.
>>>>
>>>>
>>>>
>>> AC is 3 something.
>>> So if my receiver expects 5V and it is getting less, am I hurting it?
>>>
>>>
>>>
>>>> HTH,
>>>>
>>>> Roo.
>>>> ___________________
>>>>
>> If you are getting 0 DC and 3AC, I am surprised. I would expect it to
>> be the other way around (0AC and 2-3DC). No matter, less it good and
>> your receiver is probably saying it can take anything up to 5 volts
>> and it can probably take much less, like maybe .1 volts. Some people
>> on this list have said their equipment works all the way to .025
>> volts. I would double check your numbers and readings then try it.
>>
>>
>> Allen
>>
>> _
>>
> Summarizing:
>
> the signal is digital manchester coded and probably bipolar, so will not
> contain a DC component.
> It's sampling rate is up to 96kHz, to high for most multimeters.
> Multimeters do not measure peak values, but only average (they are even
> "calibrated" in RMS (root MEAN Square). So you will never know what peak
> voltages are actually present.
> Only way to be sure is to use an oscilloscope.
>
> know it does not help, but clarifies a shortfall in the measuring
> technique..
>
> Johan
>
That is why I was surprised he measured 3 volts on AC and 0 on DC. When
I measured the output on my MB, it was between 2 and 3 on DC and 0 on AC
for the reasons you state and the fact that the signal levels were TTL
and not spdif. I AC coupled and attenuated it so now I measure 0 and 0.

btw, you can measure the peak voltage if you use a diode and a small
capacitor in front of the DC voltmeter, but that is another discussion
and is not without its issues.

Allen

roo.watt at gmail

Jul 5, 2008, 5:37 AM

Post #19 of 19 (1024 views)
Permalink

Re: HDMI_SPDIF directly to reciever [In reply to]

2008/7/5 James <bjlockie[at]lockie.ca>:
> So if my receiver expects 5V and it is getting less, am I hurting it?

In my experience it would be *highly* unlikely that it would be
damaged. Consumer equipment needs to be hardened against all sorts of
misconfigurations/misconnections.

Cheers,

Roo.
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