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From: JosephKK on 29 Jul 2010 21:46
On Thu, 29 Jul 2010 17:28:06 +0100, Dirk Bruere at NeoPax
<dirk.bruere(a)gmail.com> wrote:

>On 29/07/2010 12:40, Dirk Bruere at NeoPax wrote:
>> On 29/07/2010 05:52, JosephKK wrote:
>>> On Tue, 27 Jul 2010 00:34:12 +0100, Dirk Bruere at NeoPax
>>> <dirk.bruere(a)gmail.com> wrote:
>>>
>>>> On 24/07/2010 14:45, JosephKK wrote:
>>>>> On Fri, 23 Jul 2010 16:52:36 +0100, Dirk Bruere at NeoPax
>>>>> <dirk.bruere(a)gmail.com> wrote:
>>>>>
>>>>>> On 23/07/2010 05:09, JosephKK wrote:
>>>>>>> On Tue, 20 Jul 2010 17:39:17 +0100, Dirk Bruere at NeoPax
>>>>>>> <dirk.bruere(a)gmail.com> wrote:
>>>>>>>
>>>>>>>> I want to drive a digital audio signal over CAT5.
>>>>>>>> I intend to use the DA103 transformer but need to check impedance
>>>>>>>> matching.
>>>>>>>>
>>>>>>>> Will 100R each end of the CAT5 be suitable?
>>>>>>>> Should the 100R on the transmitting end be before, or after, the
>>>>>>>> xformer?
>>>>>>>
>>>>>>> The terminating restance should be at the far end of the cable. I
>>>>>>> gotta ask though, in there any reasonable way that you could send the
>>>>>>> signal digitally? like manchester encoded? The whole thing can work
>>>>>>> much better that way.
>>>>>>
>>>>>> Forgot to add...
>>>>>> The input signal is standard SPDIF.
>>>>> OK.
>>>>>> I'm going to bump it up to TTL level and use that to feed into a
>>>>>> am26C31
>>>>>> line driver and then into the transformer. The other end is an SPFIF
>>>>>> receiver, so I have to do an impedance match (and voltage reduction to
>>>>>> around 1V).
>>>>>
>>>>> Actually, i think all you really need is the impedance match (both
>>>>> ends and let the voltage scale). Unless you are going a lot farther
>>>>> than SPDIF is rated for, in which case the driver may be called for.
>>>>
>>>> The only worry is that the receiving chip is 3V3 and I do not want to
>>>> risk damaging it by feeding it some overvoltage. Can bad impedance match
>>>> bump up the voltage through reflections?
>>>
>>> Yes it can. With this configuration and guessed line lengths it may
>>> show up as increased overshoot / undershoot, more ringing or leading
>>> pedistals on the pulses at the receiver.
>>>
>>> I still recomment just Z matching both ends and just using Cat 5 / Cat
>>> 5E cable. It really is nice cable for fast signals. I know, i done
>>> got me a copy of TIA-568 set.
>>>
>>>>
>>>> I checked the specs for the am26c31 and the output is around 3V (5V
>>>> Vcc), so after the xformer and resistors it will certainly be less.
>>
>> Given that the SPDIF input is 75R, a couple of 12R resistors in each
>> signal path at the SPDIF end should be sufficient?
>
>On a related issue, how important is termination over short runs with
>low(ish) frequency? Audio is around 10Mhz and I doubt we will ever go
>beyond 30m in length. In this case the wavelength is around the same
>lenth as the cable. Of course, this is square wave and obviously there
>are higher frequency components.

It mostly depends on the edge speeds you need to maintain. They
determine the highest frequency components with signifcant (spectral)
power. So if you need 10 ns edges you have stuff up in the 100 MHz
range involved. Or if you use another approximating rule 35 MHz.

From: Dirk Bruere at NeoPax on 30 Jul 2010 21:27
On 30/07/2010 02:40, JosephKK wrote:
> On Thu, 29 Jul 2010 12:40:24 +0100, Dirk Bruere at NeoPax
> <dirk.bruere(a)gmail.com> wrote:
>
>> On 29/07/2010 05:52, JosephKK wrote:
>>> On Tue, 27 Jul 2010 00:34:12 +0100, Dirk Bruere at NeoPax
>>> <dirk.bruere(a)gmail.com> wrote:
>>>
>>>> On 24/07/2010 14:45, JosephKK wrote:
>>>>> On Fri, 23 Jul 2010 16:52:36 +0100, Dirk Bruere at NeoPax
>>>>> <dirk.bruere(a)gmail.com> wrote:
>>>>>
>>>>>> On 23/07/2010 05:09, JosephKK wrote:
>>>>>>> On Tue, 20 Jul 2010 17:39:17 +0100, Dirk Bruere at NeoPax
>>>>>>> <dirk.bruere(a)gmail.com> wrote:
>>>>>>>
>>>>>>>> I want to drive a digital audio signal over CAT5.
>>>>>>>> I intend to use the DA103 transformer but need to check impedance matching.
>>>>>>>>
>>>>>>>> Will 100R each end of the CAT5 be suitable?
>>>>>>>> Should the 100R on the transmitting end be before, or after, the xformer?
>>>>>>>
>>>>>>> The terminating restance should be at the far end of the cable. I
>>>>>>> gotta ask though, in there any reasonable way that you could send the
>>>>>>> signal digitally? like manchester encoded? The whole thing can work
>>>>>>> much better that way.
>>>>>>
>>>>>> Forgot to add...
>>>>>> The input signal is standard SPDIF.
>>>>> OK.
>>>>>> I'm going to bump it up to TTL level and use that to feed into a am26C31
>>>>>> line driver and then into the transformer. The other end is an SPFIF
>>>>>> receiver, so I have to do an impedance match (and voltage reduction to
>>>>>> around 1V).
>>>>>
>>>>> Actually, i think all you really need is the impedance match (both
>>>>> ends and let the voltage scale). Unless you are going a lot farther
>>>>> than SPDIF is rated for, in which case the driver may be called for.
>>>>
>>>> The only worry is that the receiving chip is 3V3 and I do not want to
>>>> risk damaging it by feeding it some overvoltage. Can bad impedance match
>>>> bump up the voltage through reflections?
>>>
>>> Yes it can. With this configuration and guessed line lengths it may
>>> show up as increased overshoot / undershoot, more ringing or leading
>>> pedistals on the pulses at the receiver.
>>>
>>> I still recomment just Z matching both ends and just using Cat 5 / Cat
>>> 5E cable. It really is nice cable for fast signals. I know, i done
>>> got me a copy of TIA-568 set.
>>>
>>>>
>>>> I checked the specs for the am26c31 and the output is around 3V (5V
>>>> Vcc), so after the xformer and resistors it will certainly be less.
>>
>> Given that the SPDIF input is 75R, a couple of 12R resistors in each
>> signal path at the SPDIF end should be sufficient?
>
> Might be. You may also try 15R or 18R to see what works best, then a
> 1:1 transformer right into the receiver. Resistors at both ends, it
> will cost some signal amplitude, maybe 40% in voltage. (105/75)^1/2
> ~= 1.18 so 1.2:1 transformers are likely to work better, 1.2 side on
> the Cat5 cable side.

The SPDIF input is already xformer isolated, 1:1
However, there should be plenty of signal amplitude

--
Dirk

http://www.transcendence.me.uk/ - Transcendence UK
http://www.blogtalkradio.com/onetribe - Occult Talk Show
From: JosephKK on 31 Jul 2010 00:39
On Sat, 31 Jul 2010 02:27:52 +0100, Dirk Bruere at NeoPax
<dirk.bruere(a)gmail.com> wrote:

>On 30/07/2010 02:40, JosephKK wrote:
>> On Thu, 29 Jul 2010 12:40:24 +0100, Dirk Bruere at NeoPax
>> <dirk.bruere(a)gmail.com> wrote:
>>
>>> On 29/07/2010 05:52, JosephKK wrote:
>>>> On Tue, 27 Jul 2010 00:34:12 +0100, Dirk Bruere at NeoPax
>>>> <dirk.bruere(a)gmail.com> wrote:
>>>>
>>>>> On 24/07/2010 14:45, JosephKK wrote:
>>>>>> On Fri, 23 Jul 2010 16:52:36 +0100, Dirk Bruere at NeoPax
>>>>>> <dirk.bruere(a)gmail.com> wrote:
>>>>>>
>>>>>>> On 23/07/2010 05:09, JosephKK wrote:
>>>>>>>> On Tue, 20 Jul 2010 17:39:17 +0100, Dirk Bruere at NeoPax
>>>>>>>> <dirk.bruere(a)gmail.com> wrote:
>>>>>>>>
>>>>>>>>> I want to drive a digital audio signal over CAT5.
>>>>>>>>> I intend to use the DA103 transformer but need to check impedance matching.
>>>>>>>>>
>>>>>>>>> Will 100R each end of the CAT5 be suitable?
>>>>>>>>> Should the 100R on the transmitting end be before, or after, the xformer?
>>>>>>>>
>>>>>>>> The terminating restance should be at the far end of the cable. I
>>>>>>>> gotta ask though, in there any reasonable way that you could send the
>>>>>>>> signal digitally? like manchester encoded? The whole thing can work
>>>>>>>> much better that way.
>>>>>>>
>>>>>>> Forgot to add...
>>>>>>> The input signal is standard SPDIF.
>>>>>> OK.
>>>>>>> I'm going to bump it up to TTL level and use that to feed into a am26C31
>>>>>>> line driver and then into the transformer. The other end is an SPFIF
>>>>>>> receiver, so I have to do an impedance match (and voltage reduction to
>>>>>>> around 1V).
>>>>>>
>>>>>> Actually, i think all you really need is the impedance match (both
>>>>>> ends and let the voltage scale). Unless you are going a lot farther
>>>>>> than SPDIF is rated for, in which case the driver may be called for.
>>>>>
>>>>> The only worry is that the receiving chip is 3V3 and I do not want to
>>>>> risk damaging it by feeding it some overvoltage. Can bad impedance match
>>>>> bump up the voltage through reflections?
>>>>
>>>> Yes it can. With this configuration and guessed line lengths it may
>>>> show up as increased overshoot / undershoot, more ringing or leading
>>>> pedistals on the pulses at the receiver.
>>>>
>>>> I still recomment just Z matching both ends and just using Cat 5 / Cat
>>>> 5E cable. It really is nice cable for fast signals. I know, i done
>>>> got me a copy of TIA-568 set.
>>>>
>>>>>
>>>>> I checked the specs for the am26c31 and the output is around 3V (5V
>>>>> Vcc), so after the xformer and resistors it will certainly be less.
>>>
>>> Given that the SPDIF input is 75R, a couple of 12R resistors in each
>>> signal path at the SPDIF end should be sufficient?
>>
>> Might be. You may also try 15R or 18R to see what works best, then a
>> 1:1 transformer right into the receiver. Resistors at both ends, it
>> will cost some signal amplitude, maybe 40% in voltage. (105/75)^1/2
>> ~= 1.18 so 1.2:1 transformers are likely to work better, 1.2 side on
>> the Cat5 cable side.
>
>The SPDIF input is already xformer isolated, 1:1
>However, there should be plenty of signal amplitude

So let us know how it all works out, ok?
From: JosephKK on 31 Jul 2010 23:59
On Tue, 27 Jul 2010 00:34:12 +0100, Dirk Bruere at NeoPax
<dirk.bruere(a)gmail.com> wrote:

>On 24/07/2010 14:45, JosephKK wrote:
>> On Fri, 23 Jul 2010 16:52:36 +0100, Dirk Bruere at NeoPax
>> <dirk.bruere(a)gmail.com> wrote:
>>
>>> On 23/07/2010 05:09, JosephKK wrote:
>>>> On Tue, 20 Jul 2010 17:39:17 +0100, Dirk Bruere at NeoPax
>>>> <dirk.bruere(a)gmail.com> wrote:
>>>>
>>>>> I want to drive a digital audio signal over CAT5.
>>>>> I intend to use the DA103 transformer but need to check impedance matching.
>>>>>
>>>>> Will 100R each end of the CAT5 be suitable?
>>>>> Should the 100R on the transmitting end be before, or after, the xformer?
>>>>
>>>> The terminating restance should be at the far end of the cable. I
>>>> gotta ask though, in there any reasonable way that you could send the
>>>> signal digitally? like manchester encoded? The whole thing can work
>>>> much better that way.
>>>
>>> Forgot to add...
>>> The input signal is standard SPDIF.
>> OK.
>>> I'm going to bump it up to TTL level and use that to feed into a am26C31
>>> line driver and then into the transformer. The other end is an SPFIF
>>> receiver, so I have to do an impedance match (and voltage reduction to
>>> around 1V).
>>
>> Actually, i think all you really need is the impedance match (both
>> ends and let the voltage scale). Unless you are going a lot farther
>> than SPDIF is rated for, in which case the driver may be called for.
>
>The only worry is that the receiving chip is 3V3 and I do not want to
>risk damaging it by feeding it some overvoltage. Can bad impedance match
>bump up the voltage through reflections?

Yes it can. Depending on line length and signaling rate it may be in
the form of overshoot and undershoot or maybe ringing. Or simple
changes in volatge amplitude. Or a mixture of these.

I still recommend Z match and go for it, Cat 5/ Cat 5E is pretty nice
cable for fairly fast signals. I done bought me a copy of TIA-568
set.
>
>I checked the specs for the am26c31 and the output is around 3V (5V
>Vcc), so after the xformer and resistors it will certainly be less.
From: Dirk Bruere at NeoPax on 2 Aug 2010 18:15
On 31/07/2010 05:39, JosephKK wrote:
> On Sat, 31 Jul 2010 02:27:52 +0100, Dirk Bruere at NeoPax
> <dirk.bruere(a)gmail.com> wrote:
>
>> On 30/07/2010 02:40, JosephKK wrote:
>>> On Thu, 29 Jul 2010 12:40:24 +0100, Dirk Bruere at NeoPax
>>> <dirk.bruere(a)gmail.com> wrote:
>>>
>>>> On 29/07/2010 05:52, JosephKK wrote:
>>>>> On Tue, 27 Jul 2010 00:34:12 +0100, Dirk Bruere at NeoPax
>>>>> <dirk.bruere(a)gmail.com> wrote:
>>>>>
>>>>>> On 24/07/2010 14:45, JosephKK wrote:
>>>>>>> On Fri, 23 Jul 2010 16:52:36 +0100, Dirk Bruere at NeoPax
>>>>>>> <dirk.bruere(a)gmail.com> wrote:
>>>>>>>
>>>>>>>> On 23/07/2010 05:09, JosephKK wrote:
>>>>>>>>> On Tue, 20 Jul 2010 17:39:17 +0100, Dirk Bruere at NeoPax
>>>>>>>>> <dirk.bruere(a)gmail.com> wrote:
>>>>>>>>>
>>>>>>>>>> I want to drive a digital audio signal over CAT5.
>>>>>>>>>> I intend to use the DA103 transformer but need to check impedance matching.
>>>>>>>>>>
>>>>>>>>>> Will 100R each end of the CAT5 be suitable?
>>>>>>>>>> Should the 100R on the transmitting end be before, or after, the xformer?
>>>>>>>>>
>>>>>>>>> The terminating restance should be at the far end of the cable. I
>>>>>>>>> gotta ask though, in there any reasonable way that you could send the
>>>>>>>>> signal digitally? like manchester encoded? The whole thing can work
>>>>>>>>> much better that way.
>>>>>>>>
>>>>>>>> Forgot to add...
>>>>>>>> The input signal is standard SPDIF.
>>>>>>> OK.
>>>>>>>> I'm going to bump it up to TTL level and use that to feed into a am26C31
>>>>>>>> line driver and then into the transformer. The other end is an SPFIF
>>>>>>>> receiver, so I have to do an impedance match (and voltage reduction to
>>>>>>>> around 1V).
>>>>>>>
>>>>>>> Actually, i think all you really need is the impedance match (both
>>>>>>> ends and let the voltage scale). Unless you are going a lot farther
>>>>>>> than SPDIF is rated for, in which case the driver may be called for.
>>>>>>
>>>>>> The only worry is that the receiving chip is 3V3 and I do not want to
>>>>>> risk damaging it by feeding it some overvoltage. Can bad impedance match
>>>>>> bump up the voltage through reflections?
>>>>>
>>>>> Yes it can. With this configuration and guessed line lengths it may
>>>>> show up as increased overshoot / undershoot, more ringing or leading
>>>>> pedistals on the pulses at the receiver.
>>>>>
>>>>> I still recomment just Z matching both ends and just using Cat 5 / Cat
>>>>> 5E cable. It really is nice cable for fast signals. I know, i done
>>>>> got me a copy of TIA-568 set.
>>>>>
>>>>>>
>>>>>> I checked the specs for the am26c31 and the output is around 3V (5V
>>>>>> Vcc), so after the xformer and resistors it will certainly be less.
>>>>
>>>> Given that the SPDIF input is 75R, a couple of 12R resistors in each
>>>> signal path at the SPDIF end should be sufficient?
>>>
>>> Might be. You may also try 15R or 18R to see what works best, then a
>>> 1:1 transformer right into the receiver. Resistors at both ends, it
>>> will cost some signal amplitude, maybe 40% in voltage. (105/75)^1/2
>>> ~= 1.18 so 1.2:1 transformers are likely to work better, 1.2 side on
>>> the Cat5 cable side.
>>
>> The SPDIF input is already xformer isolated, 1:1
>> However, there should be plenty of signal amplitude
>
> So let us know how it all works out, ok?

Well, feeding straight into CAT5e and AES/EBU i/f it all works fine.
SPDIF will have to wait until next week.

--
Dirk

http://www.transcendence.me.uk/ - Transcendence UK
http://www.blogtalkradio.com/onetribe - Occult Talk Show
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