Hi guys
I would like to ask about BNC connector types.
Should I change all my rca's to bnc together with spdif coax input and use it throughout the chain ?
If yes will it yield better sound quality ?
Which bnc to buy ?
And does crimp tool required or I could manage without ?
Thx
Ivan
I would like to ask about BNC connector types.
Should I change all my rca's to bnc together with spdif coax input and use it throughout the chain ?
If yes will it yield better sound quality ?
Which bnc to buy ?
And does crimp tool required or I could manage without ?
Thx
Ivan
I would not bother. Others would. An RCA is the wrong impedance, but short enough not to cause much reflection. Long tails on the connections to the socket could be worse than the socket itself. Those who know about RF wiring will know how to get it right, but they are also likely to be those who believe that the change is not worth doing.
A BNC connector has a 50 or 75Ohm impedance. Your RCA/Phono connectors are more suited for higher impedance signals like audio cables etc.
If there were any improvement in the use of BNC, I feel sure Quad, NAD, Arcam etc would use them.
If there were any improvement in the use of BNC, I feel sure Quad, NAD, Arcam etc would use them.
Basically I have cheap chinese rca's on my amp and pre. I am not sure if I d better be buying sophisticated (more) expensive rca's or to go BNC route.
I know some even won't bother with either option and stick to the ordinary RCA.
I know some even won't bother with either option and stick to the ordinary RCA.
Decent connectors and cable should help if you have a lack of brightness in your signal. Don't purchase really expensive leads as it is not worth it.
What I had read is that you may want to use BNC for SPDIF or audio for very different reasons.
For SPDIF, BNC has a correct characteristic impedance (which is of course a very different beast from the DC resistance) whereas RCA does not. The characteristic impedance depends on the size and geometry, like for coax cables. RCA plugs and connectors are not shaped with this parameter in mind.
This is relevant for SPDIF, because of the frequencies transmitted along the line. I am not competent enough to explain it, but you find info on this very easily.
SPDIF is specified to be transmitted over a 75 ohm transmission line, so the entire "chain" should have this uniform characteristic impedance. That's the connector at the source, the cable, the connector at the end and a termination. So you want 75 ohm BNC hardware for SPDIF.
For audio signals, what I had read is that the advantage of BNC can be the better mechanical construction, which makes better contact. But at the frequencies of an audio signal the mismatch in characteristic impedance is negligible.
(Footnote:
Now, why the consumer market decided to use RCA for SPDIF is one of those unexplained suboptimal choices, like there are so many.
Probably the impact is not big enough to make the device "go back to after-sales", and that's all they need to get away with cheaper components. I mean, the two boxes successfully communicate and play music. Whether it could play even better is something that is left to us DIYers...
Counterexample: satellite TV didn't get away with less than the F-connector - which is by the way 75 ohm characteristic impedance as well).
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For SPDIF, BNC has a correct characteristic impedance (which is of course a very different beast from the DC resistance) whereas RCA does not. The characteristic impedance depends on the size and geometry, like for coax cables. RCA plugs and connectors are not shaped with this parameter in mind.
This is relevant for SPDIF, because of the frequencies transmitted along the line. I am not competent enough to explain it, but you find info on this very easily.
SPDIF is specified to be transmitted over a 75 ohm transmission line, so the entire "chain" should have this uniform characteristic impedance. That's the connector at the source, the cable, the connector at the end and a termination. So you want 75 ohm BNC hardware for SPDIF.
For audio signals, what I had read is that the advantage of BNC can be the better mechanical construction, which makes better contact. But at the frequencies of an audio signal the mismatch in characteristic impedance is negligible.
(Footnote:
Now, why the consumer market decided to use RCA for SPDIF is one of those unexplained suboptimal choices, like there are so many.
Probably the impact is not big enough to make the device "go back to after-sales", and that's all they need to get away with cheaper components. I mean, the two boxes successfully communicate and play music. Whether it could play even better is something that is left to us DIYers...
Counterexample: satellite TV didn't get away with less than the F-connector - which is by the way 75 ohm characteristic impedance as well).
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I live in Bromley, not far from you, I work in Broadcasting and we are throwing out lots of CTP's so if you need some BNC chassis connectors let me know.
At audio frequencies, sure there is no transmission line at all and the impedance doesn't matter much. For audio, the shielding is important, and the capacitance is also a factor. The connector doesn't matter as long as there is good electrical contact and shielding.
S/PDIF doesn't operate at audio frequencies, it extends into at least 10's of MHz and up there Zo does matter (admittedly not as critical as at GHz). At 192 kHz sampling, the S/PDIF signal's 3rd harmonic is at ~75 MHz and the 5th is at ~125 MHz. So Zo matters.
RCA was chosen because that is what was used for composite video. The signal itself was also designed to be compatible, using similar voltage levels and bandwidth as video. This meant that existing line driver and receiver circuits for video could often be re-used for S/PDIF.
~125 MHz, that seems a little high but let's go with it. After all S/PDIF is a bandwidth limited signal.
So at 125MHz the wavelength is about 2.4 meters or about 94 inches. So 1/10 would be maybe 0.24 meter or 9.4 inches. I have never seen an RCA connector that long.
It could go up beyond 125MHz. It depends on the rise time of whatever is generating the signal. Then velocity factor shortens the physical length. Nevertheless, a short impedance discontinuity will do little harm.
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