light relief time. This is what a million dollar domestic system looks like in 2018.
Day One's RMAF Odyssey Continues | Stereophile.com
To be honest underwhelmed. But you have to love comments like
Day One's RMAF Odyssey Continues | Stereophile.com
To be honest underwhelmed. But you have to love comments like
Does it mean that Stereophile finding on jitter using analyzer in 1993 no longer applies to equipment with modern coaxial SPDIF receiver? If so then RCA connectors no longer pose any issue and BNC connectors do not measure any better in terms of jitter?
Hi chris,
at least WBT offers a true 75 Ohms RCA combination (quite pricey though), others claim to have 75 variants but judging from the pictures i´ve my doubts........
It's true, and years ago the 50 ohm center pin was larger, and if plugged into a 75 ohm female expanded it to the point where subsequently a 75 ohm male would make intermittent contact if any. Conversely if a 75 ohm plug was inserted into a 50 ohm jack the contact would be intermittent from the get-go. I believe the standards have been changed to prevent these two issues.
At AMI we had over a hundred cassette recording slaves, each wired with with 4 channels of audio inputs on BNCs. The actual buffer amps inside were over 5k ohms impedance, so we just daisy chained rows of them with tees. A rough calculation gives over 400 BNC cables we made up with double shielded Alpha 75 ohm RG-6, high-quality BNCs specifically designed for that cable along with several $$$ crimping tools from Alpha. In the middle of the process the idiot engineer on the project (me) accidentally specified 75 ohm plugs which my techs dutifully crimped in place. Not surprisingly we suffered intermittent random signal loss for weeks until I took a hard look at the system. A tough way to learn the difference...
Cheers!
Howie
My Amphenol 50 ohm and 75 ohm connectors use a .050" center pin. The difference is in the plastic insulator extension. My Kings 75 ohm BNC connector has a center pin of .051" also without the inside plastic extension, so it does seem the issue is gone with center pin differences.
My old feed-throughs though expect a .035" pin.
My old feed-throughs though expect a .035" pin.
It's not physically possible to make a 75 Ohm RCA plug that can mate with an RCA socket. The center metal part must be much smaller than an RCA id.
In the past you could get BNC's with smaller pins (same as 75 Ohm N connectors). Those have largely vanished. BNC are not really used above 1 GHz normally so some requirements can be relaxed. 75 Ohm N are good to 3 GHz. Above that everyone moves to 50 Ohms and SMA variants or 7mm. Exceptions always exist just to make this stuff harder.
In the past you could get BNC's with smaller pins (same as 75 Ohm N connectors). Those have largely vanished. BNC are not really used above 1 GHz normally so some requirements can be relaxed. 75 Ohm N are good to 3 GHz. Above that everyone moves to 50 Ohms and SMA variants or 7mm. Exceptions always exist just to make this stuff harder.
Hi Ed, Demian,
They may have eliminated the fit problems with the BNC connectors, but the old ones are still floating around out there. People don't normally replace and throw out old connectors. They will use them up first, and are rightfully loath to replace the connectors on a running system. Just being aware of the different standards is enough to hopefully keep younger techs out of trouble.
On new equipment the mechanical size issue may no longer exist, but the tech still needs to recognise each type of system (50R and 75R) and use the correct connector. As for RCA connectors, I thought they were all 75R types. I'm not aware of an instrumentation use for a 50R RCA plug.
-Chris
They may have eliminated the fit problems with the BNC connectors, but the old ones are still floating around out there. People don't normally replace and throw out old connectors. They will use them up first, and are rightfully loath to replace the connectors on a running system. Just being aware of the different standards is enough to hopefully keep younger techs out of trouble.
On new equipment the mechanical size issue may no longer exist, but the tech still needs to recognise each type of system (50R and 75R) and use the correct connector. As for RCA connectors, I thought they were all 75R types. I'm not aware of an instrumentation use for a 50R RCA plug.
-Chris
Very nice application note on Surge Protection Devices inside equipment
I don't think this has been posted here before; if it has & I missed it, sorry for the duplication.
Full app note: https://www.mtl-inst.com/images/uploads/datasheets/tan/TAN1002.pdf
Amusing figure ("GDT" is a 3 terminal Gas Discharge Tube):
I don't think this has been posted here before; if it has & I missed it, sorry for the duplication.
Full app note: https://www.mtl-inst.com/images/uploads/datasheets/tan/TAN1002.pdf
Amusing figure ("GDT" is a 3 terminal Gas Discharge Tube):
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No RCA is 75R or 50R. The ratio between inner and outer simply will not allow this; as I said, I would guess something more like 30R. The best you can do is add series inductance to offset the shunt capacitance so that in lower frequency circuits the combination does not look too far from whatever impedance you want. This will be plenty good enough for uncritical uses such as digital audio.anatech said:
I am not aware of any instrumentation use for any sort of RCA.
The WBT nextgen plug and socket _are_ 75 Ohm as they found an ingenious solution.
This problem of RCA connector's impedance has been addressed by various manufacturers and inventors over the decades. It is a real problem. Ingenious solutions have been found, but they are not cheap or convenient to implement. Better RCA's sometimes 'might' get closer to 75 ohms than 30 ohms, but I can't be more specific. Listen to Demian, he knows about these sorts of things.
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Ingenious in relation to the stated impossibility of such a combination...
Well yes but ultimately pointless when there are a plethora of properly designed and cheap connectors already out there. I'd rather remove all RCAs from my system than be in a position where i needed £90 connectors.
I built the preamp in the image (top) in 2003. We agreed with the customer that it would have BNC connectors instead of RCA-CINCH, though it was non-standard.
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Ingenious in relation to the stated impossibility of such a combination...
Not ingenious, just expensive.
Ingenious is designing the female such that the rca is 50 ohms regardless of what male is used.
And keeping it at 10 cents per pop.
It's easily doable, but why bother?
John
@ billshurv,
But does that mean it isn´t allowed to mention the WBT combo?
If the impossibility is stated i think it is appropriate to mention that such a combo exists.
@ jneutron,
I won´t dispute that this might be even more ingenious, but do still think that the WBT (or J.Reich´s) idea was ingenious.
I remember that you couldn´t disclose your idea a lot of years back, but maybe the constraints are relieved by now so that you could share it?
But does that mean it isn´t allowed to mention the WBT combo?
If the impossibility is stated i think it is appropriate to mention that such a combo exists.
@ jneutron,
I won´t dispute that this might be even more ingenious, but do still think that the WBT (or J.Reich´s) idea was ingenious.
I remember that you couldn´t disclose your idea a lot of years back, but maybe the constraints are relieved by now so that you could share it?
Thank you Howie, not much documentation has been left. I found one photo of the inside.
Power supply was in a separate Al box, in fact 2 power supplies one for each channel. Input BNC's were connected directly to the metal case to minimize RFI input.
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