Phantom power blocker for synth outputs

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Why on earth would he have done that? To what possible advantage?

In those days, phantom was rarely required. It was a bit of an afterthought. Phantom power is a very poor design concept and I suspect Rupert knew it. In any case most condenser mics were tube based and came with their own power supply. Dynamics were often used for snare and guitar cabs. Ribbons were rarely used.
A really rough way for people to find out they had a ribbon mic with faulty wiring! But hot-plugging also NOT recommended for most condenser mics either (?!).
If some fool wires a mic wrongly you can hardly blame phantom power for that. The real lesson is not that phantom is bad, but that you should take more care wiring your ribbons.

Cheers

Ian
 
What I would personally do in that situation, and the cheapest way (for Free) to be protected would be to dedicate some channels of the mixer for Line Inputs and in those channels I would remove (desolder) one leg of the 390r resistor after the 48V switch.
I would desolder one leg of it from the PCB and put heatshrink tube around it so that it could be reversed back to stock easily in the future in case needed.
This way you don't need any DI boxes, you don't need to spend money on DI boxes, you are protected from phantom power because it's not reaching the input anylonger, and don't forget that besides the Line inputs you can still use those channels for Dynamic microphones in case you need to use the Mic Pres

I not saying this is the only solution, or the best of all solution, other people might have much better ideas,
I'm just saying that this would be what I would do in a pinch in the situation you described


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Many Output sections and output IC's have phantom power protection,
but not all have, and we never know which ones are protected and the ones that aren't...
So the best thing to do is to never send Phantom power into a Line level output.
People that are not well versed on Bantam Patchbays do that mistake easilly all the time.
Could it also be possible to move the legs of the 6.8ks to M1 or M2 (pre switch) so that it only affects the input you’d like to use with microphones, if that is the case that one is being connected to synths continuously? Or is that still too risky
Would there be a risk of spikes when switching between inputs still…
S
 
Could it also be possible to move the legs of the 6.8ks to M1 or M2 (pre switch) so that it only affects the input you’d like to use with microphones, if that is the case that one is being connected to synths continuously?

If I'm seeing it correctly yes, you could move the 2x 6k8 resistors to Pin 2 and Pin 3 of M1, before the M1/M2 switch.
That way you would have Phantom Power only in Input M1 and not in Input M2.
You could use then input M1 for Microphones and input M2 for your synths

But you still need to check something, please read below

Or is that still too risky
Would there be a risk of spikes when switching between inputs still…

As far as I can see, and please guys correct me if I'm wrong,
to do this you need to check if the Switch that changes between M1 and M2 is a Make before Brake switch (shorting) or a Break Before Make switch (non-shorting).
If it's a BBM switch then I don't think you have any risk and problem is solved.
But if it's a MBB (shorting )switch then if phantom is turned on when you move the switch from input M1 to input M2 there will be for a tiny fraction of time 48V on input M2 (during the travel) until the switch reaches the final position and then there's no 48V.

I don't know if this tiny fraction of time would be enough to cause any danger, but I think you should check what type of switch is installed there just to be sure.

Some reading about BBM and MBB switches:

https://e2e.ti.com/support/switches...tches-multiplexers-and-how-are-they-different

https://e2e.ti.com/support/switches...tches-multiplexers-and-how-are-they-different
 
Ribbons were rarely used.

Hi mate,
you made me think about this, I though that Ribbon microphones were used a lot during that time,
seen many old photos in classic recording studios using the RCA 44 and 77, STC/Coles and Beyer M160 and M130.
I see know I was not defining correctly the different eras, even in the same decade, as those photos are from "vintage" studios but from very time frames.
The time frame you're talking about I think is late 60s until Mid 70s.

So while doing some research on this I learned a lot, thanks for spicing up my curiosity.
RCA 44 and 77 were used mostly in 30s, 40s and 50s and it seems they lost popularity to Condenser microphones that were introduced by Neumann,
the U47 (1949) then the U67 (1960) and the U87 (1967).
By 1976 RCA was out of business.

The STC Coles I've seen in the Beatles recordings photos used on Overheads are probably from their records from 63 to 66 (or 67),
maybe in the late 60s and 70s they were not that popular anylonger.
Anyway production of the 4038 never stopped from the 50s to the present. But maybe there's a reason production went from STC to Coles in the Mid 70s.
But thinking about it I don't think I've seen photos of recording sessions from the 70s with the 4038 being used, maybe I was distracted.

The exception I remember of Ribbons being used in the 70s in very successful records was in Led Zeppelin IV record (1971) where Beyerdynamic M160 were used and actually some of the technics used became classics like the sound of "When the levee breaks".
But I guess this use was an exception and not the most popular mic choice of the time.

So like you said, late 60s and 70s (and 80s and probably 90s), Ribbon mics were Rarely used,
and it seems they fell out of favor to condenser microphones between the mid 50s to mid 60s being rarely used from the late 60s on,
until the Digital age of recording came.

There's a lot of reasons for that,
but what I think are the main reasons are these ones:

"Ribbons are known for a very musical, natural sound. But, in the 1960s, ribbons fell out of favor — not because of the microphone itself, but due to changes in the way voices and music were recorded.

Ribbon microphones have an inherent, high-frequency roll off that is similar to the way people hear. Between the 1930s and 1990s, the majority of people were recording to tape machines through consoles which both had a high-frequency roll off. Those tapes were then put on vinyl which also had a high-frequency roll off.

Then those vinyls were played on radio, which also had a high-frequency roll off. By the time the original source track hit the home listener, much of the high-frequency content was totally lost.

Until the late 1950s, condenser microphones could not compare to the ribbon’s frequency response. But condensers steadily improved and swept the recording industry. They became the “go to” mic for many recording studios. Because of their high-tuned system, frequencies in condensers in the top-end were exaggerated and hyped.

Sometimes these condensers were so hyped that monitoring vocals directly through the console would sound harsh. But by the time the condenser was recorded to tape and then transferred to vinyl and then played back on radio, the top end was greatly rolled off and sounded smooth.

The difference between a condenser and a ribbon at the end of the chain was pretty drastic with an RCA 44BX sounding muddy next to a condenser sounding crystal clear. By the 1970s, ribbon mics had passed out of style and RCA’s ribbon mic division was closed down."


https://www.thebroadcastbridge.com/...crophones-make-a-full-circle-in-audio-history


This last part of my past I already knew and found, but I write it anyway to complete the post,
In the Digital Age of recording the High End frequencies are not lost in the recording process, or on each playback, or in mixing, mastering or in transfer to a CD or Streaming (final consumer format), so condenser microphones might sound too harsh in some situations.
The Ribbon microphones comeback made sense because now, although they're darker than condensers the limited high end they have will not get lost, and can make when needed digital recordings sound warmer or less harsh for some people (myself included, but I like all mics and having all the tools)

Sorry for hijacking the thread with this post,
This subject is interesting to me because this is my passion and my job, but also because I'm a tutor of Recording for 7 years, and I always start my lectures with the History of Recording.

Thanks Ian
 
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If some fool wires a mic wrongly you can hardly blame phantom power for that. The real lesson is not that phantom is bad, but that you should take more care wiring your ribbons.

Other potential dangers that can happen in a recording studio with Phantom Power and Ribbon mics is hot pluging a TRS Bantam patch cable between Mic Pre input and Mic Tie Lines.
And also an XLR cable that failed and some of the wires inside the connector broke and are shorting to other pins.

But most of the times even those situations are not guaranteed to break the Ribbon.

Anyway, I think equipment should always have switches for turning Phantom On/Off in each input individually,
and engineers should know very well the safe procedures to use phantom power.
 

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