Re: UPDATED; Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW
« Reply #200 on: April 08, 2021, 01:01:43 PM »
As I think I mentioned somewhere in this thread, Len Page worked for E.M.I. under Alan Blumlein going back as far as the 1930's.  Blumlein was, of course, killed in a plane crash during the second world war while on a test flight for the radar system which he was working on for the war effort. 

REDD was simply a department of E.M.I. set up in 1955 and headed by Len Page.   Record Engineering Development Department. 

The name of the engineer who worked at E.M.I.'s studio in Cologne who helped with th desk design was Peter Burkowitz, not Bukowski.


Thank you very much!

Noted on all posts. I am now laying out a timeline and design on our website.

More soon :)
If you are curious, you'll find the puzzles around you. If you are determined, you will solve them.
Erno Rubik


Re: UPDATED; Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW
« Reply #201 on: April 09, 2021, 12:00:05 AM »
... It sounds like very close Blumlein with a couple spot mics for soloists, though it's possible it's a very well spaced pair, it collapses to mono very nicely.

Ah OK, my mistake.   I just assumed the work in the US followed on from the earlier work done there.

I'm not sure of the exact year off hand, but it's interesting to me that EMI failed to renew the patents granted to Blumlein for his stereo techniques in the '30's  when the time ran out in the mid 1950's.  I suppose at that point, those techniques became fair game.

If you come across that NBC recording again it'd be great to hear it.   

Thanks

 
D. J. H.

The standard way to reduce much of the noise and distortion in audio gear in 1955 was to have a couple of beers.
 Anything else was too fiddlesome and too expensive.

ruffrecords

Re: UPDATED; Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW
« Reply #202 on: April 09, 2021, 03:36:12 AM »
I'm not sure of the exact year off hand, but it's interesting to me that EMI failed to renew the patents granted to Blumlein for his stereo techniques in the '30's  when the time ran out in the mid 1950's.  I suppose at that point, those techniques became fair game.
There is a story that when RCA "invented" the stereo microgroove record they offered to license it to EMI who promptly showed them their own prior (Blumlein) patent for the idea and suggested that instead RCA should license it from them.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: UPDATED; Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW
« Reply #203 on: April 09, 2021, 07:16:21 AM »
Winston,

Also, I recommend reading that paper by  Clarke, Dutton and Vanderlyn that you posted as it gives you an insight to the ‘Shuffler’ circuit and control on the REDD consoles, and why the consoles and their controls are laid out the way they are.  It then becomes obvious that the consoles were designed to physically implement the research of that paper.

They were very much ahead of their time.
 

Absolutely, it's a must read.
One thing to note is that the circuit referred to as shuffler in the paper, and incorporated in the REDD desks, is not the same as the shuffler circuit described by Blumlein in the 1931 patent. 

In the REDD desks, the 'shuffler' circuit was a low pass filter network (along with phase correction) inserted into the difference channel in order to bring the apparent stereo positioning of higher frequency signals (above 700Hz) in line with lower frequency signals.   The loss at frequencies above 700Hz in the difference channel having a factor of 0.7 (-3dB).

Very neat stuff and, sadly, a long since forgotten circuit. 

There is a story that when RCA "invented" the stereo microgroove record they offered to license it to EMI who promptly showed them their own prior (Blumlein) patent for the idea and suggested that instead RCA should license it from them.
 


Haha  :D I've never heard that story.  I like it. 
D. J. H.

The standard way to reduce much of the noise and distortion in audio gear in 1955 was to have a couple of beers.
 Anything else was too fiddlesome and too expensive.

Re: UPDATED; Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW
« Reply #204 on: April 09, 2021, 12:08:40 PM »
I can't remember if I've ever posted this picture on here or not. 
It's the prototype of the REDD.37 desk. 

No Painton quadrant faders, no provision for switching out the eq type between 'pop' & 'classic'...
Still, I wouldn't kick it out of bed at night or say "no thanks" if I had the chance to own it. 

D. J. H.

The standard way to reduce much of the noise and distortion in audio gear in 1955 was to have a couple of beers.
 Anything else was too fiddlesome and too expensive.

Re: UPDATED; Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW
« Reply #205 on: April 09, 2021, 06:20:27 PM »
I can't remember if I've ever posted this picture on here or not. 
It's the prototype of the REDD.37 desk. 

No Painton quadrant faders, no provision for switching out the eq type between 'pop' & 'classic'...
Still, I wouldn't kick it out of bed at night or say "no thanks" if I had the chance to own it.

What a Gem! Would this prototype include the V72? mic pres?
If you are curious, you'll find the puzzles around you. If you are determined, you will solve them.
Erno Rubik

Re: UPDATED; Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW
« Reply #206 on: April 09, 2021, 08:10:15 PM »
What a Gem! Would this prototype include the V72? mic pres?

Yes sir.
The sides of both the left and right upper and lower cases contain the V72S amplifiers.
I don't have the details in front of me and forget the exact number off hand but there are over 30 of them in total (vs. the REDD.17 which has 22 of them if memory serves).
The same amplifier type is used for all signal amplification duty so, mix amps,  output amps, sum & difference amps,  even the talkback amp, as well as the input mic/line pre amps.




D. J. H.

The standard way to reduce much of the noise and distortion in audio gear in 1955 was to have a couple of beers.
 Anything else was too fiddlesome and too expensive.

pucho812

Re: UPDATED; Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW
« Reply #207 on: April 09, 2021, 08:16:01 PM »
what was the different between the v72S and the v72?
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

Re: UPDATED; Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW
« Reply #208 on: April 09, 2021, 08:39:39 PM »
what was the different between the v72S and the v72?

Correct me if I am wrong, but the V72s would have the 200ohm? setup custom for A.R.S?
If you are curious, you'll find the puzzles around you. If you are determined, you will solve them.
Erno Rubik

Re: UPDATED; Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW
« Reply #209 on: April 09, 2021, 10:01:58 PM »
Correct me if I am wrong, but the V72s would have the 200ohm? setup custom for A.R.S?

Not really.  The internal output impedance of the V72S is about 32 ohms,  ever so slightly higher than a standard V72 due to the extra 6dB gain of the V72S  To this output impedance was added a 168 ohm resistor on the hot side of the output signal, which brought the output impedance up to 200 ohms:  32 ohms + 168 ohms = 200
It wasn't unusual back then to "build out" an amplifiers internal output impedance like this.

However, this 168 ohm resistor wasn't part of the V72S proper, it was added outside the amplifiers' chassis on the tuchel connectors in the rack chassis.

It made no practical difference other than ensure all the passive controls following an amplifier (eq, fader etc.) behaved as they should with respect to correct dB attenuation or frequency of eq points. 

If you look at the schematics of the REDD.47 amplifier, or the RS.124 compressor, you see that they are also built out to 200 ohms (with a 150 ohm resistor in the case of the REDD.47) and, in those two particular cases, the "build out" happens inside the amplifier chassis.

But again, there's not much practical difference if you were to audition a built out V72S amplifier that's running into a modern Hi-Z load. 

Hope that makes sense  ;)





D. J. H.

The standard way to reduce much of the noise and distortion in audio gear in 1955 was to have a couple of beers.
 Anything else was too fiddlesome and too expensive.


Re: UPDATED; Audio Historians - REDD/RCA/Langevin/RFT Lorentz/WSW New
« Reply #210 on: April 10, 2021, 06:15:21 AM »
what was the different between the v72S and the v72?

6dB of additional gain with the V72S.   Two ways that I've seen this done: 

Units built that way by Siemens & Halske replaced the 80K feedback resistor with 165K and a correspondingly lower value parallel capacitor.

Earlier units modified by E.M.I. split the first valve cathode resistor in two (the 1K25 became a 680R & 560R) and then both feedback points were taken to/from the mid point.

Oliver Archut had details that indicate the Siemens units had  a mechanically different input transformer. 
Earlier E.M.I. units I saw had the standard V72 input transformer. 
I've seen two or three different IPT secondary termination resistors too, depending on batch/vintage.

But all in all, quite small differences really. 

Edit:  A small detail I forgot:  some of the amps in the desk (echo send etc.) utilized the V72's built in bass filter that was engaged by leaving the tuchel connector pins 2a & 2b open which puts an internal 1uF cap in the middle of the input transformer windings.  However, an additional .25uF was wired across pins 2a & 2b which is then, of course,  in parallel with that internal 1uF.
The now 1.25uF value gives a slightly lower frequency of bass cut off. 
 
« Last Edit: April 10, 2021, 06:33:00 AM by Winston O'Boogie »
D. J. H.

The standard way to reduce much of the noise and distortion in audio gear in 1955 was to have a couple of beers.
 Anything else was too fiddlesome and too expensive.


 

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