Re: Audio Historians - REDD/RCA
« Reply #20 on: March 12, 2021, 07:25:05 PM »
Last posts tonight as I can't deal with this computer. 

From the EMI archives in Hayes, hidden away are 'minutes' of the meetings from the time.

I've posted this before, but it's worth remembering how much a REDD.37 cost EMI at the time  - £12,000 to them, which they marked up by a thousand £'s for EMI Europe desks.  And why not, if you control the purse strings!
 
Whatever.  That's A LOT of 1957/1958 money!   Inflation puts it up there in "a nice villa instead' territory if someone wanted to build one exactly the same today:


Edit:  Also note that the desks for the rest of Europe were designated either 'pop' or "classic"
This was the eq type and was fixed in place on those desks.
 
EMI St.John's Wood (& the EMI classical recording location venue Kingsway Hall too I believe) had the only desks where the eq was switchable by inserting (plugging in) a box containing different reactive elements (L's & C's) underneath the EQ "T" attenuators.
On those desks you could easily see the eq type on an engraved  label showing through a wee oval window on the control surface.   

So all in, it cost EMI UK £1000 less than Italy et al. - for desks with twice as many limited (primitive?) eq options!      :D


« Last Edit: March 12, 2021, 07:54:40 PM 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.


Re: Audio Historians - REDD/RCA
« Reply #21 on: March 12, 2021, 07:29:32 PM »
And £4,000 less, at  £8,000 total for the firstREDD.51, which used EMI's 'in-house' REDD.47 amps instead of buying Siemens & Halske V72S'

A lot of money saved on the 51 except, I don't believe this accounted for man hours needed to build the amps as, the folks who did that work were already on salary building other stuff that EMI were involved in such as T.V. systems (EMI cameras & switchers etc. were considered the dog's bollocks in the UK at the time), defense contracts (too secret to mention, even now, 60 yrs later! ...  O.S.A and all that ;) ),  tape machines (BTR-2's for the BBC) , consumer audio stuff etc.
Still a lot of dosh for the time whichever way you look at it though:



« Last Edit: March 12, 2021, 08:08:16 PM 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.

Re: Audio Historians - REDD/RCA
« Reply #22 on: March 12, 2021, 07:47:24 PM »
AMAZING! Let me chew a pot of coffee and make notes on these conversations.

Thanks Gang! Feels like a Scooby Doo mystery is unfolding :)
If you are curious, you'll find the puzzles around you. If you are determined, you will solve them.
Erno Rubik

ruffrecords

Re: Audio Historians - REDD/RCA
« Reply #23 on: March 13, 2021, 10:54:20 AM »
There should be quite a bit of EMI and RCA info in the Tech Docs section here.

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: Audio Historians - REDD/RCA
« Reply #24 on: March 14, 2021, 05:28:43 PM »
There should be quite a bit of EMI and RCA info in the Tech Docs section here.

Cheers

Ian

And what isn't there won't probably be that useful to you if you're building a tube desk in the modern world.

Better to follow something like your approach with your line amp and EQ interpretation.

The REDD's were VERY over engineered, and a lot of the parts are made of unobtanium such as the Painton 200 ohm "T" faders.   You could build 32 position rotary switches with the same taper (which I've done), but, why?

The EQ is also not practical to build on a small scale as none of the inductor values are anywhere near stock values.  It was also just a non selectable (unless you change the plug-in box) 2 band EQ.   

EMI had a factory in Wales which wound all their transformers and inductors.  We don't have that luxury.
They could also call Painton and have a specific value and taper switch or fader made up.   
The cost to tool up and build Painton type faders with silver contact studs today would be astronomical.
 
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: Audio Historians - REDD/RCA
« Reply #25 on: March 14, 2021, 06:13:10 PM »
Noted. Got some docs to review. Thanks

Should be known we are focusing on the CTC designs. All other elements we are researching are for audio recordings of our programs. Building a narrative is important and we appreciate all the great info in this thread. There are dozens of covnersations we can pull from.

Yes, the Painton fader has been a on/off discussion here at the house. Its becoming irrelevant as we get closer to designing/building out our fader sections.

Wall
If you are curious, you'll find the puzzles around you. If you are determined, you will solve them.
Erno Rubik

Re: Audio Historians - REDD/RCA
« Reply #26 on: March 14, 2021, 07:03:41 PM »

Should be known we are focusing on the CTC designs. 

OK sounds good.

Ian's approximation of the REDD EQ and how he's configuring his amps and his desks is perfectly fine, uses excellent engineering practice,  and makes it all doable and more flexible in the modern world. 

I have a goal I set myself recently, to build a mini valve desk for myself.  It'll be a slow, 2 year project.  Maybe longer... ?
Anyway, even though I have all the docs for the REDD's, what I did was enter the original REDD circuit elements off the EQ's etc.  into a simulator to see the curves.
I then took an approach similar to Ian's and just matched the curves using an easier to implement topology -  just as Ian did with his EQ.   
Slight differences with what I'm playing with and what Ian did, but nothing that means a 'hill o' beans' in real use.

Oh, almost forgot:  I won't be using Painton constant z faders either  ;)   Penny and Giles, TKD's, or good but lesser expensive similar types it'll be. 

1K log is where it sits right now, but I reserve the right to upscale things to 10K in the next 2 years ;)
 
« Last Edit: March 14, 2021, 07:13:09 PM 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.

Re: Audio Historians - REDD/RCA
« Reply #27 on: March 15, 2021, 05:25:19 AM »
Thank you very much indeed Winston. Great reading!

Re: Audio Historians - REDD/RCA
« Reply #28 on: March 15, 2021, 11:54:40 AM »
Thank you very much indeed Winston. Great reading!

Thanks Warpie.

There's some info that's historically interesting as far as pan-pots and the 'bass-boost' switches that were incorporated into the REDD desks that some might find noteworthy.  I'll write a little blurb off line and paste/post it here later.
Current online situation keeps crashing on me and I end up losing most of what I wrote so... 

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: Audio Historians - REDD/RCA
« Reply #29 on: March 15, 2021, 03:55:07 PM »


There's some info that's historically interesting as far as pan-pots and the 'bass-boost' switches that were incorporated into the REDD desks that some might find noteworthy.  I'll write a little blurb off line and paste/post it here later.
Current online situation keeps crashing on me and I end up losing most of what I wrote so...

Thanks for all the info Winston,  it was a joy to read over the weekend.
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.


Re: Audio Historians - REDD/RCA
« Reply #30 on: March 15, 2021, 03:59:25 PM »
Passive switchable ’Bass Boost’ or “10dB pad” before the microphone signal even hit the first amplifier (whether V72S or REDD.47)
Note:  Not the bass control of the eq:

The REDD desks, starting with the REDD.17, and even more so with the REDD.37 & REDD.51, were designed with stereo recording of classical music in mind.
Classical was the only genre issued in stereo by EMI at the time (late 1950’s).  Everything considered ’Pop’ was issued strictly in mono.

There were 2 stereo techniques used by EMI at this time - the  90 degree angled pair of figure of eights  pioneered by EMI’s own Alan Blumlein in the 1930’s, and the mid-side technique which was favoured when there needed to be some control of how much free field reverberation was part of the signal.

By then, the mics used for for classical were condenser type rather than ribbon so:  - M49, KM56, U47/U48 etc. 

In figure-eight setting, all these mics ( and all other) condenser mics have a bass deficiency when placed in mid and far field positions. 

Therefore, each channel of a pair  had a bass boost circuit to compensate  for this.   Since this was passive and at mic level, there was loss at mid frequencies involved - about half loss caused by the pad and reactive capacitor values, and about half loss caused by loading on the mic.
In total, the loss was 10dB.

In crossed figure-eight mics, the bass boost was applied to both mics. 
In mid-side, the boost was applied to the ’side’ microphone and a straight 10dB pad (same circuit minus the capacitor) was applied to the ‘mid’ mic so that mic sensitivity was equal on both channels.

     
Sum and Difference next…
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: Audio Historians - REDD/RCA
« Reply #31 on: March 15, 2021, 04:02:22 PM »
Thanks for all the info Winston,  it was a joy to read over the weekend.

Cheers my man  :)
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: Audio Historians - REDD/RCA
« Reply #32 on: March 15, 2021, 04:26:04 PM »
There were two sets of "stereosonic" channels on the '37 and '51, these were the channels which also accepted the line inputs (via a 20:1 transformer) from the tape machine.  On the above desks these were channels 1 + 2 on the very left, and channels 7+8 on the very right.
There were no pan pots on these channels as stereo, in the minds of EMI at the time, meant 2 sets of stereo recorded material.  Say, stereo orchestra on tape tracks 1 & 2, and stereo soloist or whatever on tape tracks 3 & 4.
IOW, stereo wasn't envisioned as being compiled from a bunch of pan'ed mono sources.
If, during recording, a spot microphone was needed, then that microphone would be run through another desk channel: 3, 4 & (4a), 5 & (5a), or 6 which did have pan pots, and then placed in the stereo field being recorded through the stereosonic channels.

These stereo sonic channels had two sets of sum and difference transformers (transformer A14), one set before the EQ and faders, and one set after.

Regardless of whether the source was recorded in M/S S+D or not, the A.14 transformers were designed to be engaged on stereo Classical recordings.
What this meant was that, with a crossed figure eight stereo source, it would then be converted to sum and difference before it hit theEQ and faders.
This meant that, if there was a fader move and one fader accidentally landed on an adjacent higher or lower stud, there wouldn't be a level difference between the two signals, but a slight collapse or expanding of the stereo field.  This was considered less objectionable than a shift of a dB or two in left/right signal.
The whole thing would then be converted back from S+D with the 2nd set of post fader transformers.

When processing Mid/Side, this was already a S+D signal so the first set of A14 transformers were not included in the path, the 2nd set post fader would then convert back to left and right.

All well and good for classical recording.
But what about when 'Pop' began to be released in stereo (mixed from 4 distinct mono channels) and the desk channels used for the tape returns had no pan pots?

More later...


Edit: typos.
« Last Edit: March 16, 2021, 11:43:33 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.

Re: Audio Historians - REDD/RCA
« Reply #33 on: March 15, 2021, 05:05:19 PM »
Little bit about what channels 4 + 4a and 5 + 5a were about.

These channels were the same as channels 3 and 6, except that a 2nd microphone could be switched in and passively mixed with the main mic:  4a with 4 and 5a with 5.
This was at mic level, before the first amplifier, and naturally, there was a -6dB combining loss.

The relative levels of the two mics were adjusted by means of a 2dB per step (20dB max total) attenuator on the "A" channels.  This would then be combined as two 400 ohm sources into one 200 ohm source for the regular mic channel.

This combined signal could then be routed through the "Bass Boost/-10dB stuff I mentioned above, and also the standard "Pre-Set" attenuator which was on all channels.
This "Pre-Set"  attenuator was a 6dB per step pad which went from 0dB to -30dB. 

For loud sources where you can afford the 6dB loss (drum mics) it's actually a neat little circuit to be able to combine 2 mics down one channel.

 


« Last Edit: March 15, 2021, 11:01:24 PM 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.

Re: Audio Historians - REDD/RCA
« Reply #34 on: March 15, 2021, 05:48:31 PM »
As we know, Sgt. Pepper was the first Pop/Rock release where EMI decided to release in stereo as well as mono.

Prior to that, any stereo Pop mix from the time (I'm discounting recent remixes here) was either an afterthought, or in the case of some early Beatles tapes sent to Capitol for US release, simply a mistake where the uncombined twin-track mono was released as stereo with vocals and other little stuff on one side, and the band on the other.

For most Pop mixes, the mixed mono signal was derived from the "Delta" mono combiner which took all 4 tape tracks and allowed a little adjustment of relative level compared to the fader position.  This Delta mono combiner was located under the formica arm rest and, to the best of my knowledge, was rarely touched as it had already been set for accurate mono combining from the fader positions.
 

When there were stereo Pop mixes made, since these tracks came back through the desk on the stereosonic channels, there was no pan-pot.   So all that could be done was a little reduction of the stereo width etc.  That's why that stuff sounds as it does.  It wasn't necessarily a creative decision to have stuff all the way over one side with no real 'phantom' centre, more a limitation of the equipment use.

I don't know at what point the engineers decided to do a little jiggery-pokery with tape tracks and re-patch them to the channels with pan, but at some point, you can hear that they did.

On the pan-pots themselves:  They were initially 11 position and calculated exactly for angle of incidence, with -3dB being the centre (45 degrees**) point.   
11 positions seems more than adequate for classical stuff and being able to place a spot mic accurately in the stereo field, but at some point in the 1960's the pan-pots were converted to 21 position.

The signal for the pans was derived from the faders via an auto former.  The fader signal entered the centre of the auto former, and the signals for pan taken from the top and bottom of the winding.  Pan impedance was then at 400 ohms rather than 200.

For combining the pan signals, this was done at 400 ohms, then run through another A14 transformer (same transformer as used for the Sum and Difference) which then transformed it down to 200 ohms where that signal was combined with any other 200 source from channels 1, 2, 7,  8, or echo etc.

Thus endeth pan-pots and my rambles for now.


**. Edit:  I suppose I should have said that the centre -3dB point be considered 0 (zero) degrees, and that either side of that be considered -tve or +tve degrees up to 45 if total angle is 90.

« Last Edit: March 16, 2021, 11:22:22 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.

Re: Audio Historians - REDD/RCA
« Reply #35 on: March 15, 2021, 05:58:50 PM »
One thing I should have already stated but forgot:

There were only three amplifiers in any one given signal path through the desks.

One being for "Mic" or line in, the second being the "Inter" amp which was the make-up gain after the  EQ, faders etc., and the third amp was the "Output" channel which was after the group/master faders and was the signal sent to tape.   

All the same amps were used throughout, either V72S or REDD.47 depending on the desk.
« Last Edit: March 15, 2021, 11:25:27 PM 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.

Re: Audio Historians - REDD/RCA
« Reply #36 on: March 15, 2021, 06:54:52 PM »
Hopefully, without posting any more schematics etc., what I've written above would allow anyone who's familiar with how things were done in the 1950's (read Tremaine's Audio Cyclopedia if you're not), to basically figure out how the REDDs were designed as far as EQ, mixing etc.

If I missed anything basic out, just ask and I'll answer as best I can.
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: Audio Historians - REDD/RCA
« Reply #37 on: March 15, 2021, 10:37:36 PM »
This is not information I can easily graze over. We are excited to begin disecting this and connecting it to our CTC REDD Card Build. Good times! Thanks all! Winston thanks!
If you are curious, you'll find the puzzles around you. If you are determined, you will solve them.
Erno Rubik

Re: Audio Historians - REDD/RCA
« Reply #38 on: March 15, 2021, 11:17:33 PM »
This is not information I can easily graze over. We are excited to begin disecting this and connecting it to our CTC REDD Card Build. Good times! Thanks all! Winston thanks!

Yep I undestand completely Wall.
I could possibly have written what I did in a more concise or easier to grasp way, but I'm not really that talented a writer and so I just typed out what made sense in my own head. 
Nevertheless, I think I covered the overall scheme and, despite the information overload, I do think there is a lot of info that can be gleaned about the REDD desks from the posts.

As I said before though, just ask if something isn't clear  :)

I did say they were over engineered pieces of equipment and that a lot of what was engineered into them isn't necessarily practical or useful these days...   ???

 8)

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.

EmRR

Re: Audio Historians - REDD/RCA
« Reply #39 on: March 16, 2021, 01:39:12 AM »

I did say they were over engineered pieces of equipment and that a lot of what was engineered into them isn't necessarily practical or useful these days... 

Um, yeah, autoformers to feed pans.  Yeah, why not?
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde


 

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