Soundcraft 1600/800B

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RogerAF

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First: let me thank you all for a "lively" discussion.
Second: since JR suggests I ask a question, here are some: did anyone read any of the sources I posted? Or all of them? Or none?
Third: I can understand using parallel input resistance to obtain noise figures. I wasn't aware that that was the subject being discussed. Sorry about that.
Fourth: the summing circuit has been around for a long time. It gets its name from its use first in analog computing. It behaves in pretty much the same way with DC--doesn't need to be AC.
Fifth: I appreciate the efforts to educate me in audio electronics. I began my career in the early 80s and recognize I still don't know all there is to know. My thanks.
Sixth: Since I am new to this forum I understand my knowledge and experience are unknown to y'all. A little bit of my CV: I stopped being a working musician at age 30 and went to electronics school. After gaduating, I began working as a service tech for a concert sound company in Honolulu in the mid-80s. I branched into recording studio service in the late 80s. I was the only independent electronic tech serving Honolulu for almost 20 years (1987-2007). I have worked on consoles by Amek, MCI, Neve, Soundcraft, SSL, and Yamaha; among God only knows what others. I can't think of a single one of those that has a different basic summing design--inverting summing op amp. Perhaps my understand of the technical electronic engineering principals is flawed--I'm still a guitar player at heart. I have designed and built mods, and custom interfaces, and even though retired now, I still fiddle around with stuff that interests me. Like audio electronics.
I promise not to jump on every thread and pontificate on things I know little or nothing about. I will always try to be polite and well spoken. If someone knows more than I about a subject, I hope to be a good student. New knowledge is always welcome.
 

JohnRoberts

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First: let me thank you all for a "lively" discussion.
welcome
Second: since JR suggests I ask a question, here are some: did anyone read any of the sources I posted? Or all of them? Or none?
none. I did look at the links to see if they looked like new information.
Third: I can understand using parallel input resistance to obtain noise figures. I wasn't aware that that was the subject being discussed.
what is the subject being discussed? This is thread from 2020 awoken from the dead by a drive by post about op amps.
Sorry about that.
Fourth: the summing circuit has been around for a long time. It gets its name from its use first in analog computing. It behaves in pretty much the same way with DC--doesn't need to be AC.
I recall an old analog computer in the college basement when I was freshman (Northeastern 1960s, I did not graduate). Analog consoles are just glorified analog computers (with more bells and whistles).
Fifth: I appreciate the efforts to educate me in audio electronics.
Life is short, we mainly try to answer questions to solve specific problems. Thus my requesting a specific question we might answer. Do not assign me homework.... teach.
I began my career in the early 80s and recognize I still don't know all there is to know. My thanks.
like most of us, but some started earlier than you did.
Sixth: Since I am new to this forum I understand my knowledge and experience are unknown to y'all. A little bit of my CV: I stopped being a working musician at age 30 and went to electronics school. After gaduating, I began working as a service tech for a concert sound company in Honolulu in the mid-80s. I branched into recording studio service in the late 80s. I was the only independent electronic tech serving Honolulu for almost 20 years (1987-2007).
If you started mid-late 80s you might not have read my console performance article published in RE/P magazine in 1980.

I have worked on consoles by Amek, MCI, Neve, Soundcraft, SSL, and Yamaha; among God only knows what others. I can't think of a single one of those that has a different basic summing design--inverting summing op amp.
There are indeed a number of different summing topology variants. A search here would probably turn up discussions about them over the last several years. By inverting summing op amp I ASSume you mean VE (virtual earth) one category of the several.
Perhaps my understand of the technical electronic engineering principals is flawed--I'm still a guitar player at heart. I have designed and built mods, and custom interfaces, and even though retired now, I still fiddle around with stuff that interests me. Like audio electronics.
I promise not to jump on every thread and pontificate on things I know little or nothing about. I will always try to be polite and well spoken. If someone knows more than I about a subject, I hope to be a good student. New knowledge is always welcome.
Sorry if I came down hard on you, but offering to teach electronics to Abbie is not reading the room very well.

Of course you are welcome and might help raise the IQ around here, but don't underestimate the audience.

Maybe do a few searches and absorb some of the wealth that has been shared and accumulated around here over the years.

Welcome to the scrum

JR
 

Newmarket

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re "In any case, the input resistance as seen from the Op Amp has no relationship to how many RIns are connected. The output gain is still a condition of RF's value. For RF = any single RIn, (and all RIn being equal) then Av = 1."

The second sentence there is true relative to an input signal. But the first is clearly not the case.
The input resistance "seen" by the op amp does not determine the signal gain of an individual input - that is indeed -Rf/Ri.
But it does determine the "noise gain" - regard the circuit as a non-inverting amplifier configuration with all input resistances tied to 0V.
And that is the gain at which the op amp is working. So the more channels, the higher the op amp closed loop gain, reduced NFB...
 

Matt Syson

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Borrowed from Roger AF {Analog consoles are just glorified analog computers (with more bells and whistles}.
As an observation, Digital consoles are hanging on the coat tails of the computer industry, much like the audio world following the 'development' of a universal gain block (op amp) which made putting audios systems together considerably easier. Then some damn fool put them into tiny plastic chips so ruining the 'art' of many designs.
 

JohnRoberts

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Borrowed from Roger AF {Analog consoles are just glorified analog computers (with more bells and whistles}.
Actually borrowed from my comment in response to roger AF's mention of op amps coming from analog computing.
As an observation, Digital consoles are hanging on the coat tails of the computer industry, much like the audio world following the 'development' of a universal gain block (op amp) which made putting audios systems together considerably easier. Then some damn fool put them into tiny plastic chips so ruining the 'art' of many designs.
Actually digital audio is not driven by the computer industry but by consumer audio industry... Pro audio is a flea, on the tail, of the consumer audio dog. I've watched this relationship play out for decades and we all benefited from the hand me down technology.

There is art and creativity in circuit design but only few get to see and appreciate it. This forum is one of they few looking under the covers.

JR
 

RogerAF

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Pro audio is a flea, on the tail, of the consumer audio dog.
Well yes, but we have come a long way from hanging one microphone over the conductor's head to capture the orchestra. (My grandmother had many 78rpm discs that were recorded in this way.) The dog used to be a Chihuahua, now it's a St. Bernard.
 

JohnRoberts

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My father worked for Western Electric back in the 30s... He sent over to England to record the coronation of King Edward VIII (1937) for newsreels.

[edit actually coronation of King George VI in 1936... my memory can suffer about events that occurred before I was born /edit]

In the 50s he was a recording engineer in NYC for RCA. Nipper was a fox-terrier mix, the consumer audio dog is a mutt..

JR
 
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Winston OBoogie

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My father worked for Western Electric back in the 30s... He sent over to England to record the coronation of King Edward VIII (1937) for newsreels.

Edward abdicated 5 months before the planned coronation so that must have been a pretty long trip for your dad ;)
 

JohnRoberts

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Thanks for the royal family history not my area of expertise or interest. My fathers gig over there was before I was born so I am operating from family heresay and dots I have connected from his work papers. He died in the 1950s when I was still a young puke so I never had a proper chat with him about his career.

JR

PS: I just dug out his boat passage receipt. $375.55 round trip purchased august 14, 1936 (NYC to Plymouth, and back leaving from Southhampton). The passage was paid for by ERPI, his employer at the time. I just searched coronations again and get George VI this time (DEC 1936). This timeframe is more consistent with his SS Statendam passage.
 

Winston OBoogie

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Yep, that sounds right John. I wasn't trying to be a smartass, I knew Edward was never actually "crowned" but I had to look up dates etc too.

Edward abdicated in December 1936, and the coronation of his brother George went ahead on the same date as had been arranged for Edward, which was 12 May 1937. So it may be that your father was indeed in London for quite some time.

Given the public interest there must have been in the US with Edward wishing to marry Wallis Simpson, an American citizen, it's actually quite something that your dad was chosen as the man tasked with recording the event.

I'm not a royalist, but I'm very interested in history. Especially if it also involves 1930's Western Electric and 1950's RCA 👍


Edit: I had to look up ERPI, thanks for the prompt. All the big players of the time involved, including JFK's father.

Corrected spelling, and reversed inadvertent gender reassignment.
 
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JohnRoberts

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Especially if it also involves 1930's Western Electric and 1950's RCA 👍


Edit: I had to look up ERPI, thanks for the prompt. All the big players of the time involved, including JFK's father.
erpi.jpg

If you like history, here is a postcard sent to my dad by Stan Watkins a big dog from ERPI days. ... My dad also worked at Vitaphone the first sound movie company, a joint venture between WE and Warner Brothers.

JR

[edit some of those references are obscure... back in the early days of sound movies, WE/ERPI/warner Brothers ran a sound stage in NYC (Flatbush). They had to deal with leaky roofs, pigeons, subway noise, et al. Mammy was from 1927 "Jazz Singer" movie, sung by Al Jolson in black face. /edit]
 
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Winston OBoogie

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View attachment 83487

If you like history, here is a postcard sent to my dad by Stan Watkins a big dog from ERPI days. ...

Oh wow, that's very cool John. I actually came across the name Stan Watkins while reading up on ERPI earlier today. That's a great memento/artefact you have there.
His son is currently working on a documentary about Stan (looking for more funding still but...), I bet he'd love to see that picture. Here's a link if you feel like contacting him:

Thanks for the background info too :)




So, it actually occured after she had a gender reassignment? :LOL:

Damn, I actually typed Wallis* but didn't check before it posted and my stupid laptop autocorrected it and decided to change their/her/his/them/it's gender in the process.

Cheers ;)

* I must have watched far too many of those Wallace and Gromit porno movies or something!
 

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Winston OBoogie

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I tried to leave a message but lame wordpress website was too needy.

JR
Damn, that's too bad. I hear ya on not wanting to give up too much info just so's to leave a message.
I was watching a YouTube video earlier from the current head of Bell Labs on the project. Maybe I'll see if I can get a real email address of someone through my significant other's YouTube account.
 

JohnRoberts

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nah I tried and jumped through several hoops... but the website is canned software blogish... we'll see if he gets my message or not.

I am not that hard to find on the WWW, just last week I was answering repair questions about a SKU I designed 40 years ago...

JR
 

Winston OBoogie

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nah I tried and jumped through several hoops... but the website is canned software blogish... we'll see if he gets my message or not.

I am not that hard to find on the WWW, just last week I was answering repair questions about a SKU I designed 40 years ago...

JR

Haha :D 40 years is good going if it only now needs help.


Got ya on the blog message. Maybe the one you sent gets through.
 
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JohnRoberts

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Haha :D 40 years is good going if it only now needs help.
it was an audio test set. the guy banged the sine wave output with 350V DC while trying to inject signal into a tube circuit.

I had clamp diodes on the output line but that wasn't enough to protect it. He got it working again by replacing two damaged op amps.

JR
Got ya on the blog message. Maybe the one you sent gets through.
 
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