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Author Topic: How the NEVE 1073 works??  (Read 32862 times)

opacheco

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How the NEVE 1073 works??
« on: September 20, 2010, 02:04:55 pm »

Hi,
I readed some post about the 1073 NEVE preamp in many places and forums in the web, but none of them explained in detail how it works electronically.

Do you know how it electronically works???....We might think that the BA283
and BA284 cards as discrete op amps controlled by external
resistors(feedback netwoks)???...How can this be???...which ones simulte these feedback resistors in its schematics???

It will be interesting to give a mayor serious electronic analysis for this kind of vintage equipments in order to know in deep its technical implications...Do you??

I would like to get the overall tecnical performer/funtionality of this
pre??

I will appreciate any comment about.
Thanks for your time.
Opacheco.
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Opacheco
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ssltech

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Re: How the NEVE 1073 works??
« Reply #1 on: September 20, 2010, 03:06:08 pm »

I get the impression that if you're struggling to see how it works, you may struggle with any explanation you receive here.

Keith
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MDM (maxdimario) wrote on Fri, 16 November 2007 21:36

I have the feeling that I have more experience in my little finger than you do in your whole body about audio electronics..

opacheco

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Re: How the NEVE 1073 works??
« Reply #2 on: September 21, 2010, 02:00:27 pm »

ssltech wrote on Mon, 20 September 2010 14:06

I get the impression that if you're struggling to see how it works, you may struggle with any explanation you receive here.

Keith



Yes, ofcourse, I will do.

Thanks
Opacheco.
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Opacheco
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sshhh....Tone is the Big Secret!

Nick Sevilla

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Re: How the NEVE 1073 works??
« Reply #3 on: September 22, 2010, 09:19:31 am »

Hi,

Do you have a degree in Electronics?

Cause you'll need one...

Simply put :

Great sound in, even better sound out.

Copying the 1073 sound is not impossible, but it is expensive.

Cheers
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sodderboy

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Re: How the NEVE 1073 works??
« Reply #4 on: September 22, 2010, 10:32:08 am »

If you haven't already, download the manual at amsneve.com.  They also have the 1081.  There is a block diagram, schematics, and they have circuit descriptions.  You can read the block like a roadmap, and the schemo the same way but deeper.

You can also do the same with Urei LA-2A, LA-3A, dbx 160 and 161.  They all have block diagrams, schematics, and circuit descriptions.

Specifically, the 283 is 2 opamps and the 284 is three on one card.  The manuals show this.
Mike
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John Klett

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Re: How the NEVE 1073 works??
« Reply #5 on: September 28, 2010, 11:44:44 am »

As above… explaining to a neophyte, in any detailed way, exactly how an entire collection of circuits and components go together to make something like a 1073 module work as it does is… not practical in a forum like this.  It's not like this is particularly esoteric stuff but there are lots of different bits of information that all has to be explained and tied together.  All these bits can be found in various forums but if you really want to know you really have to start with the basics and follow some structured path.  The are some good books on electronics… typically you would need to look around for used books to find much useful info on how transistor amplifiers and active analog equalizers and filters work but the info exists.  Doing D.I.Y. work helps but the painting by numbers approach only gets you so far.  Doing D.I.Y. and reading and having a schematic in front of you is not bad…  and if you get some project to work using the paint by number technique you can then multiply your learning by messing with it.  I have learned a bunch of stuff by breaking and then fixing things…  what happens if I change this part "oops the smoke got out…  why did the smoke come out…  hmmmm…  and so on".

anyway - reading and building and fixing…  rinse and repeat

now - actually the reason I decided to post was to pick nits on the term "operational amplifier" with respect to old discrete Neve modules.

Actually none of the amplifiers in a 1073 module are "opamps" and, as far as I know, Neve never employed a fully discrete operational amplifier in any of their designs.

An opamp or operational amplifier is a high-gain DC-coupled amplifier with differential inputs, and they are called operational amplifiers because their original application was in analog computing where they were configured for various mathematical operations.  The original opamps were vacuum tube based and made useful primarily by Philbrick.  Philbrick later moved to solid state devices.  Teledyne Philbrick, Analog Devices, Burr Brown and others produced discrete transistor opamps in what we now refer to as a 2520 footprint.  This was well before Saul Walker (at Melcor and API) came up with what became the actual 2520 opamp.

Walt Jung wrote a decent history re opamps…

http://www.analog.com/library/analogDialogue/archives/39-05/ Web_ChH_final.pdf

and for some insight into Philbrick...

http://www.philbrickarchive.org/

back to Neve

The five amplifier circuits used in classic Neve modules (three types in the 1073 "class A" family and two types in the 1081 "class AB" family - and I'm not counting followers here) are simply discrete amplifiers and, despite the fact that in some of the Neve documentation the term "operational amplifier" is mentioned, these are not "op amps" in the sense that they can be programed to do many different things. They are all purpose built.

Neve amplifiers can use some external feedback like a true opamp does but most of the feedback is local to the module or card and none of the amplifiers have fully differential inputs, nor do they possess nearly as much "open loop" gain as opamps do.  The two amplifiers (not counting the followers) used in 1081 modules have more inherent gain but negative feedback is applied locally on the amplifier module and gain may be increased by shunting some of that feedback to ground…  but you have nowhere near the 100+ dB "open loop" gain typical in a general purpose operational amplifier.

So…

In a 1073 module there are three types of amplifiers.  

On the 284 board there are two inverting amplifiers used for the EQ circuits.  These are three transistor amplifiers that are inverting only.  There is one transistor used for voltage gain followed by two transistors set up for current gain.  

The second amplifier type used in the 1073 is a three transistor pre-amplifier with more voltage gain.  There is one on the 284 board and one on the 283 board.  This has two transistors set up for voltage gain and the third is used as a follower for the output.  One or both of these preamplifiers are used in conjunction with the sensitivity switch to set the gain of the mic/line preamp in the module.  The second preamp is switched in only at high gains because a single preamp of this configuration does not have enough gain to do much more than 35dB of gain while at the same time keeping enough feedback around it to maintain low distortion.  

The third amplifier type in a 1073 module is the output amplifier that is on the 283 board.  This is also a three transistor amplifier that has some voltage gain in the first transistor and then significant current gain in the two transistors that follow.  This is called a single element class A circuit in that the large TO-3 output device is working by itself to vary the current passing through the primary of the output transformer, as opposed to working into an active current source or in push pull like the later class AB output pair on the BA240/340/440 output amplifiers used in 1081's etc.

The amplifiers in a 1081 module have more inherent voltage gain and can therefore maintain linearity at higher gains, so in a 1081 module you see only one preamp module used for the entire gain range in the sensitivity switch.  

The BA338 preamp (BA238/338/438) uses five transistors.  This is a class A amplifier in that all devices are always conducting.  One of the two output devices is a current source and the other is a current amplifier (or a follower).  There is an inverting and non-inverting input but they are not configured in the traditional "long tail pair" you would find in most opamps and really can't be used, say, as a differential amplifier…  both both pins are there so the EQ elements can feed back into to "-" input but other characteristics one would ascribe to general purpose operational amplifiers are not present here.  

The BA340 output amplifier (BA240/340/440) has a similar "front end" to the 338 preamp but there are eight transistors used in this amplifier and the output pair is biased class AB…  meaning that when idling and with low level signals both output devices are conducting (class A) but as the amplifier swings it's output wider one of the two devices is no longer conducting so the amplifier is operating class B at those times.  The transition points or crossover points where we move from Class A to Class B operation is managed by TR5 which spreads the bases of the output pairs enough so they both conduct some current at midpoint (idle) but not so much that they short the supply and cook the parts.  An advantage of class AB outputs is that they can deliver more current to a load over a wider portion of output swing without requiring a lot of current in idle…  so the 440 can be smaller and use less current than the output on a 283 card.

ALL of these amplifiers are AC coupled…

as far as how the modules around these amplifiers actually work - someone else will have to pick that up - I am out of time and have to move on.

Read, Build, Break, Fix, Rinse, Repeat
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Dusk Bennett

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Re: How the NEVE 1073 works??
« Reply #6 on: September 29, 2010, 02:17:01 pm »

John Klett wrote on Tue, 28 September 2010 08:44

As above… explaining to a neophyte, in any detailed way, exactly how an entire collection of circuits and components go together to make something like a 1073 module work as it does is… not practical in a forum like this.  It's not like this is particularly esoteric stuff but there are lots of different bits of information that all has to be explained and tied together.  All these bits can be found in various forums but if you really want to know you really have to start with the basics and follow some structured path.  The are some good books on electronics… typically you would need to look around for used books to find much useful info on how transistor amplifiers and active analog equalizers and filters work but the info exists.  Doing D.I.Y. work helps but the painting by numbers approach only gets you so far.  Doing D.I.Y. and reading and having a schematic in front of you is not bad…  and if you get some project to work using the paint by number technique you can then multiply your learning by messing with it.  I have learned a bunch of stuff by breaking and then fixing things…  what happens if I change this part "oops the smoke got out…  why did the smoke come out…  hmmmm…  and so on".

anyway - reading and building and fixing…  rinse and repeat

now - actually the reason I decided to post was to pick nits on the term "operational amplifier" with respect to old discrete Neve modules.

Actually none of the amplifiers in a 1073 module are "opamps" and, as far as I know, Neve never employed a fully discrete operational amplifier in any of their designs.

An opamp or operational amplifier is a high-gain DC-coupled amplifier with differential inputs, and they are called operational amplifiers because their original application was in analog computing where they were configured for various mathematical operations.  The original opamps were vacuum tube based and made useful primarily by Philbrick.  Philbrick later moved to solid state devices.  Teledyne Philbrick, Analog Devices, Burr Brown and others produced discrete transistor opamps in what we now refer to as a 2520 footprint.  This was well before Saul Walker (at Melcor and API) came up with what became the actual 2520 opamp.

Walt Jung wrote a decent history re opamps…

 http://www.analog.com/library/analogDialogue/archives/39-05/ Web_ChH_final.pdf

and for some insight into Philbrick...

http://www.philbrickarchive.org/

back to Neve

The five amplifier circuits used in classic Neve modules (three types in the 1073 "class A" family and two types in the 1081 "class AB" family - and I'm not counting followers here) are simply discrete amplifiers and, despite the fact that in some of the Neve documentation the term "operational amplifier" is mentioned, these are not "op amps" in the sense that they can be programed to do many different things. They are all purpose built.

Neve amplifiers can use some external feedback like a true opamp does but most of the feedback is local to the module or card and none of the amplifiers have fully differential inputs, nor do they possess nearly as much "open loop" gain as opamps do.  The two amplifiers (not counting the followers) used in 1081 modules have more inherent gain but negative feedback is applied locally on the amplifier module and gain may be increased by shunting some of that feedback to ground…  but you have nowhere near the 100+ dB "open loop" gain typical in a general purpose operational amplifier.

So…

In a 1073 module there are three types of amplifiers.  

On the 284 board there are two inverting amplifiers used for the EQ circuits.  These are three transistor amplifiers that are inverting only.  There is one transistor used for voltage gain followed by two transistors set up for current gain.  

The second amplifier type used in the 1073 is a three transistor pre-amplifier with more voltage gain.  There is one on the 284 board and one on the 283 board.  This has two transistors set up for voltage gain and the third is used as a follower for the output.  One or both of these preamplifiers are used in conjunction with the sensitivity switch to set the gain of the mic/line preamp in the module.  The second preamp is switched in only at high gains because a single preamp of this configuration does not have enough gain to do much more than 35dB of gain while at the same time keeping enough feedback around it to maintain low distortion.  

The third amplifier type in a 1073 module is the output amplifier that is on the 283 board.  This is also a three transistor amplifier that has some voltage gain in the first transistor and then significant current gain in the two transistors that follow.  This is called a single element class A circuit in that the large TO-3 output device is working by itself to vary the current passing through the primary of the output transformer, as opposed to working into an active current source or in push pull like the later class AB output pair on the BA240/340/440 output amplifiers used in 1081's etc.

The amplifiers in a 1081 module have more inherent voltage gain and can therefore maintain linearity at higher gains, so in a 1081 module you see only one preamp module used for the entire gain range in the sensitivity switch.  

The BA338 preamp (BA238/338/438) uses five transistors.  This is a class A amplifier in that all devices are always conducting.  One of the two output devices is a current source and the other is a current amplifier (or a follower).  There is an inverting and non-inverting input but they are not configured in the traditional "long tail pair" you would find in most opamps and really can't be used, say, as a differential amplifier…  both both pins are there so the EQ elements can feed back into to "-" input but other characteristics one would ascribe to general purpose operational amplifiers are not present here.  

The BA340 output amplifier (BA240/340/440) has a similar "front end" to the 338 preamp but there are eight transistors used in this amplifier and the output pair is biased class AB…  meaning that when idling and with low level signals both output devices are conducting (class A) but as the amplifier swings it's output wider one of the two devices is no longer conducting so the amplifier is operating class B at those times.  The transition points or crossover points where we move from Class A to Class B operation is managed by TR5 which spreads the bases of the output pairs enough so they both conduct some current at midpoint (idle) but not so much that they short the supply and cook the parts.  An advantage of class AB outputs is that they can deliver more current to a load over a wider portion of output swing without requiring a lot of current in idle…  so the 440 can be smaller and use less current than the output on a 283 card.

ALL of these amplifiers are AC coupled…

as far as how the modules around these amplifiers actually work - someone else will have to pick that up - I am out of time and have to move on.

Read, Build, Break, Fix, Rinse, Repeat



This should be a sticky.

Hard to imagine that my API transistors could also be used to add 2+2. I just figured they were signal amplifiers.
Dusk
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Dusk Bennett
Artist Development/Production
Audio Engineering
Los Angeles CA
www.duskbennett.com

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