Retro Hardware: Neve Class-A Microphone Preamp-Only Modules (no EQ!)

Everyone is familiar with the Neve class-A channel amps, especially the 1073 and 1084 which are back in current production (and, of course, those who have read my previous Neve installments now know far more about lots of other models!).  So question: can you name a Neve module that features a class-A mic preamp without the EQ?  "Of course," some of you just said, "I have a pair of 1272's, and they don't have EQ."  The 1272 is probably the most well-known class-A Neve mic preamp module that lacks an EQ, but did you know the 1272 wasn't actually a mic preamp at all?  It was a bus amp used to drive bus outputs, aux sends, etc. on the old, all class-A consoles.  So why has a bus amp become so popular as a mic preamp?  To understand why this is so it is worth briefly discussing what actually made up a proper microphone preamp back in the class-A days of Neve.

Neve's proper class-A microphone amplifier design, used in all their channel amplifiers discussed so far in this series, consisted of a 10468 mic input transformer (a twin-bobbin, hi-nickel affair wound by either Marinair or St.Ives), two, identical preamp gain stages, an output stage, and a large, steel-core output transformer (wound only by Marinair).  Gains up to 50dB are provided by one of the preamp stages and the output stage, while higher gains use both preamp stages with the output stage.  While intended for lower total gains, the 1272 bus amplifier nevertheless makes a great alternative to the proper mic preamp modules in that it shares the same input and output transformers as the mic preamps as well as one of the preamp stages and the output stage.  As such it can be modified for proper mic preamp use up to 50dB total gain.  Above this, however, and you have to squeeze more gain out of one or both stages, which can sound good, but technically differs from the performance of the proper mic preamp design at higher gains.  Whether it is better or worse is in the ears of the beholder... I must say I am personally a fan as evidenced by my own Rascal Audio microphone amplifier designs.

So back in the 1980s, as people started tearing apart older Neve consoles to rack up and sell off the channel amps they were left with lots of 1272 bus amp modules.  Some enterprising folks realized that, given their component compliment, 1272's could rather easily be modified for mic preamp duty, so they got modded and/or sold off as well.  Given the reduced price of these non-EQ capable modules, coupled with their relative abundance (at the time), they quickly became the alternative choice for people who wanted a vintage class-A Neve preamp but who didn't have the coin for a full-blown channel amplifier.

Neve 1272 Bus Amplifier Modules

And in the interest of full-disclosure (and because more informed readers are likely shouting at their computers right about now) I will concede that Neve did in fact use the 1272 as a microphone amplifier... for the talkback mic in some early consoles.  That's it (as far as I have been able to determine).  They apparently never intended them to be used for actual tracking duties. 

As far as actual, proper, class-A microphone amplifier modules that lacked EQ I know of exactly two models Neve made.  One is very much based on their common mic pre design and the other is... well... not.

First up, the 1290.  Housed in a module the exact same size as the 1272 (5.25" H x 1.8" W x 8.5" D), the 1290 featured the full mic preamp treatment with both preamp stages and an output stage.  Because of its limited real-estate, however, the 1290 module only had room for the 10468 input transformer with any output transformer to be used located elsewhere outside the module.  The preamp provides the same 20dB-80dB gain range design as the full blown Neve channel amps had save one practical difference -- no "OFF" position between 50dB and 55dB gain settings. 

Neve 1290 Microphone Amplifier

I mentioned in an earlier post about the various functions handled by the 'gain' knob on Neve channel amps: mic and line pad networks, signal routing between various gain stages, actual gain of one stage, etc.  Remember that gains up to 50dB use only two active gain stages, while the 55dB and above positions use all three.  To avoid a very nasty (and potentially damaging) 'pop' when switching from two to three gain stages Neve engineers thoughtfully put an "OFF" position between them.  On the 1290 their is no such "OFF" position.  Instead Neve used several 12k resistors strategically placed to minimize pop-inducing interaction between the gain stages being routed, and for the most part it worked quite well.  The rest of the design is pretty much straight off the drawings of other class-A channel amps. 

The other facility provided by the 1290 is an input select switch that provides settings for "LZ" (300 ohm) and "HZ" (1200 ohm) mic input loads as well as an oscillator input. 

The 1290 has no fader on it, so any such fader would have to be wired externally.

Interestingly, I don't believe Neve ever coupled the typical, gapped LO1166 output transformer with the 1290 as they did with virtually all other uses of their class-A output stage.  Instead, it appears they loaded the output with a large inductor (wound by Marinair, called a T1310) and then took the output signal, unbalanced, from the collector of the large 2N3055 output transistor.  While this works just fine I personally prefer the tone of proper output transformer instead.  Oddly, I was actually reprimanded by one Neve modder/technician many years back for even suggesting the use of an LO1166 output transformer with a 1290 as, according to him, it wouldn't function properly.  But clearly the output stage is the identical design used in all the class-A gear Neve built, and it works brilliantly.  I guess he was glued to the schematic which showed only the inductor/unbalanced output arrangement. 

The only remaining class-A, true microphone preamp that Neve ever built was an odd little jewel given the designation "B002."  I must confess I am a bit in the dark about the history of this module and its actual application, but clearly it is a microphone amplifier, all class-A (using the same two gain stages found in a 1272, btw), providing a maximum gain of only 50dB, using a gain arrangement unlike anything else I have ever seen from Neve.  Unlike most other Neve mic preamps of this era the input was hardwired to present the microphone a 1200 ohm load (instead of being switchable between 300 and 1200).

Neve B002 Six Pack

Neve B002 Module

From what I have been able to gather these were generally mounted in groups of six which formed a little 2-bus mixer of sorts to be used as needed to expand the total available inputs of a Neve desk.  There are several unique features of this preamp:

Firstly, the B002 is the ONLY Neve class-A preamp I know of to use what we might refer to today as a proper input pad.  The gain switch design uses 4 gain settings of its preamp stage, along with a -20dB pad and a -40dB pad to achieve the total net gains available from the unit.  These pads are balanced, placed at the input transformer's primary like a normal mic pad is these days (whereas the pad positions on the typical Neve class-A mic preamp are unbalanced, placed between the input transformer's secondary and the first active gain stage). 

At the unity ("0") position on the B002 we have 40dB of total gain with a -40dB pad in front of the input transformer.  The next gain position jumps the active gain up 5dB, the next 10dB, and then it drops the actual gain back down 15dB while switching the input pad from -40dB to -20dB for of 15dB total module gain.  Then gain up another 5, 10 and 15dB, and then gain back down -15dB and remove the -20dB pad altogether for 35dB of total gain, etc.  A rather different approach to gain staging, but seeing as the modules are only designed to provide 50dB of gain the design, while unique, is simple and effective. 

There is also provided a 10k audio taper potentiometer wired as fader between the preamp gain stage and the output gain stage.  Each B002 provides assignments for 2 unbalanced busses along with an unbalanced solo buss selection as well. (I believe the B002 six pack at Steve Albini's Electrical Audio has been modified to provide transformer balanced outputs for all three of these available output busses, creating a rather niftly little class-A Neve submixer).

The other thing that makes the B002 unique compared to all other class-A modules is that its output stage, while identical to that used in all other Neve class-A gear, isn't inductively loaded (using either the primary winding of an output transformer or an actual inductor).  Instead the B002's output is loaded with a resistor and the output signal is sourced from the collector of the output transistor (where one side of an LO1166 output transformer's primary winding is usually connected).  This unbalanced output is fed through a pair of 80uF capacitors in parallel to block the approximately 70mA of DC coming off this connection.  This signal is then coupled to the busses by way of switches and buss resistors.  No output transformers or inductors are used at all.  I know of no other class-A output arrangement in the world of Neve that isn't inductively loaded.

I have never personally used, or ever even touched, a B002, so I cannot speak directly about its performance, but I suspect, given its design, that it sounds very solid and focused, though a bit more neutral owing to the missing output transformer that is such a big part of the classic Neve girth. 

So there you have it!  This post wraps up discussion of all the actual class-A Neve mic preamps I have ever been aware of up to this point.  I am always eager to learn about more, so if you know of models not covered in this series of posts, or if you have more information about modules I have discussed (or corrections), please do share, as I would love to know and share myself.

Thanks for reading!