First impressions

[chriscavell]

As an engineer who has had the great pleasure of using some phenomenal vintage equipment and boards, I thought I'd give a couple of my first impressions about the 4 N72's and 4 A12's (with SC25 opamps set to 18volts) that I recently finished building. Just a quick note before reviewing: i grew up on API consoles and absolutely love them. They seem to be few and far between lately though, and usually find myself on Neve 80 series. I may have a little bias toward API as a result...

First the A12:
In much the same way that people often describe Dirk Brauner's mics as "pre-war Neumann, only better"...that's how I'd describe the A12...definitely like an API, just more. I find the bottom end to be more defined and clearer when compared to standard API X12 pre's (3124, 512, etc). The top end is pleasant and seems to extend forever without any harsh quality to it, very much like API - but not as dark sounding. If I'm not in absolute need of some eq before tape (which is rare these days - I tend to shoot for the sound I'll use in the mix with instrument and mic selection/placement), I'd probably reach for this module over my API's every time. I wouldn't hesistate to use this pre on every track for certain genre's...like small jazz or classical ensembles. Some would reach for more "accurate" pre's (like a jensen twin servo design for instance) for classical and jazz, but i prefer music to be pleasant over accurate any day of the week. In rock or country settings, I'd be more purpose specific in the selection - basically anywhere you want pleasant high's and/or a solid defined bottom end. My final thoughts on the A12's...it's like digging through a box of api 512's and finding a couple gems in the bunch...every A12 would be one of the "gems".

The N72:
If you're familiar with 80 series boards using the Neve BA183 or BA283 design...this sound will be very familiar to you. Not really a complaint, but it's almost a charicature of this sound...the creamy mids are very emphasized, moreso I think than the originals upon which it is based. It's a great forward creamy and pleasant mid range which will dramatically compliment certain tracks...but it's not for everything in my opinion. It's a great way to give emphasis to the chords of a rhythm acoustic being strummed, where other pre's typically emphasize the chanky-chank rhythm of the strumming. Chances are if you're familiar with the above boards, you're typically tracking everything through the board...these pre's would just be a little "more"...you could put them on a lead guitar or vocals to help give it the extra mid and lower mid range oomph to cut through the mix even when tracking everything through a Neve 80 series console.

Overall:

Save placing the modules in the chassis until all of them are built...and wire up the power harness to the last module prior to putting it in the chassis. That 8th slot is a tight fit.

Buy a 4-40 tap. Buy some 3-in-1 oil. Put the oil on the tap. Tap the screw holes. If you don't...you need a stern talking to.

As a rule of thumb, every time you populate polarized caps or diodes, double and triple check orientation prior to soldering.

Another good idea I found to help keep me from forgetting something vitally important on the current revision of the N72...when you start to work on jumpering and prepping the leads of the input transformer, set a penny on the circuit board where you will eventually place it. The penny serves merely as a reminder to grab the fish paper before putting the tranny in place...removing the tranny is NOT something you want to do after the fact.

Biasing the N72:
At first I tried adjusting to 22.2 volts...but the voltage drop across r40 was too great for comfort. If i adjusted for 3.8 volts across r40, the collector voltage seemed too far off expected to be right. So I just biased them the same way I bias other lunchbox pre's around town. I plug a tone plug into the input set for a 1kHz sine wave (it's relatively low output compared to a separate signal generator). Crank up the gain all the way (with a hotter signal than a tone pulug you won't need to do this). I hook up the o-scope as described in the fine-bias instructions...though I adjust scale divisions to magnify the signal as much as possible without going off the screen, and I show just one cycle of the wave. I turn up the trim until i barely begin to see clipping. Rather than bias for symmetry in clipping as in the instructions, I bias so that both begin to clip at the exact same point. On most amps this would be the same thing by any other name, but on class A neve's, setting for symmety with easy to see harsh clipping will result in one side of the waveform clipping before the other. However, bias'ing with my method results in slightly assymetrical clipping if driven far far into clipping (way beyond typical AD input clipping typically though). After biasing this way, the resultant collector voltage and voltage drop across r39 are perfectly acceptable (an average across the four pre's of 22.6 volts and 3.70 volts in my case).

I have to say, I've been very pleased with the outcome of these kits Tim. I'm looking forward to purchasing several more in the near future.

[shane]

..and wire up the power harness to the last module prior to putting it in the chassis. That 8th slot is a tight fit.

Buy a 4-40 tap. Buy some 3-in-1 oil. Put the oil on the tap. Tap the screw holes. If you don't...you need a stern talking to.

For sure. I made the mistake of installing a module in the 8th slot before connecting the wire harness and had to backtrack. Completely dumb, but I just didn't think about it beforehand. Seems like a sticky thread in each forum with concise tips and lessons learned would be really helpful...