NEVE: 1073 Channel Amplifier

I went down the Neve rabbit hole with this post, looking at how the channel amplifier works and trying to use one of the preamp stages as a fuzz/overdrive.

Long story short - I couldn't come up with something that I was happy with using the mic preamp stage, so I have walked away from this one for the moment.   Came close, but just not worth spending any more time on.

I will try the other amplifier sections and see if I have better luck.

On the upside, it got me interested in what other preamps were out there, and I had much better luck with the Revox A77, the same as a Trident A-Range mic preamp.   I ended up making one of these and boxing it up, and it's pretty cool.  

- - - - - - - - - 

So what am I trying to do?

• Modify/abuse a Neve preamp so it can be a fuzz or overdrive

• Preferably running at 9v, but I can live with something larger using a charge pump (the Neve runs at 24V)

• Maybe include some EQ from the Neve, but simplify to keep it pedal friendly

• Avoid transformers.  Yes, I know, everyone says the transformers are a big part of the sound, but I don't care what everyone says cause proper Neve-style transformers are costly and large, and I'm not making an overdrive/fuzz pedal with a really expensive studio grade transformers known for their low distortion

• Avoid the insanely complicated Sensitivity switch (it's the input gain control, which sweeps all the way from mic to line level)

So what am I not trying to do?

• Recreate a Neve channel amplifier on vero (madness)

• Use unobtainable and/or expensive parts

• Reverse engineer a JHS Colourbox

NEVE 1073 CHANNEL AMPLIFIER SCHEMATIC

You can find a full manual, including schematics, here    This may be better than what you have seen previously, as it is the complete manual with tech specs.

SIGNAL PATH / BLOCK DIAGRAM FOR CHANNEL AMPLIFIERS 1066, 1073, 1078

A few partial schematics floating around on the web do not contain this diagram, which is very easy to understand compared to the next one, which is more commonly found on the net.

BLOCK DIAGRAM

This diagram is confusing, but it makes more sense with the reference above and the other items below, where I've covered the EQ sections individually.

NEVE MIC PREAMP SCHEMATIC

Three different preamps are used in the channel amplifier, which are used as gain stages in various places.  The multiple boards are made up of two or three of these preamps combined.  Some are used as gain stages for the active EQ, Mic and Line inputs and, finally, an output amplifier.

As it happens, this was used as the clean preamp on the Way Huge Pork Loin.  

MODDED MIC PREAMP SCHEMATIC

Just gain and level at the moment.  The frequency response is very flat for a pedal, so for my taste, it doesn't need a tone control.  Even though it has an element of fuzz, it doesn't have excessive high frequencies.

LTspice

It doesn't look exactly like this on the scope; the wave isn't as squared off as this.  It was more triangular with flat tops.  Hopefully, after I work out the gain sweep properly, I'll add some actual traces at a later date.

OUTPUT AMPLIFIER

LTspice

Frequency response varies quite a bit, depending on where I take the trace from (note letters on trace vs schematic).  I have done a bit of a dodgy workaround where the transformer should be, so it might be a result of this.

MISC

Now I know you can't see any details here, and there's still a little more to add - but this is why I will not be attempting to recreate a Neve channel amp on vero - it would be gigantic.

THE NEVE 1073 EQ SECTION

NEVE BA205 BOARD (LOW & HIGH SHELF EQ)

THE ASSOCIATED PREAMP

WHICH TRANSLATES INTO THIS

It's quite similar to an active James EQ, with the low shelf frequency being selected by a rotary switch (switching between different values capacitors), with a pot to control cut and boost.  The high shelf just has a cut and boost pot.

Hopefully, this is easier to understand, and it gives me a starting point if I ever decide to use some of it in a pedal or adapt it in some way.  The next section in the signal chain is the mid-range control (Presence), which looks quite challenging.   

NEVE BA211 BOARD (SWEPT LO-MIDS TO HIGHS)

I'm pretty sure this has an error - instead of C & E (which are preamp in/outs), it should read K & M.  K & M are the in/outs of the other preamp on the same board.  C & E have already been used for the low-high EQ section. 

There also seems to be some differences between the schematic, some including a 10k option, others not.  There's also an alternate schem for the board above, with an extra resistor. 

THE ASSOCIATED PREAMP

WHICH TRANSLATES INTO THIS (HOPEFULLY)

I say hopefully, as the frequency response didn't exactly match the stated values for 2, 3, & 4.  Looked good for the rest.

NEVE BA182 BOARD (HIGH PASS FILTERS)

This is the simplest of all the EQ sections, but it did have me stumped for a while as to why there are two identical sections with the same lettering - it's pretty obvious now; it is because they are connected...    As mentioned above, this is a passive filter, so no preamp is required. 

WHICH TRANSLATES INTO THIS