matched pair of Neve 1084s + step attenuators OR EZ1084 + EZ1290LE the hard way

[rainton]

Hi guys,

I just finished one of my rather challenging projects so far and wanted to share it with you guys here on GDIY because this is the place I learned all I know in terms of electronics and building gear - and I'm telling you it's so inspiring what so many of you contribute to this forum! Thanks!

So I thought maybe I can inspire others, too

First of all thanks to Jim (Bluzzi) for offering the pcbs for the EZ1084 project - they are absolutely HQ and make it very easy to build a 1084 EQ - even easier if you use Dan's case for it.

But for my build I wanted to go some steps further in several ways:

- 2 channels in 2RU enclosure, all parts stereo-matched
- 24-pos step attenuators instead of pots (most pots measure 20% tolerance, my ladder-step-attenuators are at 1% tolerance)
- concentric switches as per the original
- one gain switch per channel which controls both mic and line stages as in the original (with EZ1084 + EZ1290 you usually need two separate switches for Mic and Line)
- frontpanel layout as close to the original as possible
- output attenuator switchable via push-pull pot so it's only in the signal chain if output attenuation is needed
- still enough space in the enclosure to retrofit 2 of Bluzzi's EZ1290LE pcbs in there when they become available

Ok - first started populating the pcbs - measuring and matching the parts for the 2 channels for possible stereo use. Since populating the pcbs is documented perfectly well in Jim's build manual I won't go in too much detail here.
The only difference for me here was, since I wanted to use a 22pos gain switch with 7pos. for the Line stage (+ OFF pos.) and another 14 pos. for both mic stages (incl. another OFF pos.) I had to alter the number and values of the gain switch resistors compared to the EZ1084 (which is Line signal only and offers 11 pos. for line signal)

I used the original Neve schematic to find the needed values and wiring and made the changes to Jim's layout as needed.
To get both channels into one 2U enclosure I had to stack the pcbs

 

[rainton]

At the same time I started designing the custom front panel for the "2-1084" on my computer. This was the final design I came up with...

 

[rainton]

I then sent the final design to Frank at NRG (thanks so much Frank by the way - great service as always!!) who CNC'd and powder coated it for me.

With my custom signature of course

 

[rainton]

In the meantime I spent hours and hours with soldering the six 24-pos. ladder attenuators and building the custom concentric switches and switch arrays so when I finally received the finished front panel from Frank I could put it together for the first time to get an idea of the final unit:

 

[rainton]

Since there's a lot of stuff going into this 2U enclosure, it has to be very deep.
While searching for a new 35+cm deep 2U enclosure I found a broken power amp on ebay for a couple euros that seemed to offer the perfect home for my 2-1084. The enclosure is 38cm deep and already offers holes for xlr sockets on the back panel. There's even enough holes to add two balanced 1/4" jacks for line ins.

 

[rainton]

Off to hand wiring all those switches - bottom pcb first...yeah I know it looked kind of wild at the beginning  ;D

 

[rainton]

bottom pcb wired up - now following with the top pcb...

 

[rainton]

Wiring completed - man what a trip! 

 

[rainton]

Now it's time for the first run (actually I did one first run when the bottom pcb was wired up to see if it was working, just in case )

IT'S ALIVE!!!!

 

[rainton]

And here are the push-pull output pots, so I can take the pots in and out of circuit.
I thought if go as far as using ladder-step-attenuators (also for better noise specs) it's kind of lame to have that attenuator pot in the circuit all the time.
So if use the 2-1084 on the 2bus for instance I will most likely not need an output attenuator.

But if I want to use it for tracking and drive the input stage a little harder I can pull the output pot and and attenuate the output as needed.

In this picture you can see - the scale underneath the knob only becomes visible when the pot is pulled and IN-circuit  8)

 

[rainton]

Finished unit in the rack - and I have to say it sounds absolutely fantastic!!!
Again thanks Jim for these great pcbs!! Even though I hand wired all the switches (wiring them was quite a PITA btw) instead of using pcb mounted switches this thing is dead quiet!!

I'm loving it already and the step attenuators make recalling and stereo matching settings a breeze...

Alright let me know what you think and if you have any questions I'll be glad to answer them if possible 

Martin

 

[shabtek]

hats off!
that looks great, what a labor of love.
I have considered doing something similar with a pair of those--
I am not pleased with the serviceability of stacked pcb projects in the past so i think i'll go separate enclosures.

 

[dmp]

Nice front panel. What software did you use?

 

[rainton]

hats off!
that looks great, what a labor of love.
I have considered doing something similar with a pair of those--
I am not pleased with the serviceability of stacked pcb projects in the past so i think i'll go separate enclosures.

Thanks!! I put a lot of love and time into it.

But you're right - in terms of serviceability stacked pcbs are not the best way to go but since I used terminal blocks for all connections except the rotary switches - it's at least possible to just unscrew the wires there and flip the top pcb upwards to access the bottom pcb...

@dmp: I used Frontpanel Designer - in Germany offered by SCHAEFFER AG - in the states it's offered by Frontpanel Express I think...

 

[electrisizer]

very nice!!!!
even i have pots i use the 1084 on 2bus very often...  yes color, but good color!

 

[pvision]

That looks fabulous.  The Neve-style knobs make a huge difference to the look.  The designs still look good forty (fifty?) years on

Nick Froome

 

[Bluzzi]

This is a very impressive build! I would not have attempted this myself (and I designed the EZ1084EQ pcb). Just beautiful work. I had some fear at first that all that wiring to the small holes for the Grayhills would be almost impossible due to their close proximity to each other (not a lot of space for wires).

But Martin you pulled it off and in aces! This work is something to be very proud of (and I feel proud for you). It is a great accomplishment and very inspiring DIY.

Now it's getting me thinking of doing one of these! Oh no!  ;D

Martin if you read this, you should make a video of you using it on the 2 buss. Just to see those concentric switches working.

Cheers

Jim

 

[rainton]

Thank you so much everybody!!!

Yeah Jim you're right - there were some moments when I was thinking "Dude why couldn't you use the Grayhills and have it nice and easy..."

But now I'm really glad I did it - I learned a lot and even though wiring to the small holes was kind of a drag I found it much harder to wire everything to the correct spot and building the custom concentric switches that offer exactly what the schematic says... That was where the challenge was for me - because when you have a pcb in front of you with perceived hundreds of wires staring at you...I had a hard time focussing on the task - sometimes feeling like "ok don't twinkle now or I'm gonna lose it completely" hahaha!  ;D

This picture that I took with my phone while wiring up the 1084 shows a little bit of what I mean

If you use the Grayhills there's not many mistakes that can be made.

What was another challenge was designing a front panel that could hold everything I wanted but still to make sure that everything will fit in the 2RU enclosure (with the huge switches and step attenuators) - and I'm telling you - it was darn scarce! This thing is packed and I can just close the lid of the enclosure!


Anyway, I love this thing - and if you like I can make a little vid. how I use it on the 2bus.
I'm so glad I went the extra mile and stereo matched components and built the step attenuators - it's so easy to dial in everything when using it for stereo applications...

...have I mentioned that the only thing missing is the 1290LEs Jim?  haha!

 

[jensenmann]

Well done, mate. That for sure is something you can be proud of.

 

[Govinda Doyle]

Awesome post and build!!
Now you know how the boys at neve and Brent avrill feel when wiring up all those stepped switches, you even did stepped pentiometers!! Legendary!!