NV73 preamp - journey

[canidoit]

P wiring at the underside of board

As in one of onlymee's diagram pic, using single core shielded cable I connected the core of the cable to P to *P of the board and shield to 0 of the board and cut the other shield on the other end connected to nothing.

I used about 9.6cms in length of the single core shielded cable for this. I used a patch of electrical tape to keep the wire against the board to keep it tidy which is not in  the picture below.

* the little white stand offs for all the PCBs is best to angle them parallel with the board to minimize protrusion and keep the length and width of the unit within requirements.

 

[canidoit]

Carnhill VTB9045 and VTB9045 PCB

There's no info on this process and looking at onlymee's video on pause, I tried to imitate how his one looks but I didn't like the actual result of it.

So here is the approach I used.

I placed the Headers & Wire Housings 36P STRT 1 ROW GOLD of 7 and solder one pin for alignment.

Once I was satisfied with the alignment, I soldered the rest.

I flipped the board and broke apart the plastic bit so that I was able to move it away from the PCB board but still there to keep the pins together. I was careful not to damage or cut off the pins when doing this.

I then soldered the pins again from the back of the PCB and this time held the iron long enough so that the solder would run down the pin to the other side to cause the pins to be soldered on the other side. This also allowed for the solder on the pins on the back side to be more flush with the PCB board.

I then removed the black plastic bit of the headers and snipped away the pins on the back side.

I am able to keep some solder and pins on the back side of the board because the transformers leads itself has a little lip that pushes the board off the VTB9045.

I mounted the PCB onto the VTB9045 and soldered the VTB9045 pins to the board. I then screwed the board onto the VTB9045. This caused the board to have a slight bend.

I then trimmed about 1.5mm off the long pin end of the header.

Making sure that there was enough length that when you install the VTB9045 transformer that the pins would atleast reach the screw section of the molex.

 

[canidoit]

VTB-1148 and VTB1148 PCB board

The pins on the VTB1148 has bits of solder on it straight out of the shop. I could not slide the holes of the board onto it.

I filed down the pins and used pliers to move the pins around so that it would fit and align with the board.
I soldered the board at about this height on the VTB1148 pins.

 

[canidoit]

Grayhill GR-03-001 switch and pin

This is the position of the shaft and pin I used for the switch which gave me 11 clicks when turned.
I placed the shaft at the following angle and placed the pin at 12o'clock.

The lead of a resistor which I used as a pin in this pic is just temporary for illustration purpose only. The real pin, you place inside in the hole and then you place the silver sticker over it to stop the pin from popping out.

For the grayhill to act a particular way (12 position), the angle of the shaft and the hole the pin is dropped at the time of initial setup is dependent to each other.

The best way is to test the setup using resistor legs before actually dropping the pin in the hole. Once you are happy with the way it functions, restart how to set it up and this time use the actual pin and drop it in the hole. There have been many dramas when people set the grayhill switches incorrectly and tried to take the pin back out of the hole. Best to get it right the first time and save yourself some dramas!

 

[canidoit]

Soldering grayhill GR-03-001

I was concerned when I was soldering those grayhill switches because they are very small solder points and at certain points the solder will automatically bridge other solder points as shown in pic.
It has been confirmed by onlymee that the following switch solder points on the switch are naturally bridged so it was O.K.

 

[canidoit]

The heatsink that goes on the 2N3055G

I have been informed that it is O.K. to use thermal paste on the heatsink for it will not act like a glue with time. This means I should be able to install, remove and re-install the heatsink if need be.

*I will only apply the thermal paste on the heatsink once I have tested the unit to be working and it has been calibrated.

 

[rodabod]

I'm impressed with how far you've got on (from whe you first started and weren't sure if you wanted to build). Well done. Looks like fairly neat work.

 

[onlymeeee]

Very good assembly ... Very talented guy, just lacking in a bit self confidence hey.. Need to get you trained up a bit more on schematics.. and you'd be really be flying then.. 

Quite like those knobs actually!

Good work!!

 

[canidoit]

** last minute info

 

[canidoit]

Assembling

This is the steps I used to assemble the unit

- place washer on the grayhill switch (had to source one myself which is about 1mm thick)

- position PCB board into case leaving space for me to attach the output pot first. This is because I am unable to slide this in due to the larger C5b component if I put the main PCB into final position first.

- place final PCB board into final position
- attach the washer and lock washer for phantom power switch since it goes behind the case.
- screw nut for grayhill switch and phantom power switch

- screw PCB board to case

- slot VTB1148 into place - *slide 4 wire to molex
- screw VTB1148 into case using nuts and bolts
- screw molex to secure 4 wire from VTB1148

- slot small PCB into place - * slide pins into molex
- screw small PCB to case
- screw molex to secure pins of small PCB

- slide VTB9045 into place - slide 7 pins to molex
- screw VTB9045 onto case
- screw molex to secure 7 pins of VTB9045

- install heatsink to the 2N3055
- screw nut that holds the heatsink

- attach knobs for the pots

 

[canidoit]

pre-final build

I did a temporary assembly while await confirmation for some of my question in the main thread.
Unit has not been tested

The large knob land on this angle when screwed on normally to hit at the flat end of the shaft. I will have to adjust it properly once the unit is good to go.
* the white plastic button for the lo z and phaze. On the aluminium inner case, I filed down the width a bit to allow for more room because the plastic tend to rub against it. This could because of the position I soldered the push switch on the board. Best to do some tests when you have soldered the switch with the button on, to see if your build needs the holes to be bigger.

*The heatsink that goes on the 2N3055G on this pic is not secured with the nuts yet because I have not tightened the screws in the molex that hold the small PCB pins. In order to tighten the screws on the molex that hold the small PCB pins, you must have the heatsink removed in order to access those screws. I guess this is why thermal paste is not used when attaching the heatsink so that it can be removed easier when needed.
** The heatsink is also touching the VTB1148 which means I will either bend that heatsink arm forward or position the VTB1148 more to the right to prevent this from happening!
*** When completed, it's good to look at all your components on the board and make appropriate position adjustments to them because I realized after the build that some components were out of position due to laying the board or moving the board around and had caused certain components to touch.

The unit looks pretty good, even with these cheap knobs!

 

[kato]

Nice documentation job. I dig the DIY enthusiasm. I hope it encourages other newbs to buck up and join in the fun!

 

[canidoit]

Notes
..................................................

3 holes leftover
That's correct, 3 holes left over. One near the output switch (output signal point), and then a chassis point and then a 0V point.

Just handy, for when you need a gnd point for either testing, or modding etc.

..................................................

 

[canidoit]

Mod for 75db gain

Doing this gain mod will change your gain settings on your gain switch to something like this:
1st click = 5db increases by 5db
...
8th click = 45db
9th click = 50db
10th click = 55db
11th click 60db
12 click 75db? <--- extra 15db jump here due to mod

With the last click having a high db increase due to mod as compared to other clicks of your switch.

If you compare the schematic from mine to AMS site's schematic...
It's not circuit changes.
It's a mechanical restriction due to not having more positions on the switch.
For example, if you have an original 1073 on 65dB setting.. it has the same circuitry as mine at 65dB.

If you want 80dB instead of 65dB, (which having used many original Neve's and many ribbon mics, have never personally needed) then it's pretty easy to mod...

This will give you an extra 10dB at highest setting...
Add a wire like so (black wire top right)

(that'll get you to 75dB)   Check for oscillation...

If all's well and you need the extra 5dB on the highest setting, then I'd jumper over 3.9k (R20) (and then make up the difference in the pad 'string' so the other switches don't change) so I'd change R21 to 7.2k.    

That.. (as I'm looking at it late at night) seems the way.  

But have a look at both schematics... either way is exactly the same as Neve did it.  It's just which positions on the switch do you want.

Fixing possible oscillation that may occur due to mod or use on certain 500 series racks
Onlymee suggests to implement this mod incase you decide to use the unit on certain 500 series racks that may cause your unit to oscillate.

Oh canidoit... you were asking about increasing gain before and if it wasn't stable what should you do... well I've troubleshooted it for you.. what you need to do is add a 100uF 35V capacitor - positive side straight on the output transformer pin 3 (+24V) and the negative end on pin 13 on the gold  connector (ground).   tested up to 75dB (no reason why 80dB wouldn't work too)
It shouldn't change the sound as it's just an extra cap on the +24V rail.  (there's already 1000uF on there, but an extra 100uF right on the transformer pin seems to clear up any stability trouble)  On a scope I don't see any changes on 65dB setting.  

As it can be done without unscrewing anything it's very easy to mod.  I've been adding it anyway for extra security as although without works perfectly fine in GDIY 51X or API lunchboxes, or my own hashed up test jig, one person was saying on a BAE rack, when unloaded and turned to max gain it oscillated.  The cap solves this.  Not sure why it would happen on BAE and not others ? Maybe the extra wiring instead the rack of PCB picks up like an little antenna(?) Speculation.

 

[canidoit]

Oscilloscope Tutorials, Videos

http://www.youtube.com/watch?v=rC8HBcsNm2g
http://www.youtube.com/watch?v=8VEg6L2QG5o

 

[kepeb]

yo dude!
you all up and running with this? how do you rate your results?

 

[canidoit]

yo dude!
you all up and running with this? how do you rate your results?

Hey Kepeb, how are you bud!

Nope, I haven't even had a chance to solder the small capacitor you gave me.

I have been busy working since and have had no chance to do any diy'ing but I will keep you posted when I get this beast up and running. Im gonna end up adding that 100uF cap mod onlymee suggested so that it keeps oscillation to a minimum on certain 500 series lunchboxes.

What did you think of your build by the way since you got yours up and running?

 

[kepeb]

hey, no i'm the same they've been sitting there fully built and calibrated for ages but as yet unused  :-[
I've been moving things around(including houses) and slowly adding bits to my home studio. I think its nearly time to bust them out tho

 

[tronax]

Just finished my NV73 build -- thanks for the great notes/pics... very helpful.

 

[canidoit]

Kepebs little capacitor is now in. Better breathing room as you can see!

Ready for callibration

Note: On my heatsink, I prefer it not touching the big red transformer, so I bent the little tenticle of the heatsink a little in. I could have probably soldered the 2N3055 more to the left so that when the heatsink was placed, the tenticles would not touch the big red transformer. Something I will take into consideration if I was to build this project from the start again.

Now I just have to figure out how to use my Oscilloscope.  ???