Neve style 500 series mic pre 1290 1073

[crisotop]

yes, the cap was completely removed, with no change. I'll double check all components tomorrow, will report back any suspicious findings...

night,
christoph

 

[canidoit]

Crisotop, hope you have your unit sorted 

Your unit looks great!

I haven't finished mine yet so may encounter the same issue.

Crisotop, if it's possible can you describe the process you performed to solve the oscillation problem.

Onlymee, are there any common build errors that usually could lead to a non smooth and non performance optimized build? Like cap too close to this will cause oscillation or noise, etc.


Thanks

 

[onlymeeee]

Onlymee, are there any common build errors that usually could lead to a non smooth and non performance optimized build? Like cap too close to this will cause oscillation or noise, etc.


Thanks

As far as I know this is the first one that's misbehaved

 

[onlymeeee]

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]

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.

Onlymee thanks!

I will probably incorporate the gain increase and oscillation prevention mod.

So let me get this right.
If I add that wire link to push my gain to 75db on my unit, does that mean that my gain knob will have 0-75db of evenly distributed gain within the 12 clicks of my switch or will it be 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

Also will this oscillation prevention mod you describe will work on my 16+ volt API 6b lunchbox version?

Will I still be able to run line level signals into my unit naturally with these mods in place?

Thanks

 

[onlymeeee]

the second way.  Sudden 15dB jump.
If you want evenly distributed.. it'll take a bit of rethinking and changing all switch resistors.. and you'll be somewhat off the Neve track. But doable of course.. is there anything that isn't!

Of course.. you could add a small toggle switch to link and unlink the jumper.. for the best of both worlds. I'm sure you can squeeze one in somewhere.  Need only be a SPDT but DPDT is fine too. 

The mod will work for your API yes.. but if you're not increasing the gain.. then on the scope I haven't seen any difference with the mod or without.. so up to you.  Probably worth it anyway incase you bring to pre to a BAE rack in a studio.  Or if you're doing the higher gain mod then it's definately needed yes. 

 

[crisotop]

After hours of double/cross checking my build I found the problem: Pin1  

The 51X Rack has a Jumper for connecting Pin1 (Chassis) of the module either to 0V/GND or to Chassis/Earth of the Rack. I had Pin1 jumpered to Chassis, as this is what I usually do on 19" builds, but since I measured no connection of Pin1 to GND on the board I thought I give that a try. Now the preamps are working as expected (with the least noise if I jumper both the In and Output Pin1 connection to GND)

thanks for the heads up,
Christoph

 

[kishibashi]

Received my two boards today! Very cleverly laid out and lots of fun to solder. Ones completely soldered up and will finish the second one tomorrow. Now if only those trannys and switch would get here from AML...

Thanks for a great project! Can't wait to power them up and run them through their paces next to my vintage and reissue 1084's!

 

[onlymeeee]

Received my two boards today! Very cleverly laid out and lots of fun to solder. Ones completely soldered up and will finish the second one tomorrow. Now if only those trannys and switch would get here from AML...

Thanks for a great project! Can't wait to power them up and run them through their paces next to my vintage and reissue 1084's!

Fast work! Thanks for the kind words!!



@crisotop.. Glad you got it sorted!

 

[kishibashi]

Finally got the transformer.... but being an idiot I didnt turn the 5k Trimmer counter clockwise before turning on for the first time :-\.. When I measure the voltage on the 3055 after I hear the relay click it swings between 22-24V and 15-16V... Im using a straight 24V rail btw. What may I have blown/broken? Any help on where to get started would help! Thanks!

 

[onlymeeee]

Well, hopefully the fuse kicked in and limited the current. 
What happens now when you turn it on?  (with trimmer counterclockwise)  Or are you saying, that now, the 24V is not working?
Was there any smoke?
How long was it on for?

I'd check the 1 Watt 12R resistor and 1 Watt 47R resistor (underneath board) - should be able to measure in circuit

 

[a_)_i]

Hi folks,

I am selling on a couple of the don's pres on ebay.  If you are interested you can look for them.  Both are untested and jumpered for 24v racks.  I am including the 16v boards + parts if people want to convert. 

 

[andre tchmil]

I went through all 31 pages but couldn't find the answer nor in the Bom . Is the DC convertor the only part to leave out when running at 24v only ?

 

[canidoit]

I went through all 31 pages but couldn't find the answer nor in the Bom . Is the DC convertor the only part to leave out when running at 24v only ?

From what I understand, you do not install the whole DC-DC converter PCB but double check with onlymeee.

 

[onlymeeee]

The whole 16Vto24V small board is not needed. If you look at http://www.thedonclassics.com/nv73bom.html and check the general bom link, you'll see all the items in red are not needed.
Then on http://www.thedonclassics.com/nv73manual.html the picture at the bottom shows what jumpers etc need to be done.

http://www.groupdiy.com/index.php?topic=36831.msg512658;topicseen#msg512658

Any other questions, just ask

Also, another handy thing, as 31 pages is a beast to read through.. remember this new forum's feature - if you are on this thread and use the search box in top right, it only searches within this thread... very handy!

 

[andre tchmil]

Building a PSU for two racks:
power consumption at +24V ?

 

[kepeb]

Max current draw is around 123mA on turn on with +-16V.
24V rail is less but haven't got my numbers on it at hand...

if it helps

 

[canidoit]

Hi,

I am now re-embarking on getting my builds completed. What sort of 100uF 35V capacitor is it?

Electrolytic, Tantalium, Film?
Will a higher voltage than 35 volts be O.K?
10 or 20% tollerance?

Will this part be ok, so I can put a reference on my journey thread? This is 50volts though because there was non in stock for the 35volts or is this too big??
http://au.mouser.com/ProductDetail/Nichicon/TVX1H101MAD/?qs=sGAEpiMZZMsh%252b1woXyUXj1O6f55gzG4WILIuKXs9DXE%3d

The 35volt one is this
http://au.mouser.com/ProductDetail/Nichicon/TVX1V101MAD/?qs=sGAEpiMZZMsh%252b1woXyUXjy%2fmIt1aQrkI9OcXxagSBYM%3d

 

[onlymeeee]

Electrolytic (axial's easiest). Higher volts is fine. Tolerance doesnt matter...value not critical. 

 

[canidoit]

Onlymee, is my callibration correct so far

Calibration - from Don Classics website http://www.thedonclassics.com/nv73manual.html

TESTS BEFORE TURN ON:

TRIM POT MUST BE TURNED COMPLETELY ANTI-CLOCKWISE

THE CASE OF THE 2N3055 MUST SHORT TO THE FIRST TERMINAL OF THE OUTPUT TRANSFORMER (PIN 1)

PIN 1 OF OUTPUT TRANSFORMER MUST NOT HAVE A RESISTANCE TO GROUND (SHOULD READ OFF THE SCALE OF YOUR MULTIMETER)
If I do not use the case for ground and use the ground on the gold finger I get a different reading?? Am I doing this part right?

My multimeter reading is "O.L."

SAME AS ABOVE FOR PIN 3 OF OUTPUT TRANSFORMER

My multimeter reading is "O.L."

ON THE GOLD FINGERS, PIN 14 MUST HAVE A HIGH RESISTANCE (NOT SHORT) TO PIN 12 OR PIN 13

My multimeter reading is between "19-20MOhms"