Neve 1290 gnd wiring, Whatever i do i'm getting hum!!!!

[Spencerleehorton]

Just a little update!!!
I have managed to rewire 48v and on the psu 48v side is much better and seems to be holding.
On the 24v side it isn’t so good!! typical, the 7824 seems to be taking to much current and overheating, it kept shutting down when i first turned it on without a heatsink, now I’ve put a heatsink on it, the voltage is dropping very slowly but after 5 minutes goes from 22.66 to 21.60v, so i think i need to re-evaluate whats going on here.
Ive changed the 7824 for a brand spankers and its just the same.
I was under the impression from the datasheet that these 7824 can handle up to 1.5A and by the info given here 4 channels of 130mA each is 520mA, so it should be able to handle it?

I also need each channel to have 22.66v so i might need to build an adjustable 24v so i can give it a bit extra maybe, thoughts?
Need to work out why the voltage is dropping, on a better note i have a nice new soldering station and the hum seems to have buggered off!!! and its all within a 2U enclosure

 

[Spencerleehorton]

With Psu two channels sit at 22.66v as they should.
Now going to check other two channels.
Have changed a 1000uf/50v cap on the 24v side to 63v.

 

[Rob Flinn]

I was under the impression from the datasheet that these 7824 can handle up to 1.5A and by the info given here 4 channels of 130mA each is 520mA, so it should be able to handle it?

That depends on how much voltage you are dropping across the regulator. ANother look at the datasheet should reveal a graph that describes this trend.

 

[Spencerleehorton]

If both sets of channels work fine on the Psu I will have to use another 7824 section to power just 2 channnels per 7824.

 

[Spencerleehorton]

right im still not out of the woods even though now i am getting all correct voltages.

this is the story so far:

I have 3 units:
1. EZ1290 with pcbs by marriane using carnhills and sowter input txf and PSU is the modded SSL 9k PCB, all voltages good and no hum at all, sounds great.

2. 2 Channel 1290 using My own PCB made from original layouts, LO1166 output txf and 10468 input txf, SSL 9k modded PSU correct voltages but 120hz hum present

3. 4 channel 1290 using my own PCB made from original layouts, LO1166 o/p txf and 10468 i/p txf, SSL 9k modded PSU correct voltages but 120hz hum present.

list of things to do:
there is a possibility it is the input txf so my next test is changing them and then see if the 120hz is gone.
i will test for ripple on PSU with hum

so close now!!!

 

[Ilya]

Does the hum change with gain setting (ie increases when you turn up the gain)? If yes - it's somewhere in the input stages. If not, it's PSU ripple.

Make sure you have large enough filter cap for each channel. 1000-1500uF per channel should be fine.

 

[Spencerleehorton]

just changed one of the input txf and yes hum is gone!!! so i need to redesign the input txf!!! hum cancelling!!!

 

[Ilya]

just changed one of the input txf and yes hum is gone!!! so i need to redesign the input txf!!! hum cancelling!!!

Redesign 10468? Or the PCB?
Make sure you don't ground input winding. Check for shorts to gnd from all windings. I once had a problem with hum that turned out to be one side of the transformer winding grounded via short through the PCB pad to tx enclosure.

 

[Spencerleehorton]

its definitely the winding of my input transformers, they all do it, so ive done something wrong, hard to tell until i unwind them and see whats happened.
Doesn't appear to be any shorts, i can only put it down to winding it wrong, possible other human error but need to investigate!!!

I now have 6 lovely and quiet Neve 1290 channels, i had some other spare 10468 style transformers which someone else built.
need to search for a couple more or use some OEP ones temporarily until i get to the bottom of the problem with these other ones.

 

[Spencerleehorton]

Also I ve worked out the 7824 is dissipating 12W!! No wonder it’s getting hot!!!
Going to see if I can put a 35ohm 10watt resistor before the 7824.

 

[Spencerleehorton]

In conclusion main source of hum was input txf not in a good isolated and EMF case.
I had some issues of ripple and screening toroidals I think is essential for cutting down EMF.
As I have three Neve units in a rack next to each other there is some noticeable hum when turning on the marianne Pcb unit so will revisit that and do more of the same.

 

[Pusch3l]

its definitely the winding of my input transformers, they all do it, so ive done something wrong, hard to tell until i unwind them and see whats happened.

Spence,
What does that mean to the units you sent out?

Greets

 

[Spencerleehorton]

I've only sent one input transformer out and it was sent out not in a case, this was understood, if i did send out anymore and they need to be put into cases i can do that now, happy to do an exchange over as soon as i receive any back.
but i thought it was only one i sent out, could be wrong!!
picture of 1st and second prototype below!!

 

[Pusch3l]

Spence,
These 2 irons sat in the Box i received a while back.



Besides that..is something wrong with your email address??

 

[Spencerleehorton]

Yes, I think you said you were going to pot them but happy for you to send back and I’ll pot them.