Neve 1290 build completed!!

[Chrome Heart]

So what gain knobs are out there? It seems like the red Marconi knobs are history. Anything that looks close?

 

[ilfungo]

hello MatthewF
from the photos I saw that you failed a 10K resistor
Why?
Thanks

 

[ilfungo]

I just finished editing JLM AC / DC power asupply,
I made some measurements and do not know why I 67V instead of 48V
any ideas?
I tried to adjust the trimmer and I burned resistor 47R 1W

 

[MatthewF]

Hi Ilfungo,

I guess you're referring to the 10k resistor which I omitted? That's because I'm using a trim pot - the pot's track resistance replaces this 10k resistance. Martin has kindly provided a wiring diagram for how to do this which can be found here:
http://s3.amazonaws.com/EZ1290/trimmer_v2.3.pdf

Cheers,

Matthew

 

[ilfungo]

sorry guys
I have  problem
I think the problem is on PSU
to JLM AC / DC I use conductive standoffs is correct?
The LM are very hot!!!!
It's normal?
Thanks

 

[cbc459]

Hey everyone, long time lurker but first time poster here!

First off, massive thanks to Martin, your project is amazing, it's the first serious build I've done and so far the experience is fantastic, and it's all thanks to you!

Now, I just had a quite possibly newbie question: in the assembly guide I'm seeing that the input XLR is connected to to input xfo pin6/GND. So by "/GND", does this mean simply that the xfo's pin 6 is grounded or do you also connect XLR pin 1 to ground (case?) as well as the xfo? Would appreciate if someone could dispel my confusion!

Otherwise, this thread has been a real treat, fantastic amount of information, and I've learned a lot just by reading it.

CBC

 

[desol]

Hey,

No. Pin 6 should just be shield....not case(AC ground), because shield is also connected to 0v. 0v should never touch ground. Anywhere that you measure continuity from 0v to ground on the case, you should get 10 ohms(which is connected through the JLM supply pcb mounting hole, if you used it). You can connect the 10468 case itself to chassis ground, with one of the little screws, as pin 6 is not connected to the transformer case; in which event, the transformer case should buzz if you touch it un-grounded.

I think this is correct. This is how i have it connected and it's quiet...and i have my 10ohms.

 

[ilfungo]

ciao
how can I connect Mnats PSU to 1290?
Where do I put the 10 ohm resistor?
thanks

 

[adam1176]

Can I get help with grounding? I kinda messed up my chassis but I need these pre's to work on Sunday. Everything is soldered up and I'm ready to plug in and check my voltages. My question is what should I ground/where/how if I am keeping these outside of a box?

Thanks!

 

[mushy]

Can I get help with grounding? I kinda messed up my chassis but I need these pre's to work on Sunday. Everything is soldered up and I'm ready to plug in and check my voltages. My question is what should I ground/where/how if I am keeping these outside of a box?

Thanks!

Put them in a box.

 

[adam1176]

Thanks mushy. Normally I'm the sarcastic one.

How about anyone else wanna chime in?

 

[mushy]

No sarcasm here.  Were you planning on just screwing them down to a piece of wood or something?  Without a proper case, they will be susceptible to EM and RF not to mention the fire and electrocution hazards.  Put them in a properly grounded box.  There are whole sections of this site devoted to metalworking for a reason. It's not a step you want to skip. Just my 2¢.

 

[mitsos]

Agree with Mushy. That said, everyone tests circuits out of a box.  At least "work, no work" type of thing. No noise shielding at all, may be a problem, maybe not.  As far as grounding, I think you'd want to tie your circuit ground direct to PSU ground and PSU ground to "case ground" through a 10 Ohm resistor (in this case the ground pin of your power cord).  Casework is a PITA, for sure, but 100% necessary. 

 

[adam1176]

fair enough. Thanks for the explanation guys.

 

[briomusic]

On my fourth build I have a really strange audible/mechanical noise coming from the output transformer. It's like a high pitched whine, not on the audio outputs, but rather eminating from the transformer itself. voltages don't seem too far out, what is going on here? bad trannie?

 

[desol]

Maybe. Did you try another transformer? Oscillation?

 

[briomusic]

hmm the other transformer does it too, but less so.
more importantly both transformers work fine on another, known-to-be-working channel.
the bad channel passes sound, but very high gain and distorted even at the lowest setting.
probing around everything seems fine up to the (base of the) 2n3055, and I am on my last one 
maybe sneak in an mje3055 just to find out whats happening....

alternatively it's the first sunny day in berlin and there is a park just 2 min from the studio....  ;D

still how can a bad transistor make a transformer sing? weird stuff.

 

[snipsnip]

got to be oscilation, no? Grounding? Tranformer positioning & wiring?

 

[briomusic]

that's the thing: both transformers perform flawlessly on the other channel, still screwed in the same place, crosswired with crocodile clips. to clarify, the whining sound is NOT coming out of the speakers but from the transformer itself, like having a mosquito in the room.

I reckon the problem is somewhere around the 2N3055/heatsink/output amp. guess I'll have to take all that apart again...  :-\

 

[redmojosteve]

Hi
I have completed (more or less) the first two of four channels of the 1290 pre. The JLM AC/DC PSU works fine and everything looks good. I noticed that in one of the early very helpful instructions for the build made reference to connecting the casings of both power supply and pre case together (via the screen of the cable connecting the PSU to the pre). However this has been deleted in the later version. The only connection to earth in the system is via the 10 ohm resistor to the case of the PSU which checks out on a meter. None of my pre's or XLR's are connected to the case.
I haven't found a specific reference to this in the thread (probably my fault for not looking properly) but is it necessary to have this electrical link? Clearly it would earth the pre case which seems a sensible idea.