Neve 1290 questions

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I did use screened cable for the gain pots and made sure that there was a connection in the screen all the way back from the input XLR but did not connect it to the PCB as I ran the ground and chassis connections separately. The documents are a bit vague and I spent heaps of time go back and forth with original schematic to understand what was going on with the boards I had.

Also of note, I getting ready to do a version 2 of my custom build and I am using JLM's swithmode PSU with his Trek2 DC converter to eliminate the need to be concerned about toriodals in the case causing noise. It's supposed to be able to power four 1290 modules.

Curious to see how your input transformer experiment works.

Thanks!

Paul
 
Just done 2 pcbs for the Psu, the normal SSL 9k Psu and I’ve done a little redesign so I don’t have to chop it about to get the 24v and 48v.
Defo going to try and lower the 24v to 23v to see if that helps keep things quiet.
Need to use the screened leads now,  Paul would you be able to put up a sketch of where exactly you used them, just so I don’t miss anything please.

Also I’ve kept the power lines one side and the audio cables the other to minimise noise.

I’m still yet to make a nice steel box for the input txf as my bandsaw is now cutting at a strange angle!! Another thing to fix!!!
 

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Doing drawings is my weakest skills set besides trying to play drums. I'll try whip something up. Is there something specific you want to know? It would be faster for me to tell you accompanied by a schematic than making a drawing.

Thanks!

Paul
 
Spence,

Here's how I connected the screened cable:

First I made sure that the chassis and one of the shield/ground connections from each board went back to the star ground as well as the PSU per Ian Thompson's Grounding 101 paper. Also the ground connections from each XLR went to the star ground.

For the screened cables, I used the approach that is found on the ez1290 instructions. Basically when you make a connection, the shield is tied to a ground/shield connection on one end but not the other so as to not to create any loops with the above connections going to the star ground. For the NV and AV boards you are using here are my suggestions:

From input XLR, make sure there is a connection between the shield and pin 1 in the cable all the way until the Preamp In connection on the AV board. Don't connect this shield to the board itself. Also the ground connection needed on the switch can be made with same run from the input XLR.

From the Stage 1 boost to the switch, connect the shield at the stage 1 boost shield connection on the AV board and not the at the switch.

From the switch to the NV Input/Stage 2 In, connect the shield on the NV board.

From the NV Out/Stage 2 In, connect the shield on the NV board.

Since you aren't using an EQ or other processing insert, On the AV board strap the Preamp Out signal to the Stage 3 Input. No shield is needed as it's on the same board. At I don't think.

For the output transformer connection, I have used both shielded and just the leads from the transformer and noticing any difference in the noise. If there aren't leads on the TX iron being used then out of habit I use shielded cable and connect the shield on the XLR side and not on the AV board.

Essentially when making your connections between boards, just connect the shield on one side of the cable. As stated above, the boards themselves already have a connection going back to the star ground, so it is not necessary to connect grounds/shields between boards.

I hope this makes sense!

Thanks!

Paul

 
Thanks Paul i get what you mean now, its been a long time since I did my EZ1290 and I gotta lot of help with it as i used these Russian Army switches and did the screening a weird way with this large cross hatched wire!!
I will need to find a decent stash of screened wire now and go through all you have said, but it does ring bells with connecting one side but not the other.
My PSU pcb is nearly finished now so will test if i get time of the next few days, gotta get through 36 hours of work first!!!
 
Sorry, Trex2

https://www.jlmaudio.com/shop/trex2-kit.html?display_tax_prices=1

He also makes a single. It's a DC-DC converter for his 48V SMPS.

Thanks!

Paul
 
Ok, so my redesign of the SSL 9k Psu to 24v and 48v went perfect, without load I get 24.65v and 48.7v, no smoke on first power up!!
Maybe I’m finally get my head round this diy business!!!
I have managed to put a stopper in the gain switched pot for 12 clicks.
Just need to wire up screened cable now and wire up 48v, pad and  phase switches.
I’m winding another 8 x 10468 input transformers and I’m going to replace some of the other cheaper transformers I have used.
 
All screened leads done now, phase, pad and 48v switches are wired and standoffs on pcb done.
Have tested and getting lovely waveform, probably my best channel yet as I’ve actually taken my time with this.
Still need to secure pcbs to enclosure and put on heat sinks then this is done.
 

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As always spoke to soon, need to check my other channels which work for what I did Psu wise as I keep blowing LM317 on 48v.
Got a slight problem with gain pot at click 7 where a pop comes in, I think there is a bit of debris inside so I’ll take switch apart.
So close!!!
 
The guy that sells the preamp boards you have also sells a selectable HPF to go with it. For the DI, it depends on what you can fit in your chassis. You could conceivably use a Bo Hansen DI board and use either a toggle switch for input selection or do something fancy like a relay on the input section that automatically swaps to the DI when a cable is inserted. Or you could use a Hi-Z plug-in DI that Volker sells. Lots of options for that, it just depends on where you are in regards to your ratio of "I want to be fancy" to "I want to be done."

Thanks!

Paul
 
I want it to be cost effective!!

Also I’ve made a couple of API eq pcbs 3 band  and wanted to incorporate these in there too!!!
I have a dual channel 1290 in a 2U which I think will house everything
 
Paul, I don’t know whether you’ve realised it yet, but I prefer to make stuff rather than buying the bits!! Call me a cheap skate!!!

As a cheat I do have some D.I boxes spare which I could repurpose in the enclosure!!

I’ve also just got hold of the bo Hansen active di schematic so will possibly knock up a pcb.

Is there a simpler way to implement HPF?
 
I’ve studied both the ssl9k Psu mod schematic and the JLM schematic and I think my mistake is my toroidal txf is a dual 12v which I’ve wired to get 29v ac, giving me 29v and 0v.
Do I send a 29v feed to both bridge rectifiers?
 
Spencerleehorton said:
Paul, I don’t know whether you’ve realised it yet, but I prefer to make stuff rather than buying the bits!! Call me a cheap skate!!!

As a cheat I do have some D.I boxes spare which I could repurpose in the enclosure!!

I’ve also just got hold of the bo Hansen active di schematic so will possibly knock up a pcb.

Is there a simpler way to implement HPF?

It's the simpliest way that I know of outside of finding your preferred HPF schematic and inserting that before one of the gain stages. I couldn't tell you off the top of my head which values and component arrangement to use.

If you can etch a Bo Hansen DI board that would be the way to go. I haven't found a more elegant, simpler, or better sounding DI circuit than that one.

Thanks!

Paul
 
Spencerleehorton said:
I’ve studied both the ssl9k Psu mod schematic and the JLM schematic and I think my mistake is my toroidal txf is a dual 12v which I’ve wired to get 29v ac, giving me 29v and 0v.
Do I send a 29v feed to both bridge rectifiers?

Which transformer are you using? How are the secondaries configured?

Thanks!

Paul
 
I’ve got a 2x12v toroidal and just put them in series to get 24v, but measures a little higher at 29v.

sorry ive been on night shifts!! brain not working, ive taken the JLM schematic and basically applied it to this SSL9k modded pcb, stupidly didnt replace the 220uf for 2 x 1000uf so got smoke after a few minutes but the circuit functions.
Just gonna change it for correct values then i'll power up again with the aid of a few more coffees!!!
 

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