JC's 1272 Finished!!

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Lowfreq

Well-known member
Joined
May 28, 2005
Messages
574
Location
Christchurch, New Zealand
Hey good people,

Just thought I'd post some pics of my Neve 1272 I've just finished.
I went with JC's design after seeing khstudio's build. It looked like the easiest way for me to get some sort of Neve happening.

I took my time, was ultra careful....and it worked first time....Love it when that happens. :cool:

Here's the usual pics.

Lets start with a home etch of the board. The Layout was great for making this at home. No real fiddly tracks or anything like that.
1272blank.jpg


A bit of a fuzzy pic, but at least you can see who's layout this is.
1272blank2.jpg


Ok, I need some bits.......looky what we have here :wink:
1272bitsnbobs.jpg


Ok, we're partway stuffed.
1272Stuffed.JPG


The heatsink was quite big, so I had to mount some bits underneath. Again a bit fuzzy.......... :roll:
1272underneath.jpg


Lets wire her up, and put her in a rack. I had some space next to my two JLM 99v pre's. I went with the JLM for the output transformer too
1272no1.jpg


And another shot
1272no2.jpg


So now I've finally heard what a Neve sounds like.... :green:
The high end is not as open as the 99v's but that seems to round vocals out nicely. Most of you have heard more Neves than I ever will, so I wont spend all day here trying to decribe it.

The only issue I've run into is sometimes if you unplug a mic, or if you plug one in while the pre is on, you get a sound like white noise or pink noise........ :? ........But if you plug in the mic before you turn on the pre eveything is sweet.

So thanks to Joel for making a great layout and Kevin for a great thread with some informative pics. :thumb:
 
Hey I recognize that board :grin:

Looks good man :thumb:

You "MAY" not be hearing what we are when it comes to this pre because of the output tranny being the JLM instead of the Carnhill... it's got to affect something I'm sure. Also, you don't really have to flange out the heatsink... they don't get that hot, just warm.

Kevin
 
[quote author="khstudio"]You "MAY" not be hearing what we are when it comes to this pre because of the output tranny being the JLM instead of the Carnhill... it's got to affect something I'm sure[/quote]Yeah, I went for the Jlm as it was the easiest, and when you take into account shipping, the cheapest for me too.
If I get the chance, I may grab a Carnhill if I see one sometime. I can always use the JLM elsewhere. But for now it sounds sweet to me. :green:

[quote author="khstudio"]Also, you don't really have to flange out the heatsink[/quote]Oh, I only did that to make it fit in the 1RU case. That heastink was really massive and I wasn't too keen for it to connect with the chassi. :wink:

[quote author="kato"]You make it look easy[/quote]JC's layout made it easy. :thumb:
 
great job - I used the JLM output and input transformers on my hotrod 1272's - they are really some great transformers for the money! Man, I really dig the 1272 sound - might have to make a few of these myself.
 
Hey, the noise you mentioned is when it goes into oscillating. It would be fine if you can trace spikes on an oscilloscope. Could be the 2N 3055 having to high beta. You might cure it by loading the output tranny as well with a zobel, even if its not an original. Cheers Bo
 
hello, I'm working too on JC's 1272 pcb. It's a really good design because most of the parts are on the pcb.
There is only a problem : I found all the infos but not the component side of the pcb...If someone can give a link or any other info.
Thank you :wink:
 
This project was really just something I had done for myself, and then I shared it with a few folks as well, but never really completed a proper presentation for the group. I should, and I plan to, but don't really have the time to do it justice at the moment.

I did a quick component placement guide using the Illustrator doc that I drew the traces with. If I remember correctly, the component designations are from the Neve documentation for the BA283, so refer to that for component values.

In fact, 'my' layout is really just the 283 traces modified slightly to allow the large output transistor to lie flat against the pcb with room for a heatsink, and also the additional coupling caps and resistors as well.

Here's the component layout. It's not particularly pretty, but it should give you what you need to build this.

JC1272compside.png


The red/pink 'dots' on the board indicate connections that aren't being used, so ignore them. This board layout is really a chopped version of a 3-stage pcb I did a year earlier, so some of the connections don't really apply for a 2-stage design. Also, the unbalanced output (pin F) I don't use on mine, but for those who wish to use it you can hang an electro (470uF or so) between pin F and the connection to the left and then take that output at the very left of the pcb either to an unbalanced output connector or to an trafo (ungapped) to balance it. You still need to hang the proper gapped transformer, or a T1310 inductor between pins B and M, however, or the circuit ain't gonna be happy.

FWIW, this board has no gain structure attached, so you can use it for whatever gain structure you chose: mine, any of Joe Malone's, BA's, whatever.

Peace,

JC

Edit - I just found that Matta hosted the original files I made for this at his place. http://www.groupdiy.com/index.php?topic=19648&postdays=0&postorder=asc&highlight=jc1272&start=30 Scroll down a little past halfway and you'll see the links on Matta's post.
 
thank you Rascalseven :thumb:
I'll try JC's1272 design.It seems to be a more practical board : All components are on a pcb.
First test on tuesday...
To follow :wink:
 
Hey guys..

It's been a while since there was action on this thread, i know , but I just picked up a "completed" dual JC 1272 1RU build which I don't really know much of the history on but it has the nice Carnhill transformers (VTB9045 input / VTB 9049 output) and power supply mounted in separate enclosure.

I only recognised that they are the "JC" PCB's from poking around on here, generally studying up on 1272 / 1290 projects, and eventually came across something that I recognised in terms of board layout.

The wiring in this unit is not great.  But I'm gonna see if I can salvage the boards and get it going in the current format.

There are the guts of an old 2 channel DI mounted in there, too.

The front panel is decent.  It says "1073" on the left rack ear, and "CA" on the right rack ear. 
Anyone know the background on these?
It has provision for MIC gain pot and LINE level, as well as OUT level.  Also a TRS DI input for each channel, the 300/1200 input impedance switching marked on the front, and 48v, Phase, and Mic vs. Line selection switch.

Will attach pic's..


 
Pic's of this ragged ol' beast..

10373110_10155522437380282_7576465966880013394_o.jpg


11212677_10155522437185282_2805936895564957496_o.jpg


11206626_10155522437375282_1784638160460509728_o.jpg


I'm not sure why the left channel PCB seems to be smaller - looks like it may be more like the size of an original Neve board.

Should I be looking at implementing stepped rotary switches for gain on this circuit?
(current mic gain switches are regular continuous type)

Also, I don't have to keep this enclosure, i guess - but it does seem decent - but if I do, I feel like I should add a LINE in, partly just to be able to put a pot on the front for this function.. seeing as it's already drilled and marked on the panel.  Any suggestions there much appreciated as well.

It also doesn't have the switching for selecting 300 vs 1200 ohm input impedance.  Is this just a matter of adding a switch and wiring over to the various posts on the input transformer?

THANKS folks.
Evan (Melb)
 
RuudNL said:
Does it sound as funky as it looks? 

I actually haven't plugged it in or powered it up.  I'm a little afraid!

But who knows.. maybe it works like this? !!

Do you dare me to try it?
 
What's odd, is that the larger PCB on the right is quite recognisable as having the same track layout and topology as the JC1272 that  I've seen here:
http://groupdiy.com/index.php?topic=19648.msg229701#msg229701
(it's basically the layout from one side of this larger board)

But the PCB on the left is smaller, not a repeat of the same layout, so I'm not sure where the layout for that one is from..
Any ideas?
 
peterc said:
My designs have many revisions, the Green pre PCB ended on V13, I think....

Ah, thanks Peter!  Did you make these boards? 
Have you still got any files to show component overlay and such?
Would be great to get ahold of any resources.
:)

THANKS
 
EvLoutonian said:
peterc said:
My designs have many revisions, the Green pre PCB ended on V13, I think....

Ah, thanks Peter!  Did you make these boards? 
Have you still got any files to show component overlay and such?
Would be great to get ahold of any resources.
:)

THANKS

Peter did the Green Pre layout and boards if thats what your're asking,
Documents for the Green are still easily available, just search Green Pre in google,
it was a really popular project.


 

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