8 Channel, 3U NEVE 1073 completed

[nikonet]

Hi every one,

I've got a small question:

I made a 4 préamp rack, with 4 PCB. What to do with the 10R resistor connected between pcb 0v and Ground? Do i need one resistor for each pcb? or do i need only one for all the Pcb? And what does it do?

I ask this question because: when i test ohm between the ground and pcb's 0v there's less than 10R.

Thanks a lot

 

[desol]

Did you use the JLM powersupply? Powerstation?

If so, it has the 10ohm resistor built in....so no need to add it. This is a floating ground. Leave the grounds unconnected on the outputs... To test it....measure ohms between 0v and case ground...you should get 10ohms.

 

[nikonet]

Hi,

No it"s an Swithed power supply. So i need to test in the PSU between OV and Ground !

If 10R not inside the PSU, do i need only 1 for 4 préamp?

Thanks

 

[bigswole]

are these boards still available?

 

[atticmike]

I know I'm a noob and pester most of the time but I got the following questions:

1: Why doesn't this build require -V?

2: Why is there no separate shielding for the input?

Mike

 

[MRecords]

Hi everyone,

i build two channels of the ez1290. One of them has about 10dB more hum than the other. Has anybody an idea where this could come from?

Thanks

 

[useme2305]

post some clear gut shots. maybe someone spots something.

also, do you use an external power supply or do you have the toroidal inside the case with the preamps? if so, is the one closer to the psu humming?

 

[MRecords]

Thanks for quick reply. I don´t have a camera at hand just my (old) handy. I´ll take better pictures soon. But optical both channels look the same at least for me. The power supply is in an external case so no interferences from there. It´s time to get a scope again.

Thanks

 

[MRecords]

And another shot from the pcb.

 

[bluesbaz]

I just finished 4 of these and my advice if you dont have a scope is to try and separate the various sections by grounding their inputs while listening to the output of the preamp. If you still hear noise the problem is after the grounded point if you stop hearing noise the problem is before the grounded point.

ground the hot leg on the output of the input transformer
then C8A
and then C8B
and lastly C1
If you still hear noise
build a stethoscope
listen to the cold leg of a cap of any value (rated higher than the voltage of your project) strapped to the hot leg of a quarter inch cable while the ground of the same cable is strapped to the ground of your project and poke around until you can hear the noise your hearing on the output.
CJ told me about this trick i will forever be grateful!
If the noise is still just everywhere I would look at your power supply

If you still haven't isolated the problem get back to us.
-s

 

[useme2305]

MRecordds, the only obvious difference i can see between your two channels is that you swapped the resistor's and cap's posistions on the output transformer.

also, i used the same enclosure from banzai. isn't it total crap? it was the first time for me working with a 19" enclosure but i can safely say that there can not be a worse 1U rack for DIY than this piece or poorly designed junk. that it's made of steel doesn't help either. it's impossible to drill cleanly.

what i noticed when working with the enclosure is that case grounding via srews does happen mostly sporadically. i don't know why but it could be the finish on the enclosure and the crappy mounting methods between the parts of it.
do some tests with your DMM to see if the transformer casings and whatnot are case grounded properly. you may need to do some sanding or filing around the screw holes.

also, you could try to swap the boards and use either board with each possible configuration of transformers to get to the problems cause. (ausschlussverfahren).

 

[MRecords]

I got it or should i say you got it useme. I use the same case for my power supply and it´s really the worst i´ve ever seen.  It really seems like the upper and down plates (hope you know what i mean) from the case aren´t grounded.  The output tranny of the noisy preamp is directly above the power tranny. I thought there is a case so there can´t be interferences but i was wrong. When i move the preamp about two inches the noise is gone.  Sometimes things can be so easy.

I´ll try the stethoscope. Sounds very interesting and can be a problem solver for future projects.

Thank you very much!!!

 

[wolfgang]

It really seems like the upper and down plates (hope you know what i mean) from the case aren´t grounded.

You should remove the lacquer or the anodising from the top and the bottom of the case were you bolt them to the Main Chassis. And also on the Main Chassis nera the Screws. A small Dremel ist your friend!

regards,
Wolfgang

 

[MRecords]

Hey wolfgang, you´re still here 

I already removed it but it´s a steel case. I´m a little bit afraid of rust and oxidation. Maybe a new case would be the best.

Thanks

 

[desol]

It's tough to remove EMI. I used some mumetal sticky sheet on the case....ultraperm 80...and it helped. I also adjusted/moved things. You may want to place the power supply in a different location in the rack away from the preamps.
For my next unit...i was thinking of trying parmetal's EMI protected case...but it may amount to little improvement for more $$$. Not sure...

 

[atticmike]

Thanks for quick reply. I don´t have a camera at hand just my (old) handy. I´ll take better pictures soon. But optical both channels look the same at least for me. The power supply is in an external case so no interferences from there. It´s time to get a scope again.

Thanks

looks like there is no star point in your build

Try to collect all the ground to a dedicated point and lead them there separately.

 

[useme2305]

question about biasing:

i just finished my first two channel unit of four planned dual preamps.

when trying to set the bias am i supposed to turn the trimmer until the clipping is equal on both sides of the waveform and then just stop turning the trimmer? because when i keep turning the trimmer the waveform looks equal on both sides for the whole 15+ more turns till the end.
meaning, when i turn the trimmer,which is a 20 turns trimmer, fully counter clockwise the waveform looks unsymmetrical. so i begin turning the trimmer clockwise and after three or maybe four full turns the waveform begins clip equally on both sides and once it reaches that status it looks like that for the whole 16 more turns of the trimmer. so i assume i just turn the trimmer until it looks good and then stop?

 

[useme2305]

anyone? 

 

[sr1200]

Yeah, as far as I remember, once you have symmetry, you're good to go.  Not a terribly complicated process (unlike the 1176's haha)

 

[dmp]

when trying to set the bias am i supposed to turn the trimmer until the clipping is equal on both sides of the waveform and then just stop turning the trimmer? because when i keep turning the trimmer the waveform looks equal on both sides for the whole 15+ more turns till the end.
meaning, when i turn the trimmer,which is a 20 turns trimmer, fully counter clockwise the waveform looks unsymmetrical. so i begin turning the trimmer clockwise and after three or maybe four full turns the waveform begins clip equally on both sides and once it reaches that status it looks like that for the whole 16 more turns of the trimmer. so i assume i just turn the trimmer until it looks good and then stop?

I think so.