8 Channel, 3U NEVE 1073 completed

[desol]

Do you have a scope? Follow the sine wave along from first to second stage to output, to see where it goes wrong.

 

[sgenevay]

I had output problem on a Channel...level was lower... It seems that there could be several reasons... But my problem was defective input transformer.
Maybe compare resistance between transformers pins. And see if u have same values.
Martin told me to check if 2n3055 either was not defective.
Hope that will help....

Sylvain.

 

[mica]

I only have a software scope so im stuck with only reading waveforms from the final output.. But what could be wrong when the output signal is lower and the waveform looks uneven like it does on Ch2? I should mention I'm not very advanced when it comes to electronics

 

[mica]

Thx Sylvain.. I'll look into that.

 

[punkrocker]

Hi all newbie here. I'm doing an EZ1290 for my 1st DIY project. I'm using everything exactly as listed in the BOM.

Here's my problem:
I tested the JLM ACDC PS outside of the case with the transformer and Qualtek piece specified in the BOM. Everything worked perfectly and I adjusted all the voltages correctly.

BUT, now I have put the powersupply in the case and everytime I turn it on the fuse blows.

I would really appreciate some advice!

UPDATE: Okay I just took the ACDC and Transformer out of the case and put them on a rubber mat. Everything is working out of the case, but the fuse still blows when its drilled into the case. Any thoughts?

 

[signalflow]

How about a pic or description of how it's mounted in the case?

-Casey

 

[snipsnip]

somethings clearly shorting to the case. your voltage regs maybe?

Pic will help.

 

[mica]

OK, trying to do the BIAS adjustment: add a 1 KHZ tone to input untill clipping.. My Ch 2 is lower in volume that Ch 1 for some reason, and the waveforms look very different:

Ch1:

Ch2:

Could someone point me in a direction on what to look for?

M

Hmmm.. made a test yesterday with some simple vocals, and the two channels sounds very much the same, also in volume, when turned up equally high.. I have no idea why the two waveforms are so different..?

 

[sr1200]

Had the same issue using metal standoffs with the case... (others say this didnt happen to them, but 3 out of 3 JLM powersupplys i had would blow if metal stand-offs were used...) perhaps the standoffs i was using were too wide and contacting a trace on the board... who knows... as soon as i used nylon s/o's everything worked perfectly.

 

[desol]

Hmmm.. made a test yesterday with some simple vocals, and the two channels sounds very much the same, also in volume, when turned up equally high.. I have no idea why the two waveforms are so different..?

Well, you wanna be sure it's not something stupid before you start desoldering. ie: connectors, cabling, etc...

Time to invest in a scope. Tek 2215 or something...you can get em for next to nothing these days. Must have.

Either way, the top waveform is not adjusted symetrically and the bottom waveform could be an incorrectly installed, valued or damaged component.

 

[mica]

Well I got the waveforms sorted out.. they look the same now, and like they shoud.. But.. I have a humming problem. When I either touch the Gain knob or put my hand in the case close to the wire between the input trafo pin 7 to PCB 7, it hums louder and louder the closer i get. Its the same on both boards. What did I forget to do? (Im using metal standoffs all round if that might be an issue?)

 

[desol]

Something isn't grounded...

 

[0dbfs]

May want to check that your mic cables are wired correctly. I had two instances pop up not long ago where the cable shield was carrying signal and GND was on one of the conductors. Both situations were pinned out slightly different but symptoms were very similar to yours.

I know it sounds sorta obvious but those mistakes apparently do happen. Even with buildings full of engineers. Ahem.

Cheers,
jb

 

[mica]

Something isn't grounded...

How should it be grounded? I'm using the Jlm psu, and metal standoffs to the case. I havn't done any specific grounding yet..?

 

[desol]

Is your case ground ok? Do you have continuity from frontpanel to ground? Scrape some paint off if you need to. Make sure that you use star washers that cut through the paint and touch the metal underneath. You should have continuity from the switch spindle to ground...

Input transformer and xlr cabling needs to be completely shielded.

Experiment, but don't touch ground to any power...obviously.  

 

[mica]

Sorry but i have no idea how to start.. My electronic skills are limited to say the least. Everything is wired ok, shielded where it should be (and my voltages and sound is ok, so im pretty sure its the ground thing ), but how do I "start" ground? Where should i draw it from? I have tried removing the PSU from the case so it doesnt touch the case, but still humming.. When I touch the case or a shield somewhere the humming stops..
Could someone maybe explain it as simple as possible.. Im really trying to learn here



M

 

[snipsnip]

Well there are some details above. Scrape the paint off the case where the screws are. Check and double check your wiring. Also try grounding the pcb to the case from the standoff hole near the 5k trim pot.

 

[desol]

Also try grounding the pcb to the case from the standoff hole near the 5k trim pot.

Actually, you don't want to do this. There should be 10ohms between 0v and ground. The resistor is actually on the JLM.
You don't want to hook 0v to ground directly.

The case, switches, metalwork, etc....should be straight to ground. There should be a nylon standoff used on that hole(i glued mine to the pcb).

 

[snipsnip]

Agreed in theory

However, linking the audio ground to chassis has resolved problems from hum to oscillation in more than one build (including mine).

I dont know why.

 

[desol]

Look here: http://www.groupdiy.com/index.php?topic=13710.0

I have 10 ohms and mine's pretty quiet. Oscillation and hum would probably be due to placement of components/proximity to pwr trans, sheilding, etc... Also, bad case grounding.