8 Channel, 3U NEVE 1073 completed

[rp3703]

So did either of you answer my question? Is it normal operation to see signals on my scope at different levels. It was the same for both channels of my two channel EZ1290.

 

[Whoops]

So did either of you answer my question? Is it normal operation to see signals on my scope at different levels. It was the same for both channels of my two channel EZ1290.

Did you read what Ian wrote?
he clearly replied to your question and much more

Ian is always a gentleman.

 

[ruffrecords]

So did either of you answer my question? Is it normal operation to see signals on my scope at different levels. It was the same for both channels of my two channel EZ1290.

The answer is with a floating transformer output such as the Neve 1073 has, there is NO SIGNAL between hot and ground or between cold and ground. Anything you measure this way is due to stray capacitances. The signal exists ONLY between pins 2 and 3 on an XLR or between tip and ring if using TRS.

Cheers

Ian

 

[rp3703]

Ok, so when I bias the output, I need to connect my probe and found to pin 2 & 3 or tip and ring in my case? Does it matter which one goes where?

 

[ruffrecords]

Ok, so when I bias the output, I need to connect my probe and found to pin 2 & 3 or tip and ring in my case? Does it matter which one goes where?

No, because the output is floating.

Cheers

Ian

 

[boomfred]

Hello there,
I am building a dual ez1290, I thought I did well but obviously, I didn’t.
Here I am with the oscillation high pitched noise. I swapped 2n3055 and I am using shielded cables for audio.
The problem is the same on both of preamp, so I assume I did something wrong but I can’t see where/when/what.
Any advice is welcomed.
Thanks.

 

[TillM]

What about testing your 1290 without the in between kit to check first, if the oscillation comes from the main board?

 

[ruffrecords]

You don not appear to have any of the XLR pins 1 connected to the chassis. You also do not appear to have B- connected to chassis at the power in connector.

Cheers

Ian

 

[boomfred]

Thanks for helping.

I did get out the Go Between too, but it didn’t change much.

You don not appear to have any of the XLR pins 1 connected to the chassis. You also do not appear to have B- connected to chassis at the power in connector.
Cheers
Ian

:-[
Yep, you’re right. I fixed that. It’s way better, but I still have a pretty high noise floor (around -36dB with the switch all the way up).

Thing is I’m waiting for a front panel, so I just put some plastic board in front of the unit for the moment.
And I do have a ground issue with the Grayhill (touching it make it buzz, and connecting a wire  from the back of it to the ground lake the buzz go).

Should I wait for my front panel before trying again ?

 

[Whoops]

Thing is I’m waiting for a front panel, so I just put some plastic board in front of the unit for the moment.
And I do have a ground issue with the Grayhill (touching it make it buzz, and connecting a wire  from the back of it to the ground lake the buzz go).

test it with the wire connected to the switch case for now.

Check also one thing:
- the PCB has 4 screw holes. If I remember correctly one of the hole has a connection to ground.
If you used metal standoffs I might have a ground loop there. Try removing that standoff and screw.

I had this problem in the past, I have buzz from a ground loop in that spot, changing the standoff for a plastic one solved it

 

[boomfred]

I only use plastic standoffs.
And yes I did clip some wires from the switches to the case.
Thanks.

Another question.
I only connect Pin 1 of the inputs to the ground.
Should I do that too on the output XLRs ?
(cause I think I shouldn’t...).

 

[Whoops]

I only use plastic standoffs.
And yes I did clip some wires from the switches to the case.
Thanks.

Another question.
I only connect Pin 1 of the inputs to the ground.
Should I do that too on the output XLRs ?
(cause I think I shouldn’t...).

Normally you dont need, but you can do it.
You can try also with aligator clips for testing

 

[Whoops]

I am building a dual ez1290, I thought I did well but obviously, I didn’t.
Here I am with the oscillation high pitched noise. I swapped 2n3055 and I am using shielded cables for audio.
The problem is the same on both of preamp, so I assume I did something wrong but I can’t see where/when/what.

1) check and inspect the PCB for any solder bridge
2) Check all electrolytic caps orientations
3) Check all resistor and caps values. sometimes is easier to fit a 200K resistor instead of 20K or 200ohms. The same with caps, installing 1nf instead of 1uf, or 10nf instead of 100nf

4)check all transistors orientation

5) re-check all connections to the transformers and from the transformers

6) do a drawing of all the ground connections, and re-check all ground connections one by one

_____

As you are having the problem in both channels, maybe there is a mistake in both, or something that affects both in the same way (cabling, grounds, PSU)

 

[Whoops]

What PSU are you using?

please post pictures

 

[boomfred]

PSU is a JLM Audio Power Plant.
I’ve been working on it for a few days now, actually rebuilt it twice, double or triple check every single element and orientation.
There was a mistake on the second card, an electrolytic cap (C6 ?) was not right labelled. I did fry two of them before I got it.

What picture do you want ?

 

[Whoops]

What picture do you want ?

photos of the PSU

As you have an external PSU you should have a separate conductor for 0V and another one for Chassis , from the external PSU into the mic amp.
Do you have this way?

The JLM PSU connects the 0V to chassis through a resistor and a CAP, You have to use a metal standoff for that as that connection is made in one of the PSU holes. You need that connection.

And then you run 0V and Chassis (case to case) from the PSU separated, and dont connect them in the mic pream case, leave them always separated.
They only connect at one point and that it's in the PSU

 

[boomfred]

Here’s a picture of the PSU.
You can see the green and yellow wire connected to the ground of the PSU. Then I have a 4 wire cable running to the rack case (case, 0v, 24v, 48v).

I will re-check the ground scheme tomorrow, that’s a lead.

 

[Whoops]

Here’s a picture of the PSU.
You can see the green and yellow wire connected to the ground of the PSU. Then I have a 4 wire cable running to the rack case (case, 0v, 24v, 48v).

I will re-check the ground scheme tomorrow, that’s a lead.

Nice.
Do you have the PSU PCB on plastic or Metal standoffs?

Check if the PSU has 0V connect to Chassis through a 10r resistor and 100nf cap, you can see that connection in the schematic.

That connection in the PSU is the only 0V to Chassis/Earth connection you should have in the whole build.

 

[boomfred]

Turns out I picked the wrong pad of the PSU board to wire the mains ground to case.
I picked red where it should be green.
(See picture below).

That’s better.

Although, I don’t get something.
If I connect XLR’s pin1 to the case of the rack, I do connect too the case to 0v of the PSU, which is not supposed to happen with the JLM PSU.
Am I wrong ?
I’m kinda lost in here.

 

[Whoops]

Although, I don’t get something.
If I connect XLR’s pin1 to the case of the rack, I do connect too the case to 0v of the PSU, which is not supposed to happen with the JLM PSU.
Am I wrong ?

I'm sorry I didn't understand your question, can you please refrase it?

Also, please check my posts, I asked you some questions you didnt replied to...