8 Channel, 3U NEVE 1073 completed

[mrdarwin]

Volker has some nice PCBs for your project.
Look at the white market @silentarts

Thanks, I'll take à look

 

[NannerPuddin]

Finally got my first four working. It was a ton of work getting them squeezed into a one unit enclosure. I made my own -20db pad with a DPDT switch and resistors rather than go the Go-Between route.  I plan on building three more for a total of 16 channels.  I have a 2u power supply Then I have built that will supply all 16 units when I am done. I hope to post more pics soon. 

 

[madriaanse]

I’m impressed you were able to squeeze four into a 1U rack! Nice work! Any problems with crosstalk?

Take care,

M.

 

[Rocinante]

Curious. If I were to convert these to line in where would I tap into?
Also I could then just use one deck of a grayhill wired off board?

 

[Whoops]

Finally got my first four working. It was a ton of work getting them squeezed into a one unit enclosure.

Hi, congratulations for your build.

I would like to advise you to rethink the position of your output transformers, the EMI between them will ramp the crosstalk between channels.

I made a video some years ago illustrating that problem, you can listen the crosstalk with the transformers in different positions.
Sound enters channel 1 input, and what you listen in the video is channel 2 output:

https://www.youtube.com/watch?v=6yXgkk52bUo

You should do the same test with your build because I'm pretty sure you can improve your crosstalk.

I would advise this output transformer placement for your build:

 

[fauxjazz]

Hi all, I recently finished assembly on a 2-channel EZ1290 with an external JLM Power Plant 2 as PSU, however I am experiencing some issues. Both pres seem to work properly with dynamic mics (and seem very quiet), however enagaging the 48v results in a lot of noise on both channels. Condenser mics are working, but other extraneous noise is introduded. I used screened cable throughout, except from the 48v from the preamp chassis to the switch/led. I have since since replaced this with screened wire and also between the 24v and 48v from Power Plant outputs to the power xlr (4 pin) in the PSU chassis. This has helped a lot, but there is still too much noise when using a condenser. The noise is not hum but rather hiss, and before replacing the unshielded wire, there were other  (PSU?) noises. All my voltages appear to be correct from the JLM, and on the xlr input pins.  I used 2 core screened cable from the 48v switches/leds, with both cores tied together at the switch end then each to a 6k9 resistor attaching to the xlr inputs (pins 2 + 3). I this a common issue? I have read through the entire thread, but couldn't find much helpful information. Do I need to add any additional power filtering at the power jack on the Preamp Enclosure? Any help with resolving this would but greatly appreciated, as otherwise the pres are sounding great! Thanks all. 

 

[Whoops]

Both pres seem to work properly with dynamic mics (and seem very quiet), however enagaging the 48v results in a lot of noise on both channels.

The noise is not hum but rather hiss

Strange, I really dont know what might be the culprit.
I never had that any hiss in my 1290 builds, I had hum one time and that was a Ground Loop because if I remember one of the pcb holes as a pad to ground and I was using metal standoffs, replacing that standoff with a plastic one solved the ground loop.

I also never used shielded cable for the voltage wires, I just used shielded cable for the audio path. From input XLR to input tx, Tx to PCB, output pcb to out transformer and out tx to XLR. Never had any hiss or hum

Hope you can find what is the source of the problem and solve it

 

[NannerPuddin]

I’m impressed you were able to squeeze four into a 1U rack! Nice work! Any problems with crosstalk?

I saw Whoops's video and it freaked me out a bit!  That's a lot of crosstalk!  I just went and did a fairly extensive test of all of the channels using a 1k sine wave, and I did not get any crosstalk on the other channels.  I am going to try a little later and use some test signal that has actually wideband musical content to see if that would cause any crosstalk.

So that video has me good and scared, so I wonder if i might be missing something in my test.  The output during the test on the hot channel close to 0dbfs.  I had the gain all the way up on the other channels and all that came through was some faint noise floor sound.  Pretty quiet, though.

Thanks,

Doug 

 

[Whoops]

So that video has me good and scared, so I wonder if i might be missing something in my test.  The output during the test on the hot channel close to 0dbfs.  I had the gain all the way up on the other channels and all that came through was some faint noise floor sound.  Pretty quiet, though.

Hi Nanner, don't  use a 1K sinewave because the crosstalk will be frequency dependent and some frequencies will bleed much more than others.
Use music for the test.
In your case I would inject music into channel 2 input, and Listen the output of channel 1 and channel 3, bring the gain up from 40 to 75 dbs to listen to the crosstalk. You can then unscrew the transformers and do the same test with the layout I suggested and see if it improves the crosstalk.

Actually the position you have the transformers is not the worst, the worst position is side by side as it is in the video, anyway even then I think the layout I suggested will reduce the current crosstalk.

Best regards

 

[sedit1]

I have built 4 of these amazing preamps. No i feel that for sime onstances the sound is littlebit dark. I’m using carnhill trafos and styrene caps.

I was thinking mayby do some mod for the two and wanted to ask if you have some ideas how to make the sound littlebit more open? Maybe experimenting with output caps?

Thank you!

 

[rp3703]

Hi All, I know this thread is a decade old now but since it has replies from 2020, it thought I'd give it a try. I built a 2 channel 1U version a few years back and biased it using the volt meter method. Last night I used an oscilloscope and noticed that the level on one side of the balanced signal is lower than the level on the other side. Is this normal? Am I looking at it wrong?

 

[Whoops]

Hi All, I know this thread is a decade old now but since it has replies from 2020, it thought I'd give it a try.

Hi, this thread is not old, this is the build thread for Madrianse 1290 mic pre. It can be used for anyone building this project at any time.

Also I really don't see any thread in general as old, a thread can be 6 years old but still be relevant nowadays so a discussion might re-start some years after and that's great because it's updated knowledge.

Last night I used an oscilloscope and noticed that the level on one side of the balanced signal is lower than the level on the other side. Is this normal? Am I looking at it wrong?

What you mean is that the signal in the output XLR Pin3 is lower than at Pin2 or vice-versa?

I would find that really strange, balancing means those signals should exactly the same but with opposite polarities.

Something is not right or there's some detail missing...

If you don't get help over here, post a thread on the LAB section so you get help from the general crowd. You should investigate whats goin on

 

[rp3703]

I actually used TRS for outputs but the Tip has a stronger signal than the Ring. I guess I need to take another look at my output wiring again.

 

[ruffrecords]

I actually used TRS for outputs but the Tip has a stronger signal than the Ring. I guess I need to take another look at my output wiring again.

The signal at a balanced XLR exists only between pins 2 and 3 and on a balanced TRS only between tip and ring. Pin3 and the sleeve are the connection for the screen. It is not a signal connection. There is no definition of a signal between tip and screen or between ring and screen. This is especially true for Neve transformer balanced floating outputs.

Cheers

Ian

 

[rp3703]

Hi Ian,

I’m not sure I understand what your saying? I connected the probe of my scope to the tip and the ground to the sleeve. When I moved the probe to the ring and left the ground connected to the sleeve, the visual signal on the scope was smaller. I am an amateur at this stuff so excuse my poor explanation. I can’t tell if you’re telling me that the + & - signals are supposed to be at different levels or if your telling me that I am hooking my probe up incorrectly.

 

[Whoops]

The signal at a balanced XLR exists only between pins 2 and 3 and on a balanced TRS only between tip and ring.

Well but those are 2 signals, one in Pin2 and another in Pin3, and those can be measured individually with a 0v reference. Am I wrong?

Thanks Ian

 

[ruffrecords]

Well but those are 2 signals, one in Pin2 and another in Pin3, and those can be measured individually with a 0v reference. Am I wrong?

Thanks Ian

Yes, I am afraid you are wrong. A floating transformer is not referenced to 0V (except perhaps through stray) winding capacitances, The signal exists only across the secondary winding of the transformer which are connected to pins 1 and 2. You do not need pin3 to send the signal to another piece of equipment.

People often get confused about this because electronically balanced signals  ARE each referenced to 0V and often they are the same value.  But they do not have to be the same value to be balanced ( e.g. impedance balanced) nor do they have to be referenced to 0V.

Cheers

Ian

 

[Whoops]

Yes, I am afraid you are wrong. A floating transformer is not referenced to 0V (except perhaps through stray) winding capacitances, The signal exists only across the secondary winding of the transformer which are connected to pins 1 and 2. You do not need pin3 to send the signal to another piece of equipment.

People often get confused about this because electronically balanced signals  ARE each referenced to 0V and often they are the same value.  But they do not have to be the same value to be balanced ( e.g. impedance balanced) nor do they have to be referenced to 0V.

Cheers

Ian

Thank you so much for explaining Ian, I really have to study better about that.

i really can't get me head around of what that is in reality. I can understand electronic balanced signals, there AC on PIN2, the same AC on PIN3 but with reverse polarity, and on the on the next input one of them has the polarity reverse and summed with the other.

With Floating I really don't understand the concept...

 

[ruffrecords]

Thank you so much for explaining Ian, I really have to study better about that.

i really can't get me head around of what that is in reality. I can understand electronic balanced signals, there AC on PIN2, the same AC on PIN3 but with reverse polarity, and on the on the next input one of them has the polarity reverse and summed with the other.

With Floating I really don't understand the concept...

It is exactly the same as the mains supply coming into you house from the local utility transformer - the voltage and the power exists only between the live and neutral. In some countries (like the UK) the neutral is connected to earth so if you measure between earth and neutral you get zero volts and between live an earth you get mains volts. In a floating system neither live nor neutral is connected to earth. You still get mains volts/power between live and neutral but it is anyone's guess what you get between live and ground because they are no connected.

The 600 ohm system we use in audio is derived from early telephone systems. These had miles of parallel wires on telegraph poles, just two wires, hot and cold (no earth in sight). One end was driven by a transformer at the exchange and the other end was your phone which had a hybrid transformer in it. It is balanced floating throughout.

The use of semiconductors and in particular op amps has led to balanced circuits that DO have an intrinsic reference to 0V and this inevitably gets connected to pin1 of the XLR. It is this misunderstanding of the role of pin 1 that led to the well known pin 1 problem. There is plenty of stuff about this that may help you understand here:

http://pin1problem.com/

Cheers

Ian

Cheers

Ian

 

[producerxtr]

In the guide it mentions 60/40 Rosin Core Solder, is 60 the Lead or Tin?

Can someone with PROPER knowledge clarify the percentages for Sn and Pb respectively?

Cheers,

Tom