Whoops

Neve Output transformers - Distance and Position ?
« on: December 09, 2016, 05:42:50 PM »
Hello,
I received an unit for maintenance.

It consists of 5 original Neve 1272 racked and wired as Mic preamps.
Theres a sixth channel it's a DIY 1272 clone with Sowter transformers.

The person that did the rack up job positioned the all Output transformers  really close to each other, some of them almost touching.

Will this created some problems related to electro magnetic interference between the different channels or is it fine?
How far should the transformers be spread apart?

What are your opinions?











Whoops

Re: Neve Output transformers - Distance and Position ?
« Reply #1 on: December 09, 2016, 05:49:23 PM »
Could this type orientation be better than the one currently used on the unit?

It's used in tube amps, it consists in rotating each transformer by 90 degrees.
Would this provide any improvement?



ruffrecords

Re: Neve Output transformers - Distance and Position ?
« Reply #2 on: December 09, 2016, 05:58:27 PM »
In adjacent real Neve modules they were on 50mm centres but there were two layers of sheet steel in between them.

Cheers

Ian

Whoops

Re: Neve Output transformers - Distance and Position ?
« Reply #3 on: December 09, 2016, 06:11:22 PM »
In adjacent real Neve modules they were on 50mm centres but there were two layers of sheet steel in between them.

Cheers

Ian

Hi Ian, yes I thought about that, on a Neve console they were really close but there was the sheet of it's own module and the sheet of steel of the neighbor .

what do you mean by *50mm centres"?

ruffrecords

Re: Neve Output transformers - Distance and Position ?
« Reply #4 on: December 10, 2016, 02:52:57 AM »
Hi Ian, yes I thought about that, on a Neve console they were really close but there was the sheet of it's own module and the sheet of steel of the neighbor .

what do you mean by *50mm centres"?

The Neve modules were 50mm wide so the distance between a line drawn down the centre of one transformer and one another line drawn down the centre of one in an  adjacent module would be 50mm apart.

Cheers

Ian

Whoops

Re: Neve Output transformers - Distance and Position ?
« Reply #5 on: December 11, 2016, 07:15:37 AM »
Yes youre right, I guess the 2 steel sheets will provide some degree of shielding.

But in the unit I have on my bench all the output transformers are really close to eachother with no shielding.

What implications this might bring?

ruffrecords

Re: Neve Output transformers - Distance and Position ?
« Reply #6 on: December 11, 2016, 10:18:32 AM »
Yes youre right, I guess the 2 steel sheets will provide some degree of shielding.

But in the unit I have on my bench all the output transformers are really close to eachother with no shielding.

What implications this might bring?

There will be some coupling between adjacent transformers but I expect it will be extremely small. Best thing to do is measure it. Send a signal through one channel and feed the output of an adjacent one into a mic pre. Slowly turn up the mic pre gain and see if you can hear anything.

Cheers

Ian

Whoops

Re: Neve Output transformers - Distance and Position ?
« Reply #7 on: December 11, 2016, 05:56:20 PM »
There will be some coupling between adjacent transformers but I expect it will be extremely small. Best thing to do is measure it. Send a signal through one channel and feed the output of an adjacent one into a mic pre. Slowly turn up the mic pre gain and see if you can hear anything.

Cheers

Ian

I will do that.

would the possible problems be only coupling between transformers?
Could also the magnetic field of one transformer interfere with the performance of the transformer next to it and vice versa?

ruffrecords

Re: Neve Output transformers - Distance and Position ?
« Reply #8 on: December 11, 2016, 06:18:08 PM »
I will do that.

would the possible problems be only coupling between transformers?
Could also the magnetic field of one transformer interfere with the performance of the transformer next to it and vice versa?

The transformer only creates a magnetic field when a signal passes through it so when there is no signal it can have no influence on the transformer next to it.

Cheers

Ian

API

Re: Neve Output transformers - Distance and Position ?
« Reply #9 on: December 12, 2016, 02:37:50 PM »
In some desks where several output transformers were mounted next to each other i have seen a large L-bracket mounted under the transformer providing some sheilding between them.



Whoops

Re: Neve Output transformers - Distance and Position ?
« Reply #10 on: December 12, 2016, 02:43:46 PM »
In some desks where several output transformers were mounted next to each other i have seen a large L-bracket mounted under the transformer providing some sheilding between them.

I can do some L brackets to place between the Neve Output transformers, what type of material sould I use for the shield?

Whoops

Re: Neve Output transformers - Distance and Position ?
« Reply #11 on: December 13, 2016, 06:27:54 PM »
There will be some coupling between adjacent transformers but I expect it will be extremely small. Best thing to do is measure it. Send a signal through one channel and feed the output of an adjacent one into a mic pre. Slowly turn up the mic pre gain and see if you can hear anything.

Cheers

Ian

Hello Ian , I haven't been in the shop, but will go there in the next days and do the test you suggested, thanks.

Sorry for the ignorance, but by coupling do you mean crosstalk between channels?

As Im trying to understand and learn on the negative sides of having the output transformer that close to each other, could you let me know what would be the expected problems signal was present in all the 6 channels and Output transformers,
Crosstalk?
Hum or induced noise from the adjacent transformer?
Lower signal because of magnetic interference?
Altered frequency response?
interference in the balanced output (signal + and -  not 180 degrees of of phase)?

Sorry if the questions are silly this is a new subject for me

PRR

Re: Neve Output transformers - Distance and Position ?
« Reply #12 on: December 14, 2016, 12:21:05 AM »
Put football program in channel 1.

Put birdsong program in channel 2.

Listen to the output of channel 2 (birdsong). Do you hear football score-roar?

That (with numbers) would be the spec for a Radio Network master control console. You should be able to patch-through two very different programs and not hear the loud one in the soft one. Pop/rock should not echo in Beethoven's pauses.

In most small-studio work ALL the outputs will eventually wind up in the same place, the same song-track. They may originate all in the same room. The leakage one can to the next is probably the least of your worries. True, if the extra-FUZZ guitar is cut from the final mix, you don't want its ghost in the remaining tracks. But over-dubbing a new fuzz guitar will mask much of that.

I believe the spacing you have will be OK for all but the most segregated sources.

Tekay

Thomas "TK" Kristiansson
----------------------------------
"The Sound Is In The Iron"
www.vintagedesign.se  www.tkaudio.se

ruffrecords

Re: Neve Output transformers - Distance and Position ?
« Reply #14 on: December 15, 2016, 04:20:46 AM »
I think you really need to find out if there is a problem before looking for solutions. Take PRRs advice and see if you can actually hear any crosstalk. I expect it will be really tiny.

Cheers

Ian

ln76d

Re: Neve Output transformers - Distance and Position ?
« Reply #15 on: December 15, 2016, 06:41:07 AM »
Fully agree with Paul and Ian. First test it, your build looks like easy to mod, so if there will be any problem with positioning then try rotating half of them as also made shielding.

Whoops

Re: Neve Output transformers - Distance and Position ?
« Reply #16 on: December 15, 2016, 07:03:01 AM »
Hello,
thank you all.

I will do the crosstalk tests like you advised and go from there.

My concern was also if there could be any other problems besides crosstalk in having the transformers so close to each other.
I probably was not clear in explaining,
what I wanted to ask also is if besides the crosstalk any of the following problems can occur also, or if crosstalk is the only concern.
Hum or induced noise from the adjacent transformer?
Lower signal because of magnetic interference?
Altered frequency response?
interference in the balanced output (signal + and -  not 180 degrees of of phase)?

PRR

Re: Neve Output transformers - Distance and Position ?
« Reply #17 on: December 15, 2016, 12:58:19 PM »
> Hum or induced noise from the adjacent transformer?

If one can is passing 13V of 50Hz hum, that might get to the next can. But why would you be feeding big hum to one channel while asking for perfection from the next channel? The transformer does not hum unless you make it.

Just by being on an E-I closed core, 99.9% of signal stays in the core. Also 99.9% of external signal will not leak in. This is still a problem when you stack a mike-amp on top of a 900W power amp's PT. It is very unlikely to be a problem for several audio programs at roughly similar levels. Paper-thin spacing between cores may be ample. As you also have a can (and presumably some space between can and core), I'd think the cans could be as close as the mount-hole drill precision allows.

ruffrecords

Re: Neve Output transformers - Distance and Position ?
« Reply #18 on: December 15, 2016, 01:01:54 PM »
what I wanted to ask also is if besides the crosstalk any of the following problems can occur also, or if crosstalk is the only concern.
Hum or induced noise from the adjacent transformer?
Lower signal because of magnetic interference?
Altered frequency response?
interference in the balanced output (signal + and -  not 180 degrees of of phase)?

There is no reason to think any of the above should occur.

Cheers

Ian

Whoops

Re: Neve Output transformers - Distance and Position ?
« Reply #19 on: January 09, 2017, 11:41:40 PM »
Hello everyone,
thank you so much for all your input and information.

I was only able to the the Crosstalk listening over the weekend, I did 2 videos showing the crosstalk at different output transformer positions.
Here are the Videos,  be prepared for a minute of distortion:

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

https://www.youtube.com/watch?v=R_dqkKAFTKE

________________________________________________________

INFO

This unit is not my build, I was just asked to do some maintenance.
It consists in 5 original Neve 1272 amplifiers that were racked as Mic Pres, it has a 6th channel that is a DIY 1272.
It was done 12 years ago or more, so before the widespread internet information on racking Neve and DIY Neve related stuff.
It is well built.

Test/Recording

I fed music from my iPod left channel into channel 2 (channel 1 is out at the moment) and listened the output of channel 3

iPod Classic Headphone output, Euro model with volume limit. The Output Volume was set to Max
This is the info I could find regarding the output signal of the iPod Heaphone amp:
"iPod Classic's headphone out into a high impedance load is Up ≈ 0.47 Vp (peak)
This means Urms ≈ 0.332 Vrms and thus Lu ≈ -7.3 dBu"
"20Hz to 20kHz freq. responce, 30mW per channel power output, and 24 ohms"

Channel 2 (input channel)
Gain was set at 6, it's a 12 position switch, I dont have a scheme of the rack up so I don't know what that translates to gain. It should be 35db's or 25db's. (I can measure the switch resistors to know for sure but it would not make a difference for my goals)
I could listen to Crosstalk even if Gain was set at 1, I increased the Gain to help monitoring levels and recording levels.

Channel 3 (Output crosstalk channel)
Gain was set at minimum, changing gain didn't make a difference.


__________________________________________________________________________

Let me just be clear:
My Goals are not measuring crosstalk, the only thing I'm looking for is to know which could be the best positions for the 6 output transformers in the free space I have available in this box.

I'm not trying to get rid of crosstalk, and I know the amount of amplification involved in my recording is huge, so this doesn't tell us anything about a crosstalk figure, it just helps me in comparing  the crosstalk for different positions and decide if there's a certain positioning inside the limited space I have in this box that could have the crosstalk minimized even if the crosstalk level at the worst case scenario was marginal or negligible in a studio session.

______________________

Conclusions:

- for all the possible positions I tried, the present positioning with all the transformers next to each other is the worst possible one

- shielding greatly reduces the crosstalk when the transformers are next to each other , in Neve desks thereswas 2 sheets of steel between the Transformers (modules cases), I used toroidal trafo shield from don audio for the test, it works fine

- Rotating the transformers 90 degrees decreases the the crosstalk to "roughly" the same level as having them next to each other with shielding

- Best position I found is having one transformer elevated and positioned horizontally. It's easier to see in the video or the drawings.










« Last Edit: January 09, 2017, 11:45:59 PM by Whoops »