AML 1073

[ilfungo]

Hi
I've bulit 2 AML 1073 kit.
I've noted that if I listen the eq at hight level when mid frequency is on  .36 and  .7 frequncy there is hum  ( not at 1.6-3.2-4.8-7.2).
Same on hpf only at 50 and 80 ( less noise)
Have someone noticed the same problem?

The real one have the same problem?
Thanks!!!

 

[AusTex64]

No, my AMS Neve 1073's don't do that. No hum.

 

[ilfungo]

Hi
thanks!
Have you listen it at hight level?

In use it's not a problem but I'm just trying to undertand if it's normal...
Thanks!

 

[BluegrassDan]

Mine is smooth as hand churned butter. Not a hair in it.

 

[Ilya]

This is often either because of the mains transformer coupling into the audio path or incorrect grounding scheme. In the first case try moving the transformer further away or rotating it. You can even experiment and remove it from the chassis while extending the leads and see if this makes any difference.
In the second case make sure to connect audio gnd to chassis at one point only. Take audio gnd from the smoothing cap at the regulator output and connect it to chassis gnd.
My 1073 builds are dead quiet and I followed the above principles.

 

[Flowjow]

Hi
I've bulit 2 AML 1073 kit.
I've noted that if I listen the eq at hight level when mid frequency is on  .36 and  .7 frequncy there is hum  ( not at 1.6-3.2-4.8-7.2).
Same on hpf only at 50 and 80 ( less noise)
Have someone noticed the same problem?

The real one have the same problem?
Thanks!!!

Hi,

I noticed exactly the same behaviour on my two AML ez1073.

I choosed to externalize the power transformers. They are now boxed out of the chassis and the hum has disappeared.

++

 

[ilfungo]

Thanks Flowjow!
I want to have all in a case....
I will experiment...
thanks!

 

[Flowjow]

Alright, keep posted if you find another "in the box" alternative please!

I actually still monitor a tiny pinch of 100Hz and 200Hz. So I think it's transmitted to the audio path, post rectification.

In original racked units, or high quality modern copies (Chandler LTD-1, Vintech X-73, Brent Averill...) not only power transfos are externalized but the whole power supply. And those PSU are  way bigger (I suppose, much more filtered with more and bigger caps...) than the AML one...

 

[SparkleBear]

About a year ago, I noticed the hum in my unit at the same frequencies. I sent a message to Colin at AML and this was the response.

"Eric,

It's a design fault... they are all like that.... only 3 people have ever noticed !

Regards,
Colin Adshead"

So I guess it should be in all of them. If you are recording rock guitars no one will be able to tell... But since i record delicate vocals and acoustic guitars i noticed right away. I will try to look into externalizing the power transformer... Or i might try something like this. http://www.ebay.com/itm/like/251674844129?chn=ps&dispItem=1  -- A Toroidal Transformer cover. I would measure the x-fo in the box to get the right size though. That would be an in the box solution. I wonder if it is traveling in the board or just infecting the signal with magnetism...

Its a bummer that this design flaw is there. Otherwise its a flawless unit!

Also, i know there is a mod to make the last stage fader go to -inf dB rather than just -10db... Thats a good thing to consider too.


Cheers!

 

[Flowjow]

Hi there,

I finally completely got rid of the humming issue in my two ez-1073.

We had spare Chandler Limited PSU-1 at the studio.

They're linear power supply based on LM317 with trim pots, that allow a wide range of DC output.

I Set the DC out to +24V instead of the factory default +28V, removed rectification and regulation sections in th ez-1073 and I finally have two perfectly silent units.

Cheers!

 

[Potato Cakes]

I've built several of these and each time I have used Ian Thompson Bell's grounding 101 principles and I haven't had this issue.

Thanks!

Paul

 

[rockprocess]

I had the hum issue mentioned here too on my pair.  I’ve since wired a parallel 4pin xlr jack to power them from a Chandler power supply.
  The hum is totally gone when powering externally via the Chandler, but I can still power internally in a pinch if I had to.

 

[core13]

Paul is it hard to mod a finished unit to use  Ian Thompson Bell's grounding?

Where an external power supply must be plugged please?
on a pcb like that it's not very obvious for me.

rockprocess could you explain exactly what you did please?

Thank you

 

[rockprocess]

Sure, I drilled a hole for a new 4pin xlr socket to accept the 4 pin power cable from the power supply.  The new socket is wired to the appropriate spade terminals for power and ground.  I left the preexisting, internal power supply parts intact.  I trimmed the voltages appropriately from the external power supply.

I noticed a significant reduction in noise using the external supply verses the internal. However I can still power it as before if I ever need too. 

 

[core13]

thank you very much, do you have a picture of where did you wire the dc voltage from the external psu please?

 

[Potato Cakes]

Paul is it hard to mod a finished unit to use  Ian Thompson Bell's grounding?

No, it is not.

XLRs -  pin 1 tied to a bus bar/wire to star ground. No Pin 1 connections from XLR to PCB

0V to star ground

Agnd to star ground

Cgnd to star ground (separate from Agnd - do not tie together)

Mains Safety to star ground.

I do not know if the difference in regional power will affect the hum. I have never noticed hum, even at extreme levels during testing.

Thanks!

Paul

 

[core13]

Thank you paul

I connect directly the 3xlr ground to star ground.

do I need to remove the connection between pin1 and xlr case?

cgnd and agnd are you talking about J4 and J5? if yes they are already connected trough the pcb,
do I need to cut the path on the pcb?

0v is the green and yellow on the transformer ?

did you close sw1 to have 600r terminated?

lot's of questions sorry

best
Léo

 

[Potato Cakes]

Thank you paul

I connect directly the 3xlr ground to star ground.

do I need to remove the connection between pin1 and xlr case?

cgnd and agnd are you talking about J4 and J5? if yes they are already connected trough the pcb,
do I need to cut the path on the pcb?

0v is the green and yellow on the transformer ?

did you close sw1 to have 600r terminated?

lot's of questions sorry

best
Léo

I'll have to double check the XLR but I'm sure that all my ez1073's do not have a connection between XLR pin 1 (either in or out) and the PCB but go straight to the star ground. XLR Pin 1 to XLR body is fine.

CGND and AGND are printed in large letters on the PCB. You can't miss it. They also are not directly connected on the board per the schematic and are separated by R1 and C1. This is why I use two separate lines for the these to the star ground.

SW1 is the very first step in the Colourbook. The power transformer connection is also shown in the Colourbook.

Keep this handy for a reference and apply to all your builds:
http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/SimpleMixer/grounding101v2.pdf

Thanks!

Paul

 

[core13]

Thank you, I need to recheck the building guide

CGND and AGND are connected together via the case,
pcb ground is in contact to the case via the screw to mount it, and also I think via the pots in contact to the frontpanel.

I think I can do nothing about that.