Neve 66 series Kingshill PSU noise...

[bradholland]

I'm going to add more to this topic when I get them set up again.

We've got two Neve 66 series consoles. one is in daily use and the other is torn down and stored which we mainly will use for spares etc.
However, we've been trying to build a little sidecar console, but every one of the 5 psus we have which are spare impart a noise into the console.

we took a good psu from the running console and tried it on the sidecar and it was fine.
we took the bad psus from teh sidecar and tried them on the main console and it imparted the sound there. the sound is a kinda hum but doesn't sound like earth hum.

We find it hard to believe that all these psus are bad and what makes it even more confusing is that when we purchased the console 4 of the 5 supplies were hooked up and were working fine.

My 1st instinct was to just start bleeting about caps but on all 5 supplies? that were good and now seem to have this noise?

any ideas?

thanks peeps.

 

[ruffrecords]

First thing to do is stick a scope on the output of a bad one and see just what the noise is.

Cheers

Ian

 

[bradholland]

Thanks Ian.
Unfortunately, we don't have a  scope yet. It's on the list of things to get though.

 

[sodderboy]

Then try a DMM set to VAC.  At least you can quantify some ripple on the DC rails.  If you can rig it use some math and lightbulbs to make properly valued dummy loads.  It is best to use a scope to view the DC outputs under load, even if only one leg at a time.
So there were 4 powered supplies connected to the console at the beginning, but now it runs on only one?  Perhaps there is some sort of wiring difference for the parallel supplies, like a difference in the earth/ 0vl wiring that would affect the integrity of the technical earth connection on the desk.
Mike

 

[SSLtech]

Whereabouts in Florida are you? East coast, south of Merritt Island isn't it?

I might be able to pay a visit and bring a scope etc...

 

[bradholland]

Hi Keith!
Yeah we're in west palm beach remember? Just off 441

 

[SSLtech]

Ah, yes, I remember now... -Let me see when my son has a triathlon down that way. -I think that North Palm Beach has a triathlon, but I'll have to research the date.

Let me check with the missus, and see if that's an opportunity.

 

[bradholland]

UPDATE:

Ok again I'm baffled. and again a seemingly schoolboy error on our part for not even trying this but we fixed it...

This noise was imparted due to too much power coming out of the psu...????

The neve 66 (at least ours) is +/- 18V / +8 / 0V /+48V

The 18v rails were causing the problem, putting a meter across the psu when connected or not was giving us 14V on those rails and so I assumed the noise was because the console was being underpowered. however, while in circuit we used teh trimpots on the PSU and turned the voltage down to 12.8V and hey presto! the noise went away and the sidecar operates just fine...

can anyone explain this?

thanks for the help!!

 

[audiomixer]

are the power supplies Neve made?

sounds like you had the power supplies working outside their regulating range - i.e. out of spec. now that you dialed down the voltage it is able to regulate better. most opamp circuits will just run fine at +/-12V even if 'designed' to operate at +/-18V. now that is as long as you keep signal swing low enough not to distort, but most consoles have enough headroom you might not notice ;-)

so may be you lowered the voltage to a level at which the supply is able to cope with the sidecars power requirement. it might start to distort at lower levels, say +18 dBu indtead of +24dBu, but that might not be an issue in your real world application...

 

[bradholland]

they are made by kingshill, but they are the original power supplies for the console...

 

[squib]

Do you have the sense lines connected?

 

[bradholland]

we do. although its difficult to tell which one is which. although I made educated guesses as to which was which.
the noise existed with or without them though.

 

[squib]

ewww! The PSUs will not regulate correctly without the sense lines and will oscillate if they are disconnected. Who knows what it will do if they are connected incorrectly.
You need to be 100% across the wiring to start with.

 

[bradholland]

well it's pretty obvious when the sense lines are on the wrong way round as it doesn't behave properly. Reasonably sure we have them on correctly as a result.