external PSU connection

finally managed my tube mixer external PSU.... phew... that was hard work..

am i good to use just 3 wires from external PSU to main enclosure, with single XLR jack (heavy gauge cable)
Ground,
B +
Heater +

do i need to connect external PSU's chassis ground to main unit's chassis ground too ?
i did some audio test, no difference.... may be i should connect it for safety reasons!

Yes. Your chassis needs a safe connection to mother earth.

thanks!
not a good news, but a safe news 

[silent:arts] said:

Yes. Your chassis needs a safe connection to mother earth.

Click to expand...

Semantics, but the chassis needs a solid connection to the neutral supply at the panel for high current faults, which should be referenced to mother earth via a ground rod.

kambo said:

am i good to use just 3 wires from external PSU to main enclosure, with single XLR jack (heavy gauge cable)
Ground,
B +
Heater +
do i need to connect external PSU's chassis ground to main unit's chassis ground too ?
i did some audio test, no difference.... may be i should connect it for safety reasons!

Click to expand...

I would use a 4 pin XLR,
pin 1 ground/common.  XLR's  pin 1 connect first.
pin 2 heater low
pin 3 heater high
pin 4 B+

the psu chassis should connect to earth.
but whether to carry that ground through to your mixer is a hot topic,
discussing politics is less divisive.
if you have unbalanced ports in your mixer, an extra connection to earth will pretty much guarantee a ground loop.
if your mixer is finding earth  via interconnecting equipment, I would not carry the ground connection through from the psu.
if your mixer is all balanced, go ahead and carry the ground through, that will make everybody happy.

With the high voltages present in a tube mixer you definitely need to connect the main unit chassis to safety earth. The best way to do this is via a dedicated wire in the cable between them. To avoid heater current in the signal 0V line you should also take both heaters in there own wires. Because I have +48V phantom power as well I use a 6 way XLR and a five way plus screen cable.

1. HT+
2.  Signal/HT 0V
3. Heater
4. Heater
5. +48V
6. Screen/chassis/ phantom 0V

In the power supply, the screen, the signal 0V and the PSU chassis are each connected directly to mains safety earth.

Cheers

Ian

thank you all!
looks like another order from mouser

For my external tube PSUs I used aviation mic/headset type connectors. Cheap and cheerful but quite rugged. They have screw locking rings. You can see them on ebay

They come in 2 sizes for 7 pin : I use the larger ones for high voltage. The smaller ones are OK for low voltage, low current apps.

They are cheap and you can also get an extra heavy duty version in 4-pin (I use for high current discrete class A amps).
The 4pin has goodly wide spaced pins and can carry some decent current.  It's quite large but still fits nicely on a 1-ru rear panel.

The 7pin version is somewhat less spaced but still easy to insulate the solder pins with heatshrink for safety.

I wouldn't use xlr type connectors with small pin spacings for psu cabling (except for tube mics!) - these  are quite a bit larger than the xlr multi pin types and much more suitable imho.

As usual, for the cheaper types, you can only get male chassis-mount types, and female line types, so there is the safety issue regarding the possibility of powering up the psu without the cable connected  ie. PSU end male chassis-mount pins exposed and live.

You can get them with a 'safety cap' hanging off the chassis-mount connector or one can make the cable captive (fixed and not removable) at the PSU end.

My stuff is not made-for-sale so it's not an issue for me.

i think i will use 2 x 4 pin connectors,
where do u gets ur wires from tho... i cant seem to find anything thicker than 24 AWG... i only need 2x3 feet

For cable, I use 'vehicle trailer' interconnect cable - its a heavy duty affair in 5 or 7 conductors of 20awg, multi-strand rated for 7A.

It's good because it is quite rigid  - with heatshrink it's fully immobilised and really solid at the connector.

I like it so, that I remove the outer insulation and use as heavy duty tube build hookup wire  in multiple colors.

And it's cheap!

ps- it is not, however, screened. I don't think it's an issue for dc psu interconnects

pps - I buy from Altronics here ins Australia - I don't think they do OS but you should be able to find 'vehicle-trailer' cable locally.

vehicle-trailer cable is a good idea! cheers

External PSUs rock!

Early indications in use are really promising with respect to noise floor performance in tube builds with lots of signal transformers - it's always been a problem for me in tube limiters - hum minimisation by placement of signal transformers and wiring always takes a lot of effort.

But no more with external 'hum-be-gone' psu  8)

It also has the benefit that you can design the psu to power a number of modules - my big unit is doing 400mA of HV and 7A of heater off two interconnects.

That's for powering my super-duper mastering limiter+eq and 7591a monitoring amps    Lots of traffos here, like about 16 or so all up in a fairly small area. Would be a real pia with co-located psu.

Good luck with it 

sounds good,

i suppose, there is no problem with external PSU on 19" rack  along with other equipment !

Best to locate the psu away from anything sensitive  ie. signal traffos

I use something like 1.5m cables for that purpose - plenty seperation even for mucho field from even larger psu traffos ..  like the big Hammonds and Edcor I favour.

I do psu at floor level of a rack and sensitive stuff at top levels of a rack  or  I put psus to one side and sensitive stuff on other side.

Another reason why I favour 20awg trailer cable is that the ground wire is plenty thick to minimise cable run resistance. ie. similar to the earth cable in mains wire, not some lightweight hookup wire.

Of course there is some resistance and inductance and capacitance with the external psu cable, but so far I haven't found any noise related issues with that.

And a good strong chassis ground connection is important, as is good continuity around all metal panels of the chassis.
ie. paint off at the chassis panel screw/bolt connection points to ensure good contacts.

One thing I'm testing at present , is the effect of an IEC mains filtering inlet.  I bought a couple of models, from super heavy duty, supposedly 'audiofool' Tokin (japan) type for my 'Class A  Stupid Monster' amps  to a more common schaeffer (swiss I think)  type in my EL34 monoblocs.

So far I haven't noticed any difference! but I am continuing to test under varying load conditions etc.

Still, an iec-mains-filter adds some snobbish cachet!

my plan was to slap 2U mixer enclosure (steel) with 2U PSU enclosure(steel) under, and connect them both with 4U aluminum front panel....
i guess that goes out of the options !

i have some mu_metal sheets from my none audio projects, may be layering them in between would help ?
( i actually dont wanna slice them, unless it would work, they are very pricey ! )

One other thing, on the subject of external psu ....  I've been using HV regulation pcbs .. from ebay .. with a lot of success.

The one I use is called 'kubota hv regulator'  http://www.ebay.com/itm/1pc-GZ34-5AR4-Kubota-Low-noise-Audio-adjust-HV-regulator-for-tube-amplifier-PCB-/201343461287?hash=item2ee10167a7:g:bNsAAOSwPgxVRuO-

Cheap as chips, adjustable HV, can use either rectifier tube or fr diodes, has a decent current/voltage capacity with the mosfet series pass element and a high speed error amp for quite good ripple performance. No need for big psu chokes

I rigged it for use in the psu I pictured above : heatsinking is with ceramic insulator (+heat gunk) onto the chassis.
I fit it into 1RU by using fr diodes and lay-down caps on the pcb + can caps on topside of rack.

It has  well spaced components, so maintenance, if required,  is a breeze and I fit into the 1ru, 2x HV regulator pcbs + 2x JLM 3-rail pcbs 

So that psu is doing 2x 300Vdc regulated at up to 100mA each, 2x 2.5A heaters unregulated *plus* 2x +/-17Vdc regulated at 100mA each (with limited heatsinking!) , and 2x 24V/48V utility rails!  I think it cost bit less than  200usd.

Its powering a pair of hybrid tube/solid state quad-preamps

Your milage may vary from mine - steel is good, seperation is good and mu-metal can be useful - try and see; leave the orientation of the transformers 'open' till you can measure the effect of placement on noise floor.

In the most challenging application, the PM670 varimu limiter, I had to work *really* hard to get acceptable noise floor in a 3RU rack.

Position and orientation of the psu traffo and signal traffo made a *huge* difference  ..  like > 15dB or so to the 'hum floor'  all up when I had completed tweaking. The most logical positioning is usually the worst!

So, good policy to seperate the signal traffos and psu traffo as much as possible within a co-located rack, then rotate either or both to give best performance.

I find mu-metal most useful in the form of signal traffo cans, although  I have measured up to 3dB improvement using 'the Don's' toroid shielding strips, which is some form of grain oriented high perm steel alloy.

All I can say is seperation is most effective that I have found. I wouldn't try doing anything sensitive without psu seperation any more.

It's also great to be able to focus on the signal part of a build 100%, having already fully sorted out the psu!

yea, i guess i have to try and see...

just ordered 2 pcb's

thanks for that

Also .. on the subject of good hum-floor performance  ....

Don't use the chassis for 'signal ground' , except for a single connection at the psu - run seperate 'signal-ground' wiring with 'ground follows signal' type of thing.

Chassis-ground is good for connecting wire-shields (one end floating, one end chassis-grounded), pot bodies, tube center pins etc.

Make sure all signal ground wiring is heavy gauge wire, except maybe at the very last link or so.

I like to use several 'star gounds'  ie. a main star ground near psu and local 'star grounds' conveniently close to signal modules.

Seperate the 'heavy current' star ground and the 'low current' local star ground(s) to try to keep heavy return-currents away from sensitive areas.

It all makes a big difference when taken together - I am completely nuts for low hum floors!

AND get used to using REW analysis software to keep an eye on hum-floor 'as-you-go' as much as practicable!

Its easiest to avoid trouble 'as-you go' rather than trying to figure out at the end of wiring where-the-&**$% did the hum come from!

10years ago I though 70dB of 'signal-to-hum' margin was acceptable. Now it's more like 90dB  for the tube stuff and 110+ for the solid state things.

cool, thanks for the tips, and taking your time 

i agree on keeping  sensitive stuff away.... i have room EQ s (Meyer Sound); even  though, they are not sensitive to anything i have noticed so far, but they are on separate rack. i feel better... and my bryston is always on the floor( couple of inches above), and well away even from the AC plugs  ;D ;D ;D
i spray them along with my computer regularly.... dust is the biggest enemy (learnt hard way after losing my
2 out hitech video card  :'( )

i have some of the missing parts arriving tomorrow, i should be able to run one half of the mixer  in full blast,
with my temp external PSU box....

cheers