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DELTA - New PS-fixed ground or iso switch?

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Anonymous
August 3, 2005 6:05:18 AM

Archived from groups: rec.audio.pro (More info?)

It's finally time to wire up the new International Power linears I picked
up to replace the original, now rather feeble Soundcraft supply feeding
my 16 frame Delta.

I have two new open frame supplies (+,- 24V @ 2.5 amps each side dialed
down to 17V, plus a 1A 48V supply). Both will nicely fit into a 2U
rack utility box with a vented top.

So here's the question: I'll tie power line ground to the new PS case, but
then should I also tie that to the power supply commons? The Soundcraft
supply is wired this way, such that pin 1 at a mic input is zero ohms
to the ground pin of the AC cord. No problems so far, but perhaps I should
put in an "earth/iso" switch to break that tie when set to the "iso"
position. (Should there then be a .1 uf cap jumpering the "iso" setting?)

My outboard preamps and some power amps do this, but perhaps I should have
some fixed central place where the audio ground always ties to powerline
"earth", such as the console, and only float peripherals if there's
problem.

Wisdom and caveats appreciated as always,

Thanks
Frank Stearns
Mobile Audio
--
.
August 3, 2005 6:05:19 AM

Archived from groups: rec.audio.pro (More info?)

Frank Stearns wrote:
> It's finally time to wire up the new International Power linears I picked
> up to replace the original, now rather feeble Soundcraft supply feeding
> my 16 frame Delta.
>
> I have two new open frame supplies (+,- 24V @ 2.5 amps each side dialed
> down to 17V, plus a 1A 48V supply). Both will nicely fit into a 2U
> rack utility box with a vented top.
>
> So here's the question: I'll tie power line ground to the new PS case, but
> then should I also tie that to the power supply commons? The Soundcraft
> supply is wired this way, such that pin 1 at a mic input is zero ohms
> to the ground pin of the AC cord. No problems so far, but perhaps I should
> put in an "earth/iso" switch to break that tie when set to the "iso"
> position. (Should there then be a .1 uf cap jumpering the "iso" setting?)
>
> My outboard preamps and some power amps do this, but perhaps I should have
> some fixed central place where the audio ground always ties to powerline
> "earth", such as the console, and only float peripherals if there's
> problem.
>
> Wisdom and caveats appreciated as always,
>
> Thanks
> Frank Stearns
> Mobile Audio
> --
> .



I have found a three way ground switch to be usefull for a DI box I
made.

Position 1 = grounds tied together
Position 2 = grounds open
Posiiton 3 = grounds tied via 100 Ohm resistor

Position 3 works for 90% of the situations I have used.
The 100 Ohms is high enough to prevent a ground loop but low enough to
keep the two grounds from getting to be many many volts apart due to
leakage. For those other problem cases position 1 or 2 works.



Mark
Anonymous
August 3, 2005 9:21:01 AM

Archived from groups: rec.audio.pro (More info?)

On Wed, 03 Aug 2005 02:05:18 -0000, Frank Stearns
<franks.pacifier.com@pacifier.net> wrote:

>It's finally time to wire up the new International Power linears I picked
>up to replace the original, now rather feeble Soundcraft supply feeding
>my 16 frame Delta.
>
>I have two new open frame supplies (+,- 24V @ 2.5 amps each side dialed
>down to 17V, plus a 1A 48V supply). Both will nicely fit into a 2U
>rack utility box with a vented top.
>
>So here's the question: I'll tie power line ground to the new PS case, but
>then should I also tie that to the power supply commons? The Soundcraft
>supply is wired this way, such that pin 1 at a mic input is zero ohms
>to the ground pin of the AC cord. No problems so far, but perhaps I should
>put in an "earth/iso" switch to break that tie when set to the "iso"
>position. (Should there then be a .1 uf cap jumpering the "iso" setting?)
>
>My outboard preamps and some power amps do this, but perhaps I should have
>some fixed central place where the audio ground always ties to powerline
>"earth", such as the console, and only float peripherals if there's
>problem.

Yes, and that IS the console. Even if audio ground must be lifted from
earth in every other piece of equipment, (and I hope that's not true),
the console should have a solid earth ground.

Why? Because the lowest signal level in the system, and the input to
the highest gain in the system, is at the mic preamp inputs. So, this
is where you can least afford to see any hum, and it should have the
most direct ground.

Ideally, all audio grounds will come back to console, and all safety
grounds will have direct connections to earth. In some equipment,
these are not easily separated.

Mike T.

p.s.: take note of Phil Allison's advice on cooling, too.
Related resources
Anonymous
August 3, 2005 12:13:44 PM

Archived from groups: rec.audio.pro (More info?)

I'd go with the dual output HDD-15-5A. 5 amps dual, these are perfect
for a 16 channel frame. It won't even get warm, so through away the
fan. Tweak it up to 16.25 volts. You will still get +26 db out of the
balanced outputs.

As to grounding, these consoles are designed with a distributed ground
scheme. There's two ground wires in the power supply cable. One is
power ground for the 0 return of the supplies, the other is chassis
ground from the AC ground pin. These are to be separated in the supply
as they join together at the master module pcb. Do not float these!

Jim Williams
Audio Upgrades
Audio Upgrades
Anonymous
August 3, 2005 6:35:38 PM

Archived from groups: rec.audio.pro (More info?)

"Frank Stearns"
> It's finally time to wire up the new International Power linears I picked
> up to replace the original, now rather feeble Soundcraft supply feeding
> my 16 frame Delta.
>
> I have two new open frame supplies (+,- 24V @ 2.5 amps each side dialed
> down to 17V, plus a 1A 48V supply).


** The makers data only specifies a +/- 5% adjustment range - but you
are claiming - 30 % ???

The heat developed by a liner PSU depends on the input to output voltage
difference. For a 24 volt supply, the needed input will be about 30 volts
DC to allow for AC supply variations and ripple voltage on the filter caps.

This gives a 8 volt difference and 8 x 2.5 = 20 watts of heat.

With an output voltage setting of 17 volts, heat dissipation in the pass
device will be 15 x 2.5 = 37.5 watts !

Those PSUs are gonna fry - you will need to add fans to prevent thermal
shutdown.

Also, Soundcraft PSUs have a "voltage tracking" circuit in them, to
prevent the positive and negative DC voltages getting significantly out of
balance during switch on or switch off cycles *OR* if one DC rail goes
out due to thermal overload etc.

Without this tracking circuit, it is possible to seriously damage the desk.



........... Phil
Anonymous
August 3, 2005 7:21:30 PM

Archived from groups: rec.audio.pro (More info?)

"Phil Allison" <philallison@tpg.com.au> writes:

>"Frank Stearns"
>> "Phil Allison"
>>
>>>> It's finally time to wire up the new International Power linears I
>>>> picked
>>>> up to replace the original, now rather feeble Soundcraft supply feeding
>>>> my 16 frame Delta.
>>>
>>>> I have two new open frame supplies (+,- 24V @ 2.5 amps each side dialed
>>>> down to 17V, plus a 1A 48V supply).
>>
>>
>>>** The makers data only specifies a +/- 5% adjustment range - but you
>>>are claiming - 30 % ???
>>
>> Actually, the specs for this particular supply say "18-24V";


> ** How about you post the model number them ??.

> Your claim above that it was 24V, 2.5 amp one is false.

It is an International Power IHCC 24-2.4. It's actually 2.4 A at 24V, but
I'd forgotten that it is derated to 1.8A at 18-20V. The sketchy "manual"
shipped with the supply doesn't even mention this; I had to be reminded by
looking out on the web. Apologies for the incomplete spec initially.

I assume those numbers seem more in line.

This should still give me 4-500 mA of current headroom, which will be
about 500 mA more than the old supply! They ran it right to the edge.

>>>Also, Soundcraft PSUs have a "voltage tracking" circuit in them, to
>>>prevent the positive and negative DC voltages getting significantly out of
>>>balance during switch on or switch off cycles *OR* if one DC rail goes
>>>out due to thermal overload etc.
>>
>>>Without this tracking circuit, it is possible to seriously damage the
>>>desk.
>>
>> This particular original Soundcraft supply is pretty simple. It uses 317
>> and 337 regulators in TO-220 cases with the standard half dozen or so
>> caps, diodes, and resistors around each device.


> ** So it is a POS baby size PSU - not a real one.

Quite right -- that's one of reasons the thing is being replaced.


> ** At the VERY least, fit reverse polarity protection diodes across each
>rail.

I assume that you mean dropping diodes across the rails like this: one
diode from minus to common (anode to minus; cathode to common) and then
another from common to plus (anode to common, cathode to plus).

Thanks for the input,

Frank Stearns
Mobile Audio
--
.
!