"Andy Evans" wrote in message
ups.com...
I'm trying to decide on that age old question of what connection to
make from seperate PSU chassis to main valve amplifier chassis. I'm
thinking in terms of a shared PSU and two monobloks, so connectors
would only have to take the power to one amp. Criteria I decided were
essential we
a) low cost (so no Amphenol connectors)
b) potentially large number of pins (at least 15)
c) locking (so can't get pulled out by accident)
d) at least one connector must safely take 360Vdc (equals 250v AC
rating).
Morning Andy.
That's odd. Most connectors and relays have a much *lower*
rating at DC than AC.
Possibly the option of two.
e) common part, not likely to become obsolete
I agonised over one cable or two, and decided one cable would
require too high density, be hard to wire, would be expensive, and
would be an uncommon part. Amphenol out the window.
Firstly you have to find a connector that is rated for the
DC voltage you need, *in a domestic environment* Some broadcast
and studio connectors, are rated at 1500V industrial but only 70V domestic.
For your private use, you have a greater freedom of choice, and are
only dependent upon what an insurance company will accept. But if
you plan to sell to the general public then the situation is different.
Secondly, unless you can buy them from scrap equipment, good connectors
never come cheap. For the purpose you are considering, I picked a nickel
plated NATO style connector as show in the pic below:
http://www.kolumbus.fi/iain.churches...earPanel01.jpg
http://www.kolumbus.fi/iain.churches...earPanel02.jpg
These are available in 9,12,16,21,26 way. The working voltage
decreases as the density of pins increases. RS part number for the
9 pin male plug is 234-685. They cost about Euro 17. The matching
female connector for the PSU end, and also the cable connectors are
about the same price. So a complete set, of chassis and cable connectors
comes out at about Euro 70.
Both the Hirschman and the Amphenol NATO connectors are much
cheaper at about Euro 8 for the 8 pin. They are either grey or olive drab.
That is not a lot of money for such a good connector. (Euro 32 for a
set)
that's a minimum of 15 connections. So my eye fell on D connectors.
Relatively easy to wire up and available in 15 way which is nicely
compact. Some are rated at 500v even, so a single 15 way D connector is
not impossible.
but while I was happy with the filaments and the -15v supply on D
connectors, I would really like better contacts for B+ and earth. My
two choices for an added connector we
a) speakon plugs in 2,4,8 way
b) XLRs
I have an uneasy feeling that the D connector female is not sufficiently
touch-proof for safe use above 70VDC.
Speakons are cheap in four way but expensive in 8 way, so 4 way remains
a possibility. I'm not quite eliminating them but I'm a bit put off by
the following:
1) they're bigger and stick out more than XLRs
2) some idiot might plug a speaker into the PSU box
The 8 way is never used for speakers, so that would be the obvious choice.
Also take a look at the Bulgin Buccaneer range.
So XLRs. they offer the possibility of using 4,5,6 or 7 way. Now, I
spoke to Neutrik about the voltage rating for these, and it's a bit
more complex than you think. Some of their paperwork specifies 50v for
the whole range, some specify 150v, some specify different voltages for
different connectors. The sales guy in the UK quoted me 250vAC for 3-6
way and 125VAC for the 7 way. Not much agreement here, and the
unbranded Chinese ones have no voltage rating. In terms of availability
the 5 ways are common, 7 quite rare and gets eliminated because won't
handle the voltage. Four and six way are more unusual, and six way is
much more expensive. Four way can be had in cheap unbranded. So I'm
thinking 4 way right now, with the 15 way D connector, because this
gives the biggest pins and widest spacing so with unbranded the chances
are they're OK for 250vDC, or at least more likely to be than the 5
way.
There used to be an XLR with three insulated pins designed for DC and also
mains use. I am told it is no longer approved above 70V
I hope you've followed all this. So any suggestions? Anything I've left
out like BNC for just the B+ (high voltage)? Never used BNC but it's
locking at least. Is my above reasoning reasonable? Bright ideas?
Andy
Both safety and reliability are involved here. As Dave points out,
connectors are rated at what is considered safe, not maximum
voltage or current. It seems to me this is not the place to economise.
I would go for two (different) multipin locking NATO connectors.
I am not sure about the UK, but in this part of the world you must
also make provision for the DC to shut off if either end of the
umbilical cable is removed. I used a ground link and a safety
relay for this - so two more pins required. You do not need to shut
the psu down, just switch the B+ into a dummy load or OC
(if the 'lytics will stand the extra voltage)
Also, care must be taken with the choice of cable for the umbilical.
For use here in Scandinavia, I was told that it must be as short as possible
to connect the two pieces of equipment, and must under no circumstances
be long enouigh to touch the ground and therefore get caught under table
legs etc. Also the cable must be armoured with an outer braded screen
connected to ground in addition to the 0VDC (black) on the inner.
You can see the cable which I used, and subsequently shortened to
30cms, at:
http://www.kolumbus.fi/iain.churches...02+PSUrear.jpg
Regards
Iain