Hi
For now treat everything as balanced everywhere and unbalance it only
where absolutely necessary. If the connectors into / out of' the desk
are unbalanced (2 pole jack) you will need to have the 'cold' side
connected to the sleeve as there will probably not be a ring connection
on the desk jacks. You could use TRS plugs and make the appropriate
connection (put a little link between ring and sleeve) which is an easy
mod and if you ever change gear you can simply cut the link out.
Matt S
Jack Stauss wrote:
I thank everyone for the very detailed answers, I need to filter
through all of this to see exactly what I need to do and how to best
proceed but...
It seems a lot like everyone has talked about the science and
engineering involved with what I want to do and not the specific
answer(s) on how to do what to do.
Do I just use TRS snakes to come out of my non-balanced outputs/sends
and into my non-balanced inputs/returns from my balanced patchbay(s)
or do I need to change the connectors to non-balances TS connectors
and lift the ground, combine the ground and cold or do I need to get
transformers across the board ect?
As far as I can tell ALL of my outboard gear, even the vintage stuff
like my LA-4's and my API lunchbox have Balanced inputs and outputs so
I don't think I need to address anything on that end...maybe I am
kidding myself. I am just worried about all the connections into and
out of my Series one that are non-balanced.
Maybe all this has been answered and I just need to dig it out of the
reply's, my head hurts...
Thanx,
Jack
Jack Dean Stauss
No Static Pro Audio Inc.
3083 N. California St.
Burbank, Ca. 91504
818-729-8554
818-729-8551 Fax
www.nostaticav.com
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On Feb 18, 2010, at 11:32 AM, Matt Syson wrote:
Hi
Regarding 'item 5'.
EVERY amplifier amplifies the difference between it's 'input' and a
reference point. In a 'balanced' amplifier the refeence is most
visible as it's 'cold' or 'antiphase' input terminal. Peturbations of
THIS amplifier's ground are largely ignored (the amount being
dependant on design and implementation).
An Unbalanced input works in essentially the same way but the
REFERENCE is the ground of THIS circuit.
In a simple system with few circuit blocks and sensibly laid out and
low impedance grounding things work pretty well. Many, practically
all mixers have this system internally, certainly at channel level
and because it is a mostly 'enclosed' system it works.
Problems start to appear if external connected equipment (cabling)
having significant ground current flowing in it being either mains
hum or 'RF' which then start to add to what should be the clean
reference point due to the inevitable resistance of the 'ground' be
it wire or circuit traces. If there were to be say 1 amp of 'ground
loop current' it would only take a resistance of 0.01 milliohm in the
'wrong place' for the hum to appear at -80dBV. OK 1 Amp sounds
excessive but then getting a resistance as low as 0.01 milliohm is
also improbably low.
From this, what I am trying to emphasise is the importance of the
'reference' following the signal so that unwanted signals are
cancelled. Having a 'balanced' input with even only 30dB 'rejection,
pays dividends in reduced noise and unwanted 'rubbish'. This is not
to say that unbalanced connections cannot work but great care must be
taken to ensure stray unwanted currents are not applied to it. The
worst scenario is with a mixer 'tape' return where you have typically
24 signals following the same physical route (same interference) and
summed, where they will add. 2 inputs giving 6dB worsening in noise,
4 another 6 dB, 8 another and so on. The 'high quality' gear will
take these constraints and ensure that the 'ground reference' is
taken to the connectors and be suitably low resistance to withstand
some 'interference' from outside.
Having a signal flow from one amplifier connected to another in a 2
channel preamp is relative childs play. Having say 10 circuit blocks
in one channel strip then attached to another 23 channels in 3
dimensions spread over a few feet becomes a logistical nightmare.
Bear in mind that any conductor with LENGTH is an aerial. A few
inches is associated with microwaves (your mobile phone).
The rules for successful interconnects are low impedance grounds
which physically follow the signals as closely as possible. An
'unbalanced' input on a desk CAN reject interference if the 'hot' and
associated ground both get to the input stage at which point it is
the design of the stage which determines whether the interference is
amplified or rejected.
Matt S
Donald Put wrote:
On Thu, Feb 18, 2010 at 8:38 AM, Ike Zimbel <[email protected]
<mailto:[email protected]>> wrote:
5) And finally, I wish everyone in the whole audio industry would
stop equating "un-balanced" with other negatives in our language
like "unclean, unstable, unsafe, unreliable, unexceptional etc." I
think "not balanced" would be more accurate! (end of rant >:o )
As usual, Ike hit it out of the park. As for the "unbalanced"
issue, it's arguably a cleaner signal path (fewer number of parts in
the way of the audio signal), and unless you have interference
issues I wouldn't worry about it at all. With the exception of mic
inputs, my whole studio is wired unbalanced and I don't have any
problems with noise. Of course, I'm in a rural area so RF et al.
has never been an issue.
Cheers,
--
Don
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