Allen & Heath GL3 Output Mod
RDOGuy
allows you to switch the six aux outputs to the balanced XLR outputs
so you can use it as a monitor console. But doing so eliminates the
possibility of using the main stereo mix for something like sidefills;
the main mix isn't routed to any connectors.
Since I want to have the six aux outs AND the main out to use for
mixes, I've been using the mixer in its regular configuration, meaning
that I have to use the 1/4" outputs for the aux sends. That's no
problem in and of itself, but it appears that there's an additional
gain stage between the main/monitor switches and the XLR outputs,
which means that the signal available at the 1/4" outputs is 6 db less
than it would be at the XLR outputs.
Digging through some information I found at the Allen & Heath site, I
found an indication that this model was available with some kind of
modification to make the aux outputs balanced. I'm guessing that this
modification also provided the same additional gain that you get when
you switch to monitor mode.
So... I sent Allen & Heath a message through their web site, asking if
it was possible to retrofit my GL3 with this modification. Naturally
there has been no response. Can anyone shed any light on this?
TIA
Rupert
The deal is the 1/4" output are impedance balanced only, meaning you
get similar or same CMRR (noise rejection) you would with a full
active balanced output as used for the XLR's, but only the tip (hot)
has an active signal. The ring, which is normally active or
"cold" (signal is in opposite polarity of the hot/tip) carries no
signal, but has source impedance matched to the hot/tip connection.
For most situations, this is adequate. What give the additional 6dB of
gain on the XLR's is that they're active balanced, meaning pins 2
(hot) and pin 3 (cold) are both active with identical signal but in
opposite polarity. When the 2 are summed at the destination, there is
a 6dB increase in level as the result of doubling identical voltages
when summing. If you need the extra drive for the 1/4" outputs, A&H
should be able to provide you with the chips (which are simple
balanced drivers) or the model number to order from a 3rd party like
DigiKey. There may be sockets to simply press them in, but I suspect
you'll have to solder them in.
Rupert
RDOGuy
> If you need the extra drive for the 1/4" outputs, A&H
> should be able to provide you with the chips (which are simple
> balanced drivers) or the model number to order from a 3rd party like
> DigiKey. There may be sockets to simply press them in, but I suspect
> you'll have to solder them in.
Many thanks, Rupert.
Based on my experience so far, I'm not confident I'll be able to get
much help from A&H on this. I've already had the console open (I
changed the jumpers so the aux sends would be post-EQ) but
unfortunately I didn't know about this issue at the time I was making
those modifications. So it looks like I'm going to have to open it up
again and take a look at the circuit cards in the master section
(which I haven't had out) and see what's what. Perhaps there will be
some additional clues there.
George's Pro Sound Company
"RDOGuy" <rdo...@aol.com> wrote in message
news:99f7503d-d082-490f...@w34g2000yqm.googlegroups.com...
Many thanks, Rupert.
Just my opinion but this seems like a lot of work and effort for a console
who was discontinued 10 years ago
with all the other marginal parts (pots, faders, jacks) inherant in a 15
year old desk, and A&H's history(intermittent outputs on groups/mains/ps
failures) reliability issues with the GL3, it seems the smarter move would
be to get your salvage value out of it and buy a (new)desk that does what
you need
George
jakdedert
to. What I don't get is why the extra 6 dB is so important on an
output. It's undoubtedly connected to other outboard gear where the
needed gain can be made up...much easier (and safer, unless you know
what you're doing) than trying to hotrod the console internally.
jak
Rupert
Email David at American Music & Sound.
david.m...@americanmusicandsound.com
He's a tech that's very knowledgable about Allen & Heath and responds
very quickly. He can also get you the part info. AMS is an authorized
A&H service center.
Rupert
RDOGuy
with the board (and hopefully the modification) and who can therefore
tell me if it's worth attempting. You see... I do have the option to
pick up the gain further down the chain (that's what I've been doing
up to now) but it seems to me this is a better way to do it... as long
as it isn't terribly difficult or expensive to do,
Thanks again, Rupert.
RDOGuy
David was of enormous help, Rupert. Thank you again!
For the benefit of anybody else who might travel this particular road,
David says that all is required is to insert a SSM2142 IC into an
existing socket and cut two adjoining jumpers on each affected PCB -
an operation that doesn't even require removing the PCBs, will cost
less than $50 (the ICs are $5.50 each from DigiKey - you need the 8
pin DIP version) and should take about 15 minutes. The 1/4" jacks are
already TRS, so the outputs become fully balanced.
David even sent me PDFs of the schematics and PCB drawings for the
console - which I am glad to have.
Rupert
I figured he would be. Very knowledgeable. Have fun with the upgrade
Rupert