Hi Brent,
Can you clarify a few things, like:
-Do you only hear the noise when a solo is engaged?
-Does the noise print to the 2-mix?
-Are the monitors clean with another source selected?
You might also try removing U-4 on the Monitor module altogether. If
the noise is still present, but at a reduced level, than as Matt
suggested, it may be coming from a channel module. If the noise is the
same level, that would point to Q-103, the Left Solo switching FET.
If it turns out to be coming from a module, you can narrow it down to
the left or right side of the desk by pulling the 16-pin headers at the
top of the motherboard (carefully, the pins bend easily), there's two
per side...sorry I don't have the numbers handy. The only voltage on the
top two ribbons (the bussing) is -25 volts on one header (Pin-14, can't
recall which header)...probably best to power down 1st.
best,
Ike
Matt Syson wrote:
Hi
I would suspect that the left mix bus is shorted to ground or that a
channel is 'contributing' to it all the time which,without the DC bus
being engaged you won't hear in the monitors until you solo something
else.The FETs are used in a 'switching' mode rather than in a linear
amplifier fashion so I would not really be looking at these until
other things were checked.
Matt S
Ike Zimbel wrote:
Hi Brent,
Have a look at the switching FET's in that circuit. I don't have
my docs in front of me but I believe they are 2N5638's.
best,
Ike
Brent Punshon wrote:
Hi all,
Just wondering if anyone has seen this before? An extremely raised
broadband hiss noise floor. When stereo solo is engaged the right
side is fine.
The left solo amp is also the mono solo amp so clearly it's related.
I just swapped out all the BJTs and the JFETs in that area along
with the solo bus amp (U4). No change.
Haven't yet prodded around in situ. My back was hoping to avoid that
(but somehow I don't think it's going to). Just thought it might
ring some bells.
Thanks
Brent Punshon
Head Gap
Melbourne, Australia
Ph :+613 9480 6280
www.headgap.com.au
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Ike Zimbel
Zimbel Audio Productions Ltd.
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416-720-0887
"Studio House Calls" - Repairs and upgrades to analog audio equipment including:
Amek, Allen & Heath, Neve, Neotek, MCI, Soundcraft and more.
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