Focusrite Octopre owners - please reply.

Channels 7 and 8 of my Focusrite Octopre have a low-level hum that doesn't
show up on channels 1-6. Before I request warranty service, I'd like to know
if anyone else using an Octopre hears a similar low-level hum? If that's
just the way the unit behaves, I'll not complain and reserve channels 7 and
8 for high-level sources.

A few details: channels 7 and 8 are physically closest to the power supply
with its 117vac and power transformer (probably the source of the hum). The
hum is most audible with no microphone connected and with the input level
turned all the way up. The hum is not affected by switching in/out the
low-cut filter or phantom power.


Thanks.

Vland wrote:

Focusrite Octopre owners - please reply.

Channels 7 and 8 of my Focusrite Octopre have a low-level hum that doesn't
show up on channels 1-6. Before I request warranty service, I'd like to know
if anyone else using an Octopre hears a similar low-level hum? If that's
just the way the unit behaves, I'll not complain and reserve channels 7 and
8 for high-level sources.

A few details: channels 7 and 8 are physically closest to the power supply

That's exactly what I was thinking.


with its 117vac and power transformer (probably the source of the hum). The
hum is most audible with no microphone connected and with the input level
turned all the way up. The hum is not affected by switching in/out the
low-cut filter or phantom power.

Why would you be bothered about hum with no mic connected ? Do you plan to
record the sound of the mic pre open circuit ?

How bad is it with a 200 ohm source ? A 200 ohm ( 180 or 220 if you don't have
E96 values ) resistor in an XLR connected across pins 2 and 3 will tell you.


Graham

"Pooh Bear" wrote in message
...


Vland wrote:

Focusrite Octopre owners - please reply.

Channels 7 and 8 of my Focusrite Octopre have a low-level hum that
doesn't
show up on channels 1-6. Before I request warranty service, I'd like to
know
if anyone else using an Octopre hears a similar low-level hum? If that's
just the way the unit behaves, I'll not complain and reserve channels 7
and
8 for high-level sources.

A few details: channels 7 and 8 are physically closest to the power
supply

That's exactly what I was thinking.


with its 117vac and power transformer (probably the source of the hum).
The
hum is most audible with no microphone connected and with the input
level
turned all the way up. The hum is not affected by switching in/out the
low-cut filter or phantom power.

Why would you be bothered about hum with no mic connected ? Do you plan to
record the sound of the mic pre open circuit ?

How bad is it with a 200 ohm source ? A 200 ohm ( 180 or 220 if you don't
have
E96 values ) resistor in an XLR connected across pins 2 and 3 will tell
you.


Graham


Now, now -- no need to make me feel too dumb! I tested without a microphone
since I wanted to compare the noise level in all eight channels without the
distraction of room ambience. I hear only low-level random noise in channels
1-4, a very slight hum along with random noise is channels 5-6, and a higher
low-level hum in channels 7-8. I'll make up an XLR with a 200-ohm resistor
and see what difference that makes. I agree that the power supply is
probably the source, so my question is: are all Octopres like mine in this
regard, or is this something that could be fixed?

"Vland" wrote ...
I tested without a microphone since I wanted to compare the
noise level in all eight channels without the distraction of room
ambience. I hear only low-level random noise in channels 1-4,
a very slight hum along with random noise is channels 5-6, and
a higher low-level hum in channels 7-8. I'll make up an XLR
with a 200-ohm resistor and see what difference that makes. I
agree that the power supply is probably the source, so my question
is: are all Octopres like mine in this regard, or is this something
that could be fixed?

Until you test it with an input load (200 ohm resistor), you
don't know if you actually have anything that needs fixing.

Vland wrote:

Now, now -- no need to make me feel too dumb! I tested without a microphone
since I wanted to compare the noise level in all eight channels without the
distraction of room ambience.

That's what dumby loads are for ! ;-)


Graham

"Richard Crowley" wrote in message
...
"Vland" wrote ...
I tested without a microphone since I wanted to compare the
noise level in all eight channels without the distraction of room
ambience. I hear only low-level random noise in channels 1-4,
a very slight hum along with random noise is channels 5-6, and
a higher low-level hum in channels 7-8. I'll make up an XLR
with a 200-ohm resistor and see what difference that makes. I
agree that the power supply is probably the source, so my question
is: are all Octopres like mine in this regard, or is this something
that could be fixed?

Until you test it with an input load (200 ohm resistor), you
don't know if you actually have anything that needs fixing.


I wired up a 200 ohm dummy XLR and tried it with the hummy channels. Loading
the input succeeds in dropping out most of the random noise but does nothing
to reduce the hum. I can hear both a 60 hz and a 120 hz component, so per
other consultations, it may be that the 60 hz is from a badly shielded power
transformer (physically closest to the hummy channels) and the 120 hz may be
because of a weak filter capacitor on the branch of the power supply that
powers channels 7 and 8.

At normal monitoring levels, the hum begins to be potentially audible with
the level controls set a bit above "1 o'clock." I've found that I typically
record acoustic instruments with levels set between 2 and 3 o'clock, so the
hummy channels are out for such recordings.

I expect my future use of the Octopre will be as preamps 1-6 for my MOTU 828
MkII's first six channels, with my FMR-RNP feeding channels 7 and 8. If I
need two more, the MOTU also includes a couple of fairly decent pres. Not a
bad scheme, but too darn bad about the Octopre living up to only 3/4 of its
potential.

-- Vland

Vland wrote:

"Richard Crowley" wrote in message
...
"Vland" wrote ...
I tested without a microphone since I wanted to compare the
noise level in all eight channels without the distraction of room
ambience. I hear only low-level random noise in channels 1-4,
a very slight hum along with random noise is channels 5-6, and
a higher low-level hum in channels 7-8. I'll make up an XLR
with a 200-ohm resistor and see what difference that makes. I
agree that the power supply is probably the source, so my question
is: are all Octopres like mine in this regard, or is this something
that could be fixed?

Until you test it with an input load (200 ohm resistor), you
don't know if you actually have anything that needs fixing.


I wired up a 200 ohm dummy XLR and tried it with the hummy channels. Loading
the input succeeds in dropping out most of the random noise but does nothing
to reduce the hum. I can hear both a 60 hz and a 120 hz component, so per
other consultations, it may be that the 60 hz is from a badly shielded power
transformer (physically closest to the hummy channels) and the 120 hz may be
because of a weak filter capacitor on the branch of the power supply that
powers channels 7 and 8.

Most likely it's actually 180Hz. Transformers radiate 3rd harmonic nicely too.
Your suggestion doesn't tie in with likely actual circuitry.


At normal monitoring levels, the hum begins to be potentially audible with
the level controls set a bit above "1 o'clock." I've found that I typically
record acoustic instruments with levels set between 2 and 3 o'clock, so the
hummy channels are out for such recordings.

I expect my future use of the Octopre will be as preamps 1-6 for my MOTU 828
MkII's first six channels, with my FMR-RNP feeding channels 7 and 8. If I
need two more, the MOTU also includes a couple of fairly decent pres. Not a
bad scheme, but too darn bad about the Octopre living up to only 3/4 of its
potential.

Why not contact Focusrite and complain ? They may have done an upgrade since you
bought yours.


Graham

"Pooh Bear" wrote in message
...

Vland wrote:

"Richard Crowley" wrote in message
...
"Vland" wrote ...
I tested without a microphone since I wanted to compare the
noise level in all eight channels without the distraction of room
ambience. I hear only low-level random noise in channels 1-4,
a very slight hum along with random noise is channels 5-6, and
a higher low-level hum in channels 7-8. I'll make up an XLR
with a 200-ohm resistor and see what difference that makes. I
agree that the power supply is probably the source, so my question
is: are all Octopres like mine in this regard, or is this something
that could be fixed?

Until you test it with an input load (200 ohm resistor), you
don't know if you actually have anything that needs fixing.


I wired up a 200 ohm dummy XLR and tried it with the hummy channels.
Loading
the input succeeds in dropping out most of the random noise but does
nothing
to reduce the hum. I can hear both a 60 hz and a 120 hz component, so
per
other consultations, it may be that the 60 hz is from a badly shielded
power
transformer (physically closest to the hummy channels) and the 120 hz
may be
because of a weak filter capacitor on the branch of the power supply
that
powers channels 7 and 8.

Most likely it's actually 180Hz. Transformers radiate 3rd harmonic nicely
too.
Your suggestion doesn't tie in with likely actual circuitry.


At normal monitoring levels, the hum begins to be potentially audible
with
the level controls set a bit above "1 o'clock." I've found that I
typically
record acoustic instruments with levels set between 2 and 3 o'clock, so
the
hummy channels are out for such recordings.

I expect my future use of the Octopre will be as preamps 1-6 for my MOTU
828
MkII's first six channels, with my FMR-RNP feeding channels 7 and 8. If
I
need two more, the MOTU also includes a couple of fairly decent pres.
Not a
bad scheme, but too darn bad about the Octopre living up to only 3/4 of
its
potential.

Why not contact Focusrite and complain ? They may have done an upgrade
since you
bought yours.

Thank you for your responses concerning my issue. I had been reluctant to
send my Octopre off to Focusrite, but I looked them up and, wonder of
wonders, their North American Service Operation is nearby in the San
Francisco Bay Area, about a half-hour from my East Bay home. I'll give them
a call and hand deliver my unit next week.