Millenia Media RF Interference

[Martin]

I have been reading newsgroup posts about the Millenia Media and Great River
preamps. Time and time again I read quotes like these.

"The Millennia is a lot more prone to RF troubles."

"The Millenia Media preamp is extremely transparent, but is more susceptible
to RF interference because it is transformerless."

"Another high-regarded preamp in this class would be the Millenia Media, but
the unbalanced input requires some care to avoid RF interference and hum."

Can anyone give me examples of how one might trigger this RF interference?

Is it really that easy to introduce RF interference into the signal chain of
a Millenia Media preamp?

Thanks.

Martin

[Rob Adelman]

Post by Martin
Is it really that easy to introduce RF interference into the signal chain of
a Millenia Media preamp?

I have an 8 channel unit and have had no problem with RF intererence. I
was having a hum problem with the power supply on my original unit, and
sent it in Millennia for repair. They were having trouble fixing it to
my satisfaction, so they sent me a new unit, even though I bought it 2nd
hand. Need I say more?

(and the new unit is quiet as a mouse)

[LeBaron & Alrich]

Post by Rob Adelman

Post by Martin
Is it really that easy to introduce RF interference into the signal chain of
a Millenia Media preamp?

I have an 8 channel unit and have had no problem with RF intererence. I
was having a hum problem with the power supply on my original unit, and
sent it in Millennia for repair. They were having trouble fixing it to
my satisfaction, so they sent me a new unit, even though I bought it 2nd
hand. Need I say more?

Yes, you could say how many remote gigs you've recorded with that pre
and how it did in RF infested territory...

--
ha

[Rob Adelman]

Post by LeBaron & Alrich
Yes, you could say how many remote gigs you've recorded with that pre
and how it did in RF infested territory...

Zero. But I was having a major problem with light dimmers and low
voltage lighting, and it wasn't having a problem with that, unlike some
of my other gear.

-Rob

[Mike Gilmour]

Post by Martin
I have been reading newsgroup posts about the Millenia Media and Great River
preamps. Time and time again I read quotes like these.
"The Millennia is a lot more prone to RF troubles."
"The Millenia Media preamp is extremely transparent, but is more susceptible
to RF interference because it is transformerless."
"Another high-regarded preamp in this class would be the Millenia Media, but
the unbalanced input requires some care to avoid RF interference and hum."
Can anyone give me examples of how one might trigger this RF interference?
Is it really that easy to introduce RF interference into the signal chain of
a Millenia Media preamp?
Thanks.
Martin

My 2 channel has never experienced RF problems even with 60' mic leads in
areas of thyristor controlled lighting, mobile phones, etc. but I don't use
any unbalanced feeds - maybe unbalanced is best avoided.

Mike

[Justin Ulysses Morse]

Post by Martin
Is it really that easy to introduce RF interference into the signal chain of
a Millenia Media preamp?

I don't use a Millenia, but I've got some other preamps (SX202s) that
can suffer the same kind of RFI problems under certain conditions.
There are a bunch of different factors that determine how much, if at
all, RF can be a problem for you beyond simply the preamp's
susceptibility. You have to consider the amount of RF trash in your
recording environment (a broadcast studio in an office building in
Manhattan or a home studio in a farm house in Nebraska?). You have to
consider the RF susceptibility of the mircrophones you're using. And
the one big factor you have control over is the lenght and quality of
your mike cables. Longer cables are going to pick up more trash, and
poorly shielded cables are going to let more of it into the signal
lines. I suppose the quality of the ground at your preamp chassis will
come into play as well, since the inputs will attempt to shunt RF noise
to chassis ground in a couple of different ways. And then, I find, the
amount of RF interference I get (with the SX202) depends on the
position of the gain control as well. I don't know why, but I wouldn't
be surprised if the same is true of the Millenia. I find with a
certain microphone and a certain cable and snake combination, I might
get the worst RF with the gain control between 2 and 5 o'clock (60% and
80%), while higher and lower settings aren't as bad. But it varies.

Using good microphones with short, well-shielded cables in a
well-grounded installation in an environment relatively free of RF is
the best bet. If that's not possible, you might want to look at
preamps with good input transformers.

ulysses

[ScotFraser]

<< I've got some other preamps (SX202s) that
can suffer the same kind of RFI problems under certain conditions. >>

Ditto. The certain conditions seem to be a particular gain range of the unit,
long cables, Neumann KM84s, & using Canare StarQuad mic cable as a two channel
multicore. Changing mics & cables generally alleviated the RF issue with the
SX202.
No RF issues with my Millennias, even at maximum gain, although they've only
been used in studio settings.


Scott Fraser

[Jim Williams]

Post by Justin Ulysses Morse

Post by Martin
Is it really that easy to introduce RF interference into the signal chain of
a Millenia Media preamp?

I don't use a Millenia, but I've got some other preamps (SX202s) that
can suffer the same kind of RFI problems under certain conditions.

If you remove the ferrite beads mounted by the XLR inputs and
replace them with 100 uh inductors, you will nip the rf those SX202's
have a problem with. Also replace the .01 uf psu bypass caps with .1
uf mono ceramics. The output opamps are a bit unstable and show low
level oscillations that are cleaned up with the .1 uf caps.
Your welcome, Jim Williams
Audio Upgrades

[Justin Ulysses Morse]

Post by Jim Williams
If you remove the ferrite beads mounted by the XLR inputs and
replace them with 100 uh inductors, you will nip the rf those SX202's
have a problem with.

I've always wondered though...Shouldn't these inductors be very closely
matched to preserve HF CMRR? I wouldn't know how to begin measuring an
inductor. Of course the same probably applies to the original ferrite
beads.

Post by Jim Williams
Also replace the .01 uf psu bypass caps with .1
uf mono ceramics. The output opamps are a bit unstable and show low
level oscillations that are cleaned up with the .1 uf caps.

I knew about this instability, and your suggestion makes sense. Thanks!

Post by Jim Williams
Your welcome, Jim Williams
Audio Upgrades

ulysses

[Jim Williams]

Post by Justin Ulysses Morse

Post by Jim Williams
If you remove the ferrite beads mounted by the XLR inputs and
replace them with 100 uh inductors, you will nip the rf those SX202's
have a problem with.

I've always wondered though...Shouldn't these inductors be very closely
matched to preserve HF CMRR? I wouldn't know how to begin measuring an
inductor. Of course the same probably applies to the original ferrite
beads.

That inductance reacts at rf frequencies, in audio it would be seen as
pure resistance. I suppose you could match some using a micro-ohm
meter, although the probe contact resistance would skew it a bit.
Jim Williams
Audio Upgrades

Post by Justin Ulysses Morse

Post by Jim Williams
Also replace the .01 uf psu bypass caps with .1
uf mono ceramics. The output opamps are a bit unstable and show low
level oscillations that are cleaned up with the .1 uf caps.

I knew about this instability, and your suggestion makes sense. Thanks!

Post by Jim Williams
Your welcome, Jim Williams
Audio Upgrades

ulysses

[Justin Ulysses Morse]

Post by Jim Williams
That inductance reacts at rf frequencies, in audio it would be seen as
pure resistance. I suppose you could match some using a micro-ohm
meter, although the probe contact resistance would skew it a bit.

I'm not worried about a series resistance of a few micro-ohms at all.
My concern was that, in order to attenuate RF going into a differential
amplifier, you'd want to attenuate the RF itself equally on both sides,
so that the impedance balancing, even at RF, would be relevant. No?
Yes? No? Idunno, so I ask. In an extreme example, suppose you start
out with lots and lots of RF coming in exactly equally on both legs of
the microphone input. In theory it would get pretty well attenuated by
the differential input amplifier, no? Then suppose you were able to
completely choke off all the RF on one leg, but not at all on the
other. Would the result be more or less RF getting through the input
stage and wreaking havoc on the rest of the amplifier?

ulysses

[Eric K. Weber]

If you move the common grounding point to the chassis between the connectors
instead of the circuit board most rf problems will go away.
The factory issue on mine, used the circuit board for the grounding point
leaving a nice 6 inch loop antenna inside the chassis to radiate RF.

Rgds:
Eric

Post by Justin Ulysses Morse

Post by Jim Williams
That inductance reacts at rf frequencies, in audio it would be seen as
pure resistance. I suppose you could match some using a micro-ohm
meter, although the probe contact resistance would skew it a bit.

I'm not worried about a series resistance of a few micro-ohms at all.
My concern was that, in order to attenuate RF going into a differential
amplifier, you'd want to attenuate the RF itself equally on both sides,
so that the impedance balancing, even at RF, would be relevant. No?
Yes? No? Idunno, so I ask. In an extreme example, suppose you start
out with lots and lots of RF coming in exactly equally on both legs of
the microphone input. In theory it would get pretty well attenuated by
the differential input amplifier, no? Then suppose you were able to
completely choke off all the RF on one leg, but not at all on the
other. Would the result be more or less RF getting through the input
stage and wreaking havoc on the rest of the amplifier?
ulysses

[Scott Dorsey]

Post by Justin Ulysses Morse

Post by Jim Williams
That inductance reacts at rf frequencies, in audio it would be seen as
pure resistance. I suppose you could match some using a micro-ohm
meter, although the probe contact resistance would skew it a bit.

I'm not worried about a series resistance of a few micro-ohms at all.
My concern was that, in order to attenuate RF going into a differential
amplifier, you'd want to attenuate the RF itself equally on both sides,
so that the impedance balancing, even at RF, would be relevant. No?
Yes? No? Idunno, so I ask.

I _bet_ that the differential amp ceases to be a differential amp entirely
at RF... the two sides are probably not balanced well enough at high
frequencies (even the lead lengths make a huge difference here) for it to
be useful.

What you want to do is keep RF out of the front end in the first place,
since the nonlinear junction on the front end is going to create an AM
detector. Catching the stuff before it makes it to the front end is the
most effective ploy.

In an extreme example, suppose you start

Post by Justin Ulysses Morse
out with lots and lots of RF coming in exactly equally on both legs of
the microphone input. In theory it would get pretty well attenuated by
the differential input amplifier, no? Then suppose you were able to
completely choke off all the RF on one leg, but not at all on the
other. Would the result be more or less RF getting through the input
stage and wreaking havoc on the rest of the amplifier?

Maybe, but most of the havoc is probably at the front end anyway.
--scott

[Justin Ulysses Morse]

Hey, thanks Eric and Scott and Jim for the great posts on this topic.
I've learned a lot today. I bet I wouldn't have learned this stuff in
Engineering school (I bet that's not where you learned it either), so
I'm glad I spent my seven years on and art degree instead.

ulysses

[Mike Rivers]

Post by Justin Ulysses Morse
I've always wondered though...Shouldn't these inductors be very closely
matched to preserve HF CMRR? I wouldn't know how to begin measuring an
inductor. Of course the same probably applies to the original ferrite
beads.

Well, you can measure it with an inductance bridge, or measuring the
voltage drop across it at a known frequency. I don't have my abacus
handy, but if I got the decimal in the right place, at 1 MHz, a 100 uH
choke has a reactance of 628 ohms (2 pi x 100, the M(Hz) and u(H)
cancel). That's about 6 dB of attenuation just as a voltage divider
with the input impedance of a typical preamp. When you get up in
frequency, the cable shield probably does a pretty good job of keeping
the common mode noise out.



--
I'm really Mike Rivers - (***@d-and-d.com)

[S O'Neill]

Well, you can measure it with an inductance bridge, or measuring the voltage
drop across it at a known frequency. I don't have my abacus handy, but if I
got the decimal in the right place, at 1 MHz, a 100 uH choke has a reactance
of 628 ohms (2 pi x 100, the M(Hz) and u(H)

Divided by 2 because there's one on each side, for common mode, and times 2 for
the differential effects.

When you get up in frequency, the cable shield probably does a pretty good
job of keeping the common mode noise out.

Maybe. The shield acts as an antenna (perhaps a good one), and if the input
ground layout has any amount of impedance from long or arduous traces you might
find an unintended receiver in the input devices.

[Mike Rivers]

Post by S O'Neill
The shield acts as an antenna (perhaps a good one), and if the input
ground layout has any amount of impedance from long or arduous traces you might
find an unintended receiver in the input devices.

This is the classic case of "The Pin 1 Problem." The shield will act
as an antenna, but it should properly go directly to ground and not
introduce whatever it picks up into the signal path. Unfortunately a
lot of shield terminations aren't properly constructed or designed, so
the signal that this 'antenna' picks up gets where you don't want it.



--
I'm really Mike Rivers - (***@d-and-d.com)

[Dan Popp]

Martin,
I've owned an HV-3 for years, and had an STT-1 on loan for awhile. I've never
had a problem with RF running a regular condensor or dynamic mic. BTW, the
inputs are transformerless BALANCED. (Duh - 48v phantom power requires 2 signal
paths). I did try the 130-volt unbalanced option (this is the powering scheme
for DPA mics) and experienced some RF problems this way. Maybe this is what the
other posters are talking about. When Celine uses 100-million channels of
Millennia on stage, I don't think she's worried about RF.

Call or email the company if you have concerns - they've been extremely
responsive to me.

Yours,
Dan Popp
Colors Audio
USA

Post by Martin
I have been reading newsgroup posts about the Millenia Media and Great River
preamps. Time and time again I read quotes like these.
"The Millennia is a lot more prone to RF troubles."
"The Millenia Media preamp is extremely transparent, but is more susceptible
to RF interference because it is transformerless."
"Another high-regarded preamp in this class would be the Millenia Media, but
the unbalanced input requires some care to avoid RF interference and hum."
Can anyone give me examples of how one might trigger this RF interference?
Is it really that easy to introduce RF interference into the signal chain of
a Millenia Media preamp?
Thanks.
Martin

[Scott Dorsey]

Post by Martin
Can anyone give me examples of how one might trigger this RF interference?

Work in a hall with a 2KW FM broadcast rig on the roof.

Work in a club with the cheapest possible dimmers, and inductive loads hanging
off the dimmers. And poorly maintained neon signs.

Post by Martin
Is it really that easy to introduce RF interference into the signal chain of
a Millenia Media preamp?

No. And the new HV-3D is WAY less sensitive to RF trash than the older ones.
But it will still pick up junk that transformer-input devices will reject.
That's the price you pay for wide bandwidth.
--scott

[Ron Capik]

< ...Snip.. >
Work in a club with the cheapest possible dimmers, and inductive loads hanging
off the dimmers. And poorly maintained neon signs.

Hmmm, just wondering how does one "maintain" a neon sign?

Ron Capik <<< cynic in training >>>
--

[Scott Dorsey]

Post by Ron Capik

< ...Snip.. >
Work in a club with the cheapest possible dimmers, and inductive loads hanging
off the dimmers. And poorly maintained neon signs.

Hmmm, just wondering how does one "maintain" a neon sign?

Replace the transformer when it starts making spitting sounds and smelling
funny, for one thing.
--scott

[Bruce L. Bergman]

On 3 Oct 2003 19:03:54 -0400, someone who calls themselves

Post by Scott Dorsey

Post by Ron Capik

< ...Snip.. >
Work in a club with the cheapest possible dimmers, and inductive loads hanging
off the dimmers. And poorly maintained neon signs.

Hmmm, just wondering how does one "maintain" a neon sign?

Replace the transformer when it starts making spitting sounds and smelling
funny, for one thing.

That, and keep all the high-voltage insulation, neon tube stand-off
insulators, and wiring both outside and inside the sign relatively
clean and in good shape - corona leakage to ground through dirt tracks
and bad insulation makes a horrendous amount of RF hash. The original
spark transmitter.

Oh, and if your local power utility has a high-tension transmission
line going past your building (on foot-long insulators), they can make
a lot of RF noise from flashover on dirty insulators, and the salts
from being near the ocean makes it worse. If you come in on foggy
mornings and hear corona zapping high up on the pole, call the
utility. They can send out the insulator cleaner truck to spray the
insulators clean with de-ionized water.

--<< Bruce >>--

[ScotFraser]

<< Whomever wrote this is VERY incorrect I beleive. Just because the HV3 is
transformerless doesn't mean it's unbalanced, far from it. >>

Right. I asked John LaGrou if he could add a trim pot mod to the HV3 & he said
there aren't any stereo pots that track well enough to make it work, & a stereo
pot would be needed because the circuit is balanced all the way from in to out.
Scott Fraser

[Matthew Champagne]

Post by Martin
I have been reading newsgroup posts about the Millenia Media and Great River
preamps. Time and time again I read quotes like these.

[snip]

Post by Martin
"Another high-regarded preamp in this class would be the Millenia Media, but
the unbalanced input requires some care to avoid RF interference and hum."

[snip]


Hi, Martin-

I have a Millennia HV-3B and, like other posters have commented, have
never had any problems with 100'+ runs of Canare star-quad with any of
my microphones (all Neumann KM series).

Though the unit is indeed balanced, the B&K/DPA high-voltage
microphones do not, as I understand them, have balanced outputs. This
makes them susceptible to interference CMR circuitry would normally
eliminate, and is a very good reason to put the preamp as close to the
source as possible in this circumstance.

John LaGrou has addressed this issue and, I believe, recommends a
particular model of Mogami cable to use when long runs are necessary
to the preamp.

I consider my HV-3B to be the most reliable and consistently
exceptional piece of gear I have ever used and don't plan to ever let
it go.

-Matt

[John La Grou]

On Wed, 24 Sep 2003 04:32:21 GMT, "Martin"

Post by Martin
Is it really that easy to introduce RF interference into the signal chain of
a Millenia Media preamp?

Martin,

Someone brought this up on RAP about three years ago.

http://groups.google.com/groups?q=+RF+OR+RFI+author:jl%40jps.net&hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=390ed765.612234326%40news.jps.net&rnum=1

If your Millennia micamp is model HV-3B, HV-3C, Quad, HV-3D, Origin,
MSD-2, or TD-1, it has no known RF issues (though if you get close
enough to a tower, you can eventually modulate anything).

A few of the very first production HV-3 micamps could exhibit some RF
sensitivities. Some basic improvements were made, e.g., modified
ground routing, improved front-end power supply rejection, ferrite
beads added near input XLRs, etc... Since those improvements (ten
years ago and 13,000 channels later) RF complaints are virtually
non-existent.

p.s., I'll be chairing an AES tutorial session on microphone
preamplifiers. I've asked Geoff Daking, Eric Blackmer (Earthworks),
Lynn Fuston (3D Audio), and Dan Richards (The Listening Sessions) to
join me on the panel. Each panelist brings an in-depth and unique
perspective on micamps.

The session is Saturday 3:30 - 5:00 and a large portion of the time
will be open for audience Q&A. Please join us if you can.

Best wishes,
John La Grou
Millennia Music @ Media Systems
http://www.mil-media.com

[Fletcher]

Post by John La Grou
p.s., I'll be chairing an AES tutorial session on microphone
preamplifiers. I've asked Geoff Daking, Eric Blackmer (Earthworks),
Lynn Fuston (3D Audio), and Dan Richards (The Listening Sessions) to
join me on the panel. Each panelist brings an in-depth and unique
perspective on micamps.

Well, I reckon that's a safer list than the panel from the Tape Op Conference...
--
Fletcher
Mercenary Audio
TEL: [phone]
FAX: [phone]
http://www.mercenary.com
"this is not a problem"

[LeBaron & Alrich]

Post by Fletcher

Post by John La Grou
p.s., I'll be chairing an AES tutorial session on microphone
preamplifiers. I've asked Geoff Daking, Eric Blackmer (Earthworks),
Lynn Fuston (3D Audio), and Dan Richards (The Listening Sessions) to
join me on the panel. Each panelist brings an in-depth and unique
perspective on micamps.

Well, I reckon that's a safer list than the panel from the Tape Op Conference...

Yeah, at least they get one guy interested in transparency.

--
ha