Just finished setting up a band in my rehearsal facilty, and had a bit of
trouble locating some mic feedback.. It was still there even after pulling
the mic cables.

Turned out it was a guitar. Even with the strings full damped, the whole
thing was 'live' when you tapped it, and would start squealing if the amp
was turned up to a reasonable degree.

But what took the cake was that I could sing into it ! And my voice came
throught he guitar amp sounding not too bad ! Well, pretty much like a very
rooted 58 really.

Never come across such a bad case of microphonics before. The guitarist
didn't seem to mind, or notice......


geoff

That's interesting! What kind of guitar/pickup?

mike

"Geoff Wood" -nospam wrote in message
...
Just finished setting up a band in my rehearsal facilty, and had a bit of
trouble locating some mic feedback.. It was still there even after pulling
the mic cables.

Turned out it was a guitar. Even with the strings full damped, the whole
thing was 'live' when you tapped it, and would start squealing if the amp
was turned up to a reasonable degree.

But what took the cake was that I could sing into it ! And my voice came
throught he guitar amp sounding not too bad ! Well, pretty much like a
very
rooted 58 really.

Never come across such a bad case of microphonics before. The guitarist
didn't seem to mind, or notice......


geoff

Geoff,

squealing if the amp was turned up to a reasonable degree.

Yes, "microphonic" is the correct word, and the solution is easy if a little
messy: Remove the pickup and any metal shroud around it, and soak it in
candle wax. I've done this many times for myself and for friends.

Put a small (empty) coffee can on the stove and set the heat to medium-low.
Put some plain clear/white candles in the can and let them melt. Then grab
the pickup with a needle nose pliers, dip it into the wax until it's fully
submerged, and slosh it around so the wax fully gets into the windings on
the outside AND inside. Then take out the pickup and hold it over the can
until the excess wax drips off, let it dry, and that problem is gone for
good.

--Ethan

"Geoff Wood" -nospam wrote in message ...
Just finished setting up a band in my rehearsal facilty, and had a bit of
trouble locating some mic feedback.. It was still there even after pulling
the mic cables.

Turned out it was a guitar. Even with the strings full damped, the whole
thing was 'live' when you tapped it, and would start squealing if the amp
was turned up to a reasonable degree.

But what took the cake was that I could sing into it ! And my voice came
throught he guitar amp sounding not too bad ! Well, pretty much like a very
rooted 58 really.

Never come across such a bad case of microphonics before. The guitarist
didn't seem to mind, or notice......


geoff




I trust you tried different cabling.


How much for the pickup ??

--
David Morgan (MAMS)
http://www.m-a-m-s.com
http://www.artisan-recordingstudio.com

"Geoff Wood" -nospam wrote in message
...
Never come across such a bad case of microphonics before. The guitarist
didn't seem to mind, or notice......

I had a strange one like this recently...
A guitar amp was making a quite loud slow clicking sound every time just
before the guitarist was about to do a take.
Eventually narrowed it down to the watch he was wearing, it was a crystal
driven analog style watch, and the
tiny energy used in the motor was being picked up electromagneticly by the
pickup!

In article -nospam writes:

Even with the strings full damped, the whole
thing was 'live' when you tapped it, and would start squealing if the amp
was turned up to a reasonable degree.

But what took the cake was that I could sing into it !

I was visiting a Kaleidoscope recording at Columbia Studios in
Hollywood in the early '70's (I think it was their 3rd album, Bernice)
and they recorded the amplified saz by putting the electric Dobro
against the front of the saz amp, and taking its pickup direct to the
console. It didn't sound like either a saz or a Dobro, but that was
the idea.




--
I'm really Mike Rivers - )

"Mike Turk" wrote in message
. rogers.com...
That's interesting! What kind of guitar/pickup?



A yellow one ! Dunno - some cheap modern-thrash thing with 2 humbuckers and
a single-coil in the middle. Thing was so live (scratchplate, pickups,
body) it was impossible in the circumstances to locate exactly where it was
from. The pickups did seem of the semi-open variety - not 'potted'.


geoff

"Geoff Wood" -nospam wrote in message
...

I was momentarily disorientated when driving the other day. I kept trying
to turn the indicators off, but htey weren't on. Turned out is was a
high-hat on the radio !

Not my week for extraneous noises...

Some things that keep me amused while gigging...
Samples of 50hz hum and a crackling lead on my keyboard, and the ability to
vocalise a sound like mobile phone interference into mics.
Watch those sound guys run! (Then watch me run faster when they find out
where it's coming from.)





geoff

"philicorda" wrote in message
...

"Geoff Wood" -nospam wrote in message
...

I was momentarily disorientated when driving the other day. I kept
trying
to turn the indicators off, but htey weren't on. Turned out is was a
high-hat on the radio !

Not my week for extraneous noises...

Some things that keep me amused while gigging...
Samples of 50hz hum and a crackling lead on my keyboard, and the ability
to
vocalise a sound like mobile phone interference into mics.
Watch those sound guys run! (Then watch me run faster when they find out
where it's coming from.)


Mobile ringtones - watch everybody dive for theirs !

geoff

"Mike Rivers" wrote in message

Yeah, you've gotta watch those impedance mismatches. You might get the
wrong number of electrons per second moving past a point in the wire.
That might cause a loss of quality in the sound.


Comes from the days when amplification of a signal wasn't a relatively
trivial matter to acheive, and matched impedences were essential for
'maximium power transfer'. But I'm sure you know that.

geoff

In article -nospam writes:

Maximum power transfer was never a consideration for microphone
inputs. But I'm sure you know that.

I think you will find that in thew 50's and 60's they actually were pretty
anal about attemting to match such things.

True for console outputs to recorders, but microphone inputs were
rarely as low impedance as microphone outputs. Microphones don't put
out any significant power so it's silly to try to transfer maximum
power. If one of you vintage preamp experts can clear this up once and
for all, I'd appreciate it. I could be wrong about this, but I'd be
surprised if mics and preamps were ever really impedance-matched.

I think you'll find that by the time the Beatles were recording,
engineers were starting to understand their equipment a little better
than in the past.



--
I'm really Mike Rivers - )

Mike Rivers wrote:

True for console outputs to recorders, but microphone inputs were
rarely as low impedance as microphone outputs. Microphones don't put
out any significant power so it's silly to try to transfer maximum
power. If one of you vintage preamp experts can clear this up once and
for all, I'd appreciate it. I could be wrong about this, but I'd be
surprised if mics and preamps were ever really impedance-matched.

No, it's BECAUSE mics don't put out any significant power that they
used to be matched! The reason being that lost power ends up
reflected in a worse S/N ratio. Back when preamps were significantly
noisier that was important. A typical vintage setup was a mic
(typically 50 Ohms or 150-200 Ohms or 600 Ohms) into an Input
transformer (I still own some dandy Shure ones tapped for...
you guessed it...50, 150 or 600 Ohms). The other side of the
transformer was typically 100k Ohms to feed a tube grid input.
By power matching the mic to the grid you got maximum signal
and hence the maximum signal to noise ratio.

Note that today many mics are designed with low impedance outputs
that MUST be run into a higher impedance input. In other
words the mic specs may say "50 Ohms out" but if you actually
loaded the output with 50 Ohms it wouldn't work right. If you
pluged that mic into a vintage board you'd be in trouble!
Usually these mics are designed to run into several KOhms as
a load.


----
And as an aside, let me mention that I built a passive DI
which is basically an old UTC "crystal to line" transformer.
it has 200k in the high side and the typical 50, 150, 600 taps
on the low side. Works like a freakin' champ. I also included
a switchable attenuator because quite frankly a bass (or guitar)
can put out a pretty healthy voltage through a straight transformer
and you can overload some mic preamps if you don't cut it back.
Thus if you have an overload problem you simply add a few dB
attenuation.

The whole idea of a DI is to take a single ended Guitar signal
at about 100k ohms. Then you want to isolate it from board
to eliminate grounding problems. And finally you want to
lower the impedance and convert to a balanced output
that looks like a microphone. As I noted sometimes you
need to attenuate a tad to bring the levels down to those
of a typical mic.

Interestingly enough, a plain old vintage mic input transformer
run backwards does all these things (except the attenuation which
isn't big deal).

Benj

--
SPAM-Guard! Remove .users (if present) to email me!

"philicorda" wrote in message I
had a strange one like this recently...
A guitar amp was making a quite loud slow clicking sound every time just
before the guitarist was about to do a take.
Eventually narrowed it down to the watch he was wearing, it was a crystal
driven analog style watch, and the
tiny energy used in the motor was being picked up electromagneticly by the
pickup!


Yup, I've had a similar experience with that.

Slightly related:

I was doing a gig about 10 years ago as the SR engineer. Literally two
minutes to the band taking the stage, a guy with a video camera and tripod
comes up to me and asks for a feed from the desk. There were no free auxes,
no free outputs on the desk, and I wasn't about to try and find y cables etc
at that late stage. I was about to tell him to shove off, but an oddball
idea occurred to me. I grabbed a spare single coil guitar and lead, laid it
on the ground above the nearby hearing aid loop and handed him the lead
plugged into the guitar. "See if you've got something useful coming out of
that" I said as I turned away 'cos the band was coming out.

He did, and from all reports the resulting audio was reasonably good !
--
John Cafarella
End Of the Road Studio
Melbourne, Australia