Scott Dorsey , Harvey Gerst al, ML-52 Mod Question
Michael Joly
A question about the Oktava ML-52 Ribbon mic. I just took the
windscreen off the base of the mic to have a look under the hood.
There are two vertical ribbons pretty well hidden inside the magnet
structure. Mounted to the surface of the magnets is a metal plate with
a series of 7 vertical holes in front of each ribbon.
Now the interesting part...suspended in front of the holes in the
metal plate is a brass fixture shaped like a goal post - the two
uprights block direct access to the holes in the plate in front of the
ribbons.
Question, what's the purpose of the brass plate. Some sort of HF
tuning?
On another note (literally), the windscreen seems to be made of the
same ringing cast alloy that makes the MK-219 boink before it is
damped in some way. I'm thinking of cutting out the radiator grilles
and replacing them with another layer of wire mesh. But first, inside
the windscreen, next to the wire mesh screen, is a layer of very fine
weave textile. It doesn't look too open to my eye and I wonder about
its HF transparency. I'm wondering if I can just pull this stuff out
and use an external popper stopper instead.
Where I'm going with all this is...the frequency response graph of
this mic shows -1dB at 1.5kHz, +1dB at 3kHz, a narrow -5dB notch at
5kHz returning to -3dB from 6-9kHz, then +3 at 12kHz followed by a
rapid cut-off. I'm wondering if the holes and brass plate is an
attempt to boost the HF but introduces response bobbles and phase
problems in the 5-9kHz region.
If this is indeed a mechanical top boost, I'll pull the sucker out and
hopefully straighten out the response curve. There's too much 12k in
the world anyway.
The transformer investigation will have to wait for another day.
MJ
Scott Dorsey
>Now the interesting part...suspended in front of the holes in the
>metal plate is a brass fixture shaped like a goal post - the two
>uprights block direct access to the holes in the plate in front of the
>ribbons.
>
>Question, what's the purpose of the brass plate. Some sort of HF
>tuning?
I think it's to protect the ribbon from direct wind blasts. Probably
very important if you're using it as a vocal mike, but I bet you can
take it out freely if you aren't.
It probably also provides a resonant chamber to bring the HF response up
too but I don't know by how much. I suspect the damage it does to the
pattern more than makes up for HF benefit.
>On another note (literally), the windscreen seems to be made of the
>same ringing cast alloy that makes the MK-219 boink before it is
>damped in some way. I'm thinking of cutting out the radiator grilles
>and replacing them with another layer of wire mesh. But first, inside
>the windscreen, next to the wire mesh screen, is a layer of very fine
>weave textile. It doesn't look too open to my eye and I wonder about
>its HF transparency. I'm wondering if I can just pull this stuff out
>and use an external popper stopper instead.
I don't see any reason not to remove it, but I'd first try felt and/or
silicone RTV on the inside of the thing to try and kill the boink.
>Where I'm going with all this is...the frequency response graph of
>this mic shows -1dB at 1.5kHz, +1dB at 3kHz, a narrow -5dB notch at
>5kHz returning to -3dB from 6-9kHz, then +3 at 12kHz followed by a
>rapid cut-off. I'm wondering if the holes and brass plate is an
>attempt to boost the HF but introduces response bobbles and phase
>problems in the 5-9kHz region.
I would not be surprised if it did some top boost, but I don't think that
was the primary reason for the thing.
>If this is indeed a mechanical top boost, I'll pull the sucker out and
>hopefully straighten out the response curve. There's too much 12k in
>the world anyway.
Try it and let me know what happens. Also try and do a crude pattern
measurement too; I bet the null gets a lot better with that thing removed.
>The transformer investigation will have to wait for another day.
Swapping the transformer is easy and not much work. Tuning the thing
acoustically is hard.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Stephen Sank
sheet metal "blast shields" do more harm than good in all respects. I
removed them & installed some fairly open weave silk to front & back of the
motor in it's place. The biggest problem on these mics, in my opinion, is
how sloppy the ribbon clamps' machining is, and, because of this, how sloppy
the ribbons are installed. I frankly can't see how Oktava can make any two
of these mics sound much alike under these circumstances. After re-shaping
the ribbon clamps so that they actually fit properly & make a firm & even
hold on the ribbons, and then installing two new RCA ribbons(is the regular
ML-52 a double ribbon mic?), the mic sounded pretty darn good. I think the
client said he would post a report about it here after he's had a chance to
use it on a few things.
--
Stephen Sank, Owner & Ribbon Mic Restorer
Talking Dog Transducer Company
http://stephensank.com
5517 Carmelita Drive N.E.
Albuquerque, New Mexico [87111]
505-332-0336
Auth. Nakamichi & McIntosh servicer
Payments preferred through Paypal.com
"Scott Dorsey" <klu...@panix.com> wrote in message
news:bo5vhn$ibj$1...@panix2.panix.com...
Michael Joly
one with, and one without the "ribbon goal posts". Here's what I
found:
The "goal posts" provides 9dB boost @ 20kHz, 5dB boost @ 18kHz and
<=1dB change between 5kHz and 17kHz. But...with the "goal posts" in
place, 2kHz is down 3dB.
Subjectively, two things are noticable. 1.) The stock mic with the
goal posts in place is brighter at the very top...but, 2.) the
high-end is more smeared. The sentence "she sells, sea shells, by the
sea shore" sounds more like "she shells, she shells, by the she
shore". Similarly, the letter "F" sounds broader and less focused.
I prefer the mic with goal posts removed. I don't mind giving up 5dB @
18k, I like the extra 2kHz - 5kHz presence, (really just bringing it
back to flat compared to the stock mic's 4-5kHz dip)and the improved
phase response on "S" and "F" sounds is noticable and quite sweet.
My null test was inconclusive. If anything, I noticed a bit more
12-16K leakage in the null when the goal posts were removed, but this
might have been a mic placement error.
I did end up cutting out the vertical grilles (which ping like
crazy)and removed the windscreen fabric. I'm using a double layer of
bronze bug screen for sheilding until my order of two different guages
of stainless steel wire mesh arrives from www.smallparts.com. Once I
install the wire mesh I'll goop every resonant surface thats left with
RTV.
Any thoughts about a suitable Jensen transformer model?
Michael Joly
>The biggest problem on these mics, in my opinion, is
> how sloppy the ribbon clamps' machining is, and, because of this, how sloppy
> the ribbons are installed. I frankly can't see how Oktava can make any two
> of these mics sound much alike under these circumstances.
Stephen,
Would the ribbon installation problem show up mostly as LF resonant
tuning variances? I ask because I auditioned a bunch of these at
Guitar Center and picked the one that had the most complimentary
proximity effect resonance on my voice. I noticed greater differences
in the mics in the LF rather than in the MF and HF.
I'd have to say, pulling out the goal post blast screen and re-working
the grille has made something that sounds pretty righteous.
Oh, another question. Does the top of the mic have to be acoustically
transparent to the outside world, or can I do a combination of RTV
gooping and installation of a foam plug up there to dampen the boink
of the top grille pieces?
Stephen Sank
that it's less problematic to make the top screen as acoustically
transparent as possible than it would be to make it a damped solid body.
It'd be damned hard to completely damp the cavity effects of a closed top.
The most ideal ribbon mics have been those with as little solid structure as
possible, with the prime example being the RCA SPX-2 lab reference mic,
which had just a small motor suspended in the center of a large cloth
globe(pictured on my website's mic service page).
--
Stephen Sank, Owner & Ribbon Mic Restorer
Talking Dog Transducer Company
http://stephensank.com
5517 Carmelita Drive N.E.
Albuquerque, New Mexico [87111]
505-332-0336
Auth. Nakamichi & McIntosh servicer
Payments preferred through Paypal.com
"Michael Joly" <mic...@electricspace.com> wrote in message
news:a884fa43.03110...@posting.google.com...
Scott Dorsey
>
>The "goal posts" provides 9dB boost @ 20kHz, 5dB boost @ 18kHz and
><=1dB change between 5kHz and 17kHz. But...with the "goal posts" in
>place, 2kHz is down 3dB.
This makes perfect sense. I do expect the mike is a good bit more
delicate this way, though.
>Subjectively, two things are noticable. 1.) The stock mic with the
>goal posts in place is brighter at the very top...but, 2.) the
>high-end is more smeared. The sentence "she sells, sea shells, by the
>sea shore" sounds more like "she shells, she shells, by the she
>shore". Similarly, the letter "F" sounds broader and less focused.
This is probably the result of group delay caused by that resonance.
>I did end up cutting out the vertical grilles (which ping like
>crazy)and removed the windscreen fabric. I'm using a double layer of
>bronze bug screen for sheilding until my order of two different guages
>of stainless steel wire mesh arrives from www.smallparts.com. Once I
>install the wire mesh I'll goop every resonant surface thats left with
>RTV.
There has to be a better way to do this... there has to be some easy way
to reinforce the grille so it doesn't ping so much.
>Any thoughts about a suitable Jensen transformer model?
I don't think Jensen can make anything with that high a ratio, but Lundahl
makes a pretty good 1:37 transformer intended for ribbon mikes. It's a
bit odd to wire up since you are paralleling a whole bunch of secondaries.
While you're at it, replace the wires from the ribbon to the transformer
with carefully twisted 16AWG solid core.
Michael Joly
Lundahl
> makes a pretty good 1:37 transformer intended for ribbon mikes. It's a
> bit odd to wire up since you are paralleling a whole bunch of secondaries.
> While you're at it, replace the wires from the ribbon to the transformer
> with carefully twisted 16AWG solid core.
> --scott
Is this the one? http://www.lundahl.se/pdfs/datash/7101.pdf
And if so, how do I wire it?
Scott, have you put a square wave through the stock ML-52 transformer
or are you assuming from past experience with the transformers in the
MK219/319 that the Lundahl is going to perform better on both
transient signals and high level bass?
Scott Dorsey
>klu...@panix.com (Scott Dorsey) wrote in message news:<bo8i0r$me5$1...@panix2.panix.com>...
>
>Lundahl
>> makes a pretty good 1:37 transformer intended for ribbon mikes. It's a
>> bit odd to wire up since you are paralleling a whole bunch of secondaries.
>> While you're at it, replace the wires from the ribbon to the transformer
>> with carefully twisted 16AWG solid core.
>
>And if so, how do I wire it?
I don't know since I have no way to see a pdf file today. But the data
sheet will show you how to wire it; all of the primaries go in parallel
with the + sides together and the secondary goes to the output.
>Scott, have you put a square wave through the stock ML-52 transformer
>or are you assuming from past experience with the transformers in the
>MK219/319 that the Lundahl is going to perform better on both
>transient signals and high level bass?
I have swapped the transformers on the ML-52 and ML-19 with the Lundahls and
it is like night and day. It is MUCH harder to make a ribbon mike transformer
than a low ratio transformer like the MK-219 uses.
I have no way of doing a square wave response on a transformer with such a
low primary impedance. I'm not sure anybody can really do it under real
world conditions but it might be interesting to try.
Michael Joly
1. Body dampening -
a.) Cut out front and back vertical grilles and replaced them with two
layers of stainless steel wire mesh from www.smallparts.com (Part
Code: CX-16-A S/S TYPE 304 MESH #16 3"x6" and Part Code: CX-30-A S/S
TYPE 304 MESH #30 3"x6" )
b.) Fit black rubber strip around the circumference of the top
windscreen covering the mounting screws. (rings like crazy before
dampening)
c.) Fit a narrow black rubber strip over the mid section of the top
windscreen grilles and secured it under the strip above. (also pings
before dampening)
2. Motor mod -
a.) Removed the HF boost / wind blast protector in front of ribbons on
both front and back of mic.
b.) Replaced skimpy stranded wire from motor to transformer with
tightly twisted #18 guage solid copper.
3. Transformer mod -
Installed Lundhal LL2911 (available from Kevin Carter at
www.kandkaudio.com)
Results - The real deal. Rich, smooth low end and very natural top end
with very tight transient response that takes EQ well.
Kurt Albershardt
A. & G. Reiswig
could get in a lot of trouble.
George Reiswig
Song of the River Music
"Kurt Albershardt" <ku...@nv.net> wrote in message
news:10682741...@nnrp2.phx1.gblx.net...
A. & G. Reiswig
compare to, say, a Beyer M260?
George Reiswig
Song of the River Music
"Michael Joly" <mic...@electricspace.com> wrote in message
news:a884fa43.03110...@posting.google.com...
Michael Joly
> So how much $$ do you have into this project, and how does the end product
> compare to, say, a Beyer M260?
ML52: $200, parts: $60, Learning: Priceless
I don't own a Beyer M260 so I can't offer any A/B comments. I did a
session yesterday with a mid-40's Orpheum archtop in a powerpop,
rather than trad jazz context. Incredibly big and punchy with a
shimmery, not brittle top. In my accoustic guitar rhythm playing I go
for a John Lennon / J160 sound. I think the Lundhal transformer adds a
harmonic richness and slightly aggressive quality I like for my
purposes. Also recorded my reed flutes with it, again nice mid-range
presence and much less breath/wind noise than most condensors I've
used. Works great for voice-overs too, just slide a HP filter to the
right cut-off frequency to tame the proximity effect to fit the track.
The null on this mic is terrific. I can record quiet flute stuff in
close proximity to a tape machine or workstation and pick up almost no
machine noise.
Then there is the indescrible vibe of this mic. Subjectively, standing
in front of this thing turns on the performer in me, sort of like the
old red "RECORDING" light that means, "ok you're on, go for it".
Because I've modded the mic myself there's an energetic resonance
between me and it that's pretty cool.
I do these sort of projects for the sheer love it, I'm not trying to
beat eBay for cost/value. Though in this case I think I did. I find it
interesting to get under the hood and try to understand why designers
make the design tradeoffs they do, becuase in some cases, I find that
I would make different choices. The choice of the mechanical HF boost
/ wind blast filter for example...
Now, it is true that this little mechanical device adds some HF boost
to the mic and protects the ribbon from blasts. But, I prefer the
sound of really tight transients not smeared by the group delays
created by a mechanical filter, so I revoved it. And as far as ribbon
wind blast protection goes...I think presence of mind is a good thing.
The other serious design constraint in this mic is the cast aluminium
case. Sure it looks great and retro and is cheap to produce but it
resonates severely unless the grilles are removed or modified.
This activity is sort of like Miata racing or urban Toyota
customization.
best, MJ
Mike Rivers
> The null on this mic is terrific. I can record quiet flute stuff in
> close proximity to a tape machine or workstation and pick up almost no
> machine noise.
It's a sad commentary on the state of recording that this is the
criteria for a microphone, but if that's what you need in order to
make your Grammy winning recording, go for it.
--
I'm really Mike Rivers - (mri...@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, decode mm1100atyahoo
and reach me there.
A. & G. Reiswig
curious as to comparisons with your modded mic against other ribbons.
Thanks for posting!
George Reiswig
Song of the River Music
"Michael Joly" <mic...@electricspace.com> wrote in message
news:a884fa43.03110...@posting.google.com...
Michael Joly
My attempt to dampen the top portion of the ML-57 grille with rubber
strips was not entirely successful. Last night, in the wee quiet
hours, I was listening to room tone with about 75dB of gain applied
and could hear the mic oscillating at 570Hz!
There is a genetics research factory about 200 feet from my house with
massive air-conditioning and air handling machinery that generates
some pretty substantial <40Hz rumble.
This rumble finds its way through the wood frame construction of the
house, up the mic stand and into the mic, where, it sets into
oscillation the top "ring" of the ML-52 enclosure.
Sure enough, when I clasped my thumb and forefinger around the ring,
the oscillation stops. I couldn't believe it. My next task is going to
be to put a felt strip around the ring and then clamp down on it with
hose clamp.
I discovered this ring resonance only after I had tamed the other two
mechanically resonant systems in the mic – the vertical grille fins
and the arched, top grille fins. These arched fins "ping" rather than
"boink" when excited. My solution was to tie the arched fins to the
underlying wire mesh screen with thin beads of epoxy applied to the
junction of the fin and the screen. This effectively eliminated any
resonance of the arched fins and allow the "top ring ping" to show
through in all its glory.
So I only discovered these problems by exciting the mic with very low
frequency vibrations – well below the audio band – and listening
intently to the audio pass band.
MJ
A. & G. Reiswig
the DynaMat type tar-based material used in dampening metal panels in cars.
Messy if you have to remove it, but no more so than silicone. ;-)
George Reiswig
Song of the River Music
"Michael Joly" <mic...@electricspace.com> wrote in message
news:a884fa43.03111...@posting.google.com...
> Body Dampening - continued.
>
> My attempt to dampen the top portion of the ML-57 grille with rubber
> strips was not entirely successful. Last night, in the wee quiet
> hours, I was listening to room tone with about 75dB of gain applied
> and could hear the mic oscillating at 570Hz!
>
> There is a genetics research factory about 200 feet from my house with
> massive air-conditioning and air handling machinery that generates
> some pretty substantial <40Hz rumble.
>
> This rumble finds its way through the wood frame construction of the
> house, up the mic stand and into the mic, where, it sets into
> oscillation the top "ring" of the ML-52 enclosure.
>
> Sure enough, when I clasped my thumb and forefinger around the ring,
> the oscillation stops. I couldn't believe it. My next task is going to
> be to put a felt strip around the ring and then clamp down on it with
> hose clamp.
>
> I discovered this ring resonance only after I had tamed the other two
> mechanically resonant systems in the mic - the vertical grille fins
> and the arched, top grille fins. These arched fins "ping" rather than
> "boink" when excited. My solution was to tie the arched fins to the
> underlying wire mesh screen with thin beads of epoxy applied to the
> junction of the fin and the screen. This effectively eliminated any
> resonance of the arched fins and allow the "top ring ping" to show
> through in all its glory.
>
> So I only discovered these problems by exciting the mic with very low
> frequency vibrations - well below the audio band - and listening
Scott Dorsey
>Seems to me a better damping choice than silicone, felt or rubber would be
>the DynaMat type tar-based material used in dampening metal panels in cars.
>Messy if you have to remove it, but no more so than silicone. ;-)
It's got a lot of density, but it's less flexible. Same goes for roofing
tar mixed with sand, or automotive undercoating spray, both of which are
old standards for taming Altec cast aluminum horns.
A. & G. Reiswig
backing on it, too. I have no doubt that it would easily conform to a 1/2"
ID housing, provided you could figure out a way to get it inside. Actually,
with the foil backing, you can kind of pre-shape it, then use a tool to
press it into place.
Easily cut, pretty easy to work with, doesn't smell...I really think this is
what experimenters ought to try if they need to dampen a mic body.
I don't have a mic that needs it right now, or I'd try it myself. I do
think that there's more to it than just adding mass: you could do that by
adding silicone. But substances like this asphalt are not quite solids, not
quite gels...they tend to absorb vibration because of their physical
characteristics, which aren't shared by dry silicone.
Scott, I'd be happy to send you an envelope full of this stuff if you'd
like.
George Reiswig
Song of the River Music
"Scott Dorsey" <klu...@panix.com> wrote in message
news:boog5n$nki$1...@panix2.panix.com...
Scott Dorsey
>Boy, I've got some stuff that is VERY flexible. And it has a lead film
>backing on it, too. I have no doubt that it would easily conform to a 1/2"
>ID housing, provided you could figure out a way to get it inside. Actually,
>with the foil backing, you can kind of pre-shape it, then use a tool to
>press it into place.
Is it as flexible as RTV, though? RTV is hard to beat... it is very soft
compared with most damping material, even if it's not very heavy.
>I don't have a mic that needs it right now, or I'd try it myself. I do
>think that there's more to it than just adding mass: you could do that by
>adding silicone. But substances like this asphalt are not quite solids, not
>quite gels...they tend to absorb vibration because of their physical
>characteristics, which aren't shared by dry silicone.
>
>Scott, I'd be happy to send you an envelope full of this stuff if you'd
>like.
Sure. I won't complain a bit.
P Stamler
>>the DynaMat type tar-based material used in dampening metal panels in cars.
>>Messy if you have to remove it, but no more so than silicone. ;-)
>
>It's got a lot of density, but it's less flexible. Same goes for roofing
>tar mixed with sand, or automotive undercoating spray, both of which are
>old standards for taming Altec cast aluminum horns.
I've used stainless putty for that sort of thing; it even worked on a Klipsch
Heresy midrange. It's available at any plumbing supply store or department.
Also useful but stickier and lower mass: 3M Strip-Calk. Sometimes the stickier
is nice, though.
Peace,
Paul
A. & G. Reiswig
It is not stretchy like RTV, but it's probably every bit as flexible.
Picture lead foil with about 2mm of tar on one side. Tar is pretty
flexible.
George Reiswig
Song of the River Music
"Scott Dorsey" <klu...@panix.com> wrote in message
news:boono2$rd9$1...@panix2.panix.com...
Dan
d
A. & G. Reiswig" <NOSPAM...@bigfoot.com> wrote in message news:<VOSrb.32741$p9.1...@nwrddc02.gnilink.net>...
A. & G. Reiswig
Contact me off-list if you want some of this stuff.
George Reiswig
Song of the River Music
"Dan" <ddila...@yahoo.com> wrote in message
news:1a3ce7f4.03111...@posting.google.com...