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stainless Offline
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PostPosted: Fri Mar 23, 2012 6:35 pm    Post subject: Ribbon mod Reply with quote

this may be more correctly titled- complete ribbon make over

here's my Karma K6 after my first mod (cutting out the "grills"

[urlhttp://www.recordingproject.com/bbs/viewtopic.php?t=37276&highlight=mod[/url]

I thought this was a great improvment.... that was a few years ago

then I recently bought an AEA R84... OMG... night and day

so, now we embark on making this a bit more 'palatable" I've ordered a Luhndahl LL2913 and both 2u and 1.8 u aluminum foil, a pair of nylon gears so I can corrugate.

The photo is what the destroyed mic looks like (no use being able to turn back right?)

The circuit board which is active circuitry will be tossed, the basket replaces with a more open mesh screen... and I may not use the perf sreens which covered the original ribbon (easy to put on/take off)

There are posts elsewhere (LR) where this mic was used. Tone was good (or so I thought, but compared to the R84, the Karma was woofy, and lacked clarity in the HF's

we'll see how it stacks up after the mods


 

Ribbon RIP.jpg


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PostPosted: Fri Mar 23, 2012 6:49 pm    Post subject: Reply with quote

and special thanks to Michael Jolie who directed me to the sources for needed materials
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PostPosted: Thu Mar 29, 2012 6:55 pm    Post subject: Reply with quote

2 micron ribbon arrived today..Luhndahl and 1.8 ribbon next week... gears.... all I've gotten is a confirmation of receipt of order.....

I need a source for small quantities of stainless mesh screen... any ideas?

everything I've found would require me to buy a lifetime supply (and no i don't want to start a business on the side)

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PostPosted: Sat Mar 31, 2012 2:31 am    Post subject: Reply with quote

any particular weave? wire diameter by center to center preference? you might just pick up a cheap food colander from the dollar store?
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PostPosted: Sat Mar 31, 2012 8:05 am    Post subject: Reply with quote

A foodcollander is a good idea!

I'm thing a 100 mesh would be about right, that's little more open than the typical window screen. I mainly want it as a physical barrier for the ribbon. The K6 original had/has a steel screen (I know it's not stainless as it's magnetic) that looks almost like an electric razor .."shield"....

I could put those in place , but I want to try the mic first with as much "access" as possible.

Michael Jolie has written about improving the cheap ribbons by removing the basket completely to improve response.

Apparently most of the Chinese ribbons are (reportedly 4 micron ribbons), a bit sturdier, but less responsive. I've order 1.8 and 2micron foil

I expect to destroy a few attempts before I get it correctly corrugated and then mounted

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PostPosted: Sat Mar 31, 2012 1:37 pm    Post subject: Reply with quote

If you get to liking working on ribbons I will send you mine!(LOL)
It is a stellar and it sounds like the ribbon might be rubbing on the motor (or magnet or whatever it is caled)

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PostPosted: Sat Mar 31, 2012 1:42 pm    Post subject: Reply with quote

let me see how many times I have to redo mine....Rolling Eyes
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PostPosted: Sat Mar 31, 2012 2:08 pm    Post subject: Reply with quote

Got the gears set to corrugate.

The ribbon is really delicate so I "practiced" on kitchen foil. Also, NEW razor blade/knife, and use the thin paper sheets that come with the foil when cutting... I wiped out about half of the 2 micron sheet already DOH

If you cut it even slightly wider than the gears then it curls to the side... My gears (from a hobby shop that's into RC cars) have 1/4 face which is slightly wider than the clearance between the magnets in the motor.

Below are so pics of the magnets, cutting the foil (fortunately my wife didn't catch me using her make-up mirror)...

I've mounted a ribbon... but it's difficult to tell if I have it not touching the side... (my camera doesn't get close up enough to show...)

and I've discovered that I'll need to modify the casing/mounting for the Luhdahl to fit.....it will fit, just not as the existing chassis id made

as soon as I find the battery charger for the camera I'll get some more pics... for now I have to ponder how to mod the chassis


 

gears.jpg

 

foil.jpg

 

Corrugation.jpg


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PostPosted: Sat Mar 31, 2012 4:53 pm    Post subject: Reply with quote

I've never been patient... got 3 more pics before the battery failed....

The "motor" . assuming it's not rubbing which , (with a magnifying glass) "looks good"... but I see what appears to be a pinhole in one of the corrugations, so we may be revisiting this. I can see it vibrate when I talk into it

The Luhndal LL2913 is PCB mount (and the PCB is on;ly $3... so this seemed easier than having a transformer bounce around inside rhe ~ 2" diameter body, and it has mounting holes conveniently the same spacing as the chassis from the previous active PCB.

The Luhndal PCB can only be loaded one way as the pins are not the same on each side.

could be it for today....

If you've not do ne much soldering on PCB's it just takes a brief instant and a very slight amount of solder... hold the iron too long and you risk lifting the traces... too much solder and you've created an unwanted "new circuit"

The 2 of the pin outs for the XLR are VERY close, so be careful. As a general practice, I test all solder joints and end points with a VOM as i go... makes life much easier

sigh...."damn it Jim, I'm a surgeon, not a bricklayer"

I can't use the mounting holes on the chassis for the Lundahl... In fact the chassis needs to be modified, by which I mean cutting the center portion of it out

Hadn't planned on that


 

motor.jpg

 

Luhndahl.jpg

 

Arghhhhh.jpg


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PostPosted: Sun Apr 01, 2012 6:31 am    Post subject: Reply with quote

are you going to have to "round" the corner of the transformer over some so it will fit inside, or like you said remove some of the chassis rail some it comes up in between the rails...what about spinning the pcb 90 degrees...it looks narrower that way?
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PostPosted: Sun Apr 01, 2012 7:38 am    Post subject: Reply with quote

I cut the chassis apart and made 2 "connecting "struts"...

no mater how I turned it, the chassis would need to be modified

battery should be fully charged. I'll get some photo's up today

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PostPosted: Sun Apr 01, 2012 11:18 am    Post subject: Reply with quote

after removing 1 1/4" of the center portion of the chassis, some 1/4" x 1/16" brass mini flat bar and fitting the Luhndahl inside the brass housing.

The head basket frame has been soldered back together, and if the basket screen doesn't fit in like I'm hoping, taking the top off taks a few passes of a propane torch to lift off. It doesn't take much heat to solder and "I think" I could resolder without discoloting the stainless screen... as soon as I find some... so far 20" x 60" is the smallest section I can find... and that's limited to 16 mesh... i was looking more for 24 mesh... but I don't want to buuy 1 sq feet to have that.

So now, some paining of the body pieces , then I'll solder the XLR and see if it works and what it sounds like

so far, a fun project, and total cost is about $180, which includes the gears and enough foil to do a "few"more mics...... cost to mod this mic about $100- $110.

If any of you should take this on... brass screwdivers, stainless tweezers are really helpful as the magnets are damn strong and it takes constant focus to not have a tool (or hardware) pulled into the magnets.

It also makes me wonder about the design of the ribbon... this is pretty much unchanged from the early RCA's (and others) from "back in the day". Transformers are better, magnets are stronger, but design is pretty much the same.

so, what if you used 3 magnets (L-C-R) and used 2 ribbons (rather than just 2 ribbons side by side)?

What if the "face of the ribbons was angled, so instead of being parallel/perpendicular to the magnet sides, they were at a 45? or if 2 ribbons each at opposite angles to each other

what if you wired in series?

are longer ribbons a thicker foil?

would a wider ribbon in a wider magnetic gap work as well, better, worse, favor HF, or LF, or more mids?

I can't find much on "why" they are made the way they are... is this the best design... or is it just one that works, and others have focused on the electronics


 

that works.jpg

 

getting closer.jpg


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PostPosted: Sun Apr 01, 2012 1:37 pm    Post subject: Reply with quote

it works!!! I'm a bit nervous to use it much until I get a head basket on it, though I suppose I could use as is (especially if I were to secure the screens which are presently held in place by the magnets... Thou I'd like to try the mic with out those, as I wonder if the added "iron content" metal (meaning is is attracted to a magnet) affects the field and thus the performance of the mic.

I've posted a sound byte over in LR.

This is with the mic (in a shock mount) set about chest high as I'm sitting and playing. I'm about 30" off the mic. Signal chain is into the TRP pre and then into the A/D. there is no processing on this

how does it compare to the AEA's... have to tackle that another time... now I need to go get some of the weekend stuff I was originally planning on

though damn this was fun!


 

Almost finished robbon mod.jpg


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PostPosted: Sun Apr 01, 2012 2:09 pm    Post subject: Reply with quote

Stainless,

You are now the ribbon mic answer man, this is one cool thread!!

I've got the hots for one of them Nady ribbons (cheap bastard productions).

Which is better a longer, or a shorter ribbon? I would by it locally, in case the ribbon's loose, so I could exchange.

Would my Soundcraft mixer have enough gain?

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PostPosted: Sun Apr 01, 2012 2:16 pm    Post subject: Reply with quote

I don't know about that, for it brought up more questions than answers, but I got a feeling this is the beginning of a new obsession LOL

I found a source for neodymium magnets and they have 3" and 4" magnets (and they aren't that expensive).... as well as 1/4/x/14/x/2 like the ones in the K-6 I modded. The frame is pretty straightforward and Austin Mics uses what looks like acrylic or some type of plastic for their frame and uses Gorilla Snot to glue the magnets in..... though the advantage of a steel frame is the magnets hold themselves in place....

transformers are a fixed cost, as is the foil (especially as I get a bit better at cutting and corrugating... a wider set of gears would be helpful...
now I need a small vertical mill...

anyway, glad you liked it, It has been both fun and rewarding (would have really sucked if it hadn't worked Laughing

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PostPosted: Sun Apr 01, 2012 2:22 pm    Post subject: Reply with quote

I'm "guessing" at this point a longer ribbon is more responsive... just seems that, consider speakers, larger speakers handle LF better than small ones... I'm guessing that may be true of ribbons.

What I don't know is whether longer ribbons are thicker foil (the stuff is like pixie breath.....)

as to mixers... don't know... I have an older Yamaha mixer that has HOT pre's ... i'll have to check it out, but that may be the reason for keeping, just for use with ribbons.

The AEA TRP smokes my Prism pre when it comes to output, and the added output made a huge difference in the way the mic worked... I want to try it on dynamic.... damn I wish I'd won the lottery...

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PostPosted: Sun Apr 01, 2012 2:24 pm    Post subject: Reply with quote

and again (as a footnote) Michael Jolie gets a giant THANK YOU for advising and providing links for materials (I'll post those here in a bit)
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PostPosted: Mon Apr 02, 2012 1:22 pm    Post subject: Reply with quote

stainless wrote:
I don't know about that, for it brought up more questions than answers, but I got a feeling this is the beginning of a new obsession LOL

I found a source for neodymium magnets and they have 3" and 4" magnets (and they aren't that expensive).... as well as 1/4/x/14/x/2 like the ones in the K-6 I modded. The frame is pretty straightforward and Austin Mics uses what looks like acrylic or some type of plastic for their frame and uses Gorilla Snot to glue the magnets in..... though the advantage of a steel frame is the magnets hold themselves in place....

transformers are a fixed cost, as is the foil (especially as I get a bit better at cutting and corrugating... a wider set of gears would be helpful...
now I need a small vertical mill...

anyway, glad you liked it, It has been both fun and rewarding (would have really sucked if it hadn't worked Laughing


I've got a bad feeling about neodymium magnets. I've got a EV 767 neodym, and I'm not thrilled with the way it acts (too hot, too bright, too forward, and not as clean), over my standard magnet mics. I may be wrong.

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PostPosted: Mon Apr 02, 2012 2:01 pm    Post subject: Reply with quote

hmmm

it's hotter than a SM57... but I'm not sure I'd necessarily blame the magnets, could be the transformer

in contrast to the SM57, the 767 has a flatter response curve- I think there freq range is a bit exagerated, the the HF doesn't cascade off like the SM57

my money's on the transformer.

I've heard SM57s with the Luhndahl xformers put in them and they're noticeable hotter and a bit more sensitive.

The SM57 might be a poor choice for comparison as it's been around (and basically unchanged) for a long time

I'm sure you can find other type magnets, as weak as ribbons output is, I'd think this a plus

but it'd be interesting to try other magnets just to see what effect that might have

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PostPosted: Mon Apr 02, 2012 8:32 pm    Post subject: Reply with quote

I found this table on magnets

Magnet Mr (T) Hci (kA/m) BHmax (kJ/m3) TC (C)

Nd2Fe14B (bonded) 0.60.7 6001200 60100 310400

Alnico (sintered) 0.61.4 275 1088 700860

Sr-ferrite (sintered) 0.20.4 100300 1040 450

The bonded Neo magnets are the more common. Alnico we're all familiar with, and the Sr-ferrite are the "ceramic magnets"

don't ask me what any of this means Laughing

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PostPosted: Mon Apr 02, 2012 8:48 pm    Post subject: Reply with quote

here's some links that anyone interested in delving into this might find useful

magnets http://www.kjmagnetics.com/products.asp?cat=11

Luhndahl transformershttp://www.kandkaudio.com/linestage.html

Gears http://www.smallparts.com/

Foil http://www.lebowcompany.com/

Best (least amount) source for mesh screen (so far) http://www.benfranklin.com/item.php?id=MP-AO50029S&c=a&s1=Crafts,+Modeling+&+Home+Decorating&s2=Armatures&s3=Woven+WireForm&zmam=47182733&zmas=1&zmac=1&zmap=MP-AO50029S

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PostPosted: Tue Apr 03, 2012 11:50 am    Post subject: Reply with quote

stainless wrote:
here's some links that anyone interested in delving into this might find useful

magnets http://www.kjmagnetics.com/products.asp?cat=11

Luhndahl transformershttp://www.kandkaudio.com/linestage.html

Gears http://www.smallparts.com/

Foil http://www.lebowcompany.com/

Best (least amount) source for mesh screen (so far) http://www.benfranklin.com/item.php?id=MP-AO50029S&c=a&s1=Crafts,+Modeling+&+Home+Decorating&s2=Armatures&s3=Woven+WireForm&zmam=47182733&zmas=1&zmac=1&zmap=MP-AO50029S


If I had a penny for each one of those magnets, hell, I'd move to the North Pole!!

GT Rolling Eyes
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PostPosted: Tue Apr 03, 2012 11:57 am    Post subject: Reply with quote

stainless wrote:
I found this table on magnets

Magnet Mr (T) Hci (kA/m) BHmax (kJ/m3) TC (C)

Nd2Fe14B (bonded) 0.60.7 6001200 60100 310400

Alnico (sintered) 0.61.4 275 1088 700860

Sr-ferrite (sintered) 0.20.4 100300 1040 450

The bonded Neo magnets are the more common. Alnico we're all familiar with, and the Sr-ferrite are the "ceramic magnets"

don't ask me what any of this means Laughing


I'm assuming that Neo magnets can be much smaller, and acheive the same amount of gausse, they use them in the new lightweight class of speakers. I know my EV 767 Neo is much lighter than my EV Cobalt 9 standard magnet. As you know I much prefer my 9, over my 767.

I think only time will tell, as this seems to be a fairly new set of rules. Lighter may not allways be better.

GT Confused
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PostPosted: Sat May 19, 2012 8:29 pm    Post subject: Reply with quote

Spammer alert, Spammer alert!!!!!!
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PostPosted: Thu May 24, 2012 7:12 am    Post subject: Reply with quote

Spammer has been taken care of.... in future, just click the report spam on the post Wink

Daniel

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