To someone who got a TnC ACM-3. Can you help?

  • Thread starter Thread starter tarnationsauce2
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Those pics are good evidence that I am sending to China. My plane leaves for Chicago at midnight and I will be back on Saturday morning, I won't be able to get E-mail, but will try to check in here from time to time. There will be another large shipment going out on Monday even tho I am not here
 
kojdogg said:
Michael Joly did any awesome job modding a Nady RSM-5 for me (as well as three Oktavas-- a MK-219 and two MK-012's). I know he offers a ribbon repair service through his website: www.oktavamod.com
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I second that.I have two stock 012's, and two 012's that Michael operated on and what a big difference. When I set up my O/H mics, I always reach for my MJ-012's knowing they will deliver.
 
chance said:
I second that.I have two stock 012's, and two 012's that Michael operated on and what a big difference. When I set up my O/H mics, I always reach for my MJ-012's knowing they will deliver.
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Third. . .
I'm sure Michael hasn't jumped right in on all of these problems because he doesn't want to use the forum as an advertising tool. As much work as he puts into this research AND his business, he has a genuine interest in furthering the knowledge of the community as a whole. (which is why in ALL of these threads he has tips and pointers on how to do these things yourself)

That being said, Michael has worked on several of my microphones as well. Not only has he done a great job, his customer service is unmatched. I know he offers ribbon retensioning / transformer swaps for the current chinese branded mics, but i'm not sure about the group buy mics. (they seem to be a little different) FORTUNATELY, he's one of the easiest people to contact personally and find out! Just go to oktavamod.com

-James
 
Ribbon tension technique

Speaking of tips, here's how you can adjust the tension of the ribbon in your mic, and get it pretty close to where it should be - without any test equipment. This technique relies on a characteristic of our eyesight to set the resonant frequency of the ribbon.

You know how people can't see any flicker with 60Hz AC light bulbs, and only see the slightest flicker with fluorescent tubes? And for you folks in 50 Hz land, you've probably noticed fluorescent tubes emit an almost constant but subtle flicker, right? So our visual system allows us to see mechanical oscillations, but only up to a certain frequency range - then the oscillations become too rapid and blend into a constant image. We can use that aspect of our sight to look for something close to the proper resonant frequency of a ribbon.

Today I spent quite a bit of time tensioning ribbons, measuring resonant frequencies with a spectrum analyzer and retensioning. It is fairly easy to set the resonant frequency of a vibrating ribbon by eye - and this turns out to be close to where it would be set if measuring equipment was used.

Here's the technique in a nutshell - remove all grille and damping screens from the mic so you can see the ribbon clearly. Bring the ribbon up to a tension just beyond the point where it sags. Tighten the clamps just enough to hold the ribbon in place. (You'll be repeating the process a couple of times and don't want the ribbon to fuse solidly to the ribbon clamps by clamping tightly).

Now tap the body of the mic with your index finger - you'll induce a vibration in the ribbon. You should see the ribbon oscillate up and down for a few cycles. If you tap the body and don't see any oscillations the ribbon is too tight and set to a frequency above the point at which your eye can discern oscillatory movement - probably above 50Hz.

So the trick is to bring the ribbon up to a point of tension so the resonant frequency oscillation is still just barely visible. If you do this, the resonant frequency will be in the 40Hz range - very useful musically and not so loose as to resonate with infrasonic noise like footfalls and drum / piano pedal noise.
 
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now i'm just pullin this one out of my ass, BUT...

i've noticed that when tuning a guitar, if you get a fretted string tuned to the same pitch as the string below it, picking one string will cause the other to vibrate - i'm assuming because they're resonating at the same frequency

would it be possible to apply this same concept to a ribbon mic by using a sine wave generator and adjusting the ribbon until it vibrates with the specific frequency that's being played back?
 
Brilliant!

Like that old high school physics experiment used to demonstrate sympathetic resonance - one tuning fork is struck and brought close to a second tuning fork which then begins to vibrate.

The technique you suggest would definitely work if the ribbons clamps were adjustable by means of a lead-screw. It would be possible to leave a ribbon firmly clamped but dial in the tension by small lead-screw adjustments. Its going to be a bit more difficult to match the ribbon oscillating frequency to a known-value sine wave with the current-design ribbon motors which require the clamps to be loosened in order to tension the ribbons.

Btw, a known-frequency sine wave is how Oktava sets the diaphragm resonant frequency in their condenser mics.
 
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ribbon sag

Chance,

As you know I ordered lots of ribbon mics. At the time I thought that maybe I could resell them on E-bay for a profit. Now that the cost of ribbons has come down considerably that profit is looking pretty slim. Oh well, if I get my money back I'll be happy.

Anyway, I thought you might want a report on ribbon sag since I have a pretty good sample (ten of each). I inspected all of them and here are the results:

ACM 1 -- 10 good, 0 Bad
ACM 2 -- 6 good, 4 Bad
ACM 3 -- 2 good, 8 Bad
ACM 4 -- 10 good, 0 Bad

I hope that helps. The ACM 3's are the real stinkers. Not only was there sag, but there was lots of sag.

It is interesting that the ACM 4's were all good when you consider that it is a dual ribbon so there is actually 20 good ribbons and no bad ones. Whoever was working on those mics in the factory should get a raise. On the other hand, whoever was tensioning the ACM 3's needs some help.

And Chance, don't feel bad about the QC issues. No one is holding that against you. You've done a great job. Anyone buying a mic, sight unseen, direct from a factory in China has to know that they are taking a bit of a gamble.

I hope you don't get discouraged and will keep trying things like this.
 
chance said:
Some of those pics of the ribbons are so loose, I can't believe that would happen in the transport from China to you all. I am dying of couriousity how China will rectify this. Will they make restitution? I flat out told them "THIS IS NOT ACCEPTABLE"

edit Is there any one mic that this problem exists on ? Or is it ALL the ribbon mics. I'm going to be yaking with them later and want all the information/ammunition ahead of time
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Hi Chance,

My ACM-3 arrived with a sagging ribbon too. Much too delicate work for me to do myself and I'm not willing to pay to have it re-tensioned when it did not arrive properly tensioned to begin with. Had the mic been in my possession for a long enough time that I had caused this damage, I would have no problem forking out the dough to have it done, but this sadly is not the case. Not to beat a dead horse, but I'm really disappointed by this turn of events, as I'm sure you are too. ...But let's put it into perspective, right? It's only a frikkin' mic, and nothing more.

;)

My ACM-3 Woes (link)

-mr moon
 
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mr moon-- what you did with the mic is very cool and a nice gesture.
 
I'm still in Chicago and will be back on Saturday morning. China realizes their breach in trust with us and promises to make things right. I can't call them from here, and I can't get my E-mail either. I will report what their solution is on Saturday
 
kojdogg said:
mr moon-- what you did with the mic is very cool and a nice gesture.
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Thanks. I figure I have a truckload or two worth of Karmic mess to clean up from my youth, maybe this will help?

:D

-mr moon
 
Well, my ACM-3 is a sagger too.

You can see the sag problem without even opening the mic (just hold it up to the light - the ribbon looks droopy). Also, when I hold the mic horizontally and then rotate it 360 degrees, you can hear the ribbon make noticeable little "pop" noises thru the speakers as gravity pulls the ribbon back down towards the ground.

No worries here. Just more evidence for China's next QA meeting.

Aj
 
chance said:
Hmm,, so maybe the folds in the ribbons are losing memory. Maybe when they manufacture the ribbons they should increase angle of the folds to compensate for memory loss so when they relax they will be where they're supposed to be?
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Yes, indeed the folds lose memory, especially under severe impacts, such as shipping, etc.
The increase of angle of the folds is not the answer.
Looking at all those mics, apparently, even though some motors are OK, it is obvious they use louzy, not properly tuned corrugators, with wrong pitch and broad tolerances.

I already wrote many times here and would like to stress again. The corrugator and precise ribbon installation with very tight tolerances is the most important and expensive part of ribbon microphones--something what defines the quality of the mic, and most of all quality of the sound.

If you hope to pay let's say even $100 for a mic, it is not gonna be a quality product.
That's why Royer, AEA, C&T are so expensive--they do it right and the ribbons don't lose memory in shipping.

To be fair, I saw one Chinese ribbon manufacturer who does it right.
 
Marik said:
Yes, indeed the folds lose memory, especially under severe impacts, such as shipping, etc.
The increase of angle of the folds is not the answer.
Looking at all those mics, apparently, even though some motors are OK, it is obvious they use louzy, not properly tuned corrugators, with wrong pitch and broad tolerances.

I already wrote many times here and would like to stress again. The corrugator and precise ribbon installation with very tight tolerances is the most important and expensive part of ribbon microphones--something what defines the quality of the mic, and most of all quality of the sound.

If you hope to pay let's say even $100 for a mic, it is not gonna be a quality product.
That's why Royer, AEA, C&T are so expensive--they do it right and the ribbons don't lose memory in shipping.

To be fair, I saw one Chinese ribbon manufacturer who does it right.
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How does Cascade (Fathead) and Shinybox get around this problem? Haven't heard any complaints about them and they're cheap and Chinese.
 
PhiloBeddoe said:
How does Cascade (Fathead) and Shinybox get around this problem? Haven't heard any complaints about them and they're cheap and Chinese.
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I'm not sure about the Cascade ribbons, but I know that ShinyBox modifies the mics before they are sold and shipped out.

Here's what the ShinyBox website says:

"Each 46MX ribbon microphone is hand assembled at the bench by Jon Ulrigg. Every ribbon motor is hand tuned in Jon's shop, which offers a level of quality control and performance that sets these ribbon microphones apart from the competition."

Basically, they are a Chinese mic that have been modified here in the states.

I own a 46 with the Lundahl output transformer, and have been floored by it. It's a great mic!!

-mr moon
 
Mr. Moon said:
I'm not sure about the Cascade ribbons, but I know that ShinyBox modifies the mics before they are sold and shipped out.

Here's what the ShinyBox website says:

"Each 46MX ribbon microphone is hand assembled at the bench by Jon Ulrigg. Every ribbon motor is hand tuned in Jon's shop, which offers a level of quality control and performance that sets these ribbon microphones apart from the competition."

Basically, they are a Chinese mic that have been modified here in the states.

I own a 46 with the Lundahl output transformer, and have been floored by it. It's a great mic!!

-mr moon
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Jon has his own design for the motor as well. My understanding is that he has the parts shipped unassembled and then puts everything together so it's more than just modification/tuning.

He does a great job for not much more than the stock price.
 
MichaelJoly said:
This suggests the currugation folds in some mics are relaxing after manufacture and allowing the ribbons to sag. Becuase if a ribbon was installed very slack I would expect to see more corrugations between clamps than found in a ribbon with proper tension.
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Any thoughts on how much impact damage would be necessary to make one look like this?

-----------'\/\/\/\/\/\/`-------------

:D

That's how at least one of mine looked—the last several corrugations completely straightened. Well, of course, it was sagging in addition to that, which I obviously can't represent with text, but you get the picture.

I can't see how the ribbon's mass could possibly be enough to cause anywhere near that much straightening, so I suspect somebody sneezed during assembly or hosed it with an air compressor or....

Thoughts?
 
That's a first for me. I've never seen a Chinese ribbon mic with ribbon ends pulled flat as you've described - usually just sagging uniformly.
 
the corrugations along the outer area of the ribbon on my ACM-3 were pretty flattened out as well, which is why i haven't bothered to re-tension it
 
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